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the chemical evolution of protoplanetary disk materials begins in the earliest prestellar phase of star formation. under the dark, cold conditions of cores the initial icy mantles of grains are built up. already at this point, grain-surface chemistry starts to set the composition of these icy layers. once collapse is initiated, the central protostars can boost chemical processing of the ices by serving as a source of additional uv photons, thereby enhancing photochemistry in both phases, and by heating the dust grains, which allows higher mobility of radicals in the solid phase. regionally, the heating is sufficient to thermally desorb the ice mantles entirely. in such regions, the chemistry is set via gas-phase reactions. protoplanetary disks are built up from the collapsing core materials, which are exposed to variable intensities of uv irradiation and heating. the build up of complex organic molecules initiates in the prestellar phase and continues across the subsequent evolutionary stages. i will highlight the chemical connection across various stages of evolution by presenting the latest observational constraints. for this purpose, the results from the alma-pils survey on the infant solar system analogue iras16293-2422 will be presented in the context of in situ measurements made by the rosetta mission on comet 67p/churyumov-gerasimenko. such comparative studies shed light on the earliest physicochemical conditions for our infant solar system and give hints on the uniqueness of the ingredients to life. | the chemical connection between 67p/c-g and iras 16293-2422 |
jaxa's hayabusa2 mission was launched in december 2014 to explore the pristine c-type asteroid (162173) ryugu, whose bulk material can be considered representative for the volatile rich building blocks that formed the terrestrial planets. c-types are the most common variety of asteroids, and 75% of all known asteroids are of this type. they mainly occur at the outer edge of the asteroid belt, where 80% of asteroids are c-type, but chondritic meteorites are rare in our sample collections, which makes (162173) ryugu a special target. hayabusa2 reached ryugu after a 3.5 years cruise on june 27th, 2018, and after initial characterization and landing site selection, the hayabusa2 spacecraft delivered the dlr/cnes built mascot lander to the asteroid's surface on october3rd, 2018, where mascot successfully performed in situ investigations. the mascot payload consisted of a wide angle camera (mascam), an imaging ir spectrometer (micromega), a multichannel radiometer (mara), and a magnetometer (masmag), gathering a wealth of data during the 17h and 7min surface operations. the asteroid's surface was characterized down to the millimeter scale, and mascam images revealed a surface dominated by rocks and boulders without showing fine-grained material. most boulders appear dark with cauliflower-like crumbly surfaces, and inclusions observed in high-resolution images have strong similarities with carbonaceous chondrites. diurnal temperature variations of a ~60 cm diameter rock were found to be consistent with low thermal inertia around 300 j m-2 k-1 s-1/2, much lower than anticipated when compared to samples in our meteorite collections. this indicates that rocks on ryugu are highly porous and likely very friable. the remnant magnetization of ryugu's surface material on scales larger than 1 m has an upper limit of 3·10-6 am2/kg, and a preliminary analysis of the induction effect in ryugu caused by the variation in the solar wind magnetic field reveals high electrical conductivity of the order of 1 s m-1. in summary, mascot measurements indicate that c-type asteroids appear similar to carbonaceous chondrites, and that magnetization did not play a major role during the accretion of the terrestrial planets. | in-situ investigation of asteroid (162173) ryugu by the hayabusa2 mascot lander |
with the continuous progress of energy storage technology and the substantial reduction of cost, as well as the development of china’s energy internet, customer-side distributed energy storage has been applied more and more widely. considering the customer-side distributed energy storage which takes the grid-connected “distributed solar + energy storage” as the main application mode, a distributed energy storage evaluation model based on double-granularity optimal operation strategy is proposed, which is built on life-cycle cost-benefit analysis model for customer-side distributed energy storage considering its operation optimization in advance. taking large industrial and business consumers in one province in china as an example, the sensitivity analysis of customer-side distributed energy storage value is taken under different load characteristics, price policies, energy costs and energy storage technology characteristics, judging the customer-side distributed energy storage trends and potential of further development. | valuation of energy storage at user side considering total life cycle |
perovskite materials are fascinating candidates for the next-generation solar devices. with long charge carrier lifetime, metal-halide perovskites are known to be good candidates for low-light harvesting. to match the irradiance spectra of indoor light, we configured a triple-cation perovskite material with appropriate content of bromide and chloride (fa0.45ma0.49cs0.06pb(i0.62br0.32cl0.06)3) to achieve an optimum band gap (eg) of ∼1.80 ev. with low photon flux at indoor condition, minimal recombination is highly desirable. to achieve such goal, we, for the first time, combined dual usage of antisolvent deposition and vacuum thermal annealing, namely vta, to fabricate a high-quality perovskite film. vta leads to compact, dense, and hard morphology while suppressing trap states at surfaces and grain boundaries, which are key culprits for exciton losses. with low-cost carbon electrode architecture, vta devices exhibited average power conversion efficiency (pce) of 27.7 ± 2.7% with peak pce of 32.0% (shockley-queisser limit of 50-60%) and average open-circuit voltage (voc) of 0.93 ± 0.02 v with peak voc of 0.96 v, significantly more than those of control and the vacuum treatment prior to heat. | robust perovskite formation via vacuum thermal annealing for indoor perovskite solar cells |
metal halide perovskite (mhp) materials are now investigated as the active layer of semiconductor devices such as solar cells and light-emitting diodes (leds). perovskite leds (peleds) with high-quality made by a cost-effective process are needed to achieve a commercialized peled. to reach this goal, modifying and surface engineering the perovskite emissive thin films can be helpful. the manufacturing process must be economical and time-saving for fabricating an effective commercial device. this work presents an effective postprocessing method to recrystallize the perovskite emissive layer. the method includes both annealing and plasma treatment, which takes a short time and does not need vacuum tools. applying this process results in a reduction of the mapbbr3 grain size. it also increases perovskite emitters' carrier recombination rate and photoluminescence quantum yields (plqy). these results indeed can increase luminance (∼68500 cd/m2), external quantum efficiency (eqe, ∼20.5%), and lifetime (∼350 min). | applying a time-saving and cost-effective postprocessing method to achieve a high-quality perovskite light emitting diode |
the data from the closed source of the cassini ion and neutral mass spectrometer (inms) at enceladus' plumes shows a signal of h2 in significant quantities (15% mole fraction for low speed flybys). h2 would be considered a "smoking gun" for the suspected hydrothermal activity in enceladus' ocean. however the h2 quantity varies with the speed of the flyby, which is attributed to the presence of ice grains in the plumes hitting the walls of the titanium antechamber of inms and exposing fresh titanium that may react with water to form hydrogen. the large number of small ice grains arriving during a single inms integration period creates a back-ground signal in addition to large grains causing punctual spikes. we have developed a surface chemistry model of the inms, taking into account adsorption and chemisorption of species of interest to determine how much h2 is produced from the expected ice grains distribution for each flyby (given by cassini caps data ). cth simulations have been used to assess the contribution of grains of different size in terms of titanium produced. we show that the spikes in the mass 2 channel can be explained by microns-sized grains, and that smaller grains (below 500 nm) are the major contributors to reactions with titanium, accounting for most of the non-spike signal. we find that the mass 2 background signal due to titanium is strongly driven by the water available, and therefore its shape versus time can't follow the sharp rises in the data (see figure). this makes the structures seen in flyby e18 either the product of several big grains or the observation of locally high density of h2 (jets). we will analyze the effect of grains on other mass channels and comparison to cda data to de-termine whether the peaks can be attributed to multiple ice grains or to native h2. the work will be extended to the e17 and e14 flybys to reach a definitive assessment of the native h2 abundance in the enceladus plume. | evaluating the quantity of native h2 in enceladus' plumes with the cassini-inms closed source data: constraints from modeling of ice grains impact in the instrument |
recent basaltic eruption sites in iceland are considered mars analogues for surface mineralogy, constrained bioavailable chemistry, very low biomass, and (in some cases) water/ice activity. such sites also contain temperature, moisture, and geochemical gradients, both due to geochemical activity and to topology. correlating remote imagery, surface mineralogy, and biomarker assay results across such gradients will help optimize mars sample site selection for likely biomarker distribution and preservation. the feldspar team's most recent expeditions (2017 and 2018) to icelandic mars analogue sites tested a battery of physicochemical measurements and biomarker assays along transects including layered deposits, temperature, alteration, oxidation, wind and solar exposure, slope changes, and grain size sorting. here we report intermediate results. sites were holuhraun and dyngjusandur, both geologically recent basaltic lava flows. (other sites were sampled as part of the overall feldspar project, but did not target gradients.) vis/nir reflectance and xrf spectra were taken for mineralogical classification, along with temperature measurements and other field observations. biomarker assays were atp quantification (performed in a temporary field lab), qpcr, and some dna sequencing; these targets were chosen as proxies for different classes of potential mars biomarker types (biomass, bioavailable energy, etc.). the performance of the atp assay in the differing geochemical types sampled was validated using standard addition. results indicate that the assay yielded usable results in all types of samples tested, although many highly oxidized or hot sample sites indicated a level below the lowest detectable limit. dna was extracted from all 2017 samples; 2018 sample processing is still underway. spectroscopy initially proved challenging due to the very dark color and low ambient light at dyngjusandur, but a near-complete set of reflectance and xrf spectra were obtained at holuhraun and used to derive summary parameters analagous to the crism instrument. environmental monitoring devices were installed at a subset of 2018 sample sites to obtain additional information on diurnal and seasonal exposure, for collection during the planned 2019 expedition. | astrobiological assay validation across gradients in mars analogue sites: lessons from the feldspar project |
large-grain-size (>1 mm) liquid-phase-crystallized silicon (lpc-si) films with a wide range of carrier doping levels (1016-1018 cm-3 either of the n- or p-type) were prepared by irradiating amorphous silicon with a line-shaped 804 nm laser, and characterized for solar cell applications. the lpc-si films show high electron and hole mobilities with maximum values of ∼800 and ∼200 cm2 v-1 s-1, respectively, at a doping level of ∼(2-4) × 1016 cm-3, while their carrier lifetime monotonically increases with decreasing carrier doping level. a grain-boundary charge-trapping model provides good fits to the measured mobility-carrier density relations, indicating that the potential barrier at the grain boundaries limits the carrier transport in the lowly doped films. the open-circuit voltage and short-circuit current density of test lpc-si solar cells depend strongly on the doping level, peaking at (2-5) × 1016 cm-3. these results indicate that the solar cell performance is governed by the minority carrier diffusion length for the highly doped films, while it is limited by majority carrier transport as well as by device design for the lowly doped films. | impact of carrier doping on electrical properties of laser-induced liquid-phase-crystallized silicon thin films for solar cell application |
isotopic heterogeneities in terrestrial rocks resulting from the decay of short-lived radioactive isotopes provide valuable information regarding processes that occurred in early earth history, as well as possible locations of hidden reservoirs in the modern earth. two such complementary short-lived systems are 182hf-182w and 146sm-142nd, with half-lives of 9 and 103 myr, respectively. these systems were effectively dead 60 and 600 myr, respectively, into solar system history. both systems exhibit both positive and negative anomalies, relative to presumed ratios for bulk silicate earth, in certain archean rocks, as well as for some recent volcanic rocks. anomalous isotopic compositions for both systems in proterozoic rocks appear to be rare, although very few analyses of proterozoic rocks have yet been made for either system. processes proposed to generate the anomalies in one or both systems include initially grainy late accretion, disaggregation and uneven mixing of late accreted bodies, early differentiation inclduing magma ocean processes involving metal-silicate equilibration or silicate-silicate crystal-liquid fractionation, and core-mantle interactions. in rare instances, 142nd and 182w anomalies appear correlated, however in most lithologies they are not. no single process can be envoked to account for the observed isotopic variability, suggesting that earth has retained a record of different processes that have occurred throughout its history. for example, positive correlations between 182w and 142nd anomalies in some archean rocks implicate the involvement of silicate crystal-liquid fractionation in an early, large mantle domain, possibly the result of magma ocean crystallization. by contrast, 182w anomalies negatively correlate with 3he/4he in most modern ocean island basalts, yet neither he nor w variations appear to correlate with 142nd anomalies. one option for the latter observation is that at least some oib sources include materials derived from a primordial deep mantle domain that obtained its negative 182w anomaly through core-mantle isotopic equilibration. more discoveries are likely to follow. | isotopic anomalies in short-lived systems: the plot thickens |
the goal of this thesis is to engineer the interaction between surface plasmons and semiconductor nanocrystals for nanophotonic applications. plasmonic metals support surface plasmon polaritons, hybrid photon and electron waves that propagate along a metal-dielectric interface. unlike photons, surface plasmons can be confined in sub-diffraction geometries. this has two important consequences: 1) optical devices can be designed at the nanoscale, and 2) the high density of electromagnetic fields allows study of enhanced light-matter interactions. surface plasmons have been exploited to demonstrate components of optoelectronic circuits, optical antennas, surface enhanced spectroscopy, enhanced fluorescence from fluorophores, and nanolasers. despite the advances, surface plasmon losses limit their propagation lengths to tens of micrometers in the visible wavelengths, hindering many applications. recently, the template-stripping approach was shown to fabricate metal films that exhibit larger grains and smoother surface, reducing the grain boundary and roughness scattering. to further improve the plasmonic properties, we investigate the importance of deposition conditions in the template-stripping approach. we provide insight and recipes to enhance the plasmonic performance of the most commonly used metals in the ultraviolet, visible, and near-infrared. we also explore the potential of low temperatures to improve the performance of metal films, where the electron-electron and electron-phonon scattering should be reduced. this sets a limit on the minimum loss metals can exhibit. using this knowledge, we study the optical properties of quantum-confined semiconductor nanocrystals near metal structures. semiconductor nanocrystals have many attractive characteristics that make them suitable for solid-state lighting and solar cells among others. specifically, cdse nanocrystals have been heavily studied for their large absorption and emission cross-sections, size dependent emission wavelengths, photostability, and high quantum yields. here, we focus on studying the emission from cdse nanocrystals near plasmonic structures in the weak and strong coupling regimes. in the weak coupling regime, plasmonic structures can be used to selectively modify the radiative rates at the desired wavelengths. we tailor plasmonic structures to enhance and tune the emission from the surface states of cdse nanocrystals throughout the visible. due to their size, a significant fraction of atoms are on the surface; however, electron-hole recombination via surface states is typically dark. we further use electrochemistry to probe the energy levels of the surface states. in the strong coupling regime, the energy levels of the surface plasmons and nanocrystals hybridize to form polariton states. in this regime, we demonstrate polariton emission from cdse/cdszns core/shell/shell nanocrystals on silver hole arrays. emission from these polariton states should be coherent and has implications for thresholdless lasing. while the above studies focus on the change in nanocrystal behavior near metals, these nanocrystals can also be used to improve plasmonic performance. we study the potential of thin layers of cdse nanocrystals to amplify surface plasmons and enhance their propagation lengths. when the nanocrystals are excited using an external pump, propagating surface plasmons can stimulate emission from these nanocrystals and amplify. if more surface plasmons are generated than lost, then surface-plasmon signals can propagate over extremely long distances and even amplified. we calculate the gain provided and discuss the importance of key parameters such as the absorption and emission cross section, spacer layer thickness, nanocrystal lifetime, and temperature. finally, we systematically study the emission properties and exciton decay in ag-doped cdse nanocrystals, which were recently shown to exhibit enhanced photoluminescence. overall, this thesis aims to improve plasmonic performance with and without the presence of a gain medium, and advances the understanding of optical behavior of cdse nanocrystals near metal structures in the weak and strong coupling regimes. | coupling of surface plasmons and semiconductor nanocrystals for nanophotonics applications |
chemcam on curiosity has used libs to obtain elemental compositions of >6000 target points at distances to 7.4 m from the rover. observations include igneous clasts, sediments, diagenetic features, and other details often not accessible by the rover arm. a major re-calibration was recently completed using >350 standards. this significantly improved the accuracies of mineral end-members including plag-feldspars, hi-si compositions, oxide grains, mg-rich end-members (presumably mg saponites; not yet confirmed by chemin), and mg and ca sulfates. here we draw conclusions from the overall compositional distributions observed in gale crater from landing until the present using the new calibration. observations from bradbury rise (sols 0-53, 326-520) show a scattering of compositions toward mineral end-members from igneous clasts and pebbles transported from the crater rim. in contrast, sheepbed mudstones (first drill location; sols 126-300) form a tight cluster close to average mars composition. the nearby shaler fluvial sandstone outcrop (sols 306-325)--the first outcrop of potential deltaic foreset beds--shows k enrichment. this enrichment reaches a peak of 6 wt % k2o (sol 625) in the mt. remarkable member of the kimberley formation, kimberley being a drill location flanked by foreset beds 7 km sw of shaler. the pahrump outcrop (sols 753-919)—first observed material of the murray formation at mt. sharp's base—shows lower mg, higher si, and much higher al, consistent with stronger alteration. further along the traverse chemcam discovered an outcrop of light-toned murray formation rock (sols 992 on) of nearly pure sio2+tio2. overall, the chemcam database points to a very strong diversity of inputs and alteration processes within a relatively short distance within gale. igneous compositions: while jake matijevic, a float analyzed early by apxs, appeared nepheline normative, no clear nepheline has been found by chemcam. additionally, despite the significant number of coarse-grained feldspar-rich rocks observed by chemcam, only a small number of points show excess silica, and quartz has not been clearly observed, leading to the suggestion that the leucocratic igneous clasts are dioritic/trachybasaltic rather than granitic. | major-element compositional diversity observed by chemcam along the msl traverse: the first three years |
the natural history museum is working closely with the european space agency (esa) and the uk space agency to develop a european collection of analogue materials with appropriate physical/mechanical and chemical (mineralogical) properties which can support the development and verification of both spacecraft and scientific systems for potential science and exploration missions to phobos/deimos, mars, c-type asteroids and the moon. as an esa collection it will be housed at the esa centre based at harwell, uk. the "esa sample analogues collection" will be composed of both natural and artificial materials chosen to (as closely as possible) replicate the surfaces and near-surfaces of different solar system target bodies of exploration interest. the analogue samples will be fully characterised in terms of both their physical/mechanical properties (compressive strength, bulk density, grain shape, grain size, cohesion and angle of internal friction) and their chemical/mineralogical properties (texture, modal mineralogy, bulk chemical composition - major, minor and trace elements and individual mineralogical compositions). the collection will be fully curated to international standards including implementation of a user-friendly database and will be available for use by engineers and scientists across the uk and europe. enhancement of the initial collection will be possible through collaborations with other esa and uk space agency supported activities, such as the acquisition of new samples during field trials. | starting a european space agency sample analogue collection for robotic exploration missions |
