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recent advances in our understanding of the dynamical history of the solar system have altered the inferred bombardment history of the earth during accretion of the late veneer, after the moon-forming impact. we investigate how the bombardment by planetesimals left-over from the terrestrial planet region after terrestrial planet formation, as well as asteroids and comets, affects the evolution of earth's early atmosphere. we develop a new statistical code of stochastic bombardment for atmosphere evolution, combining prescriptions for atmosphere loss and volatile delivery derived from hydrodynamic simulations and theory with results from dynamical modelling of realistic populations of impactors. we find that for an initially earth-like atmosphere, impacts cause moderate atmospheric erosion with stochastic delivery of large asteroids, giving substantial growth (× 10) in a few ${{\ \rm per\ cent}}$ of cases. the exact change in atmosphere mass is inherently stochastic and dependent on the dynamics of the left-over planetesimals. we also consider the dependence on unknowns including the impactor volatile content, finding that the atmosphere is typically completely stripped by especially dry left-over planetesimals ( $\lt 0.02 ~ {{\ \rm per\ cent}}$ volatiles). remarkably, for a wide range of initial atmosphere masses and compositions, the atmosphere converges towards similar final masses and compositions, i.e. initially low-mass atmospheres grow, whereas massive atmospheres deplete. while the final properties are sensitive to the assumed impactor properties, the resulting atmosphere mass is close to that of current earth. the exception to this is that a large initial atmosphere cannot be eroded to the current mass unless the atmosphere was initially primordial in composition. | evolution of the earth's atmosphere during late veneer accretion |
the impact of the double asteroid redirection test spacecraft into dimorphos, moon of the asteroid didymos, changed dimorphos's orbit substantially, largely from the ejection of material. we present results from 12 earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. after an initial brightening of ~1.4 mag, we find consistent dimming rates of 0.11-0.12 mag day-1 in the first week, and 0.08-0.09 mag day-1 over the entire study period. the system returned to its pre-impact brightness 24.3-25.3 days after impact though the primary ejecta tail remained. the dimming paused briefly eight days after impact, near in time to the appearance of the second tail. this was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, though movement of the primary ejecta through the aperture likely played a role. | ejecta evolution following a planned impact into an asteroid: the first five weeks |
we performed in-situ analysis on a ~ 1 mm-sized grain a0080 returned by the hayabusa2 spacecraft from near-earth asteroid (162173) ryugu to investigate the relationship of soluble organic matter (som) to minerals. desorption electrospray ionization-high resolution mass spectrometry (desi-hrms) imaging mapped more than 200 chn, cho, cho-na (sodium adducted), and chno soluble organic compounds. a heterogeneous spatial distribution was observed for different compound classes of som as well as among alkylated homologues on the sample surface. the a0080 sample showed mineralogy more like an ivuna-type (ci) carbonaceous chondrite than other meteorites. it contained two different lithologies, which are either rich (lithology 1) or poor (lithology 2) in magnetite, pyrrhotite, and dolomite. chn compounds were more concentrated in lithology 1 than in lithology 2; on the other hand, cho, cho-na, and chno compounds were distributed in both lithologies. such different spatial distribution of som is likely the result of interaction of the som with minerals, during precipitation of the som via fluid activity, or could be due to difference in transportation efficiencies of soms in aqueous fluid. organic-related ions measured by time-of-flight secondary ion mass spectrometry (tof-sims) did not coincide with the spatial distribution revealed by desi-hrms imaging. this result may be because the different ionization mechanism between desi and sims, or indicate that the tof-sims data would be mainly derived from methanol-insoluble organic matter in a0080. in the orgueil meteorite, such relationship between altered minerals and som distributions was not observed by desi-hrms analysis and field-emission scanning electron microscopy, which would result from differences of som formation processes and sequent alteration process on the parent bodies or even on the earth. alkylated homologues of chn compounds were identified in a0080 by desi-hrms imaging as observed in the murchison meteorite, but not from the orgueil meteorite. these compounds with a large c number were enriched in murchison fragments with abundant carbonate grains. in contrast, such relationship was not observed in a0080, implying different formation or growth mechanisms for the alkylated chn compounds by interaction with fluid and minerals on the murchison parent body and asteroid ryugu. | the spatial distribution of soluble organic matter and their relationship to minerals in the asteroid (162173) ryugu |
the sensitivity of alma makes it possible to detect thermal mm/submm emission from small and/or distant solar system bodies at the sub-mjy level. while the measured fluxes are primarily sensitive to the objects' diameters, deriving precise sizes is somewhat hampered by the uncertain effective emissivity at these wavelengths. following recent work presenting alma data for four trans-neptunian objects (tnos) with satellites, we report on alma 233 ghz (1.29 mm) flux measurements of four centaurs (2002 gz32, bienor, chiron, chariklo) and two other tnos (huya and makemake), sampling a range of sizes, albedos, and compositions. these thermal fluxes are combined with previously published fluxes in the mid/far infrared in order to derive their relative emissivity at radio (mm/submm) wavelengths, using the near earth asteroid standard model (neatm) and thermophysical models. we reassess earlier thermal measurements of these and other objects - including pluto/charon and varuna - exploring, in particular, effects due to non-spherical shape and varying apparent pole orientation whenever information is available, and show that these effects can be key for reconciling previous diameter determinations and correctly estimating the spectral emissivities. we also evaluate the possible contribution to thermal fluxes of established (chariklo) or claimed (chiron) ring systems. for chariklo, the rings do not impact the diameter determinations by more than ~5%; for chiron, invoking a ring system does not help in improving the consistency between the numerous past size measurements. as a general conclusion, all the objects, except makemake, have radio emissivities significantly lower than unity. although the emissivity values show diversity, we do not find any significant trend with physical parameters such as diameter, composition, beaming factor, albedo, or color, but we suggest that the emissivity could be correlated with grain size. the mean relative radio emissivity is found to be 0.70 ± 0.13, a value that we recommend for the analysis of further mm/submm data. | the thermal emission of centaurs and trans-neptunian objects at millimeter wavelengths from alma observations |
the lucy mission to the trojan asteroids in jupiter's orbit carries an instrument named l'ralph, a visible/near infrared multi-spectral imager and a short wavelength infrared hyperspectral imager. it is one of the core instruments on lucy, nasa's first mission to the trojans. l'ralph's primary purpose is to map the surface geology and composition of these objects, but it will also be used to search for possible tenuous exospheres. it is compact, low mass (32.3 kg), power efficient (24.5 w), and robust with high sensitivity and excellent imaging. these characteristics, and its high degree of redundancy, make l'ralph ideally suited to this long-duration multi-flyby reconnaissance mission. | l'ralph: a visible/infrared spectral imager for the lucy mission to the trojans |