nasa's mars 2020 mission is the first step in a potential campaign to bring martian samples back to earth for detailed study. after launch in the summer of 2020, the mars 2020 rover will land in jezero crater on february 18, 2021. this landing site was selected for its compelling evidence for ancient habitability: sometime in the late noachian or early hesperian (i.e., > ~3.5 billion years ago), the crater hosted a ~400 meter deep, 40 km diameter, open-system lake in which a now well-exposed delta system was deposited. in its one mars year (686 earth day) prime mission, the curiosity-heritage mars 2020 rover will explore the delta, associated fluvio-lacustrine mudstone and sandstone deposits, an enigmatic magnesium carbonate lithology, and possible volcanics. in addition to multiple high-resolution cameras, the rover carries instruments to characterize chemistry, mineralogy, and structure both at the outcrop scale and at the microscale. these observations will be used to interpret the geologic setting and habitability potential of the site, and to seek possible evidence of past microbial life. identification, collection, and documentation of rock and regolith samples for possible return to earth by future missions are central objectives of the mars 2020 mission. high priority samples will be those with the greatest potential to have once hosted martian life and to answer key questions about the geology and environment of mars and its evolution as a planet. rock cores ~1.3 cm in diameter and ~6 cm long (~15 grams) will be drilled from surface outcrop directly into individual ultraclean sample tubes. unconsolidated samples will be obtained by cascading grains into a sample tube inserted into sand, dust, or regolith. after collection, sample tubes will immediately be inspected, hermetically sealed, and stored on board the rover. the rover carries 38 sample tubes that can be used for rock or regolith, and 5 tubes designed for blank characterization. of these, approximately 30 (samples + blanks) are considered likely to be returned to earth in the future, with the remainder allowing for collection failures and for scientific prioritization. the mars 2020 rover will ultimately deposit all sample tubes on the surface of mars, leaving retrieval and return of the highest value tubes up to a possible future mission. during the mars 2020 surface mission, the site(s) at which samples will be deposited will be chosen for ease of access/relocation and to minimize dust cover. deposited tubes are designed to remain at temperatures <20oc at jezero, and to survive at least 50 years on the surface and in transit to earth. | mars 2020 as the first step in a potential mars sample return campaign |
near-surface freeze-thaw cycling of salty fines on mars could be producing regolith instability that contributes to recurring slope lineae (rsl) formation. this process would require abundant sulfates and chlorides in a fine-grained permafrost-type matrix. such light-toned gypsum- and chloride-bearing sediment zones are observed in the antarctic dry valleys a few cm below the surface [1]. on mars, sulfates and chlorides are widespread in equatorial sites [2,3] and near-surface ice is found in several crater walls [4]. thus, shallow salty permafrost zones could be present on mars in equatorial regions today. most rsl occur at tectonically fractured regions at valles marineris or along crater rims covered by impact ejecta with higher porosity [5]. gradual melting of this near-surface ice on sun-facing slopes provides monolayers of liquid water that percolate around soil grains. cacl-bearing salts are hygroscopic and would become increasingly hydrated until they deliquesce. surrounding the dead sea in israel, sink holes are currently forming where gypsum and halite in the soil facilitate brine migration, deliquescence, and disruption of surface soils [6]. similar collapse events have occurred in gypsum-chloride-rich karst systems [7], but are not observed in carbonate-rich karst systems. lab experiments also illustrated subsurface hydration of salts, migration of salty brines around basaltic soil grains, and formation of subsurface gaps and surface collapse features. on mars, tiny brine droplets would coalesce around near-surface soil grains, causing them to slip, producing gaps and instability in the regolith. deposition of dust on these unstable surfaces could cause dry flow along steep slopes. the dark streaks observed at rsl sites on mars could be the result of unstable surface grains and bright dust slipping downhill. this would be a dry process on the surface of mars and would not result in accumulation of hydrated cl or s phases on the surface, but would be the result of subsurface brines. gibson et al. (1983) jgr, 88, a912-a928. ehlmann & edwards (2014) ann.rev.eps, 42, 291-315. leask & ehlmann (2019) 9thmars conf. #6252. dundas et al., 2018) science, 359, 199-201. singleton et al., 2011) maps, 46, 1774-1786. yechieli et al., 2016) hydrogeology, 24, 601-612. gutiérrez et al. (2016) geomorphology, 267, 76-97. | martian near-surface s and cl brines in fractured and porous regolith could trigger microscale soil collapse and cause recurring slope lineae |
in this thesis chemical and physical processes in the ice mantles on interstellar dust grains are studied. with the atacama large millimetre/submillimetre array molecules of interest to the formation of bigger, life-bearing molecules are detected for the first time around the sun-like low-mass protostar iras 16293-2422. these detections give clues about the earliest conditions our solar system formed under and potentially how life on earth emerged. laboratory studies investigate the formation of these complex species in a laboratory set-up mimicking the conditions on interstellar icy dust grains. in this ways formation routes for molecules with a so-called amide functional group are mapped. | the astrochemical factory: a solid base for interstellar reactions |
in the early solar system, internal heating by short-lived radiogenic nuclides led to significant melting of rocky planetesimals. this altered their physical and chemical interior structure on a time scale comparable to disk-stage accretion processes. two hypotheses for the evolution of heated planetesimal interiors are prevalent in the literature. in the global magma ocean scenario, the whole interior of sufficiently early-formed planetesimals experienced nearly complete melting, resulting in turbulent convection and core-mantle differentiation via the rainfall mechanism. in the magma sill scenario, ascending buoyant melts gradually depleted the deep interior of the radiogenic heat source. in this case, core formation may have proceeded via percolation; erupted lavas buried the primitive lid and chemically stratified the body. to investigate the parameter controls that separate the magma ocean and magma sill end-member scenarios, we study the genesis and segregation of silicate melts in early solar system planetesimals using a novel computational method for reactive, disequilibrium, multi-component melting and two-phase fluid flow. we find that for planetesimals with rapid magma transport, melt segregation produces distinct radial structure. a key control on this segregation is the mean grain size of silicate minerals, suggesting that the time scale of grain growth - either before or after planetesimal accretion - governed internal magma flow. furthermore, the formation time of the body sets the total amount of energy available for melting. as a result of this, our models indicate a peak in the propensity for melt segregation in bodies formed at around ∼1 myr after cai formation. regardless of whether a planetesimal evolves toward a global magma ocean or melt-segregated sill structure, temperature inversions due to rapid aluminum-26 redistribution are limited to bodies formed earlier than ∼1 myr after cais. in general, if grains did not grow beyond sizes of ∼1 mm before the peak of internal melting, only strongly reducing environments, such as found for enstatite chondrite compositions, could generate substantial magma segregation due to their elevated solid-melt density contrast. our findings suggest a link between the time and orbital location of planetesimal formation and their subsequent structural and chemical evolution. the results have implications for the mode of core formation and the redistribution of planetary materials in the crustal stripping paradigm of planetary accretion. | magma ascent in planetesimals controlled by grain size |
the thermophysical properties of planetary surfaces have the potential to help illuminate key characteristics that cannot be addressed otherwise. specifically, by detailed analysis of the thermal inertia (ti) both from orbit and landed assets a robust understanding of the particle sizes, degree of induration, and surface physical properties can be derived. these parameters can be used to place important constraints on present and past environments including key environmental transitions. as the mars science laboratory (msl) curiosity rover has continued its traverse up aeolis mons, it has explored a variety of past aqueous environments and a significant range of ti values (e.g. 150-550+ j m-2 k-1 s-1/2). more specifically, as curiosity transitioned upslope through the murray formation to the vera rubin ridge (vrr) member, significant differences in ti, but not necessarily particle size (mostly below the resolution limits of the mars hand lens imager (mahli)) have been noted. the vrr has the highest orbitally-derived ti from the thermal emission imaging system (themis) encountered by msl to date; however, the cause of elevated ti, especially when considering the fine-grained rocks, lack of obvious sedimentological and geochemical changes between units, remains unknown. in this effort, we present a continuing thermophysical record derived by the msl rems ground temperature sensor (gts) following well-established methods. we compare these results to the thermophysical properties and particle sizes derived from themis, and link these measurements to ground truth particle size upper limits determined from mahli images. we consider a variety of thermophysical scenarios, including subsurface layering/fracturing, lateral heterogeneity, and pore filling cements that would increase the ti beyond what is expected for loose particulates. we compare these scenarios with the context provided by other rover observations (e.g. presence of concretions, veins, scarps, changes in texture, morphology, or composition, etc.). importantly, given the lack of an obvious grain size transition from the murray formation to the vera rubin ridge, we will provide estimates on the fraction of extra cements to account for the increased thermal inertia over the mudstone underlying the vera rubin ridge. | the thermophysical variability of the vera rubin ridge as explored by the mars science laboratory |
complex organic molecules, some of which became the building blocks of life, could have been synthesized in the interstellar molecular cloud stage at very low temperatures (10 k), preserved in the ice grains, and transported through the protoplanetary stage in cometary precursors. some tracer molecules of such preservation are identified. | evolution of organic molecules in pre-solar ice |
ephemeral coronal holes are short-lived, low-density regions of the solar corona observed as dark features at euv wavelengths, and are associated with open magnetic field lines due to a single dominant polarity. these structures are distinct from longer-lived equatorial and polar coronal hole regions, and remain relatively unexplored. ephemeral coronal holes are primarily characterized by a lifetime substantially less than a single solar disk crossing, typically lasting only a few days. we conduct a systematic search for these events using atmospheric imaging assembly (aia) data provided by the solar dynamics observatory (sdo), examine their characteristic properties and investigate the relationship with the underlying magnetic field structure. a preliminary examination of the sdo/aia database between 2010-2016 identified 5 clear examples of ephemeral coronal holes, suggesting that they are rare phemonena. for each event we determine its key properties, including spatial extent over time, growth and decay rates, total lifetime, average flux within the coronal hole, and associated magnetic field properties. we also examine links between the coronal hole evolution and granulation processes occuring in the lower atmosphere. further research will reveal the prevalence of these apparently rare phenomena, and shed light on the properties of the magnetic field that lead to their rapid formation and dissolution. | characteristics of ephemeral coronal holes |
on mars day 1800 of the mars science laboratory mission - in september 2017 - the curiosity rover reached vera rubin ridge (vrr) in gale crater, mars. vrr is a prominent, but discontinuous, topographic shoulder that fringes the central mound, aeolis mons (mt. sharp) in gale crater. in-situ rover observations indicate that rocks of the vrr comprise fine-grained mudstones that are planar-laminated similar to rocks of the underlying member of the murray formation and interpreted to have been deposited in an ancient lake environment. this supports the hypothesis that the vrr rocks represent a conformable continuation of the murray formation. unlike underlying murray members, vrr possess a strong hematite spectral signature as mapped from orbit. a key goal of the vrr investigation has been to characterize and understand the geochemical signature of the ridge forming rocks to ascertain the role of primary versus diagenetic controls on the chemistry of vrr rocks. our investigations of vrr include three (n-s) traverses of the stratigraphy of vrr by the curiosity rover: an initial ascent, a descent back down below vrr to the east of the initial ascent, and a second ascent east of the initial ascent and west of the descent. as these traverses follow different routes, the finely spaced bedrock geochemistry observations of the chemcam ("chemistry and camera") instrument on curiosity provides fine-scale geochemical stratigraphy of vrr along three laterally distinct vertical transects. while the geochemistry of vrr baseline bedrock is observed to be within the compositional range observed over the previous 7-8 km of traverse over the murray formation covering 250+ m of stratigraphy, notable absolute and relative variations are observed across vrr. key element variations include a slight decrease in al2o3 and increase in k2o. this leads to the chemical index of alteration (cia), which has otherwise risen with increasing elevation in the murray formation, to decrease in vrr rocks. additionally, li decreases notably with elevation across the vrr stratigraphy. these changes possibly signal a decrease in clay-content in vrr rocks. importantly, the three separate transects of vrr highlight that the observed chemical variations appear to follow the geomorphology of vrr rather than elevation; this would suggest a strong diagenetic control. | geochemical evidence from the chemcam instrument highlighting the role of diagenesis at vera rubin ridge in gale crater, mars |
we investigate the nonradiative electron and hole recombination facilitated by native point and extended grain boundary defects in methylammonium lead iodide perovskite (mapbi3) using an ab initio nonadiabatic molecular dynamics (namd) approach in conjunction with density functional theory. the recombination rates are due to elastic and inelastic temperature-dependent electron-vibrational interactions, and are the main energy loss mechanisms in the solar sensitizer. we focus our study on the most stable defects under different synthesis conditions, which include shallow defects under moderate and poor iodine conditions, and defects with deep-level transition levels under iodine rich conditions. this investigation using namd combining with time-domain density functional theory will determine the lifetimes, decay mechanism, and the extent these defects can affect the solar efficiency. | defect-assisted hole and electron recombination in methylammonium lead iodide perovskite |
teller et al. (1997) suggested deploying fine-grained aluminum oxide (al2o3, or corundum) as an atmospheric aerosol for solar radiation management (srm) to offset the anthropogenic contribution to climate change. unfortunately, corundum is an abrasive (mohs hardness = 9) that portends ill health to air-breathing life. we suggest a more promising material: nacl with anti-caking agent 552 (calcium silicate), a.k.a. morton® table salt. we investigated the reflectance properties of both al2o3 (nelson et al., 2018) and morton® salt in well-sorted particle sizes. our results are in agreement with basic light-scattering theory, which holds that at very small phase angles, particles that are larger than the wavelength λ of incident light are highly reflective (backscattering), and well-dispersed particles that are smaller than λ tend to be forward-scattering. a comparison between al2o3 and nacl indicates that the latter is a far better choice for aerosol dispersal for srm. nacl is several times more reflective at small phase angles. as an already abundant, naturally-occurring aerosol it is environmentally benign at the low concentrations required to reduce the solar forcing function by several w/m2, the amount estimated by the ipcc to be the anthropogenic contribution to global warming. furthermore, as a particulate aerosol, nacl would have short residence time if distributed in the upper troposphere, where it would not interfere with stratospheric ozone. with great trepidation, we suggest potential use in these areas: - temporary regional application to mitigate short-term, life-threatening conditions in areas where extreme temperature events are expected on timescales of days, and - global application for immediate relief during a near-term transition period to an atmosphere that is generally free of anthropogenic greenhouse gas. we offer this as a temporary relief measure and not a solution, somewhat analogous to the application of morphine in a medical situation. refs: teller et al., 1997. ucrl-jc-128715; nelson et al., 2018. icarus, 202, 483-498. | particulate sodium chloride - an outstanding candidate for solar radiation management |
serpentinization encompasses a series of disequilibrium reactions that occur when ultramafic rocks composed of olivine and pyroxene are exposed to circulating aqueous fluids at temperatures lower than 400ºc. the production of hydrogen that follows serpentinization is central to the current origin of life hypothesis, as well as the search for microbial life on the icy moons of jupiter and saturn. in recent years different studies had shown that fluid composition and salinity are some of the most important variables affecting the kinetics of serpentinization reactions (andreani et al., 2013; lafay et al., 2012; lamadrid et al., 2017, 2018). however, most experimental studies conducted so far have tried to characterize serpentinization using fluid compositions that can be related to the earth system. recently, evidence of active hydrothermal systems in the icy worlds of europa and enceladus have been detected (hsu et al., 2015; waite et al. 2018). the composition of these oceans is thought to be different from seawater on earth, and it was suggested that mgso4 is the dominant dissolved salt in them (vance et al. 2016). here we show preliminary results of an ongoing experimental study to understand the effects that mgso4 exerts on the serpentinization reaction at the estimated p-t conditions of the porous rocky cores of europa and enceladus. we ran cold seal pressure vessel experiments for 25 days at 250ºc and 500 bars, reacting powdered olivine (<30 μm grain size) in gold capsules with an aqueous solution containing varying concentrations of mgso4 (0, 0.5 and 1) and nacl (3.5, 3, 2.5 and 0 wt.%) to emulate an extraterrestrial ocean-like fluid composition. xrd, ftir analyses and sem images show that the usual serpentinization mineralogy (serpentine, brucite and magnetite) is not present in the experiments with mgso4 in the starting solution in comparison with the control experiments using an earth-like seawater composition. these results suggest that the serpentinization pathways might be different and that mgso4 slows down or halts the serpentinization reaction. further long duration experiments and analytical work are being conducted to understand the alteration mineralogy, chemistry and rates of reaction to provide further constraints on the serpentinization reactions of these extraterrestrial hydrothermal systems. | the effect of mgso4 on serpentinization rates: implications for the icy moons of jupiter and saturn |
we investigate the use of different rheological models to describe the viscoelastic behavior in planetary mantles using geophysical observations. rheology is strongly dependent on temperature and, as a consequence, imposes strong constraints on the interior structure of planets. in principle, shear modulus reduction and attenuation related to the viscoelastic relaxation occur as a result of dislocation creep and grain-boundary processes. several rheological models have been proposed in the literature to describe these mechanisms. however, the choice of the most appropriate model to represent the dissipation in a planetary mantle remains an open issue. to examine this, we consider four different rheological models: extended burgers, andrade, sundberg-cooper, and a power-law approximation to compute tidal dissipation, and illustrate this for mars. in order to construct geophysical models of mars' crust and mantle, we compute elastic moduli and density by using self-consistent mineral phase equilibria calculations from which rock mineralogy and its elastic properties are predicted as a function of pressure, temperature, and bulk composition. these profiles are then combined with an fe-s model applied to the core to build up the entire planetary model. based on the obtained interior structure and viscoelastic models, we can predict the corresponding geophysical response. subsequently, we invert the available geophysical data for mars (mean density, moment of inertia, tidal love number, and global dissipation) for a set of model parameters representing the interior structure and viscoelastic behavior. for this, we employ a bayesian approach to sample solutions to the inverse problem and determine the uncertainties. the results reveal that each of the aforementioned rheological models is capable of fitting the geophysical data. the resultant probability distributions for the major interior properties, such as core radius and composition, mantle thermal state, and crustal properties generally overlap for all investigated rheological models. the inversion results indicate that within the existing uncertainties and assumptions, the difference caused by the rheological models is less significant in determining interior structure. models and data from other studies (e.g. seismology and geodynamics) can be combined with current study to improve the knowledge on the rheological models. tidal love numbers and dissipation rate, among others, affect the orbital evolution of phobos and are used to estimate its lifetime. the models of mars proposed here can be used to predict the higher-degree love numbers, which may have non-negligible impact on modeling the orbital evolution of phobos. in exoplanets, tidal heating is believed to be more significant and the choice of an appropriate type of rheology can be more determining. the model proposed in this research can be applied in the case of exoplanets for better understanding of the processes in these worlds. | investigating rheological models in the context of geophysical inversion for planetary structure |
the msl rover curiosity crossed the contact between aeolis palus and lower mt. sharp on sol 700 and found the basaltic, mugearitic, and potassic sedimentary rocks of aeolis palus transition sharply into the silica-enriched (45-75 wt%) murray fm. however, curiosity has discovered alkalic float rocks reminiscent of aeolis palus on mt. sharp units as far as the vera rubin ridge (vrr) 3 km southeast and 300 m above aeolis palus. here, we present alpha particle x-ray spectrometer (apxs) results for the alkalic float. seven alkali-enriched targets (na2o = 3.0-4.5 wt%; k2o = 0.5-3.2 wt%) were encountered over sols 940-1600, most of which are associated with dark, blocky deposits of loose material on top of the murray fm. (e.g., ravalli, badlands, and sonneblom). on sol 2015, curiosity discovered a diverse deposit of float scattered over 70 m2 on top of the vrr. two of the nine rocks (tyndrum and arrochar) have textures, colors, and compositions (na2o+k2o 8 wt%) nearly identical to jakem, a mugearitic float rock found on sol 46 and an apxs class with 15 targets (sols 46-564). two targets (hopeman and waternish) are conglomerate with intermediate total alkali (4.0-5.5 wt%) suggesting a mixture of soil-like and alkalic material. one target (minginish) is potassic (k2o = 2.4 wt%; na2o = 3.1 wt%), having the fine-grained texture and composition of the bathurst inlet class, named after a sol 54 target and representative of potassic rocks that co-occur with mugearitic jakem rocks on aeolis palus. the mugearitic rocks have no detectable ge, whereas the potassic minginish has 250 ppm ge. this contrast in ge enrichment is typical of aeolis palus rock classes. two of the rocks have unique, silica-enriched (61-66 wt%) compositions (askival and sanquhar) with depletions in most major and minor elements relative to jakem, but with enriched total alkali (3.8-5.8 wt%). both are a bimodal mixture of dark gray, fine-grained material and white material. we speculate that the dark material is mugearitic and the white material is a highly altered silica-rich phase. elevated ge (40-85 ppm) indicates hydrothermal alteration. the co-occurrence of potassic bathurst inlet class rocks with mugearitic jakem class rocks is evidence that the alkalic deposits on lower mt. sharp have a common source region and/or genetic history with the aeolis palus units. | alkalic float on lower mt. sharp units in gale crater, mars: results from curiosity's alpha particle x-ray spectrometer |
solar energy harvesting through photovoltaic conversion has gained great attention as a sustainable and environmentally friendly solution to meet the rapidly increasing global energy demand. currently, the high cost of solar-cell technology limits its widespread use. this situation has generated considerable interest in developing alternative solar-cell technologies that reduce cost through the use of less expensive materials and processes. perovskite solar cells provide a promising low-cost technology for harnessing this energy source. in chapter two, a moisture-assist method is introduced and studied to facilitate grain growth of solution processed perovskite films. as an approach to achieve high-quality perovskite films, i anneal the precursor film in a humid environment (ambient air) to dramatically increase grain size, carrier mobility, and charge carrier lifetime, thus improving electrical and optical properties and enhancing photovoltaic performance. it is revealed that mild moisture has a positive effect on perovskite film formation, demonstrating perovskite solar cells with 17.1% power conversion efficiency. later on, in chapter four, an ultrathin flexible device delivering a pce of 14.0% is introduced. the device is based on silver-mesh substrates exhibiting superior durability against mechanical bending. due to their low energy of formation, organic lead iodide perovskites are also susceptible to degradation in moisture and air. the charge transport layer therefore plays a key role in protecting the perovskite photoactive layer from exposure to such environments, thus achieving highly stable perovskite-based photovoltaic cells. although incorporating organic charge transport layers can provide high efficiencies and reduced hysteresis, concerns remain regarding device stability and the cost of fabrication. in this work, perovskite solar cells that have all solution-processed metal oxide charge transport layers were demonstrated. stability has been significantly improved compared with cells made with organic layers. degradation mechanisms were investigated and important guidelines were derived for future device design with a view to achieving both highly efficient and stable solar devices. organometal halide based perovskite material has great optoelectronic proprieties, for example, shallow traps, benign grain boundaries and high diffusion length. the perovskite leds show pure electroluminescence (el) with narrow full width at half maximum (fwhm), which is an advantage for display, lighting or lasing applications. in chapter five, perovskite leds are demonstrated employing solution processed charge injection layers with a quantum efficiency of 1.16% with a very low driving voltage. | interface engineering and morphology study of thin film organic-inorganic halide perovskite optoelectronic devices |
in earth's deep subsurface the presence of life and the ecological and evolutionary aspects of life, are dictated by a host of physical and chemical constraints. these factors include temperature, pressure, redox and other chemical potential gradients, overlying productivity, hydrologic recharge, water availability, sediment or rock age, and microbial power requirements. we have historically viewed these parameters through a lens that conforms to the convenience of our analytical methods and that occurs over human time scales. but as we learn that microbes respond to phenomena beyond these limited spatial and temporal extents, new questions arise: how are subsurface microbes responsive to rhythmically or acutely changing earth processes like tectonism, planetary precession, or eustatic sea level change? how do various processes interact with each other to enable or challenge the possibility of life in a given place? how can we conceptualize the inextricably coupled, multiple large-scale geological and biological processes even though they are hidden from observation? geological processes occur on spatial and temporal scales (molecular to planetary and instantaneous to multi-millennial) that are familiar to geologists and overlap with the range of projected microbial survival conditions in earth's subsurface. we hypothesize that microbiologists who study the subsurface are still acquainting themselves with meaningful geological and planetary processes that define life in the subsurface. a more complete understanding of deep life - and its capacity for survival, ability to exploit unique niches, and issues related to dispersal, mutation, and biotic interactions - should emerge as we scale habitats spatially from mineral grains to continents and ocean basins and temporally from the short lifetime of some rna molecules to long, dynamic earth cycles. such a reckoning will also help us to conceive of where life might be sustained in places other than earth, where light from the sun, or another star, may be too distant or weak to serve as a substantial source of energy, or in contrast, where life in the subsurface is the only possible option because the surface is too energetically illuminated to be inhabited. | expanding life's boundaries: a grand challenge of estimating where and how life survives in earth and other planets |
energy applications are essential for the development of technologies capable of confronting the challenges inherent to a growing global population. among the different renewable energies, the solar resource has advanced as the most promising due to its omnipresence in earth life. this work investigates the synthesis and properties of three materials with the potential to contribute to the utilization and storage of solar energy. in detail, this dissertation addresses the feasibility of cu2znsns4 (czts) as a novel thin film photovoltaic material by studying the role of process parameters on the phase segregation and grain-to-grain homogeneity of czts thin films. it also studies the stability of silicon-carbon heterostructures for lithium-ion batteries and introduces a non-thermal plasma/chemical vapor deposition (cvd) process that offers good control on particle size and composition. finally, this work presents a comprehensive investigation of plasmonic titanium nitride nanoparticles synthesized with a non-thermal plasma method. it demonstrates their potential as photocatalysts and photothermal absorbers with good thermal stability as compared to conventional plasmonic materials based on costly noble metals. | nanomaterials for energy applications: from photovoltaics to plasmonic catalysis |
we used local correlation tracking to estimate horizontal velocities in an image sequence of convection at the solar photosphere, at high spatial and temporal resolution (0.034'' pixels and 10-second cadence, respectively) observed in tio (705.7 nm) with the goode solar telescope. a key goal of our study was to estimate the lifetimes of flows in granules, which have implications for models of coronal heating that rely upon rapid evolution in photospheric forcing of coronal magnetic field evolution. we estimate flow lifetimes by fitting the decorrelation times of flow maps. for lct apodization windows near 200 km (8 pixels), we find flow lifetimes of about 60 sec. on these scales, we also find flow speeds consistent with previous reports, of order a few km/sec. with the lct apodization window set to 100 km (4 pixels), we found flows to be faster and shorter-lived. the observed flow evolution is therefore rapid enough to excite turbulent interaction between upward- and downward-propagating alfvén waves between the photosphere and corona, consistent with the predictions of a coronal heating model proposed by van ballegooijen et al. (2011). | rapid evolution of small-scale flows in solar granulation |
since its landing at gale crater five years ago, the curiosity rover has provided us with unparalleled data to study active surface processes on mars. repeat imaging campaigns (i.e. "change-detection campaigns") conducted with the rover's cameras have allowed us to study martian atmosphere-surface interactions and characterize wind-driven sediment transport from ground-truth observations. utilizing the rover's periodic stops to image identical patches of ground over multiple sols, these change-detection campaigns have revealed sediment motion over a wide range of grain sizes. these results have been corroborated in images taken by the rover's hand lens imager (mahli), which have captured sand transport occurring on the scale of minutes. of particular interest are images collected during curiosity's traverse across the bagnold dune field, the first dune field observed to be active in situ on another planet. curiosity carried out the first phase of the bagnold dunes campaign (between ls 72º and 109º) along the northern edge of the dune field at the base of aeolis mons, where change-detection images showed very limited sediment motion. more recently, a second phase of the campaign was conducted along the southern edge of the dune field between ls 312º to 345º; here, images captured extensive wind-driven sand motion. observations from multiple cameras show ripples migrating to the southwest, in agreement with predicted net transport within the dune field. together with change-detection observations conducted outside of the dune field, the data show that ubiquitous martian landscapes are seasonally active within gale crater, with the bulk of the sediment flux occurring during southern summer. | the bagnold dunes in southern summer: active sediment transport on mars observed by the curiosity rover |
we study the transport of small-scale magnetic elements on the solar photosphere using both observations and simulations. observational data was obtained from hinode - solar optical telescope (sot/sp) instrument and simulations from muram code. the magnetic flux elements were tracked in both data sets and statistics were obtained. we compute the probability density of the eulerian distances traveled by the flux elements along lagrangian trajectories. for a two-dimensional random walk process this distribution should be rayleigh. preliminary results show that the measured probability distribution in both the observed and simulated data approximates a random walk, on time scale close to the lifetime of granules, but deviates from it for longer times. this implies that diffusion may not be an appropriate framework for transport in the solar photosphere. we explore the roles of flux cancelation and element trapping in producing this result. work is ongoing. | turbulent transport of small-scale magnetic flux elements on solar photosphere |
the >230 m thick murray formation is the lower-most unit of the mount sharp group, and interpreted as primarily lacustrine. representative mudstone, siltstone and fine sandstone targets, encountered above -4330 m elevation, trend to lower si, al, ti, cr and ca, and higher fe, mn, zn, p and mg than the murray below. less common, distinctive, coarser grained sandstone lenses tend to exhibit slightly different compositions to the more typical murray but, overall, show similar elemental trends with elevation, albeit exaggerated. this suggests that the variations observed with elevation in al, ti, cr, k, fe, mn, zn and p within both the coarser sandstones and finer grained murray are the result of diagenetic and/or alteration processes rather than provenance or physical sedimentary processes such as sorting. this is supported by the chemistry of obvious diagenetic, dark grey nodules, and other potential diagenetic/alteration features within this section, which show variations in the same element concentrations (i.e., p, mn, fe, zn, mg, ca and s), distinct from diagenetic features lower down in the stratigraphy, indicating mobility of these elements within this section and changing fluid chemistry. trends in feo/mno generally mimic the presence of ferric absorption features observed in visible/near infrared passive spectra from the chemcam instrument and from crism orbital data, which may be consistent with changes in redox conditions as we climb up section towards vera rubin ridge (hematite ridge). layer-parallel caso4 is also common, and not observed below -4330 m. this may represent syndepositional evaporite layers, or late bedding/laminae parallel veins emplaced after lithification, in conjunction with cross-cutting veins. the overall differences in composition between the sandstone targets and finer grained murray are attributed to distinct provenances and/or sorting during transport. we will discuss the implications of the trends and composition of the murray above -4330 m elevation and how this pertains to the history and evolution of the murray formation as a whole, climatic conditions during the formation of the murray and the nature of gale crater lake. also, what do the trends imply about how circulating fluids have evolved within the murray sediments and ph, redox, salinity conditions of these fluids? | recent compositional trends within the murray formation, gale crater, mars, as seen by apxs: implications for sedimentary, diagenetic and alteration history. |
enceladus is a medium sized icy satellite (mis) of saturn. mis are built of mixtures of rocks and ices. according to [1]: "for life to have emerged […] on the early earth, a sustained source of chemically transducible energy was essential. the serpentinization process is emerging as an increasingly likely source of that energy" (see also [2]). we consider here conditions for origin of life in the early enceladus and later proliferation of the life. mass of serpentinite: the serpentinization on the earth is often considered with hydrothermal activity in neovolcanic zones along mid-oceanic spreading centers. however, only in small part the hydrothermal activity really occurs. a simple calculations (e.g. [3]) indicate that mass fraction of silicates in enceladus is ~0.646, hence the total mass of its silicate is ~6.97 10^1^9 kg. [4] considered the process of differentiation and core forming in enceladus. he found that the result of differentiation is a relatively cold core of loosely packed grains with water between them. the entire core of enceladus was probably permeable. this could lead to formation of extensive hydrothermal convective systems. it indicates that total mass of serpententinized silicate in enceladus could be larger than on the earth. the evolution of temperature in the enceladus interior for the first a few hundreds myr is given in [4]. he found that the temperature allows for existing the life even in the center of the satellite. it is possible that for hundreds of myr the conditions in enceladus were more favorable for origin of life than on the earth. proliferation of life: the low gravity of the enceladus and its volcanic activity make transport possible. note that the low temperature of plumes from active region of enceladus does not kill the organisms. the primitive bacteria could leave the enceladus with volcanic jets in the same way as particles of the e ring. other mechanisms could transport particles to terrestrial planets. therefore it is possible that the enceladus was a cradle of the life in the solar system. references: [1] russell, m. j., hall, a. j., and martin w. (2010). geobiology (2010), 8, 355-371. [2] izawa m.r.m. et al. (2010). planet. space sci. 58, 583-591. [3] abramov, o., mojzsis, s.j., (2011) icarus 213, 273-279. [4] czechowski, l. (2014) planet. space sci. 104, 185-199 | the possibility of life proliferation from enceladus |
extraterrestrial studies are typically conducted on mg samples from cm-scale features, while landing sites are selected based on m to km-scale features. it is therefore critical to understand spatial distribution of organic molecules over scales from cm to the km, particularly in geological features that appear homogenous at m to km scales. this is addressed by feldspar, a nasa-funded project that conducts field operations analogous to mars sample return in its science, operations, and technology [1]. here, we present recent findings from a 2016 and a 2017 campaign to multiple martian analogue sites in iceland. icelandic volcanic regions are mars analogues due to desiccation, low nutrient availability, temperature extremes [2], and are relatively young and isolated from anthropogenic contamination [3]. operationally, many icelandic analogue sites are remote enough to require that field expeditions address several sampling constraints that are also faced by robotic exploration [1, 2]. four field sites were evaluated in this study. the fimmvörðuháls lava field was formed by a basaltic effusive eruption associated with the 2010 eyjafjallajökull eruption. mælifellssandur is a recently deglaciated plain to the north of the myrdalsjökull glacier. holuhraun is a basaltic spatter and cinder cone formed by 2014 fissure eruptions just north of the vatnajökull glacier. dyngjusandur is a plain kept barren by repeated aeolian mechanical weathering. samples were collected in nested triangular grids from 10 cm to the 1 km scale. we obtained overhead imagery at 1 m to 200 m elevation to create digital elevation models. in-field reflectance spectroscopy was obtained with an asd spectrometer and chemical composition was measured by a bruker handheld xrf. all sites chosen were homogeneous in apparent color, morphology, moisture, grain size, and reflectance spectra at all scales greater than 10 cm. field lab atp assays were conducted to monitor microbial habitation, and home laboratory analyses include qpcr, raman spectroscopy and community sequencing. for more information, find us on facebook @feldsparesearch. [1] amador, e. s. et al. (2015) planet. space sci., 106 1-10. [2] cockell, c. s. et al., (2011) astrobio., 11 679-694; gentry, et al., (2017) astrobio., in press. [3] bagshaw, e. a. et al., (2011) astrobio., 11 651-664. | field exploration and life detection sampling for planetary analogue research (feldspar) |
the mastcam m-34 imaging system on the curiosity rover has acquired multispectral images (445, 527, 751, 1012 nm) at multiple times of day at several locations along the traverse, sampling a variety of terrain types [1-4]. the light scattering properties of rocks and soils can be examined quantitatively using radiative transfer models with data extracted from these images [5-7], with the goals of providing information useful for understanding microphysical processes, atmospheric models, and orbital observations. navcam stereo images also were acquired to compute surface normals and local incidence and emission angles. these can be combined with sky models to correct for diffuse reflectance on individual surface facets prior to photometric modeling. here we model data sets acquired on sols 171-184 while the rover was parked at the john klein drill site in yellowknife bay [2]. regions of interest were extracted from m-34 images on soils, rocks with variable dust cover, and rover tracks to provide data sets with sufficient phase angle coverage to allow hapke radiative transfer modeling of each unit. preliminary model results performed without the atmospheric correction showed rover tracks exhibited 1-term henyey-greenstein (hg) asymmetry parameter values consistent with more forward scattering surfaces compared to rocks. the 2-term hg scattering parameters (b and c) suggested that soils and dusty rocks were more backscattering than less dusty rocks, consistent with results from the mer spirit site [5]. preliminary single-scattering albedo values for soils varied from 0.38 (445 nm) to 0.87 (1012 nm); less dusty rocks varied from 0.59 (445 nm) to 0.81 (1012 nm). macroscopic roughness values showed larger values for less dusty rocks (17-22˚). opposition effect width (h) values implied higher porosity (or less uniform grain size distributions) in rocks than soils. model results presented at the meeting will incorporate sky models. future work will include additional mastcam data sets. [1] johnson, j., et al., lpsc, 44, abstract #1374, 2013;[2] johnson, j., et al. 8th int. conf. mars, #1073, 2014; [3] johnson, j., et al., lpsc, #1424, 2015; [4] johnson, j., et al., agu, #p43b-2125 2015; [5] johnson, j., et al., jgr, 111, e02s14, 2006; [6] johnson, j., et al. jgr, 111, e12s16, 2006; [7] johnson, j. et al., icarus, 248, 25-71, 2015. | modeling of mastcam visible/near-infrared spectrophotometric observations at yellowknife bay |