we present our follow-up observations with grandma of transient sources revealed by the zwicky transient facility (ztf). over a period of six months, all ztf alerts were examined in real time by a dedicated science module implemented in the fink broker, which will be used in filtering of transients discovered by the vera c. rubin observatory. in this article, we present three selection methods to identify kilonova candidates. out of more than 35 million alerts, a hundred sources have passed our selection criteria. six were then followed-up by grandma (by both professional and amateur astronomers). the majority were finally classified either as asteroids or as supernovae events. we mobilized 37 telescopes, bringing together a large sample of images, taken under various conditions and quality. to complement the orphan kilonova candidates, we included three additional supernovae alerts to conduct further observations during summer 2021. we demonstrate the importance of the amateur astronomer community that contributed images for scientific analyses of new sources discovered in a magnitude range r' = 17 - 19 mag. we based our rapid kilonova classification on the decay rate of the optical source that should exceed 0.3 mag d-1. grandma's follow-up determined the fading rate within 1.5 ± 1.2 d post-discovery, without waiting for further observations from ztf. no confirmed kilonovae were discovered during our observing campaign. this work will be continued in the coming months in the view of preparing for kilonova searches in the next gravitational-wave observing run o4. | grandma observations of ztf/fink transients during summer 2021 |
recently, remarkable antiglitch and glitch accompanied by bright radio bursts of the galactic magnetar sgr j1935+2154 were discovered. these two infrequent temporal coincidences between the glitch/antiglitch and the fast radio burst (frb)-like bursts reveal their physical connection of them. here, we propose that the antiglitch/glitch and frb-like bursts can be well understood by an asteroid tidally captured by a magnetar. in this model, an asteroid is tidally captured and disrupted by a magnetar. then, the disrupted asteroid will transfer the angular momentum to the magnetar producing a sudden change in the magnetar rotational frequency at the magnetosphere radius. if the orbital angular momentum of the asteroid is parallel (or antiparallel) to that of the spinning magnetar, a glitch (or antiglitch) will occur. subsequently, the bound asteroid materials fall back to the pericentre and eventually are accreted to the surface of the magnetar. massive fragments of the asteroid cross magnetic field lines and produce bright radio bursts through coherent curvature radiation. our model can explain the sudden magnetar spin changes and frb-like bursts in a unified way. | tidal capture of an asteroid by a magnetar: frb-like bursts, glitch, and antiglitch |
the didymos binary asteroid was the target of the double asteroid redirection test (dart) mission, which intentionally impacted dimorphos, the smaller member of the binary system. we used the near-infrared spectrograph and mid-infrared instrument instruments on jwst to measure the 0.6-5 and 5-20 μm spectra of didymos approximately two months after the dart impact. these observations confirm that didymos belongs to the s asteroid class and is most consistent with ll chondrite composition, as was previously determined from its 0.6-2.5 μm reflectance spectrum. measurements at wavelengths >2.5 μm show didymos to have thermal properties typical for an s-complex asteroid of its size and to be lacking absorptions deeper than ~2% due to oh or h2o. didymos' mid-infrared emissivity spectrum is within the range of what has been measured on s-complex asteroids observed with the spitzer space telescope and is most consistent with emission from small (<25 μm) surface particles. we conclude that the observed reflectance and physical properties make the didymos system a good proxy for the type of ordinary chondrite asteroids that cross near-earth space, and a good representative of likely future impactors. | near to mid-infrared spectroscopy of (65803) didymos as observed by jwst: characterization observations supporting the double asteroid redirection test |
for a rendezvous space mission to a small body, the gravity field is usually modeled with large uncertainty in the preliminary mission design. consequently, the orbital motion in the vicinity of the body cannot be predicted accurately. in this research, the automatic domain splitting (ads) method is applied as an indicator to characterize the dynamical structure and nonlinearity of the orbital motion from a new perspective, which is instrumental in robust mission design. the uncertainties of the c20 and c22 terms in the gravitational potential are considered as these harmonic terms are usually dominant. asteroid steins is taken as an example. the relation among the required accuracy, the expansion order and the integration time by applying ads is firstly investigated. then the effects of the uncertainties of both the gravity and the solar radiation pressure (srp) perturbation on orbits with different geometries are studied. the orbital motion is found to be more sensitive to the uncertainty of the c22 term than that of the c20 term. srp has a significant effect on the high-altitude motion. moreover, the bounds of the state flow over the uncertainties are also evaluated along with the propagation. the results are validated against numerical integrations and monte carlo simulations. | dynamical structure of the motion around asteroids with uncertain gravity and solar radiation pressure |
nasa's first asteroid sample return mission, osiris-rex, collected a sample from the surface of near-earth asteroid bennu in october 2020 and will deliver it to earth in september 2023. selecting a sample collection site on bennu's surface was challenging due to the surprising lack of large ponded deposits of regolith particles exclusively fine enough (≤2 cm diameter) to be ingested by the spacecraft's touch-and-go sample acquisition mechanism (tagsam). here we describe the sampleability map of bennu, which was constructed to aid in the selection of candidate sampling sites and to estimate the probability of collecting sufficient sample. "sampleability" is a numeric score that expresses the compatibility of a given area's surface properties with the sampling mechanism. the algorithm that determines sampleability is a best fit functional form to an extensive suite of laboratory testing outcomes tracking the tagsam performance as a function of four observable properties of the target asteroid. the algorithm and testing were designed to measure and subsequently predict tagsam collection amounts as a function of the minimum particle size, maximum particle size, particle size frequency distribution, and the tilt of the tagsam head off the surface. the sampleability algorithm operated at two general scales, consistent with the resolution and coverage of data collected during the mission. the first scale was global and evaluated nearly the full surface. due to bennu's unexpected boulder coverage and lack of ponded regolith deposits, the global sampleability efforts relied heavily on additional strategies to find and characterize regions of interest based on quantifying and avoiding areas heavily covered by material too large to be collected. the second scale was site-specific and used higher-resolution data to predict collected mass at a given contact location. the rigorous sampleability assessments gave the mission confidence to select the best possible sample collection site and directly enabled successful collection of hundreds of grams of material. | assessing the sampleability of bennu's surface for the osiris-rex asteroid sample return mission |