many lakes may have existed in gale crater, mars. five years of investigations by the curiosity rover has revealed clear sedimentological evidence for the presence of at least two in the rover's landing ellipse. they are here named the first lake and the last lake. the first lake formed soon after the formation of the crater and was previously introduced by grotzinger et al. (2015). water rushed into the crater from its northern rim inundating the crater quickly. physical evidence for the presence of the first lake includes 300 m of mudstone of the murray formation exposed in the foothills of mt. sharp. abundance of fine-grained lithologies, dominance of laminations, absence of features suggestive of sedimentation in shallow-waters, and the lack of indicators of an ice-covered lake, all suggest that the murray formation was deposited at the bottom of a lake that was kilometers deep and was not frozen. the first lake eventually dried up and about 3 km of sediments whose characteristics are known only from orbital images filled gale crater (malin and edgett, 2000). a sediment-filled gale crater was later exhumed from its margins, leading to the emergence of mt. sharp at the crater center. afterwards, water flowed into the crater, this time from the south, forming a100 m - 200 m deep lake in the vicinity of the landing ellipse: the last lake. the evidence for the last lake is sedimentological record of two to three river deltas preserved in the rugged terrain unit. these deltas prograded rapidly from south to north depositing a 5 m-thick layer over all previously deposited strata. the first lake established the potential conditions for life to begin in gale crater. they continued until the last lake dried up and mars became permanently cold. the duration is not well known, but it may have endured for millions of years. sedimentological evidence provided by the curiosity rover suggests that multitude of opportunities existed for the inception of life between the two lakes. these include diverse shallow- and deep-water environments hospitable to life, abundant supply of liquid waters of varied geochemical characteristics, and favorable climate conditions. | between two lakes: opportunities for the inception of life in gale crater, mars |
cadmium telluride (cdte) has the highest theoretical limit to conversion efficiency of single-junction photovoltaic (pv) technologies today. however, despite a maximum theoretical open-circuit voltage of 1.20 v, record devices have historically had voltages pinned around only 900 mv. voltage losses due to high recombination rates remains to be the most complex hurdle to cdte technology today, and the subject of on-going research in the physics pv group at colorado state university. in this work, an ultrathin cdte device architecture is proposed in an effort to reduce bulk recombination and boost voltages. by thinning the cdte layer, a device's internal electric field extends fully towards the back contact. this quickly separates electrons-hole pairs throughout the bulk of the device and reduces overall recombination. despite this advantage, very thin cdte layers also present a unique set of optical and electrical challenges which result in performance losses not as prevalent in thicker devices. when fabricating cdte solar cells, post-deposition treatments applied to the absorber layer are a critical step for achieving high efficiency devices. exposure of the polycrystalline cdte film to a chlorine species encourages the passivation of dangling bonds and larger grain formation, while copper-doping improves device uniformity and voltages. this work focuses on experiments conducted via close-space sublimation to optimize cdcl2 and cucl treatments for thin cdte solar cells. sweeps of both exposure and anneal time were performed for both post-deposition treatments on cdte devices with 1.0 mum absorber layers. the results demonstrate that thin cdte devices require substantially less post-deposition processing than standard thicker devices as expected. additionally, the effects of cdte growth temperature on thin devices is briefly investigated. the results suggest that higher growth temperatures lead to both electrical and stoichiometric changes in cdte closely associated with lower carrier lifetimes and poorer overall performance. | processing and characterization of thin cadmium telluride solar cells |
paleo-lake deposits indicate that mars once sustained liquid water, supporting the idea of an early "wet and warm" mars. however, liquid water can be sustained under ice in cold conditions as demonstrated by perennially ice-covered lakes (picls) in antarctica. if martian lakes were ice-covered, the global climate on early mars could have been much colder and dryer than if the atmosphere was in equilibrium with long-lived open water lakes. modern picls on earth have diagnostic sedimentary features. unlike open water lakes that are dominated by mud, and drop stones or tills if icebergs are present, previous studies determined that deposits in picls can include coarser grains that are transported onto the ice cover, where they absorb solar radiation, melt through the ice and are deposited with lacustrine muds. in lake hoare, antarctica, these coarse grains form conical sand mounds and ridges. our observations of ice-covered lakes joyce, fryxell, vanda and hoare, antarctica suggest that the distributions of grains depend significantly on ice characteristics. deposits in these lakes contain moderately well to moderately sorted medium to very coarse sand grains, which preferentially melt through the ice whereas granules and larger grains remain on the ice surface. similarly, high albedo grains are concentrated on the ice surface, whereas low albedo grains melt deeper into the ice, demonstrating a segregation of grains due to ice-sediment interactions. in addition, ice cover thickness may determine the spatial distribution of sand deposited in picls. localized sand mounds and ridges composed of moderately sorted sand are common in picls with rough ice covers greater than 3 m thick. in contrast, lakes with smooth and thinner ice have disseminated sand grains and laterally extensive sand layers but may not have sand mounds. at gale crater, mars, the murray formation consists of sandy lacustrine mudstones, but the depositional process for the sand is unknown. the presence of a perennial ice-cover could explain the sand, but no definitive ice-related deposits have been identified to date. the murray formation is an ideal target to start analyzing for evidence of ancient picl deposits on mars. | were lakes on early mars perennially were ice-covered? |
panspermia theories require the transport of micro-organisms in a viable form from one astronomical location to another. the evidence of material ejection from planetary surfaces, of dynamical orbit evolution and of potential survival on landing is setting a firm basis for interplanetary panspermia. pathways for interstellar panspermia are less clear. we compare the direct route, whereby life-bearing planetary ejecta exit the solar system and risk radiation hazards en route to nearby stellar systems, and an indirect route whereby ejecta hitch a ride within the shielded environment of comets of the edgeworth- kuiper belt that are subsequently expelled from the solar system. we identify solutions to the delivery problem. delivery to fully-fledged planetary systems of either the direct ejecta or the ejecta borne by comets depends on dynamical capture and is of very low efficiency. however, delivery into a proto-planetary disc of an early solar-type nebula and into pre-stellar molecular clouds is effective, because the solid grains efficiently sputter the incoming material in hypervelocity collisions. the total mass of terrestrial fertile material delivered to nearby pre-stellar systems as the solar system moves through the galaxy is from kilogrammes up to a tonne. subject to further study of bio-viability under irradiation and fragmenting collisions, a few kg of original grains and sputtered fragments could be sufficient to seed the planetary system with a wide range of solar system micro-organisms. | interstellar transfer of planetary microbiota |
short-lived radioisotopes (slrs) were present in the early solar system, providing evidence that the solar system was impacted by a supernova prior to or during its formation. however, hydrodynamical models of the injection of slrs fail to achieve sufficient mixing, presenting a challenge to this hypothesis. we propose the injection of slrs via dust grains in an attempt to overcome the mixing barrier. to test this hypothesis we simulate injection into a presolar gas cloud under various assumptions. our results suggest that slr transport in dust grains is a viable mechanism for generating observed slr abundances. | tracing dust grains from supernovae to the solar nebulae |
during its >13 km traverse so far, the mars rover curiosity encountered several dark, fine-grained float rocks. the first example investigated with the apxs, et_then (sol 91), was found near the landing site. it has an enigmatic composition with very high 27% feo, elevated na and k, and low mg. a boulder with nearly identical chemistry, called secure (sol 560), was found near the kimberley waypoint, some 5 km southwest. both rocks have a unique enrichment in ga of about 70 ppm, significantly greater than the typical 20 ppm or lower that represents approximately the detection limit for ga with the apxs. while the origin of these loose float rocks is still under discussion, a recent measurement of a boulder another 7 km southwest on lower mount sharp might shed light on the formation process. two targets, named sonneblom and zambezi (sols 1407 and 1409), were measured on a dark gray boulder in a blocky deposit overlying murray formation mudstones. they share many of the compositional characteristics of the felsic jake_m class rocks, also found along curiosity's traverse, which have elevated alkaline elements and very low cr, ni, and zn. the key difference relative to the original jake_m rock is the higher fe and si and lower al. sonneblom and zambezi are similar to several isolated rocks encountered earlier during the traverse and nearly identical to oscar (sol 515). the three rock classes, jake_m, oscar and et_then, all occurring as isolated float rocks separated by >10 km, seem to form a mixing line between jake_m proper and et_then as endmembers, adding increasing amounts of iron oxides and possibly sio2 as cement to fragments of jake_m-like material. another curious piece of evidence is that the rocks sonneblom, zambezi and oscar have uniquely elevated ga of about 40 ppm as well, connecting them to et_then. whereas in-depth textural comparison of all these chemically related rocks is pending, based on the compositional trends these erosion-resistant rocks might have been part of an extensive formation that incorporated the felsic material into varying amounts of iron oxides and sio2 as cement. a connection to the hematite ridge, expected to be reached in the near future with the rover on its traverse up mount sharp, could be possible as well. the elevated fe/mn ratio of secure- and oscar-type rocks indicates an elevated fe3+ abundance. | possible diagenetic connection between the dark fe-rich rocks at gale crater, mars, and the felsic jakem class rocks |
enceladus is a tiny moon circling saturn. through cassini's discoveries we now know that it has a global, geologically long-lived salt-water ocean inside, in contact with the silicate core, at which interface there is moderate-temperature hydrothermal activity perhaps akin to the lost city vent structure on earth's seafloor, which hosts a rich ecology. the ocean water, containing nanosilica grains from the hydrothermal vents, and large organic molecules not yet identified, is expressed directly and continuously into space via fissures in enceladus' south polar region. cassini has analyzed the composition of ice grains and gas by repeatedly flying through this plume on multiple flybys, so now we know how to detect unmistakable signs of ocean life with modern instruments on a subsequent mission. this makes enceladus a natural laboratory for understanding how life - carbon- and water-based but not sharing earth life's origin -arose. to do so quickly without waiting for the next flagship opportunity requires a focussed mission that applies the most focussed and robust analytic techniques on the most easily accessed samples of the ocean—the plume itself. enceladus life finder (elf) was proposed to do just this, and we describe why a graceful, elvish approach to life detection is optimal. | the habitability of enceladus from cassini and enceladus life finder as the next step |
it was claimed that at least certain stages of the process by which life originated occurred in space, hence there is a strong interest in the range of organics in ice-rich structures in interstellar dense molecular clouds (mc) that may have contributed the precursors of life. the combination of the astronomical data regarding star-forming regions with published experimental results of energetic particle and ultraviolet (uv) processing of ices with our theoretical modelling will help estimating the contribution of the cosmic rays (cr) and uv irradiation to the changes in dust grains in the dense mc. from astrobiology's point of view, an area of rapidly growing interest, it seems important to understand the mechanisms by which large molecules, possibly of pre-biotic interest like heavy hydrocarbons and amino acids could be formed by uv and cr processing of chemically simpler solids in the environment of the clouds. if it turned out that such conversions depended, for example, on star formation efficiency not only in the cloud given, but also in the galaxy as a whole, including a time-dependent rate over the galaxy life, then these results would have interesting implications for astrochemistry and astrobiology. my conclusion is that the life origin is limited not only in space, where the solar system is located, but also in time, when its precursor molecular cloud was originated, about 6-7 billion years ago. | was the universe always a convenient place for the origin of life? |
introduction: enceladus is a medium-sized icy satellite (mis) of saturn. mis are built of mixtures of rocks and ices. enceladus with its radius of 250 km is one of the smallest of mis, however, it is geologically active. according to [1]: "for life to have emerged […] on the early earth, a sustained source of chemically transducible energy was essential. the serpentinization process is emerging as an increasingly likely source of that energy. serpentinization of ultramafic crust would have continuously supplied hydrogen, methane, […] to off-ridge alkaline hydrothermal springs that interfaced with the metal-rich carbonic hadean ocean" (see also [2]). we consider here conditions for origin of life in early enceladus and possible proliferation of the life from this satellite to the rest of solar system. mass of serpentinite: the serpentinization on the earth is found in neovolcanic zones along mid-oceanic spreading centers. however, only in small part of them the hydrothermal activity really occurs. after [3] we consider the following reaction: mg2sio4 + mgsio3 + 2h2o -> mg3si2o5(oh)4 . this reaction releases 241 000 j per kg of serpentine produced. simple calculations (e.g. [4]) indicate that mass fraction of silicatesfmas in enceladus is ∼0.646, hence the total mass of its silicate is ∼6.97 1019 kg. [4] found that the early core in enceladus was a relatively cold structure built from loosely packed grains with water between them. at that time, there was not mechanism of removing the water. since rocks are permeable up to the pressure of ∼300 mpa then the entire core of enceladus was probably permeable for liquids. this could lead to formation of extensive hydrothermal convective systems. t-p conditions in enceladus: the pressure in the center of enceladus is ∼2.3 107 pa that corresponds to pressure on the depth 2300 m in a terrestrial ocean. the evolution of temperature in the enceladus interior for the first a few hundreds myr is considered by [4]. if enceladus accreted later than 2.4 myr after formation of cai then the temperature allows for existing the life even in the center of the satellite. for hundreds of myr the conditions in the interior of enceladus were more favorable for origin of life than on the earth [5, 6]. proliferation of life: we do not know the probability of life origin. the life could be a common phenomenon originating in relatively short time if conditions are favorable. however, it is possible also that the life had originated only one time in the universe. if this option is true then the transport of primitive organism is critical. from the core to the surface. the volcanic activity offers occasion to transport organisms from the core to the surface of early enceladus. the form of the activity could be essentially the same as present in the south polar terrain (spt). from the surface to e-ring. the existence of e-ring is the evidence that cryo-volcanic jets could eject gas and solid particles (possibly with primitive organism) into orbit around saturn. from e-ring to an orbit around sun. the mechanism of gravity assist could be responsible for acceleration of some particles from the orbit around the saturn into orbit around the sun. the existence of several satellites of saturn increases the probability of this mechanism. the sequence of close encounters with these satellites could eventually transfer enough energy to the grains to leave the orbit around saturn. from orbit of saturn to terrestrial planets. to reach the terrestrial planets the grain must be substantially decelerated. there are a few possible mechanisms of loosing energy: poynting-robertson mechanism (for grains larger than a few μm), yarkovsky diurnal effect (if the grain is a retrograde rotator) and yarkovsky seasonal effect (for grains of diameter of a few meters); e.g. [7]. after [6] we consider here the poynting-robertson effect which is effective for the grains size of e-ring particles. the time of falling from the orbit with the radius 9.5 au to an orbit with the radius 1 au for the grains of density 1000 kg m-3 and radius of 10 μm is ∼650 000 yr. for large grains (e.g. ∼1 m) other processes, like yarkovsky effect, could be more effective than the poynting-robertson effect. the larger grains give better protection against the radiation. decelaration in the upper atmosphere. small ratio of mass of the considered particles to their cross section makes possible to decelerate them in upper atmospheres of terrestrial planets without substantial increase of temperature - e.g. [7]. during deceleration of larger bodies the dissipation of heat could be high, but cooling effect of ablation would reduce the temperature. the proposed mission to enceladus (enceladus life finder [8]) could solve the considered here problem. note, that if the life in the solar system has the common origin then enceladus is "a better cradle" than the earth, because high gravity and dense atmosphere makes the proliferation of terrestrial life rather difficult. references: [1] russell, m. j., hall, a. j., and martin w. (2010). geobiology (2010), 8, 355-371. [2] izawa m.r.m. et al. (2010). planet. space sci. 58, 583-591. [3] abramov, o., mojzsis, s.j., (2011) icarus 213, 273-279. [4] czechowski, l. (2014) planet. sp. sc. 104, 185-199. [5] czechowski, l. (2014). enceladus, a cradle of life of the solar system. presented in egu 2014, vienna. [6] czechowski, l. (2014) enceladus as a place of origin of the life in the solar system. - submitted. [7] pater (de), i, and lissauer j.j., (2001). planetary sciences, cambridge university press, cambridge, uk, pp. 528. [8] wainwright, m., wickramasinghe n. ch., rose, ch. e., baker, a. j., (2014). astrobiology & outreach, [8] lunine, j.i.; waite, j.h.; postberg, f.; spilker, l. (2015). 46th lunar and planetary science conference. | the possibility of life proliferation from enceladus |
the possibility that crystalline formaldehyde polymers are present in cometary dust is discussed. in common with most other parent molecules proposed for comets, (h2co)n is difficult to detect, even if it is present in relatively high concentrations. the optical properties of these polymers in the visual and infrared regions are similar to those of silicate grains, and crystalline formaldehyde polymers provide no emission at 6 cm wavelength. the lifetime of gaseous h2co in the solar radiation field is too short, and the expected transitions in the microwave region would be too weak to be detected. however, the available data concerning the physical properties of comets indicate that polymerized formaldehyde cannot be ruled out as a major constituent of cometary material. | formaldehyde polymers in comets |
the flood, one of the major natural hazards, resulted in serious damages and losses of human life and economy frequently all over the world. as we see, human activity intensify the risk of flood hazards by changing global water cycle. however, the instrumental data only limited to the last 150 years, are too short to identify decadal to centennial-scale climatic fluctuations and discuss the climate-flood relationship. therefore, we present a 6200-year long flood reconstruction from east asian monsoon margin, based on reliable dated sedimentry flood deposits in tianchi lake. we display that 13 great floods are recorded in em1 (end-member 1) decomposed from grain-size and these are verified by other proxies such as elements, redness and paleoflood records reconstructed from the yellow river and its tributaries in northern china and historical documents in weihe river. furthermore, compared to late-holocene, the frequency of great floods enhance substantially between 6200cal yr bp and 4000cal yr bp when asian summer monsoon is strengthen. the incresed flood frequncy may be triggered by enso and rising of sst over west pacific related to solar activity. in the paleoclimatic perspective, this paper point out that we should pay more attention to furture flood under the background of global warming | mid-late holocene paleoflood reconstruction at tianchi lake, liupan mountains and its possible relation with asian summer monsoon |
organic-metal halide perovskites have brought about a new wave of research in the photovoltaic community due to their ideally suited optical and electronic parameters. in less than a decade, perovskite solar cell performance has skyrocketed to unprecedented efficiencies with numerous reported methodologies. perovskites face many challenges with high-quality film morphology, interfacial layers, and long-term stability. in this work, these active areas are explored through a combination of studies. first, the importance of perovskite film precursor ratios is explored with an in-depth study of carrier lifetime and solvent-grain effects. it was found that excess lead iodide precursor greatly improves the film morphology by reducing pinholes in the solar absorber. dimethyl sulfoxide (dmso) solvent was found to mend grains, as well as improve carrier lifetime and device performance, possibly by passivation of grain boundary traps. second, applications of perovskite with tandem cells is investigated, with an emphasis for silicon devices. perovskites can easily be integrated with silicon, which already has strong market presence. additionally, both materials' bandgaps are ideally suited for maximum tandem efficiency. the silicon/perovskite tandem device structure necessitated the optimization of inverted (p-i-n) structure devices. pedot:pss, copper oxide, and nickel oxide p-type layers were explored through a combination of photoluminescent, chemical reactivity, and solar simulation results. results were hindered due to resistive ito and rough silicon substrates, but tandem devices displayed voc indicative of proper monolithic performance. third, replacement of titanium dioxide n-type layer with iron oxide (fe 2o3, common rust) was studied. iron oxide experiences less ultraviolet instability than that of titanium dioxide under solar illumination. it was found that current density slightly decreased due to parasitic absorption from the rust, but that open circuit voltage decreased drastically due to poor band alignment. fe2o3 appears to be better suited to a narrower band gap material than methylammonium lead iodide perovskite. finally, encapsulation of perovskite devices with epoxy coatings is explored as a method to improve long-term stability. perovskites are sensitive to a variety of conditions, but most importantly water and polar molecules. encapsulants act as a moisture/oxygen barrier, but also prevent outgassing of the organic components. three epoxies were tested in high heat and high humidity conditions. important factors in the curing process were uncovered such as the sensitivity of uv-epoxies to amine functional groups found in common p-type dopants and perovskite layers. moisture ingress was the failure point for high-humidity/heat devices which was confirmed through conversion to yellow lead iodide. a revised device fabrication method is proposed to reduce moisture ingress for future experiments. | a study on organic-metal halide perovskite film morphology, interfacial layers, tandem applications, and encapsulation |
jupiter's moon europa is embedded deep within the jovian magnetosphere and is thus exposed to bombardment by charged particles, from thermal plasma to more energetic particles at radiation belt energies. examples of radiation-induced surface alteration include sputtering, radiolysis and grain sintering; processes that are capable of significantly altering the physical properties of surface material. radiolysis of surface ices containing sulfur-bearing contaminants from io has been invoked as a possible explanation for hydrated sulfuric acid detected on europa's surface and radiolytic production of oxidants represents a potential source of energy for life that could reside within europa's sub-surface ocean. accurate knowledge of europa's surface radiation environment is essential to the interpretation of space and earth-based observations of europa's surface and exosphere. furthermore, future landed missions may seek to sample endogenic material emplaced on europa's surface to investigate its chemical composition and to search for biosignatures contained within. such material would likely be sampled from the shallow sub-surface, and thus, it becomes important to know to which degree this material is expected to have been radiation processed. we will present modeling results of magnetospheric electron and ion bombardment of europa's surface, including interactions between these particles and surface regolith. previous models have mostly assumed a surface that consists of pure water ice. however, we have strong indications that hydrated sulfuric acid and salts are major surface constituents. here we will discuss the effect of varying surface composition on the locally absorbed radiation dose in surface regolith. in addition to magnetospheric particles, europa is also exposed to galactic cosmic rays (gcrs) - highly energetic particles from deep space that constantly bombard its surface. these high energy particles initiate extensive secondary particle cascades that are capable of penetrating to large depths (tens of meters).we have investigated gcr bombardment at europa by carrying out particle physics simulations of gcr ions incident on europa's surface ice and we will present a comparison of gcr versus magnetospheric radiation dose. | radiation bombardment at europa by magnetospheric particles and cosmic rays |
multicrystalline (mc) solar cells made from n-type silicon feedstock have shown record efficiencies of 22.3% in a tunnel-oxide passivating contact (topcon) cell structure. still, material-related carrier recombination limits the attainable efficiency. herein, the findings of metallic impurity and structural defect concentration present in n-type mc silicon are summarized, and their limiting properties on carrier lifetime and cell performance are elaborated. applying a dedicated model for carrier recombination at precipitate-silicon interfaces, it is demonstrated that carrier recombination at metallic precipitates may dominate in the analyzed material. direct evidence of the recombination activity of iron precipitates in n-type silicon is given by an analysis of intentionally grown iron precipitates: from a comparison of micro x-ray fluorescence (μxrf) analyses of differently sized iron precipitates and local carrier recombination from micro-photoluminescence (μpl), a direct correlation with enhanced carrier recombination is found. from these results, it is concluded that the high-performance n-type mc silicon is limited by recombination at (decorated) structural defects, namely, dislocation clusters and grain boundaries, whereas defects in the inner grains are not limiting the efficiency potential. finally, cell degradation under illumination and elevated temperature for n-type mc-silicon solar cells are discussed. | limiting defects in n-type multicrystalline silicon solar cells |
one of the leading hypotheses for the emergence of life suggests that the building blocks of life were delivered to earth at an early phase by comets and asteroids. protoplanetary disks around young stars offer a unique window into the physical and chemical processes that may have occurred in the early solar system. although only a limited number of atoms and molecules have been observed in these objects, high resolution observations with the atacama large millimeter/sub-millimeter array (alma) have revolutionized the study of protoplanetary disks. these observations indicate that local physical conditions strongly affect the molecular content of disks. molecules such as n$_2$h$^+$, c$_2$h and h$_2$co show ring-like structures suggesting, for some of them, an active gas-grain chemical coupling. evidence for gas-grain chemistry has been further strengthened by the detection of two complex organic molecules, methanol and methyl cyanide. in this presentation i will show results obtained from new detailed models that solve for the thermal structure of the disk and implement a full gas-grain chemical network. the novel aspect of this framework is the use of a three-phase approximation; the gas, grain surface and grain mantle are the three phases, and the chemistry occurring at the surface and in the bulk of the ice are treated as two distinct phases in interaction. based on these results, i will show that complex organic molecules efficiently form at the surface of grains in the dense, shielded midplane of disks. i will show that the radial and vertical variations of the physical conditions have a strong impact on the spatial distribution of these molecules and that ring-like structures for molecules such as h$_2$co and ch$_3$oh are a natural outcome of these variations. finally, i will discuss the impact of various disk physical parameters (such as the mass of the disk and the dust-to-gas mass ratio) on disk chemistry. | theoretical investigations on the formation of organic molecules in protoplanetary disks |
curiosity has completed a detailed chemo-stratigraphy analysis at the pahrump exposure of the murray formation. in total >570 chemical measurements and supporting remote micro images to classify texturally were collected. chemical trends with both stratigraphic position and with texture were evaluated. from these data emerges a complex aqueous history where sediments have interacted with fluids with variable chemistry in distinct episodes. the chemcam data collected at the nearby "garden city" (gc) vein complex provides constraints on the chemical evolution of the pahrump. gc is thought be stratigraphically above the pahrump outcrop. fluids producing the veins likely also migrated through the pahrump sediments. multiple episodes of fluids are evident at gc, forming distinct ca sulfate, f-rich, enhanced mgo, and feo-rich veins. these different fluid chemistries could be the result of distinct fluids migrating through the section from a distance with a pre-established chemical signature, fluids locally evolved from water rock interactions, or both. texturally rocks have been classified into two distinct categories: fine grained or as cross-bedded sandstones. the sandstones have significantly lower sio2, al2o3, and k2o and higher feo, and cao. fine grained rocks have further been sub-classified as resistant and recessive with other textural features such as laminations and pits noted.the strongest chemical trend in the fine-grained sandstones shows enhancements in mgo and feo in erosion-resistant materials compared to fine grained recessive units, suggesting that increased abundance of mg- and/or iron-rich cements may provide additional strength. the mgo and feo variations with texture are independent of stratigraphic locations (e.g resistant material at both the bottom and top of the outcrop both are enhanced in mgo and feo). the presence of the gc mgo and feo rich veins provides additional evidence for fluids rich in these elements were present in the outcrop. other elemental trends results including sio2, al2o3, k2o and na2o will be explored in addition to key trace element signatures such as li, cr and f to understand the chemical evolution of the outcrop. | chemo-stratigraphy in the murray formation using chemcam |
multiphoton tomography based on tunable femtosecond near infrared 80 mhz laser radiation has been used to map twophoton- excited time-resolved photoluminescence with picosecond temporal resolution from in-bulk thin photovoltaic layers. the time-resolved photoluminescence reflects carrier lifetimes and is therefore an important measure for the efficiency of a solar cell. conventional one-photon solar cell characterization methods are dominated by surface effects and cannot provide information on subsurface carrier dynamics. in contrast, by using two-photon excitation, subsurface carrier dynamics can be monitored in 3d, providing morphological and spatial information on local defects and crystalline grain boundaries we present results on time-resolved photoluminescence and second harmonic generation imaging in forward and backward directions of cdte/cds films by time-resolved single photon counting and false-color photoluminescence mapping. high-resolution two-photon optical sectioning was carried out with a modified multiphoton flim tomograph mptflex employing near-infrared sensitive photodetectors. | subsurface photoluminescence lifetime imaging of photovoltaic materials using multiphoton tomography |
the mathematician john von neumann, through his work on universal constructors, discovereda generalized version of the central dogma of molecular biology biology in the 1940s, long before the biological version had been discovered. while his discovery played no role in the development of molecular biology, we may benefit from a similar mathematical approach to find clues on the origin of life. this then involves addressing those problems in the field that do not depend on the details of organic chemistry. we can then consider a general set of models that describe machines capable of self-maintenance and self-replication formulated in terms of a set of building blocks and their interactions. the analogue of the origin of life problem is then to explain how one can get to such machines starting from a set of only building blocks. a fundamental obstacle one then faces is the limit on the complexity of low fidelity replicating systems, preventing building blocks from getting assembled randomly into low fidelity machines which can then improve due to natural selection [1]. a generic way out of this problem is for the entire ecosystem of machines to have been encapsulated in a micro-structure with fixed inner surface features that would have boosted the fidelity [2]. such micro-structures could have formed as a result of the random assembly of building blocks, leading to so-called percolation clusters [2].this then leads us to consider how in the real world a percolation process involving the random assembly of organic molecules can be realized. a well studied process in the literature is the assembly of organic compounds in ice grains due to uv radiation and heating events [3,4,5]. this same process will also lead to the percolation process if it proceeds for a sufficiently long period [2].in this talk i will discuss the percolation process in more detail than has been done in [2], explaining how it leads to the necessary symmetry breakings such as the origin of chiral molecules needed to explain the origin of life. [1] eigen, m., 1971. self-organization of matter and the evolution of biological macromolecules. naturwissenschaften 58, 465-523.[2] mitra, s., 2019. percolation clusters of organics in interstellar ice grains as the incubators of life, progress in biophysics and molecular biology 149, 33-38.[3] ciesla, f., and sandford.,s., 2012. organic synthesis via irradiation and warming of ice grains in the solar nebula. science 336, 452-454.[4] muñoz caro, g., et al., 2002. amino acids from ultraviolet irradiation of interstellar ice analogues. nature 416, 403-406.[5] meinert, c,., et al., 2016. ribose and related sugars from ultraviolet irradiation of interstellar ice analogs. science 352, 208-212. | the first step from molecules to life: formation of large random molecules acting as micro-environments |
the x-ray regime is a largely underused resource for constraining interstellar dust grain models and improving our understanding of the physical processes that dictate how grains evolve over their lifetimes. this is mostly due to current detectors' relatively low sensitivity and high background, limiting the targets to the brightest sources. the improved sensitivity of the next generation of x-ray detectors will allow studies of much fainter sources, at much higher angular resolution, expanding our sampled sightlines in both quality and quantity. | astro2020 science white paper: probing the structure of interstellar dust from micron to kpc scales with x-ray imaging |
atmospheric dust plays an important role on the terrestrial climate, regulating the amount of solar radiation coming to the surface, affecting the development and the life time of the clouds and providing fundamental nutrients to the growth of the terrestrial and oceanic biomes. on mars, the global effect of dust is even stronger due to the widespread presence of sources and the lack of vegetation and oceans able to mitigate its contribution. the dreams station and the dust complex, on board of the exomars 2016 and 2020 mission respectively, have been specifically developed for the study of the martian airborne dust. during my phd i joined the team that lead the dreams experiment and the micromed sensor of the dust complex. as a part of the instruments developing and the acquisition of martian analogous data, our team has carried out various campaigns in the sahara desert, to study the environment and the lifting phenomena that are expected on mars. we monitored the dust lifting events by acquiring, for the first time in literature, synchronous measurement of meteorological data, atmospheric electric field, saltation activity and suspended dust concentration. currently, this is the most complete data set available for the study of the dust lifting processes. we worked on the development of proper detection algorithms to individuate the dust events acquired in the surveys, applicable also to the future martian missions. we studied the characteristic of the observed dust storm and dust devils activity, focusing on their electric proprieties. in particular, we obtained the first experimental indications of how the induced electric field is related to the amount of suspended grains and meteorological characteristics of the events. we compared the terrestrial results with the currently available martian data, in order to prepare the analysis of the next exomars measurements. | characterisation of dust events on earth and mars: the exomars/dreams experiment and the field campaigns in the sahara desert |
hybrid perovskite thin films have demonstrated impressive performance for solar energy conversion and optoelectronic applications. however, further progress will benefit from a better knowledge of the intrinsic photophysics of materials. here, the low temperature emission properties of ch3nh3pbi3 single crystals are investigated and compared to those of thin polycrystalline films by means of steady-state and time-resolved photoluminescence spectroscopy. while the emission properties of thin films and crystals appear relatively similar at room temperature, low temperature photoluminescence spectroscopy reveals striking differences between the two materials. single crystals photoluminescence exhibits a sharp excitonic emission at high energy, with full width at half maximum of only 5 mev, assigned to free excitonic recombination and a broad band at low energy. we analyzed the thermal evolution of the free excitonic intensity and linewidth. an excitonic binding energy of 28 mev is extracted from the quenching of the photoluminescence. we highlight a strong broadening of the emission due to lo phonon coupling. the free excitonic emission turned to be very short-lived with a sub-nanosecond dynamics, mainly induced by the fast trapping of the excitons. the free excitonic emission is completely absent of the thin films spectra, which are dominated by trap states band. the trap states energies, width and recombination dynamics present important similarities between films and crystals. these results suggest that the trap states are formed at the surface and grain interface of perovskites. | excitonic emission in organic-inorganic lead iodide perovskite single crystals |
the red rectangle is a nebula surrounding the post-agb star hd 44179. it is the prototype of a particular class of nebulae associated with post-agb binaries characterised by the presence of stable circumbinary disks in (quasi-)keplerian rotation. here we present the results of new high-resolution (20-50 mas) alma observations of continuum and line emissions at 0.9 mm. the continuum maps are analysed through a simple model of dust emission, which can reproduce the observational data. we find that most dust emission in the red rectangle is concentrated in the central regions of the rotating disk and that the settlement of dust grains onto the equatorial plane is very significant, particularly in comparison with the much larger scale height displayed by the gas distribution. the diameter of the dust-emitting region is about 250 au, with a total width of about 50 au. this region coincides with the warm pdr where certain molecules (like hcn), ci, and cii are presumably formed, as well as probably pahs. from the spectral index, we confirm the presence in the disk of large grains, with a typical radius of about 0.150 mm, which supports the long-lived hypothesis for this structure. we also confirm the existence of a compact ionised wind at the centre of the nebula, probably emerging from the accretion disk around the companion, for which we derive an extent of about 10 au and a total flux of 8 mjy. we also briefly present the results on molecular lines of 12co, 13co, and other less abundant species. | the red rectangle: a thin disk with big grains |
cdte is the most commercially successful thin-film photovoltaic technology to date. the recent development of se-alloyed cdse$_{x}$te$_{1-x}$ layers in cdte solar cells has led to higher device efficiencies, due to a lowered bandgap improving the photocurrent, improved voltage characteristics and longer carrier lifetimes. evidence from cross-sectional electron microscopy is widely believed to indicate that se passivates defects in cdse$_{x}$te$_{1-x}$ solar cells, and that this is the reason for better lifetimes and voltages in these devices. here, we utilise spatially resolved photoluminescence measurements of cdse$_{x}$te$_{1-x}$ thin films on glass to study the effects of se on carrier recombination in the material, isolated from the impact of conductive interfaces and without the need to prepare cross-sections through the samples. we find further evidence to support se passivation of grain boundaries, but also identify an associated increase in below-bandgap photoluminescence that indicates the presence of se-enhanced luminescent defects. our results show that se treatment, in tandem with cl passivation, does increase radiative efficiencies. however, the simultaneous enhancement of defects within the grain interiors suggests that although it is overall beneficial, se incorporation may still ultimately limit the maximum attainable efficiency of cdse$_{x}$te$_{1-x}$ solar cells. | spatially resolved photoluminescence analysis of se passivation and defect formation in cdse$_{x}$te$_{1-x}$ thin films |
typical galaxies emit about one third of their energy in the infrared. the origin of this emission reprocessed starlight absorbed by interstellar dust grains and reradiated as thermal emission in the infrared. in particularly dusty galaxies, such as starburst galaxies, the fraction of energy emitted in the infrared can be as high as 90%. dust emission is found to be an excellent tracer of the beginning and end stages of a star's life, where dust is being produced by post-main-sequence stars, subsequently added to the interstellar dust reservoir, and eventually being consumed by star and planet formation. this work reviews the current understanding of the size and properties of this interstellar dust reservoir, by using the large magellanic cloud as an example, and what can be learned about the dust properties and star formation in galaxies from this dust reservoir, using spica, building on previous work performed with the herschel and spitzer space telescopes, as well as the infrared space observatory. | the interstellar dust reservoir: spica's view on dust production and the interstellar medium in galaxies |