finding a common origin for various celestial bodies, especially the relations between meteoroid streams, comets and asteroids (possibly extinct comets), remains one of the important problems in solar system astronomy. different criteria, starting with one by southworth and hawkins, have been used for this purpose. ideally, they must represent some kind of metric in a five-dimensional space of orbits. unfortunately, they are not ideal. the majority of the criteria have been examined by us. it turns out that they all represent pseudometrics for which the triangle axiom is not fulfilled. besides this, they are inapplicable if at least one of the orbits is circular. we propose metrics free of all the aforementioned drawbacks. in addition, the metric properties of three factor-spaces, where orbits are identified irrespective of the values of node longitudes, pericentre arguments or both, are examined. the results are applied to the problem of searching for minor bodies of the solar system with a common origin. the relationship between comet 96p/machholz 1 and asteroid 2003eh1, as well as that between comet 2p/encke and asteroid 2004tg10, has been proved. using all criteria considered and the new metrics leads to practically identical results. this is explained by the fact that only close and essentially non-circular orbits were analysed. besides this, the measure of orbit triples for which the triangle axiom failed is likely small, though this problem has not been examined yet. | metrics in the space of orbits and their application to searching for celestial objects of common origin |
in this paper, we investigate the stability of earth co-orbital objects (ecos) based on the torus structure. the hamiltonian value is an index to evaluate co-orbital stability. according to topological characters of tadpole (tp), horseshoe (hs), quasi-satellite (qs), and critical compound surfaces in the torus space, the co-orbital area is divided into several regions in detail. we select 221 potential ecos as representative samples. numerical integration in the sun-earth system illustrates that most of objects above the collision line are short- or long-term stable ecos in the qs-hs and qs-tp motions, and most of objects in the unstable region are unstable ones, which is in agreement with our semi-analytical conclusions. the stability of an eco with a larger hamiltonian value could be stronger. an efficient method to determine the long-term co-orbital stability of a potential eco is proposed without long-term numerical integration. numerical integration in the multiplanet model demonstrates that our stability analysis is still applicable for the real solar system. as an application of our stability analysis, two well-determined qs-hs ecos above the collision line are identified and analyzed for the first time. for instance, the qs-hs state of 2019 vl5 can be sustained for more than 3000 yr, and its current hs state will be sustained for at least 800 yr. | stability analysis of earth co-orbital objects |
evidence from iron meteorites indicates that a large number of differentiated planetesimals formed early in solar system history. these bodies should have had well-developed olivine-rich mantles and consequentially such materials ought to be abundant both as asteroids and meteorites, which they are not. to investigate this "great dunite shortage" we have undertaken a geochemical and oxygen isotope study of main-group pallasites and dunitic rocks from mesosiderites. oxygen isotope analysis of 24 main-group pallasites (103 replicates) yielded a mean δ17o value of -0.187 ± 0.016‰ (2σ), which is fully resolved from the hed δ17o value of -0.246 ± 0.014 (2σ) obtained in our earlier study and demonstrates that both groups represent distinct populations and were derived from separate parent bodies. our results show no evidence for δ17o bimodality within the main-group pallasites, as suggested by a number of previous studies. olivine-rich materials from the vaca muerta, mount padbury and lamont mesosiderites, and from two related dunites (nwa 2968 and nwa 3329), have δ17o values within error of the mesosiderite average. this indicates that these olivine-rich materials are co-genetic with other mesosiderite clasts and are not fragments from an isotopically distinct pallasite-like impactor. despite its extreme lithologic diversity the mesosiderite parent body was essentially homogeneous with respect to δ17o, a feature best explained by an early phase of large-scale melting (magma ocean), followed by prolonged igneous differentiation. based on the results of magma ocean modeling studies, we infer that mg-rich olivines in mesosiderites formed as cumulates in high-level chambers and do not represent samples of the underlying mantle. by analogy, recently documented mg-rich olivines in howardites may have a similar origin. although the dawn mission did not detect mesosiderite-like material on vesta, evidence linking the mesosiderites and heds includes: (i) their nearly identical oxygen isotope compositions; (ii) the presence in both of coarse-grained mg-rich olivines; (iii) both have synchronous lu-hf and mn-cr ages; (iv) there are compositional similarities between the metal in both; and (v) mesosiderite-like material has been identified in a howardite breccia. the source of the mesosiderites remains an outstanding question in meteorite science. the underrepresentation of olivine-rich materials amongst both asteroids and meteorites results from a range of factors. however, evidence from pallasites and mesosiderites indicates that the most important reason for this olivine shortage lies in the early, catastrophic destruction of planetesimals in the terrestrial planet-forming region and the subsequent preferential loss of their olivine-rich mantles. | geochemistry and oxygen isotope composition of main-group pallasites and olivine-rich clasts in mesosiderites: implications for the "great dunite shortage" and hed-mesosiderite connection |
asteroid families form as a result of large-scale collisions among main belt asteroids. the orbital distribution of fragments after a family-forming impact could inform us about their ejection velocities. unfortunately, however, orbits dynamically evolve by a number of effects, including the yarkovsky drift, chaotic diffusion, and gravitational encounters with massive asteroids, such that it is difficult to infer the ejection velocities eons after each family's formation. here, we analyse the inclination distribution of asteroid families, because proper inclination can remain constant over long time intervals, and could help us to understand the distribution of the component of the ejection velocity that is perpendicular to the orbital plane (vw). from modelling the initial break up, we find that the distribution of vw of the fragments, which manage to escape the parent body's gravity, should be more peaked than a gaussian distribution (i.e. be leptokurtic) even if the initial distribution was gaussian. we surveyed known asteroid families for signs of a peaked distribution of vw using a statistical measure of the distribution peakedness or flatness known as kurtosis. we identified eight families whose vw distribution is significantly leptokurtic. these cases (e.g. the koronis family) are located in dynamically quiet regions of the main belt, where, presumably, the initial distribution of vw was not modified by subsequent orbital evolution. we suggest that, in these cases, the inclination distribution can be used to obtain interesting information about the original ejection velocity field. | constraints on the original ejection velocity fields of asteroid families |