the brightness of the ice grain plume of enceladus is observed to vary on a diurnal timescale [1,2], consistent with predictions that the plume's mass is modulated by normal tidal stresses, which open and close cracks that reach the ocean [3]. here we extend our previous analysis [2] to a larger set of iss plume observations, including images taken since 2010, extending the temporal baseline by more than a factor of two. the observations were reduced using the same approach as in [2]. fits were performed as in [2] but now include two different assumptions of how plume brightness responds to stresses [4] plus an updated calculation of the effects of long-period librations [5]. an apparent phase lag of 30-60 degrees between the modelled and observed response is robustly present, irrespective of the data set and assumptions used. this phase lag may be the result of the viscosity structure of the ice shell [2,4], an eruptive delay caused by the hydrodynamics within tidally-pumped cracks [6], or other as yet unknown processes. an earlier suggestion [2], that the phase lag is caused by the additional stresses arising from an 0.8 degree 1:1 physical libration in the moon's ice shell, can be rejected now that this libration has been measured with an amplitude of 0.12 degrees [7]. we also find in iss images a secular decrease in plume brightness over the ten years of cassini observations; this decrease may be due to long-period (forced) librations of enceladus. [1] hedman et al., nature 2013 [2] nimmo et al., astron. j. 2014 [3] hurford et al., nature 2007 [4] behounkova et al., nature geosci. 2015 [5] yseboodt & van hoolst, fall agu, 2015 [6] kite & rubin, pnas 2016 [7] thomas et al., icarus 2016 | the tidally-modulated plume of enceladus: an update |
ca ii k grains, i.e., intermittent, short-lived (about 1 minute), periodic (2-4 minutes), pointlike chromospheric brightenings, are considered to be the manifestations of acoustic waves propagating upward from the solar surface and developing into shocks in the chromosphere. after the simulations of carlsson and stein, we know that hot shocked gas moving upward interacting with the downflowing chromospheric gas (falling down after having been displaced upward by a previous shock) nicely reproduces the spectral features of the ca ii k profiles observed in such grains, i.e., a narrowband emission-like feature at the blue side of the line core. however, these simulations are one-dimensional and cannot explain the location or the pointlike shape of the grains. here, we report on the magnetic nature of these events. furthermore, we report on similar events occurring at the largest flux concentrations, though they are longer-lived (up to 8 minutes) and exhibit the typical signature of steep velocity gradients traveling across the atmosphere. the spectral signatures of the studied events resemble their counterparts in sunspots, the umbral flashes. we then propose that magnetohydrodynamical waves are not only channeled through the magnetic field in sunspots, but they pervade the whole atmosphere. the propagation along magnetic fields can explain the pointlike appearance of the calcium grains observed in the quiet chromosphere. | on the magnetic nature of quiet-sun chromospheric grains |
one of the great discoveries at enceladus was finding salt in plume ice grains. postberg et al. (2009) inferred that these grains have a sodium chloride concentration of 0.05-0.2 mol/kg h2o. a key cosmochemical question is why this concentration for enceladus' ocean rather than a higher concentration like that in earth's ocean? previously, glein & shock (2010) assumed that enceladus started with a chlorine inventory similar to ci chondrites. however, the abundances of halogens in chondrites have been revised significantly downward (clay et al., 2017), and we have learned from comet 67p that there are also volatile carriers of halogens in the outer solar system. we also know much more about the internal structure of enceladus (e.g., hemingway & mittal, 2019) than we did a decade ago. these results motivate a revisiting of enceladus' chlorine cosmochemistry. i have attempted to quantify how much cl is in the rocky core, the ocean, and the ice shell, as well as how much cl was lost to space due to plume outgassing. the analysis suggests that the chlorine inventory of enceladus is of order 1017 kg and is dominated by the salty liquid water ocean. i have also made bottom-up models that could explain how enceladus acquired its cl inventory. these models assume that enceladus formed from mixtures of ice and rock, each with distinct chlorine abundances. interestingly, i have found that the observationally derived cl inventory can be reproduced by assuming that enceladus formed as an ice-rock mixture containing a solar bulk abundance of chlorine. therefore, a simple scenario of complete condensation of cl seems to be emerging, which makes sense theoretically because nebular condensation temperatures for cl (>160 k) are not significantly lower than that of water ice (~180 k). if enceladus did indeed accrete a solar abundance of chlorine, then its ocean may represent a fairly concentrated reservoir of isotopically solar chlorine. the solar ratio of 37cl/35cl is currently not well constrained, but a future mission to enceladus may provide a means to measure this cosmochemically important ratio. | a new model for the origin of chlorine on enceladus |
solar spicules, which can be observed when imaging the sun using the ca ii h (396.9 nm) line, mg ii k(279.6 nm) line or the h alpha (656.28 nm) spectral line filters, are thin cylindrical structures comprising of cold and dense plasma from the chromosphere making incursions -all the time- into the much hotter solar coronal plasma. spicules seen in ca ii h filter are loosely classified by solar astronomers into two classes -- type-i and type-ii, the latter being more energetic than the former. our numerical magneto-hydrodynamic (mhd) experiments in two dimensions establishes that periodic forcing due to formation and destruction of convective granules on the visible solar surface is sufficient to form the forest of spicules with physical characteristics similar to the observed spicules. in our unified model of the spicule forest, the more energetic spicules are formed when this periodic forcing is further aided by magnetic reconnection. therefore our simulations further contribute to unveiling the subtleties of spicule formation. we also study the characteristics of spicules formed in coronal holes versus in quiet sun or the active region. it is to be noted that spicules are not dependent on the 2-dimensionality of our model. we obtain spicules of similar characteristics in a 3-dimensional version of the same model. the behavior only gets richer because now the spicules can also have a torsional mode apart from the transverse kink and sausage modes also seen in the 2-dimensional model. new interesting features like short lived coronal swirls also appear in the 3-dimensional model alongside spicules but with a very small spatial overlap even though there exists striking temporal coincidence. we explore the presence of kelvin-helmholtz instability and its effect on the multi-stranded structure of spicules. finally, we analyze different oscillation modes of the synthetic spicules using time-distance diagrams and estimate the energy in the modes. | modeling the solar spicule forest and the coronal swirls |
when stars like our sun reach the end of their lives, they become giants and eject a lot of their initial mass through a slow, dense outflow. these winds are driven by microscopic solid particles (dust grains) that condense in the cool stellar atmospheres. dust is the product of a large number of chemical reactions that take place in the extended atmosphere and outflow, which also lead to the formation of several molecules. by studying the abundances and distribution of these molecules, a better understanding of the chemistry and physical properties of the ejected gas can be achieved. using 2 sample sets collected from the atacama compact array (aca) in band 6 and band 7, we identified molecular lines from the circumstellar envelopes (cse) of 68 evolved stars. from about 30 observed lines, we identify those of hcn isotopes (h13cn and hc15n) and cs isotopes (12cs and 13cs) as particularly interesting in a subsample of stars. these allow us to probe the 12c/13c and 14n/15n isotopic ratios, which are important probes of the initial stellar mass, an elusive property of agb stars. we compare our results with models for the evolution of agb stars. | the molecular-rich outflow of giant stars |
contexttitan, the largest moon of saturn, is the place in the solar system owning the most earth-like landscapes. titan's dense atmosphere and cold temperatures enable a complex methane hydrological cycle that have shaped the surface, very similarly to the water cycle on earth. titan has another peculiar feature: a wealth of organic grains is created by photochemistry in its atmosphere and progressively deposited at its surface. such atmospheric production of organics likely occurred on earth before the apparition of life; that is the reason why a better understanding of the formation processes, chemical composition and physical properties of these grains is of great interest.the dragonfly mission has recently been selected by nasa to explore titan's surface with a rotorcraft circa 2034 (lorenz et al., 2018). dragonfly will explore a region of organic sand dunes with monthly flights of a few kilometres each aiming to an impact crater named selk. in addition to chemical analyses, dragonfly is equipped with several sensors intended to characterize its environment. among them, as part of the dragonfly geophysical and meteorological (dragmet) package, the efield instrument will record the ac electric field at low frequencies (~5-100 hz).efield consists in two spherical electrodes accommodated at different locations on the rotorcraft. the main scientific objective of efield is to measure schumann resonances on titan. such resonances may have been detected by the huygens probe in 2005 (unless it was an artefact of probe motion; lorenz and le gall, 2020) and would be an indication of the existence of an underground global salty ocean (beghin et al., 2012). another scientific objective of efield is the detection and characterization of charged grains. this work is dedicated to this secondary objective.the exploration area of dragonfly is covered by sand grains, most likely organic in nature, maybe mixed with ice. surface winds can sometimes put them in saltation or suspension. in the process, these organic grains are likely to get charged by friction (triboelectric effect; méndez-harper et al., 2017), and would then induce a perturbation on the electric field detectable by the efield antennas (see figure 1). numerical simulationto estimate the significance of this perturbation and test the possibility to measure it, we have developed a numerical model that simulates the trajectory of charged particles in the probe environment, subjected to turbulent wind flows, gravity and electrostatic forces. results show that charged particles will induce a strong measurable signal on the efield spectra (see figure 2). particles > 100 µm should be detectable with a 1 mv resolution limit (see figure 3). experimental simulationto test our numerical model, we built two prototypes of efield antennas, adapted from previous models of huygens/pwa ac and dc antennas (fulchignoni et al, 2002). as analogues of sand organic grains, we used small polystyrene balls charged by friction in a rotating cylinder, itself coated with small polystyrene balls as done in (méndez-harper et al., 2017). charged balls are dropped one by one to fall close to the antennas. the experiment is performed in a nearly-closed faraday cage to avoid any electromagnetic disturbances. examples of particle detections are given in figure 4. retrieval of sand grains propertiesfinally, we investigated how we could exploit these signals to derive information on the grains (number, charge, velocity). a simple approximation of particles with a linear trajectory and constant speed give a simple equation to fit the data, from which we can infer the charge/velocity ratio of the particle, as well as the minimum distance to the probe/particle velocity ratio. we first validated the approximation with simulated data in titan's surface conditions. figures 4 and 5 give results obtained with experiments done with 3-mm polystyrene balls. the fit results have a dispersion due to the variations in the particle charges inherent to our charging method. nevertheless, the mean values are similar to a numerical simulation performed in the laboratory conditions. further developments are on-going to independently measure particle charges. conclusionthe efield sensor on board dragonfly will be able to investigate charged organic grains blown by winds at the surface of titan. the signal created by the passage of a particle in particular gives access to its charge/velocity ratio. it will be possible to estimate the particle velocity from other instruments (wind sensor, cameras…), and therefore estimate the particle charge. the measurement of particle charges with the efield antenna will be a valuable asset to understand the interaction between the particles and titan surface environment (winds, saltation, friction). referencesbeghin et al., icarus 218 (2012)fulchignoni et al, space science reviews 104 (2002)lorenz et al., johns hopkins apl technical digest 34 (2018)lorenz and le gall, icarus 351 (2020)méndez-harper et al., nature geoscience 10 (2017) | detection of sand grains blown by titan surface winds with the dragmet/efield sensor on dragonfly |
the surface of enceladus could provide one of the best places in our solar system to investigate the potential for life. material from plumes seen emanating from enceladus' south polar region[1], which are believed to be sourced directly from the subsurface ocean, is deposited onto the satellite's icy surface[2]. rapid resurfacing means that material in this area has not been heavily processed by radiation, so could be an excellent indicator of oceanic composition[3, 4]. to date, the only surface species detected with certainty are h2o and co2[5], with nh3, ch4 and low molecular weight organics tentatively detected[6, 7]. more in depth analysis will only come from future missions to the saturnian system.the main aim of this work is to develop enceladus ice analogues of a range of plausible compositions in conditions representative of the surface. the analogues will then be analysed using instrumentation that could be deployed on future missions. a cryogenic vacuum system has been designed in order to replicate the surface environment and grow ices. the analogues grown will be used to test protocols and analytical techniques relevant to future missions. they will then be subjected to simulated space weathering in order to cover all expected possibilities for different surface components and their fate. we will present the preliminary data of the ices grown and the results of testing of the system to ensure it is operating at optimum conditions. methodsin order to grow and analyse ices in conditions representative of enceladus' surface, a vacuum chamber, previously used for analysis of pure h2o ice for the development of the lunar volatiles mobile instrumentation (luvmi) rover[8], was repurposed. the chamber has a 35 l capacity and two vacuum pumps that can achieve internal pressures of 10-7 mbar. the chamber is also fitted with ports to allow it to be connected to analysis equipment such as a gc-ms. the analogues are grown within a sample holder made out of copper piping wrapped around a copper cooling plate. liquid nitrogen is injected into the chamber and flows through the piping to cool it down to temperatures of -140 °c. gas mixtures are injected into the chamber, so that they are condensed onto the cold sample holder and form ices. the system is currently undergoing preliminary calibration and testing in order to optimise operating procedures.h2o and h2o-salt mixtures will be inserted into the sample holder as liquids, then cooled and frozen, before the gas mixtures are inserted. a table showing the preliminary ice mixing ratios can be seen in table 1. these preliminary compositions are based on upper limits estimated for surface components[5, 7, 9, 10]. the ices grown will be analysed initially using a gc-ms in order to fully characterise both them and the cryogenic system. table 1. expected mixing ratios for ices mixing ratio surface component ice 1 ice 2 ice 3 ice 4 h2o 99% 98% 98% 96% co2 1% 1% 1% 1% nh3 - 2% 2% 1.5% ch4 - - 2% 1% nacl - - - 0.5% currently, the main system has the capabilities to be connected to a gc-ms, but in order to preserve the ices while in transport to other pieces of equipment for further experiments, an additional system is required. this system is in development, and is designed to replicate a perfect sample oven onboard a spacecraft. a series of valves connects to an external mini chamber, which is capable of being removed from the main system. within the mini chamber, the sample holder is connected to an external copper bar, which is submerged in liquid nitrogen in order to cool the samples. this allows the ices to be kept in relatively pristine conditions over a longer period of time while being transported. the effects of thermal and vacuum leaks on the ices within the chamber will be determined, in order to mimic potential issues with sample handling onboard a lander. the preliminary results of ice analogue development, including physical and compositional characterisation, will be presented. in addition, the limitations of the system and how potential instrumentation issues during a mission could affect enceladus ices will also be presented. future work will include investigating the effects of space weathering on the ices and their subsequent analysis. the main focus will be on impacts that are representative of e-ring grains colliding with the surface and will be investigated using a van de graaff dust accelerator. references[1] porco, c et al. (2006) science 311 1393-1401[2] kempf, s et al. (2018) enceladus and the icy moons of saturn 195-210[3] kempf, s et al. (2008) icarus 193 420-437[4] howett, c et al. (2018) enceladus and the icy moons of saturn 342-360[5] brown, r et al. (2006) science 311 1425-1428[6] brown, r et al. (2004) space science reviews 115 111-168[7] waite, j et al. (2006) science 311 1419-1422[8] gancet, j et al. (2017) 13th symposium on advanced space technologies in robotics and automation 1-8[9] emery, j et al. (2005) astronomy & astrophysics 435 353-362[10] postberg, f et al. (2009) nature 459 1098-1101 | development of enceladus ice analogues for in situ analysis |
sunspot light bridges (lbs) exhibit a wide range of short-lived phenomena in the chromosphere and transition region. in contrast, we use here data from the multi-application solar telescope (mast), the interface region imaging spectrograph (iris), hinode, the atmospheric imaging assembly (aia), and the helioseismic and magnetic imager (hmi) to analyze the sustained heating over days in an lb in a regular sunspot. chromospheric temperatures were retrieved from the mast ca ii and iris mg ii lines by nonlocal thermodynamic equilibrium inversions. line widths, doppler shifts, and intensities were derived from the iris lines using gaussian fits. coronal temperatures were estimated through the differential emission measure, while the coronal magnetic field was obtained from an extrapolation of the hmi vector field. at the photosphere, the lb exhibits a granular morphology with field strengths of about 400 g and no significant electric currents. the sunspot does not fragment, and the lb remains stable for several days. the chromospheric temperature, iris line intensities and widths, and aia 171 and 211 å intensities are all enhanced in the lb with temperatures from 8000 k to 2.5 mk. photospheric plasma motions remain small, while the chromosphere and transition region indicate predominantly redshifts of 5-20 km s-1 with occasional supersonic downflows exceeding 100 km s-1. the excess thermal energy over the lb is about 3.2 × 1026 erg and matches the radiative losses. it could be supplied by magnetic flux loss of the sunspot (7.5 × 1027 erg), kinetic energy from the increase in the lb width (4 × 1028 erg), or freefall of mass along the coronal loops (6.3 × 1026 erg). | sustained heating of the chromosphere and transition region over a sunspot light bridge |
we propose a pilot study of near-infrared reflectance spectra from dust in the kuiper belt regions of 4 nearby debris disks, 49 cet, hd 32297, beta pic, and hd 181327, using the nirspec ifu. these disks are spatially extended, each subtending several arcsec in scattered light, with already measured near-infrared surface brightnesses from hst/nicmos. they are therefore the easiest systems to study using high contrast spectroscopy. our targets have alma co emission indicative of the presence of volatile-rich planetesimals, similar to comets and kbos in our solar system. we propose to use high snr (>200), near infrared spectra at 0.6 - 5.3 micron to (1) search for solid-state reflectance features at 1.5, 2.0, and 3.2 micron from volatile frosts such as h2o, (2) constrain the dust grain properties (e.g. composition, size) from the solid-state features and the color of the scattered light, and (3) map the particle composition and size as a function of position in the disk. in doing so, we hope to understand whether exokuiper belts in exoplanetary systems contain reservoirs of volatiles, that have been critical to the development of life on earth, and are continuing to build exoplanets via giant collisions. at the present time, there are no plans by any of the guaranteed time observers (gtos) or early release science (ers) programs to obtain reflectance spectra for a debris disk. therefore, these data would be unique. finally, these observations would provide a pathyway to develop reference differential imaging (rdi) and spectral differential imaging (sdi) psf subtraction techniques for the nirspec ifu. | icy kuiper belts in exoplanetary systems |
the ability to reduce energy loss at semiconductor surfaces through passivation or surface field engineering has become an essential step in the manufacturing of efficient photovoltaic (pv) and optoelectronic devices. similarly, surface modification of emerging halide perovskites with quasi-2d heterostructures is now ubiquitous to achieve pv power conversion efficiencies (pces) > 22% and has enabled single-junction pv devices to reach 25.7%, yet a fundamental understanding to how these treatments function is still generally lacking. this has established a bottleneck for maximizing beneficial improvements as no concrete selection and design rules currently exist. here we uncover a new type of tunable passivation strategy and mechanism found in perovskite pv devices that were the first to reach the > 25% pce milestone, which is enabled by surface treating a bulk perovskite layer with hexylammonium bromide (habr). we uncover the simultaneous formation of an iodide-rich 2d layer along with a br halide gradient achieved through partial halide exchange that extends from defective surfaces and grain boundaries into the bulk layer. we demonstrate and directly visualize the tunability of both the 2d layer thickness, halide gradient, and band structure using a unique combination of depth-sensitive nanoscale characterization techniques. we show that the optimization of this interface can extend the charge carrier lifetime to values > 30 {\mu}s, which is the longest value reported for a direct bandgap semiconductor (gaas, inp, cdte) over the past 50 years. importantly, this work reveals an entirely new strategy and knob for optimizing and tuning recombination and charge transport at semiconductor interfaces and will likely establish new frontiers in achieving the next set of perovskite device performance records. | reduced recombination via tunable surface fields in perovskite solar cells |
organic molecules have been detected in the interstellar medium for decades, <alternatives>∼\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\sim \end{document}</alternatives>40% of which have six or more atoms. the latter contain at least one carbon atom and are called icoms for interstellar complex organic molecules. this class of interstellar molecules, especially those detected in solar-type star forming regions, are particularly interesting because they might have been the seeds from which larger pre-biotic molecules could have grown and started/facilitated the appearance of life on earth. at present, the formation and destruction routes of icoms are still debated. in principle, icoms can either be synthesized on the grains surfaces, like many current astrochemical models assume, or on the gas-phase, as mounting evidence from recent laboratory experiments and theoretical computations suggests, or both. in this contribution, we will review how astronomical observations can be used to put constraints on the formation routes of icoms, discussing specific examples. most importantly, we will show that we still miss a lot of information and that the ongoing coordinated effort between astronomers, modelers and chemists is the only way to understand the fascinating problem of the early steps of organic chemistry in space. | interstellar complex organic molecules in solar-type star-forming regions: from observations to laboratory, theoretical computations and models |
the saturnian moon enceladus presents a remarkable opportunity in our solar system for searching for evidence of life, given its habitable ocean and plume that deposits organic-bearing ocean material onto the surface. organic ocean material could be sampled by a lander mission at enceladus. it is of interest to understand the amount of relatively pristine, unaltered organics present on the surface, given the ultraviolet (uv) and plasma environment. here, we investigate uv penetration into enceladus's surface and the resultant effective exposure ages for various regions, using the uv reflectance spectrum of enceladus as measured by the hubble space telescope and considering the rate of resurfacing by plume fallout. in high plume fallout regions near the south pole, plume grains are buried by fresher grains within years, resulting in low levels of exposure to solar uv, which penetrates only ~100 micrometers. regions at latitudes south of ~40°s can have exposure ages <100 years, translating to relatively high abundances of pristine organic material preserved in the regolith. | low effective ultraviolet exposure ages for organics at the surface of enceladus |
the search for extraterrestrial life, especially within our solar system, is one of the biggest endeavors of mankind. the icy moons of saturn and jupiter, enceladus and europa, are particularly promising for hosting life, as they have shown evidence for the three important criteria: water, energy, and organic chemicals. both moons eject their subsurface ocean material as a plume of icy particles, providing the opportunity to study the ocean composition and potential habitability via plume flythrough sampling. the results reported here provide unambiguous laboratory evidence that we could fly through these plumes at speeds up to 4.2 km/s and successfully detect intact amino acids, an important class of biosignature molecules, in situ with a mass spectrometer. | detection of intact amino acids with a hypervelocity ice grain impact mass spectrometer |
water is crucial for the emergence and evolution of life on earth. recent studies of the water content in early forming planetary systems similar to our own show that water is an abundant and ubiquitous molecule, initially synthesized on the surfaces of tiny interstellar dust grains by the hydrogenation of frozen oxygen. water then enters a cycle of sublimation/freezing throughout the successive phases of planetary system formation, namely, hot corinos and protoplanetary disks, eventually to be incorporated into planets, asteroids, and comets. the amount of heavy water measured on earth and in early forming planetary systems suggests that a substantial fraction of terrestrial water was inherited from the very first phases of the solar system formation and is 4.5 billion years old. | we drink good 4.5-billion-year-old water |
cassini's cosmic dust analyzer (cda) generates time-of-flight mass spectra of individual grains impinging on the instruments target-plate. following the analysis of salt rich ice grains emitted by enceladus that indicated a salt-water ocean in contact with the moon's rocky core [1,2] a recent cda analysis of nano-phase silica particles pointed at hydrothermal activity at the moon's rock/water interface [3]. the results imply temperatures above 80 - 90°c and alkaline ph values around 10 reminiscent of alkaline hydrothermal vents on earth like the lost city hydrothermal field. in this context the compositional analysis of organic components in cda mass spectra of the ejected ice grains is of particular relevance. a multitude of volatile organic species has already been identified in the gas component of the plume [4]. as expected, we find more complex organic molecules in ice grains than in the gas indicating aromatic species, amines, and carbonyl group species. the composition of organic-bearing ice grains displays a great diversity indicating a variety of different organic species in varying concentrations. recent spatially resolved cda in situ measurements inside enceladus' plume indicate that these organic compounds are especially frequent in 'young' ice grains that have just been ejected by high velocity jets. we investigate the implications of our findings with respect to ice grain formation at the water surface and inside the icy vents. we constrain the generation of organic compounds at the rock/water interface in the light of hydrothermal activity and the potential for the formation of life precursor molecules in enceladus' ocean. ref:[1] postberg et al., nature 459, 1098-1101 (2009). [2] postberg et al., nature 474, 620-622 (2011). [3]. hsu, postberg, sekine et al., nature, 519, 207-210 (2015). [4] waite et al., nature 460, 487-490 (2009). | refractory organic compounds in enceladus' ice grains and hydrothermal activity |
introduction the reliable identification and quantification of biosignatures on extraterrestrial ocean worlds is key to the search for life in our solar system. saturn's moon enceladus, and potentially jupiter's moon europa, emit plumes of gas and ice grains formed from subsurface water into space (spahn et al. 2006, roth et al. 2014). the ice grains can be sampled during spacecraft flybys by impact ionization mass spectrometers, such as the cosmic dust analyzer (cda; srama et al. 2004) on board the past cassini mission, the surface dust analyzer (suda; kempf et al. 2014) on board the upcoming europa clipper mission (howell & pappalardo 2020), or the enceladus ice analyzer (enia), proposed for future enceladus missions (reh et al. 2016). cda data collected in the saturnian system revealed that enceladus's ocean is salty (postberg et al. 2009) and contains a variety of organic material, including complex macromolecules (postberg et al. 2018) as well as low-mass volatile compounds (khawaja et al. 2019), some of which could potentially act as amino acid precursors. our recent detection of phosphates in ice grains emitted by enceladus (postberg et al. 2022) further enhances enceladus's potential as a habitable environment, possibly able to support microbial life in its subsurface ocean. however, biosignatures have not yet been identified on extraterrestrial ocean worlds. impact ionization detectors, such as suda or enia, are the only instruments capable of determining the compositions of single µm-sized ice grains emitted into plumes. cassini cda results showed that refractory organics occur in only a few % of plume ice grains. these are thought to form from an organic film covering the oceanic surface (postberg et al., 2018). cell material, if present, would likely reside in such grains and would only be present in an even smaller number of ice grains, maybe just one in a thousand or less. on earth, 70% of the planetary surface is covered by a biofilm, the surface microlayer on top of the ocean water (flemming and wuertz, 2019), which hosts a distinct microbial community at cell densities 3 - 5 orders of magnitude higher than in the bulk water phase (franklin et al. 2005). after lifting, organics and cells from this layer can initiate ice crystal formation in clouds (pratt et al. 2009). methods and results to simulate such a scenario, where biosignatures are only present in a small fraction of emitted grains, but with a high cell density, we conducted laboratory analogue experiments with sphingopyxis alaskensis, an ultrasmall bacterium, extracted from various cold marine environments (ting et al. 2010) and potentially capable of fitting into µm-sized ice grains. we simulated the case of an ice grain of 15µm in diameter - constituting the worst case for enceladus where ice grains are generally much smaller (1-5 µm in diameter) - formed from a nucleation core of one single bacterial cell. we used laser induced liquid beam ion desorption (lilbid) - a proven technique to simulate accurately impact ionization mass spectra of ice grains recorded in space (klenner et al. 2019, 2020, 2020a). recent lilbid experiments predict that dna and lipids extracted from bacterial cultures will produce characteristic signals in the mass spectra of ice grains emitted from ocean worlds (dannenmann et al. 2022, under review). here we present the next steps - lilbid experiments with otherwise untreated lysed bacterial cells simulating the appearance of these microbial life forms in impact ionization mass spectra. in both polarity mass spectra, we clearly identify signatures of s. alaskensis. cation mass spectra exhibit features due to protonated amino acids, either fragments of the bacteria's proteins or metabolic intermediates. deprotonated fatty acids, fragments of bacterial lipids, are identifiable in anion mass spectra. our experiments show that even if less than 0.1% of the cell constituents would form a nucleation core of a 15µm ice grain, the bacterial signature would be apparent in the data. the recorded spectra are part of a comprehensive database containing analogue data for impact ionization mass spectrometers on board spacecraft (klenner et al. 2022, under review). conclusions our results show that biosignatures deriving from a single bacterial cell - or small fractions of it - embedded as a nucleation core in an ice grain will be clearly identifiable in impact ionization mass spectra from suda-type instruments. this demonstrates the advantage of analyzing individual ice grains in a plume over analyzing the average composition of all plume material encountered during a flyby. a modern impact ionization instrument like suda or enia would be capable of recording 10,000 - 100,000 ice grain spectra (cations and anions) during a single plume passage, allowing to assess biosignatures that are present in only 1 out of 100,000 grains during a multiple flyby mission. such low abundances would be out of reach for other analytical methods that measure the integrated - and thus extremely diluted - concentrations of such biosignatures in a plume. references dannenmann, m. et al. (2022) astrobiology, under review. flemming, h.-c. & wuerz, s. (2019) nat rev microbiol 17, 247-260. franklin, m.p. et al. (2005) environ microbiol 7, 723-736. howell, s.m. & pappalardo, r.t. (2020) nat commun 11, 1311. kempf, s. et al. (2014) epsc 9, epsc2014-229. khawaja, n. et al. (2019) mon not r astron soc 489, 5231-5243. klenner, f. et al. (2019) rapid commun mass spectrom 33, 1751-1760. klenner, f. et al. (2020a) astrobiology 20, 179-189. klenner, f. et al. (2020b) astrobiology 20, 1168-1184. klenner, f. et al. (2022) earth space sci, under review. postberg, f. et al. (2009) nature 459, 1098-1101. postberg, f. et al. (2018) nature 558, 564-568. postberg, f. et al. (2022) abscicon abstract, 505-01. pratt, k.a. et al. (2009) nat geosci 2, 398-401. reh, k. et al (2016) ieee aeroconf abstract, 1-8. roth, l. et al. (2014) science 343, 171-174. spahn, f. et al. (2006) science 311, 1416-1418. srama, r. et al. (2004) space sci rev 114, 465-518. ting, l. et al. (2010) environ microbiol 12, 2658-267. | experiments for the identification of bacterial cell material in single ice grains emitted by enceladus and europa |
solvent engineering is an important route for improving the quality of solution-processed copper-zinc-tin-sulfur-selenium (cztsse) thin films. here, blended solvents composed of dimethyl sulfoxide (dmso) and dimethyl formamide (dmf) were used to prepare cztsse precursor solution. the addition of dmf improved the wettability of precursor solution on mo-coated substrates and modified the cztsse formation. impacts of different dmf contents in solvents on morphological, structural, optical and photovoltaic properties of cztsse films were fully studied. compared with the pure dmso-based precursor solution, incorporation of an appropriate amount of dmf into dmso can effectively increase the grain size and improve the film compactness, while adding excess dfm decreased the crystallinity and deteriorated the device performance. by optimizing dmf content, the carrier lifetime of cztsse thin film was increased from 2.78 ns to 5.07 ns and the energy conversion efficiencies of solar cells were improved from 4.77% to 6.03%. | improved cztsse thin-film morphology and device performance by using dmso/dmf blended solvent |
the shape of an asteroid phase curve is influenced by the physical properties of the surface of the asteroid such as, grain size distribution, surface roughness, porosity, and composition. while phase curves are most often constructed using visible photometric data, infrared phase curves can also provide useful insight into the surface properties of an asteroid given that spectral absorption features associated with hydrated and organic materials occur at infrared wavelengths. here we present thermally and rotationally corrected 3 μm phase curves for a sample of ~100 main belt asteroids. these phase curves were constructed using photometric observations centered near 3.4 μm from the w1 band of the near-earth object wide-field infrared survey explorer (neowise) mission. our sample includes asteroids observed by the akari satellite, which collected spectroscopic data from 2.5 to 5 μm in search of absorption features associated with hydrated materials, as well as a subset of the themis dynamical family, which has several members on which volatiles have been detected. studying the w1 phase curves of these two populations provides a unique opportunity to investigate asteroids that may harbor substances important to the development of life. in this work, we determine the distribution of linear w1 phase slopes (solar phase angles > 10°) for a subset of akari asteroids and themis family asteroids. we compare akari objects to 2.7 μm and 3.1 μm band depths, while also including comparisons to visible and w1 geometric albedos from neowise. we find little correlation between the depth of 3 μm absorption features with the w1 phase slope among the akari sample, but we do observe increasing w1 phase slope vs. 2.7 μm band depth among c-complex asteroids in the sample. we also find that lower albedo taxonomies (c-types) have steeper average w1 phase slopes than higher albedo taxonomies (m and s-types), following the expectation at visible wavelengths. for themis family asteroids, we compare their w1 phase slopes to their w1 albedos and find similarities to trends observed among jupiter family comets, which showed steepening r-band phase slopes with increasing r-band albedo. we also observe steeper w1 phase slopes with decreasing object diameter. we suggest that the surface properties associated with larger and darker objects (smaller particle sizes, smoother surfaces, more pronounced shadow hiding and single particle scattering) lead to more uniform scattering and result in the observed flatter linear phase slopes for larger objects. | three micron phase curves of main belt asteroids from neowise photometry |
in this paper, we present a method of embedding physics data manifolds with metric structure into lower dimensional spaces with simpler metrics, such as euclidean and hyperbolic spaces. we then demonstrate that it can be a powerful step in the data analysis pipeline for many applications. using progressively more realistic simulated collisions at the large hadron collider, we show that this embedding approach learns the underlying latent structure. with the notion of volume in euclidean spaces, we provide for the first time a viable solution to quantifying the true search capability of model agnostic search algorithms in collider physics (i.e. anomaly detection). finally, we discuss how the ideas presented in this paper can be employed to solve many practical challenges that require the extraction of physically meaningful representations from information in complex high dimensional datasets. | neural embedding: learning the embedding of the manifold of physics data |
we develop a formalism to describe extensions of existing axion haloscope designs to those that possess directional sensitivity to incoming dark matter axion velocities. the effects are measurable if experiments are designed to have dimensions that approach the typical coherence length for the local axion field. with directional sensitivity, axion detection experiments would have a greatly enhanced potential to probe the local dark matter velocity distribution. we develop our formalism generally, but apply it to specific experimental designs, namely resonant cavities and dielectric disk haloscopes. we demonstrate that these experiments are capable of measuring the daily modulation of the dark matter signal and using it to reconstruct the three-dimensional velocity distribution. this allows one to measure the solar peculiar velocity, probe the anisotropy of the dark matter velocity ellipsoid and identify cold substructures such as the recently discovered streams near to earth. directional experiments can also identify features over much shorter timescales, potentially facilitating the mapping of debris from axion miniclusters. | directional axion detection |
currently there is a growing interest in studying the coherent interaction between magnetic systems and electromagnetic radiation in a cavity, prompted partly by possible applications in hybrid quantum systems. we propose a multimode cavity optomagnonic system based on antiferromagnetic insulators, where optical photons couple coherently to the two homogeneous magnon modes of the antiferromagnet. these have frequencies typically in the thz range, a regime so far mostly unexplored in the realm of coherent interactions, and which makes antiferromagnets attractive for quantum transduction from thz to optical frequencies. we derive the theoretical model for the coupled system, and show that it presents unique characteristics. in particular, if the antiferromagnet presents hard-axis magnetic anisotropy, the optomagnonic coupling can be tuned by a magnetic field applied along the easy axis. this allows us to bring a selected magnon mode into and out of a dark mode, providing an alternative for a quantum memory protocol. the dynamical features of the driven system present unusual behavior due to optically induced magnon-magnon interactions, including regions of magnon heating for a red-detuned driving laser. the multimode character of the system is evident in a substructure of the optomagnonically induced transparency window. | antiferromagnetic cavity optomagnonics |
a statistical analysis of the observed perturbations in the density of stellar streams can in principle set stringent constraints on the mass function of dark matter subhaloes, which in turn can be used to constrain the mass of the dark matter particle. however, the likelihood of a stellar density with respect to the stream and subhaloes parameters involves solving an intractable inverse problem which rests on the integration of all possible forward realizations implicitly defined by the simulation model. in order to infer the subhalo abundance, previous analyses have relied on approximate bayesian computation (abc) together with domain-motivated but handcrafted summary statistics. here, we introduce a likelihood-free bayesian inference pipeline based on amortised approximate likelihood ratios (aalr), which automatically learns a mapping between the data and the simulator parameters and obviates the need to handcraft a possibly insufficient summary statistic. we apply the method to the simplified case where stellar streams are only perturbed by dark matter subhaloes, thus neglecting baryonic substructures, and describe several diagnostics that demonstrate the effectiveness of the new method and the statistical quality of the learned estimator. | towards constraining warm dark matter with stellar streams through neural simulation-based inference |
the axion field, the angular direction of the complex scalar field associated with the spontaneous symmetry breaking of the peccei–quinn (pq) symmetry, could have originated with initial non-zero velocity. the presence of a non-zero angular velocity resulting from additional terms in the potential that explicitly break the pq symmetry has important phenomenological consequences such as a modification of the axion mass with respect to the conventional pq framework or an explanation for the observed matter-antimatter asymmetry. we elaborate further on the consequences of the "kinetic misalignment" mechanism, assuming that axions form the entirety of the dark matter abundance. the kinetic misalignment mechanism possesses a weak limit in which the axion field starts to oscillate at the same temperature as in the conventional pq framework, and a strong limit corresponding to large initial velocities which effectively delay the onset of oscillations. following a uv-agnostic approach, we show how this scenario impacts the formation of axion miniclusters, and we sketch the details of these substructures along with potential detecting signatures. | qcd axion kinetic misalignment without prejudice |