recent spacecraft missions detected presence of hydroxyl or water over large areas on the lunar surface. several craters near the lunar poles have increased concentrations of hydrogen suggesting impact delivery of water. using a numerical model, we have carried out computer simulations of the impacts of asteroids and comets in order to estimate the fate of water that can be contained in the projectiles. we find that at impact velocities below ~10 km/s a significant fraction of a stony projectile remains in the crater and is heated to temperatures below 1000 k. at these velocities hydrated minerals contained in carbonaceous projectiles decompose only partly. we conclude that the impacts of water-bearing carbonaceous asteroids could produce deposits of free and chemically bound water inside some lunar craters. the relative number of these craters may reach several percent. in contrast to asteroids, water from cometary impacts, even at low velocities, is vaporized, and vapor plume expands and disperses over the lunar surface. | water delivery to the moon by asteroidal and cometary impacts |
osiris-rex will return pristine samples of carbonaceous asteroid bennu. this article describes how pristine was defined based on expectations of bennu and on a realistic understanding of what is achievable with a constrained schedule and budget, and how that definition flowed to requirements and implementation. to return a pristine sample, the osiris-rex spacecraft sampling hardware was maintained at level 100 a/2 and <180 ng/cm2 of amino acids and hydrazine on the sampler head through precision cleaning, control of materials, and vigilance. contamination is further characterized via witness material exposed to the spacecraft assembly and testing environment as well as in space. this characterization provided knowledge of the expected background and will be used in conjunction with archived spacecraft components for comparison with the samples when they are delivered to earth for analysis. most of all, the cleanliness of the osiris-rex spacecraft was achieved through communication among scientists, engineers, managers, and technicians. | osiris-rex contamination control strategy and implementation |
thermal stress weathering is now recognized to be an active and significant geomorphological process on airless bodies. this study aims to understand the key factors governing thermal stresses in rocks on airless bodies through extensive numerical calculations and analytic analyses. microscopic (grain-scale) thermal stresses are driven primarily by the maximum diurnal temperature variation at said depth. macroscopic (rock-scale) thermal stresses are more complex. for rock sizes larger than the thermal skin depth, macroscopic thermal stresses are driven primarily by second (and higher) order spatial gradients of temperature. for rock sizes smaller than the thermal skin depth, macroscopic thermal stresses are primarily driven by the ratio of rock size to thermal skin depth. additionally, scaling relations for diurnal surface temperature variation, time-rate-of-change of surface temperature, as well as peak microscopic (grain-scale) and macroscopic (rock-scale) thermal stresses are derived to provide a more accessible modeling tool. these scaling relations are remarkably accurate when compared to both the numerical calculations as well as three-dimensional finite element calculations. the model formulation, results, and scaling relations provided here allow the estimation of diurnal temperatures and thermal stresses on rocks of various size and materials on airless bodies at any orbital distance with a broad spectrum of spin rates. lastly, we postulate and confirm that there is a critical spin rate where macroscopic thermal stresses will be greatest. | unraveling the mechanics of thermal stress weathering: rate-effects, size-effects, and scaling laws |
it has been proposed that all l chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the 500 ma old asteroid family gefion, located near the 5:2 mean-motion resonance with jupiter in the middle main belt. if so, l chondrite pre-atmospheric orbits should be distributed as expected for that source region. here, we present contradictory results from the orbit and collisional history of the october 24, 2015, l6 ordinary chondrite fall at creston, ca (here reclassified to l5/6). creston's short 1.30 ± 0.02 au semimajor axis orbit would imply a long dynamical evolution if it originated from the middle main belt. indeed, creston has a high cosmic ray exposure age of 40-50 ma. however, creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. this suggests, instead, that creston originated most likely in the inner asteroid belt and was delivered via the ν6 resonance. the u-pb systematics of creston apatite reveals a pb-pb age of 4,497.1 ± 3.7 ma, and an upper intercept u-pb age of 4,496.7 ± 5.8 ma (2σ), circa 70 ma after formation of cai, as found for other l chondrites. the k-ar (age 4.3 ga) and u,th-he (age 1 ga) chronometers were not reset at 500 ma, while the lower intercept u-pb age is poorly defined as 770 ± 320 ma. so far, the three known l chondrites that impacted on orbits with semimajor axes a <2.0 au all have high (>3 ga) k-ar ages. this argues for a source of some of our l chondrites in the inner main belt. not all l chondrites originate in a continuous population of gefion family debris stretching across the 3:1 mean-motion resonance. | the creston, california, meteorite fall and the origin of l chondrites |
i report results from accurate numerical integrations of solar system orbits over the past 100 myr with the integrator package hnbody. the simulations used different integrator algorithms, step sizes, and initial conditions, and included effects from general relativity, different models of the moon, the sun's quadrupole moment, and up to 16 asteroids. i also probed the potential effect of a hypothetical planet 9, using one set of possible orbital elements. the most expensive integration (bulirsch-stoer) required 4 months of wall-clock time with a maximum relative energy error ≲ 3× 10-13. the difference in earth's eccentricity (δee) was used to track the difference between two solutions, considered to diverge at time τ when max | δee | irreversibly crossed ∼10% of mean ee (∼ 0.028×0.1). the results indicate that finding a unique orbital solution is limited by initial conditions from current ephemerides and asteroid perturbations to ∼54 myr. bizarrely, the 4-month bulirsch-stoer integration and a symplectic integration that required only 5 hr of wall-clock time (12-day time step, with the moon as a simple quadrupole perturbation), agree to ∼63 myr. internally, such symplectic integrations are remarkably consistent even for large time steps, suggesting that the relationship between time step and τ is not a robust indicator of the absolute accuracy of symplectic integrations. the effect of a hypothetical planet 9 on δee becomes discernible at ∼65 myr. using τ as a criterion, the current state-of-the-art solutions all differ from previously published results beyond ∼50 myr. i also conducted an eigenmode analysis, which provides some insight into the chaotic nature of the inner solar system. the current study provides new orbital solutions for applications in geological studies. | numerical solutions for the orbital motion of the solar system over the past 100 myr: limits and new results |
in order to search for evidence of hydration on m-type asteroid (16) psyche, we observed this object in the 3 μm spectral region using the long-wavelength cross-dispersed (lxd: 1.9-4.2 μm) mode of the spex spectrograph/imager at the nasa infrared telescope facility. our observations show that psyche exhibits a 3 μm absorption feature, attributed to water or hydroxyl. the 3 μm absorption feature is consistent with the hydration features found on the surfaces of water-rich asteroids, attributed to oh- and/or h2o-bearing phases (phyllosilicates). the detection of a 3 μm hydration absorption band on psyche suggests that this asteroid may not be a metallic core, or it could be a metallic core that has been impacted by carbonaceous material over the past 4.5 gyr. our results also indicate rotational spectral variations, which we suggest reflect heterogeneity in the metal/silicate ratio on the surface of psyche. | detection of water and/or hydroxyl on asteroid (16) psyche |
robo-ao is an autonomous laser guide star adaptive optics (ao) system recently commissioned at the kitt peak 2.1 m telescope. with the ability to observe every clear night, robo-ao at the 2.1 m telescope is the first dedicated ao observatory. this paper presents the imaging performance of the ao system in its first 18 months of operations. for a median seeing value of 1.″44, the average strehl ratio is 4% in the i\prime band. after post processing, the contrast ratio under sub-arcsecond seeing for a 2≤slant i\prime ≤slant 16 primary star is five and seven magnitudes at radial offsets of 0.″5 and 1.″0, respectively. the data processing and archiving pipelines run automatically at the end of each night. the first stage of the processing pipeline shifts and adds the rapid frame rate data using techniques optimized for different signal-to-noise ratios. the second “high-contrast” stage of the pipeline is eponymously well suited to finding faint stellar companions. currently, a range of scientific programs, including the synthetic tracking of near-earth asteroids, the binarity of stars in young clusters, and weather on solar system planets are being undertaken with robo-ao. | the performance of the robo-ao laser guide star adaptive optics system at the kitt peak 2.1 m telescope |
the short-lived 182hf-182w decay system is a powerful chronometer for constraining the timing of metal-silicate separation and core formation in planetesimals and planets. neutron capture effects on w isotopes, however, significantly hamper the application of this tool. in order to correct for neutron capture effects, pt isotopes have emerged as a reliable in-situ neutron dosimeter. this study applies this method to iab iron meteorites, in order to constrain the timing of metal segregation on the iab parent body. the ɛ182w values obtained for the iab iron meteorites range from -3.61 ± 0.10 to -2.73 ± 0.09. correlating ɛipt with ɛ182w data yields a pre-neutron capture ɛ182w of -2.90 ± 0.06. this corresponds to a metal-silicate separation age of 6.0 ± 0.8 ma after cai for the iab parent body, and is interpreted to represent a body-wide melting event. later, between 10 and 14 ma after cai, an impact led to a catastrophic break-up and subsequent reassembly of the parent body. thermal models of the interior evolution that are consistent with these estimates suggest that the iab parent body underwent metal-silicate separation as a result of internal heating by short-lived radionuclides and accreted at around 1.4 ± 0.1 ma after cais with a radius of greater than 60 km. | late metal-silicate separation on the iab parent asteroid: constraints from combined w and pt isotopes and thermal modelling |
the first definitely interstellar object 1i/'oumuamua (previously a/2017 u1) observed in our solar system provides the opportunity to directly study material from other star systems. can such objects be intercepted? the challenge of reaching the object within a reasonable timeframe is formidable due to its high heliocentric hyperbolic excess velocity of about 26 km/s; much faster than any vehicle yet launched. this paper presents a high-level analysis of potential near-term options for a mission to 1i/'oumuamua and potential similar objects. launching a spacecraft to 1i/'oumuamua in a reasonable timeframe of 5-10 years requires a hyperbolic solar system excess velocity between 33 to 76 km/s for mission durations between 30 to 5 years. different mission durations and their velocity requirements are explored with respect to the launch date, assuming direct impulsive transfer to the intercept trajectory. for missions using a powered jupiter flyby combined with a solar oberth maneuver using solid rocket boosters and parker solar probe heat shield technology, a falcon heavy-class launcher would be able to launch a spacecraft of dozens of kilograms towards 1i/'oumuamua, if launched in 2021. an additional saturn flyby would allow for the launch of a new horizons-class spacecraft. further technology options are outlined, ranging from electric propulsion, and more advanced options such as laser electric propulsion, and solar and laser sails. to maximize science return decelerating the spacecraft at 'oumuamua is highly desirable, due to the minimal science return from a hyper-velocity encounter. electric and magnetic sails could be used for this purpose. it is concluded that although reaching the object is challenging, there seem to be feasible options based on current and near-term technology. | project lyra: sending a spacecraft to 1i/'oumuamua (former a/2017 u1), the interstellar asteroid |
1i/‘oumuamua is the first of likely many small bodies of extrasolar origin to be found in the solar system. these interstellar objects (isos) are hypothesized to have formed in extrasolar planetary systems prior to being ejected into interstellar space and subsequently arriving at the solar system. this paper discusses necessary considerations for tracing isos back to their parent stars via trajectory analysis and places approximate limits on doing so. results indicate that the capability to backtrace isos beyond the immediate solar neighborhood is presently constrained by the quality of stellar astrometry, a factor poised for significant improvement with upcoming gaia data releases. nonetheless, prospects for linking 1i or any other iso to their respective parent stars appear unfavorable on an individual basis due to gravitational scattering from random stellar encounters, which limit traceability to the past few tens of millions of years. these results, however, do not preclude the possibility of occasional success, particularly after considering the potential for observational bias favoring the discovery of younger isos, together with the anticipated rise in the iso discovery rate under forthcoming surveys. | prospects for backtracing 1i/‘oumuamua and future interstellar objects |
sixty-six million years ago, an asteroid approximately 9 km in diameter hit the hydrocarbon- and sulfur-rich sedimentary rocks in what is now mexico. recent studies have shown that this impact at the yucatan peninsula heated the hydrocarbon and sulfur in these rocks, forming stratospheric soot and sulfate aerosols and causing extreme global cooling and drought. these events triggered a mass extinction, including dinosaurs, and led to the subsequent macroevolution of mammals. the amount of hydrocarbon and sulfur in rocks varies widely, depending on location, which suggests that cooling and extinction levels were dependent on impact site. here we show that the probability of significant global cooling, mass extinction, and the subsequent appearance of mammals was quite low after an asteroid impact on the earth's surface. this significant event could have occurred if the asteroid hit the hydrocarbon-rich areas occupying approximately 13% of the earth's surface. the site of asteroid impact, therefore, changed the history of life on earth. | site of asteroid impact changed the history of life on earth: the low probability of mass extinction |
the mobile asteroid scout (mascot) is a small lander on board the hayabusa2 mission of the japan aerospace exploration agency to the asteroid 162173 ryugu. among the instruments on mascot is a fluxgate magnetometer, the mascot magnetometer (masmag). the magnetometer is a lightweight (∼280 g) and low power (∼0.5 w) triaxial fluxgate magnetometer. magnetic field measurements during the landing period and during the surface operational phase shall provide information about any intrinsic magnetic field of the asteroid and its remanent magnetization. this could provide important constraints on planet formation and the thermal and aqueous evolution of primitive asteroids. | the mascot magnetometer |