in some axion dark matter models a dominant fraction of axions resides in dense small-scale substructures, axion miniclusters. a fraction of these substructures is disrupted and forms tidal streams where the axion density may still be an order of magnitude larger than the average. we discuss implications of these streams for the direct axion searches. we estimate the fraction of disrupted miniclusters and the parameters of the resulting streams, and find that stream-crossing events would occur at a rate of about 1/(20 yr) for 2-3 days, during which the signal in axion detectors would be amplified by a factor ~ 10. these estimates suggest that the effect of the tidal disruption of axion miniclusters may be important for direct axion searches and deserves a more thorough study. | tidal streams from axion miniclusters and direct axion searches |
we study how the indirect observation of dark matter substructures in the milky way, using recent stellar stream studies, translates into constraints for different dark matter models. particularly, we use the measured number of dark subhalos in the mass range 107-109 m⊙ to constrain modifications of the subhalo mass function compared to the cold dark matter scenario. we obtain the lower bounds mwdm>3.2 kev and mfdm>5.2 ×10-21 ev on the warm dark matter and fuzzy dark matter particle mass, respectively. when dark matter is coupled to a dark radiation bath, we find that kinetic decoupling must take place at temperatures higher than tkd>0.7 kev . we also discuss future prospects of stellar stream observations. | implications of milky way substructures for the nature of dark matter |
a higgsino in supersymmetric standard models can play the role of a dark matter particle. in conjunction with the naturalness criterion, the higgsino mass parameter is expected to be around the electroweak scale. in this work, we explore the potential of probing the nearly degenerate light higgsinos with machine learning at the lhc. by analyzing jet images and other jet substructure information, we use the convolutional neural network to enhance the signal significance. we find that our deep learning jet image method can improve the previous result based on the conventional cut flow by about a factor of 2 at the high-luminosity lhc. | deep learning jet images as a probe of light higgsino dark matter at the lhc |
in recent years, realistic hydrodynamical simulations of galaxies like the milky way have become available, enabling a reliable estimate of the dark matter density and velocity distribution in the solar neighborhood. we review here the status of hydrodynamical simulations and their implications for the interpretation of direct dark matter searches. we focus in particular on: the criteria to identify milky way-like galaxies; the impact of baryonic physics on the dark matter velocity distribution; the possible presence of substructures like clumps, streams, or dark disks; and on the implications for the direct detection of dark matter with standard and nonstandard interactions. | implications of hydrodynamical simulations for the interpretation of direct dark matter searches |
we introduce a machine learning method for estimating the sensitivity of strong lens observations to dark matter subhaloes in the lens. our training data include elliptical power-law lenses, hubble deep field sources, external shear, and noise and psf for the euclid vis instrument. we set the concentration of the subhaloes using a vmax-rmax relation. we then estimate the dark matter subhalo sensitivity in 16 000 simulated strong lens observations with depth and resolution resembling euclid vis images. we find that with a 3σ detection threshold, 2.35 per cent of pixels inside twice the einstein radius are sensitive to subhaloes with a mass mmax ≤ 1010 m⊙, 0.03 per cent are sensitive to mmax ≤ 109 m⊙, and the limit of sensitivity is found to be mmax = 108.8 ± 0.2 m⊙. using our sensitivity maps and assuming cdm, we estimate that euclid-like lenses will yield $1.43^{+0.14}_{-0.11}[f_\mathrm{sub}^{-1}]$ detectable subhaloes per lens in the entire sample, but this increases to $35.6^{+0.9}_{-0.9}[f_\mathrm{sub}^{-1}]$ per lens in the most sensitive lenses. estimates are given in units of the inverse of the substructure mass fraction $f_\mathrm{sub}^{-1}$. assuming fsub = 0.01, one in every 70 lenses in general should yield a detection, or one in every ~ three lenses in the most sensitive sample. from 170 000 new strong lenses detected by euclid, we expect ~2500 new subhalo detections. we find that the expected number of detectable subhaloes in warm dark matter models only changes relative to cold dark matter for models which have already been ruled out, i.e. those with half-mode masses mhm > 108 m⊙. | sensitivity of strong lensing observations to dark matter substructure: a case study with euclid |
fuzzy dark matter (fdm) has recently emerged as an interesting alternative model to the standard cold dark matter (cdm). in this model, dark matter consists of very light bosonic particles with quantum mechanical effects on galactic scales. using the n-body code ax-gadget, we perform cosmological simulations of fdm that fully model the dynamical effects of the quantum potential throughout cosmic evolution. through the combined analysis of fdm volume and high-resolution zoom-in simulations of different fdm particle masses ($m_{\chi}$ $\sim$ $10^{-23} - 10^{-21}$ ev/c$^2$), we study how fdm impacts the abundance of substructure and the inner density profiles of dark matter haloes. for the first time, using our fdm volume simulations, we provide a fitting formula for the fdm-to-cdm subhalo abundance ratio as a function of the fdm mass. more importantly, our simulations clearly demonstrate that there exists an extended fdm particle mass interval able to reproduce the observed substructure counts and, at the same time, create substantial cores ($r_{c} \sim 1$ kpc) in the density profile of dwarf galaxies ($\approx 10^{9}-10^{10}$ m$_{\odot}$), which stands in stark contrast with cdm predictions even with baryonic effects taken into account. the dark matter distribution in the faintest galaxies offers then a clear way to discriminate between fdm and cdm. | no catch-22 for fuzzy dark matter: testing substructure counts and core sizes via high-resolution cosmological simulations |
in the context of structure formation with ultralight axion dark matter, we offer an alternative explanation for the mass relation of solitonic cores and their host halos observed in numerical simulations. our argument is based entirely on the mass gain that occurs during major mergers of binary cores and largely independent of the initial core-halo mass relation assigned to hosts that have just collapsed. we find a relation between the halo mass mh and corresponding core mass mc, mc∝mh2 β -1, where (1 -β ) is the core mass loss fraction. following the evolution of core masses in stochastic merger trees, we find empirical evidence for our model. our results are useful for statistically modeling the effects of dark matter cores on the properties of galaxies and their substructures in axion dark matter cosmologies. | core-halo mass relation of ultralight axion dark matter from merger history |
we use the state-of-the-art semi-analytic galaxy formation model, shark to investigate the physical processes involved in dictating the shape, scatter, and evolution of the hi-halo mass (hihm) relation at 0 ≤ z ≤ 2. we compare shark with hi clustering and spectral stacking of the hihm relation derived from observations finding excellent agreement with the former and a deficiency of hi in shark at mvir ≈ 1012-13 m⊙ in the latter. in shark, we find that the hi mass increases with the halo mass up to a critical mass of ≈1011.8 m⊙; between ≈1011 and 1013 m⊙, the scatter in the relation increases by 0.7 dex and the hi mass decreases with the halo mass on average (till $m_{\rm vir}\sim 10^{12.5}\, \rm m_{\odot }$ , after which it starts increasing); at $m_{\rm vir}\gtrsim 10^{13}\, \rm m_{\odot }$ , the hi content continues to increase with increasing halo mass, as a result of the increasing hi contribution from satellite galaxies. we find that the critical halo mass of ≈1012 m⊙ is set by feedback from active galactic nuclei (agns) which affects both the shape and scatter of the hihm relation, with other physical processes playing a less significant role. we also determine the main secondary parameters responsible for the scatter of the hihm relation, namely the halo spin parameter at ${m}_{\rm vir}\, \lt $ 1011.8 m⊙, and the fractional contribution from substructure to the total halo mass ( $m_{\rm h}^{\rm sat}/m_{\rm vir}$ ) for ${m}_{\rm vir}\, \gt $ 1013 m⊙. the scatter at 1011.8 m⊙ $\lt \, {m}_{\rm vir}\, \lt $ 1013 m⊙ is best described by the black hole-to-stellar mass ratio of the central galaxy, reflecting the relevance of agn feedback. we present a numerical model to populate dark matter-only simulations with hi at 0 ≤ z ≤ 2 based solely on halo parameters that are measurable in such simulations. | the physical drivers of the atomic hydrogen-halo mass relation |
we employ an improved methodology to insert live stellar discs into high-resolution dark matter simulations of milky way-sized haloes, allowing us to investigate the fate of thin stellar discs in the tumultuous environment of cold dark matter structures. we study a set of eight different haloes, drawn from the aquarius simulation project, in which stellar discs are adiabatically grown with a prescribed structure, and then allowed to self-consistently evolve. the initial velocity distribution is set-up in very good equilibrium with the help of the galic code. we find that the residual triaxiality of the haloes leads to significant disc tumbling, qualitatively confirming earlier work. we show that the disc turning motion is unaffected by structural properties of the galaxies such as the presence or absence of a bulge or bar. in typical milky way-sized dark matter haloes, we expect an average turning of the discs by about 40°between z = 1 and 0, over the course of 7.6 gyr. we also investigate the impact of the discs on substructures, and conversely, the disc heating rate caused by the dark matter halo substructures. the presence of discs reduces the central subhalo abundance by a about a factor of 2, due to an increased evaporation rate by gravitational shocks from disc passages. we find that substructures are important for heating the outer parts of stellar discs but do not appear to significantly affect their inner parts. | the stability of stellar discs in milky way-sized dark matter haloes |
we present the first comprehensive analysis of the segregation of dark matter subhaloes in their host haloes. using three different numerical simulations, and two different segregation strength indicators, we examine the segregation of 12 different subhalo properties with respect to both orbital energy and halocentric radius (in real space as well as in projection). subhaloes are strongly segregated by accretion redshift, which is an outcome of the inside-out assembly of their host haloes. since subhaloes that were accreted earlier have experienced more tidal stripping, subhaloes that have lost a larger fraction of their mass at infall are on more bound orbits. subhaloes are also strongly segregated in their masses and maximum circular velocities at accretion. we demonstrate that part of this segregation is already imprinted in the infall conditions. for massive subhaloes, it is subsequently boosted by dynamical friction, but only during their first radial orbit. the impact of these two effects is counterbalanced, though, by the fact that subhaloes with larger accretion masses are accreted later. because of tidal stripping, subhaloes reveal little to no segregation by present-day mass or maximum circular velocity, while the corresponding torques cause subhaloes on more bound orbits to have smaller spin. there is a weak tendency for subhaloes that formed earlier to be segregated towards the centre of their host halo, which is an indirect consequence of the fact that (sub)halo formation time is correlated with other, strongly segregated properties. we discuss the implications of our results for the segregation of satellite galaxies in galaxy groups and clusters. | on the segregation of dark matter substructure |
we examine the latest data on the cluster macsj0717.5+3745 from the hubble frontier fields campaign. the critically lensed area is the largest known of any lens and very irregular making it a challenge for parametric modelling. using our free-form method we obtain an accurate solution, identify here many new sets of multiple images, doubling the number of constraints and improving the reconstruction of the dark matter distribution. our reconstructed mass map shows several distinct central substructures with shallow density profiles, clarifying earlier work and defining well the relation between the dark matter distribution and the luminous and x-ray peaks within the critically lensed region. using our free-form method, we are able to meaningfully subtract the mass contribution from cluster members to the deflection field to trace the smoothly distributed cluster dark matter distribution. we find four distinct concentrations, three of which are coincident with the luminous matter. the fourth peak has a significant offset from both the closest luminous and x-ray peaks. these findings, together with dynamical data from the motions of galaxies and gas will be important for uncovering the potentially important implications of this extremely massive and intriguing system. | hubble frontier field free-form mass mapping of the massive multiple-merging cluster macsj0717.5+3745 |
we present initial results from the “ponos” zoom-in numerical simulations of dark matter substructures in massive ellipticals. two very highly resolved dark matter halos with m vir = 1.2 × 1013 {m}⊙and m vir = 6.5 × 1012 {m}⊙and different (“violent” versus “quiescent”) assembly histories have been simulated down to z = 0 in a λcdm cosmology with a total of 921,651,914 and 408,377,544 particles, respectively. within the virial radius, the total mass fraction in self-bound m sub > 106 {m}⊙subhalos at the present epoch is 15% for the violent host and 16.5% for the quiescent one. at z = 0.7, these fractions increase to 19% and 33%, respectively, as more recently accreted satellites are less prone to tidal destruction. in projection, the average fraction of surface mass density in substructure at a distance of r/r vir = 0.02 (∼5-10 kpc) from the two halo centers ranges from 0.6% to ≳2%, significantly higher than that measured in simulations of milky way-sized halos. the contribution of subhalos with m sub < 109 {m}⊙to the projected mass fraction is between one-fifth and one-third of the total, with the smallest share found in the quiescent host. we assess the impact of baryonic effects via twin, lower-resolution hydrodynamical simulations that include metallicity-dependent gas cooling, star formation, and a delayed-radiative-cooling scheme for supernova feedback. baryonic contraction produces a super-isothermal total density profile and increases the number of massive subhalos in the inner regions of the main host. the host density profiles and projected subhalo mass fractions appear to be broadly consistent with observations of gravitational lenses. | cold dark matter substructures in early-type galaxy halos |
we propose a novel method utilizing stellar kinematic data to detect low-mass substructure in the milky way's dark matter halo. by probing characteristic wakes that a passing dark matter subhalo leaves in the phase-space distribution of ambient halo stars, we estimate sensitivities down to subhalo masses of ∼107 m⊙ or below. the detection of such subhalos would have implications for dark matter and cosmological models that predict modifications to the halo-mass function at low halo masses. we develop an analytic formalism for describing the perturbed stellar phase-space distributions, and we demonstrate through idealized simulations the ability to detect subhalos using the phase-space model and a likelihood framework. our method complements existing methods for low-mass subhalo searches, such as searches for gaps in stellar streams, in that we can localize the positions and velocities of the subhalos today. | stellar wakes from dark matter subhalos |
we use a catalogue of stellar binaries with wide separations (up to 1 pc) identified by the gaia satellite to constrain the presence of extended substructure within the milky way galaxy. heating of the binaries through repeated encounters with substructure results in a characteristic distribution of binary separations, allowing constraints to be placed independent of the formation mechanism of wide binaries. across a wide range of subhalo density profiles, we show that subhalos with masses $\gtrsim 65 \ m_\odot$ and characteristic length scales similar to the separation of these wide binaries cannot make up 100% of the galaxy's dark matter. constraints weaken for subhalos with larger length scales and are dependent on their density profiles. for such large subhalos, higher central densities lead to stronger constraints. subhalos with density profiles similar to those expected from cold dark matter must be at least $\sim 5,000$ times denser than predicted by simulation to be constrained by the wide binary catalogue. | constraining dark matter substructure with gaia wide binaries |
aims: we propose a new mass mapping algorithm, specifically designed to recover small-scale information from a combination of gravitational shear and flexion. including flexion allows us to supplement the shear on small scales in order to increase the sensitivity to substructures and the overall resolution of the convergence map without relying on strong lensing constraints.methods: to preserve all available small scale information, we avoid any binning of the irregularly sampled input shear and flexion fields and treat the mass mapping problem as a general ill-posed inverse problem, which is regularised using a robust multi-scale wavelet sparsity prior. the resulting algorithm incorporates redshift, reduced shear, and reduced flexion measurements for individual galaxies and is made highly efficient by the use of fast fourier estimators.results: we tested our reconstruction method on a set of realistic weak lensing simulations corresponding to typical hst/acs cluster observations and demonstrate our ability to recover substructures with the inclusion of flexion, which are otherwise lost if only shear information is used. in particular, we can detect substructures on the 15'' scale well outside of the critical region of the clusters. in addition, flexion also helps to constrain the shape of the central regions of the main dark matter halos. our mass mapping software, called glimpse2d, is made freely available at http://www.cosmostat.org/software/glimpse | high resolution weak lensing mass mapping combining shear and flexion |
in the standard structure formation scenario based on the cold dark matter paradigm, galactic halos are predicted to contain a large population of dark matter subhalos. while the most massive members of the subhalo population can appear as luminous satellites and be detected in optical surveys, establishing the existence of the low mass and mostly dark subhalos has proven to be a daunting task. galaxy-scale strong gravitational lenses have been successfully used to study mass substructures lying close to lensed images of bright background sources. however, in typical galaxy-scale lenses, the strong lensing region only covers a small projected area of the lens's dark matter halo, implying that the vast majority of subhalos cannot be directly detected in lensing observations. in this paper, we point out that this large population of dark satellites can collectively affect gravitational lensing observables, hence possibly allowing their statistical detection. focusing on the region of the galactic halo outside the strong lensing area, we compute from first principles the statistical properties of perturbations to the gravitational time delay and position of lensed images in the presence of a mass substructure population. we find that in the standard cosmological scenario, the statistics of these lensing observables are well approximated by gaussian distributions. the formalism developed as part of this calculation is very general and can be applied to any halo geometry and choice of subhalo mass function. our results significantly reduce the computational cost of including a large substructure population in lens models and enable the use of bayesian inference techniques to detect and characterize the distributed satellite population of distant lens galaxies. | dark census: statistically detecting the satellite populations of distant galaxies |
we study the highly magnified arc sgas j122651.3+215220 caused by a star-forming galaxy at zs = 2.93 crossing the lensing caustic cast by the galaxy cluster sdss j1226+2152 (zl = 0.43), using hubble space telescope observations. we report in the arc several asymmetric surface brightness features whose angular separations are a fraction of an arcsecond from the lensing critical curve and appear to be highly but unequally magnified image pairs of underlying compact sources, with one brightest pair having clear asymmetry consistently across four filters. one explanation of unequal magnification is microlensing by intracluster stars, which induces independent flux variations in the images of individual or groups of source stars in the lensed galaxy. for a second possibility, intracluster dark matter subhaloes invisible to telescopes effectively perturb lensing magnifications near the critical curve and give rise to persistently unequal image pairs. our modelling suggests, at least for the most prominent identified image pair, that the microlensing hypothesis is in tension with the absence of notable asymmetry variation over a six-year baseline, while subhaloes of ∼106-108 m⊙ anticipated from structure formation with cold dark matter typically produce stationary and sizable asymmetries. we judge that observations at additional times and more precise lens models are necessary to stringently constrain temporal variability and robustly distinguish between the two explanations. the arc under this study is a scheduled target of a director's discretionary early release science program of the james webb space telescope, which will provide deep images and a high-resolution view with integral field spectroscopy. | asymmetric surface brightness structure of caustic crossing arc in sdss j1226+2152: a case for dark matter substructure |
we investigate the primordial curvature perturbation by the observation of the dark matter substructure. assuming a bump in the spectrum of the curvature perturbation in the wave number of k >1 mpc-1, we track the evolution of the host halo and subhalos in a semianalytic way. taking into account possible uncertainties in the evaluation of the tidal stripping effect on the subhalo growth, we find a new robust bound on the curvature perturbation with a bump from the number of observed dwarf spheroidal galaxies in our galaxy and the observations of the stellar stream. the upper limit on the amplitude of the bump is o (10-7 ) for k ∼103 mpc-1. furthermore, we find the boost factor, which is crucial for the indirect detection of dark matter signals, is up to o (104 ) due to the bump that is allowed in the current observational bounds. | constraining the primordial curvature perturbation using dark matter substructure |
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