the dwarf planet ceres (equatorial diameter 963km) is the largest object that has remained in the main asteroid belt (russell and raymond, 2012), while most large bodies have been destroyed or removed by dynamical processes (petit et al. 2001; minton and malhotra, 2009). pre-dawn investigations (mccord and sotin, 2005; castillo-rogez and mccord, 2010; castillo-rogez et al., 2011) suggest that ceres is a thermally evolved, but still volatile-rich body with potential geological activity, that was never completely molten, but possibly differentiated into a rocky core, an ice-rich mantle, and may contain remnant internal liquid water. thermal alteration should contribute to producing a (dark) carbonaceous chondritic-like surface (mccord and sotin, 2005; castillo-rogez and mccord, 2010; castillo-rogez et al., 2011; nathues et al., 2015) containing ammoniated phyllosilicates (king et al., 1992; de sanctis et al., 2015 and 2016). here we show and analyse global contrast-rich colour mosaics, derived from a camera on-board dawn at ceres (russell et al., 2016). colours are unexpectedly more diverse on global scale than anticipated by hubble space telescope (li et al., 2006) and ground-based observations (reddy et al. 2015). dawn data led to the identification of five major colour units. the youngest units identified by crater counting, termed bright and bluish units, are exclusively found at equatorial and intermediate latitudes. we identified correlations between the distribution of the colour units, crater size, and formation age, inferring a crustal stratigraphy. surface brightness and spectral properties are not correlated. the youngest surface features are the bright spots at crater occator ( ø 92km). their colour spectra are highly consistent with the presence of carbonates while most of the remaining surface resembles modifications of various types of ordinary carbonaceous chondrites. | fc colour images of dwarf planet ceres reveal a complicated geological history |
this paper presents an approach for co-state initialization which is a critical step in solving minimum-time low-thrust trajectory optimization problems using indirect optimal control numerical methods. indirect methods used in determining the optimal space trajectories typically result in two-point boundary-value problems and are solved by single- or multiple-shooting numerical methods. accurate initialization of the co-state variables facilitates the numerical convergence of iterative boundary value problem solvers. in this paper, we propose a method which exploits the trajectory generated by the so-called pseudo-equinoctial and three-dimensional finite fourier series shape-based methods to estimate the initial values of the co-states. the performance of the approach for two interplanetary rendezvous missions from earth to mars and from earth to asteroid dionysus is compared against three other approaches which, respectively, exploit random initialization of co-states, adjoint-control transformation and a standard genetic algorithm. the results indicate that by using our proposed approach the percent of the converged cases is higher for trajectories with higher number of revolutions while the computation time is lower. these features are advantageous for broad trajectory search in the preliminary phase of mission designs. | co-state initialization for the minimum-time low-thrust trajectory optimization |
observations from earth-based ground and orbiting telescopes indicate that the ceres’s exosphere has a time-varying water component. evidence of a transient atmosphere was also detected by dawn upon its arrival, inferred from the response on the gamma ray and neutron detector. that atmosphere appeared shortly after the passage of a large enhancement in the local flux of high-energy solar protons. solar proton events have highly variable fluxes over a range of proton energies from 10 s of kev to over 100 mev and are capable of sputtering water ice at or near the surface. herein, we examine the fluxes of solar energetic protons measured during earth-based attempts to detect water vapor and oh in the ceres’ atmosphere. we find that the presence of the cerean exosphere is correlated with the inferred presence of solar energetic protons at ceres, consistent with the event detected by dawn. | the dependence of the cerean exosphere on solar energetic particle events |
throughout the history of the solar system, mars has experienced continuous asteroidal impacts. these impacts have produced impact-generated mars ejecta, and a fraction of this debris is delivered to earth as martian meteorites. another fraction of the ejecta is delivered to the moons of mars, phobos and deimos. here, we studied the amount and condition of recent delivery of impact ejecta from mars to its moons. using state-of-the-art numerical approaches, we report, for the first time, that materials delivered from mars to its moons are physically and chemically different from the martian meteorites, which are all igneous rocks with a limited range of ages. we show that mars ejecta mixed in the regolith of its moons potentially covers all its geological eras and consists of all types of rocks, from sedimentary to igneous. a martian moons sample-return mission will bring such materials back to earth, and the samples will provide a wealth of "time-resolved" geochemical information about the evolution of martian surface environments. | transport of impact ejecta from mars to its moons as a means to reveal martian history |
photometric analyses are used to standardize images obtained at a variety of illumination and viewing conditions to a common geometry for the construction of maps or mosaics and for comparison with spectral measurements acquired in the laboratory. many models exist that can be used to model photometric behavior. two of the most commonly use models, those of hapke and kaasalainen-shkuratov, are compared for their ability to standardize messenger images of mercury. analysis of the modeling results shows that photometric corrections using the kaasalainen-shkuratov model provides significantly less contrast between images acquired at large differences in emission angle. the contrast seen between images acquired at large differences in either incidence and phase angle is smaller with the hapke model based corrections, but not significantly better than that provided by the kaasalainen-shkuratov model. photometric studies are also used to infer scattering properties of the surface regolith. the quantitative correlation between photometric model parameters and surface properties is questionable, but laboratory studies do indicate general correlations and trends between parameters and sample properties that allow for comparisons between surfaces based on photometric modeling. based on comparisons with the moon and several asteroids that have been observed by spacecraft, the photometric analyses presented here are interpreted to indicate that mercury's regolith is smoother on micrometer scales and has a narrower particle size distribution with a lower mean particle size than lunar regolith. grain structures of regolith particles from mercury are inferred to be different than those of the moon or those asteroids observed to date. mercury's regolith may contain a component compositionally distinct from lunar regolith. | application of multiple photometric models to disk-resolved measurements of mercury's surface: insights into mercury's regolith characteristics |
motivated by the hypothesis that 'oumuamua could conceivably be an interstellar probe, we used the allen telescope array to search for radio transmissions that would indicate a non-natural origin for this object. observations were made at radio frequencies between 1 and 10 ghz using the array's correlator receiver with a channel bandwidth of 100 khz. in frequency regions not corrupted by man-made interference, we find no signal flux with frequency-dependent lower limits of 0.01 jy at 1 ghz and 0.1 jy at 7 ghz. for a putative isotropic transmitter on the object, these limits correspond to transmitter powers of 30 mw and 300 mw, respectively. in frequency ranges that are heavily utilized for satellite communications, our sensitivity to weak signals is badly impinged, but we can still place an upper limit of 10 w for a transmitter on the asteroid. for comparison and validation should a transmitter be discovered, contemporaneous measurements were made on the solar system asteroids 2017 uz and 2017 wc with comparable sensitivities. because they are closer to earth, we place upper limits on transmitter power to be 0.1 and 0.001 times the limits for 'oumuamua, respectively. | radio seti observations of the interstellar object ‧oumuamua |
recently, deep neural networks (dnns) have been widely and successfully used in object detection, e.g. faster rcnn, yolo, centernet. however, recent studies have shown that dnns are vulnerable to adversarial attacks. adversarial attacks against object detection can be divided into two categories, whole-pixel attacks and patch attacks. while these attacks add perturbations to a large number of pixels in images, we proposed a diffused patch attack (\textbf{dpattack}) to successfully fool object detectors by diffused patches of asteroid-shaped or grid-shape, which only change a small number of pixels. experiments show that our dpattack can successfully fool most object detectors with diffused patches and we get the second place in the alibaba tianchi competition: alibaba-tsinghua adversarial challenge on object detection. our code can be obtained from https://github.com/wu-shudeng/dpattack. | dpattack: diffused patch attacks against universal object detection |
characterizing the surface material of an asteroid is important for understanding its geology and for informing mission decisions, such as the selection of a sample site. diurnal surface temperature amplitudes are directly related to the thermal properties of the materials on the surface. we describe a numerical model for studying the thermal conductivity of particulate regolith in vacuum. heat diffusion and surface-to-surface radiation calculations are performed using the finite element (fe) method in three-dimensional meshed geometries of randomly packed spherical particles. we validate the model for test cases where the total solid and radiative conductivity values of particulates with monodisperse particle size frequency distributions (sfds) are determined at steady-state thermal conditions. then, we use the model to study the bulk radiative thermal conductivity of particulates with polydisperse, cumulative power law particle sfds. we show that for each polydisperse particulate geometry tested, there is a corresponding monodisperse geometry with some effective particle diameter that has an identical radiative thermal conductivity. these effective diameters are found to correspond very well to the sauter mean particle diameter, which is essentially the surface area-weighted mean. next, we show that the thermal conductivity of the particle material can have an important effect on the radiative component of the thermal conductivity of particulates, especially if the particle material conductivity is very low or the spheres are relatively large, owing to non-isothermality in each particle. we provide an empirical correlation to predict the effects of non-isothermality on radiative thermal conductivity in both monodisperse and polydisperse particulates. | full-field modeling of heat transfer in asteroid regolith: radiative thermal conductivity of polydisperse particulates |
aims: we analyze the behavior of the argument of pericenter ω2 of an outer particle in the elliptical restricted three-body problem, focusing on the ω2 resonance or inverse lidov-kozai resonance.methods: first, we calculated the contribution of the terms of quadrupole, octupole, and hexadecapolar order of the secular approximation of the potential to the outer particle's ω2 precession rate (dω2/dτ). then, we derived analytical criteria that determine the vanishing of the ω2 quadrupole precession rate (dω2/dτ)quad for different values of the inner perturber's eccentricity e1. finally, we used such analytical considerations and described the behavior of ω2 of outer particles extracted from n-body simulations developed in a previous work.results: our analytical study indicates that the values of the inclination i2 and the ascending node longitude ω2 associated with the outer particle that vanish (dω2/dτ)quad strongly depend on the eccentricity e1 of the inner perturber. in fact, if e1 < 0.25 (>0.40825), (dω2/dτ)quad is only vanished for particles whose ω2 circulates (librates). for e1 between 0.25 and 0.40825, (dω2/dτ)quad can be vanished for any particle for a suitable selection of pairs (ω2, i2). our analysis of the n-body simulations shows that the inverse lidov-kozai resonance is possible for small, moderate, and high values of e1. moreover, such a resonance produces distinctive features in the evolution of a particle in the (ω2, i2) plane. in fact, if ω2 librates and ω2 circulates, the extremes of i2 at ω2 = 90° and 270° do not reach the same value, while if ω2 and ω2 librate, the evolutionary trajectory of the particle in the (ω2, i2) plane shows evidence of an asymmetry with respect to i2 = 90°. the evolution of ω2 associated with the outer particles of the n-body simulations can be very well explained by the analytical criteria derived in our investigation. | inverse lidov-kozai resonance for an outer test particle due to an eccentric perturber |
we report results from new and archival observations of the newly discovered active asteroid (248370) 2005 qn173 (also now designated comet 433p), which has been determined to be a likely main-belt comet based on a subsequent discovery that it is recurrently active near perihelion. from archival data analysis, we estimate $g^{\prime} $ -, $r^{\prime} $ -, $i^{\prime} $ -, and $z^{\prime} $ -band absolute magnitudes for the nucleus of hg = 16.62 ± 0.13, hr = 16.12 ± 0.10, hi = 16.05 ± 0.11, and hz = 15.93 ± 0.08, corresponding to nucleus colors of $g^{\prime} -r^{\prime} =0.50\pm 0.16$ , $r^{\prime} -i^{\prime} =0.07\pm 0.15$ , and $i^{\prime} -z^{\prime} =0.12\pm 0.14$ ; an equivalent v-band absolute magnitude of hv = 16.32 ± 0.08; and a nucleus radius of rn = 1.6 ± 0.2 km (using a v-band albedo of pv = 0.054 ± 0.012). meanwhile, we find mean near-nucleus coma colors when 248370 is active of $g^{\prime} -r^{\prime} =0.47\pm 0.03$ , $r^{\prime} -i^{\prime} =0.10\pm 0.04$ , and $i^{\prime} -z^{\prime} =0.05\pm 0.05$ and similar mean dust tail colors, suggesting that no significant gas coma is present. we find approximate ratios between the scattering cross sections of near-nucleus dust (within 5000 km of the nucleus) and the nucleus of ad/an = 0.7 ± 0.3 on 2016 july 22 and 1.8 < ad/an < 2.9 in 2021 july and august. during the 2021 observation period, the coma declined in intrinsic brightness by ~0.35 mag (or ~25%) in 37 days, while the surface brightness of the dust tail remained effectively constant over the same period. constraints derived from the sunward extent of the coma and width of the tail as measured perpendicular to the orbit plane suggest that the terminal velocities of ejected dust grains are extremely slow (~1 m s-1 for 1 μm particles), suggesting that the observed dust emission may be aided by rapid rotation of the nucleus lowering the effective escape velocity. | physical characterization of main-belt comet (248370) 2005 qn173 |
in this work, we employ a soft-sphere discrete element method with a cohesion implementation to model the dynamical process of sub-km-sized cohesive rubble piles under continuous spin-up. the dependences of the critical spin periods tc on several material parameters for oblate rubble piles with different diameters were explored. our simulations show that the interparticle cohesive force can strengthen the bodies as expected, especially for the smaller ones. the simulated results of tc were fitted with the continuum theory developed by holsapple, through which we find the interparticle cohesion is proportional to the best-fitting bulk cohesion and the ratio shows no dependence on the density. in addition, we find tc decreases as the density increases in the compressive regime, while the trend reverses when transitioning to the tensile regime. besides, though a higher friction angle can strengthen the bodies, its influence on tc is minimized near the separation between the two regimes. our numerical findings are generally consistent with the continuum theory, except that the latter predicts that tc should increase as the friction angle increases in the tensile regime, which is contrary to the numerical results. this remarkable difference reminds us to take caution when applying the continuum theory to critically spinning cohesive rubble piles in the tensile regime, especially when dealing with the effect of the friction angle. finally, we emphasize that the separation between the regimes can be specified by a characteristic period, which is only a function of density for a given shape. | critical spin periods of sub-km-sized cohesive rubble-pile asteroids: dependences on material parameters |
meteor physics can provide new clues about the size, structure, and density of cometary disintegration products, establishing a bridge between different research fields. from meteor magnitude data we have estimated the mass distribution of meteoroids from different cometary streams by using the relation between the luminosity and the mass obtained by verniani. these mass distributions are in the range observed for dust particles released from comets 1p/halley and 81p/wild 2 as measured from spacecraft. from the derived mass distributions, we have integrated the incoming mass for the most significant meteor showers. by comparing the mass of the collected interplanetary dust particles (idps) with that derived for cometary meteoroids a gap of several orders of magnitude is encountered. the largest examples of fluffy particles are clusters of idps no larger than 100 μm in size (or 5 × 10-7 g in mass) while the largest cometary meteoroids are centimeter-sized objects. such gaps can be explained by the fragmentation in the atmosphere of the original cometary particles. as an application of the mass distribution computations we describe the significance of the disruption of fragile comets in close approaches to earth as a more efficient (and probably more frequent) way to deliver volatiles than direct impacts. we finally apply our model to quantify the flux of meteoroids from different meteoroid streams, and to describe the main physical processes contributing to the progressive decay of cometary meteoroids in the interplanetary medium. | learning about comets from the study of mass distributions and fluxes of meteoroid streams |
meteoroids impacting the earth on a daily basis are fragments of asteroids and comets. by studying fireballs produced during their disintegration in the atmosphere, we can gain information about their source regions and the properties of their parent bodies. in this work, data on 824 fireballs presented in an accompanying paper and catalog are used. we propose a new empirical parameter for the classification of the physical properties of meteoroids, based on the maximum dynamic pressure suffered by the meteoroid in the atmosphere. we then compare the physical and orbital properties of meteoroids. we find that aphelion distance is a better indicator of asteroidal origin than the tisserand parameter. meteoroids with aphelia lower than 4.9 au are mostly asteroidal, with the exception of the taurids and α capricornids associated with the comets 2p/encke and 169p/neat, respectively. we found another population of strong meteoroids of probably asteroidal origin on orbits with either high eccentricities or high inclinations, and aphelia up to χ 7 au. among the meteoroid streams, the geminids and η virginids are the strongest, and leonids and α capricornids the weakest. we found fine orbital structures within the geminid and perseid streams. four minor meteoroid streams from the working list of the international astronomical union were confirmed. no meteoroid with perihelion distance lower than 0.07 au was detected. spectra are available for some of the fireballs, and they enabled us to identify several iron meteoroids and meteoroids deficient in sodium. recognition and frequency of fireballs leading to meteorite falls is also discussed. the catalog is available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/667/a157 | data on 824 fireballs observed by the digital cameras of the european fireball network in 2017-2018. ii. analysis of orbital and physical properties of centimeter-sized meteoroids |
global geologic maps are useful tools for efficient interpretation of a planetary body, and they provide global context for the diversity and evolution of the surface. we used data acquired by the osiris-rex spacecraft to create the first global geologic map of the near-earth asteroid (101955) bennu. as this is the first geologic map of a small, non-spherical, rubble-pile asteroid, we discuss the distinctive mapping challenges and best practices that may be useful for future exploration of similar asteroids, such as those to be visited with the hera and janus missions. by mapping on two centimeter-scale global image mosaics (2d projected space) and a centimeter-scale global shape model (3d space), we generated three input maps respectively describing bennu's shape features, geologic features, and surface texture. based on these input maps, we defined two geologic units: the smooth unit and the rugged unit. the units are differentiated primarily on the basis of surface texture, concentrations of boulders, and the distributions of lineaments, mass movement features, and craters. they are bounded by several scarps. the rugged unit contains abundant boulders and signs of recent mass movement. it also has fewer small (<20 m), putatively fresh craters than the smooth unit, suggesting that such craters have been erased in the former. based on these geologic indicators, we infer that the rugged unit has the younger surface of the two. differential crater size-frequency distributions and the distribution of the freshest craters suggest that both unit surfaces formed ~10-65 million years ago, when bennu was located in the main asteroid belt, and the smooth unit has not been significantly resurfaced in the past 2 million years. meanwhile, the rugged unit has experienced resurfacing within the past ~500,000 years during bennu's lifetime as a near-earth asteroid. the geologic units are consistent with global diversity in slope, surface roughness, normal albedo, and thermal emission spectral characteristics. the site on bennu where the osiris-rex mission collected a regolith sample is located in the smooth unit, in a small crater nested within a larger one. so although the smooth unit is an older surface than the rugged unit, the impact-crater setting indicates that the material sampled was recently exposed. several similarities are apparent between bennu and asteroid (162173) ryugu from a global geologic perspective, including two geologic units distinguishable by variations in the number density of boulders, as well as in other datasets such as brightness. | global geologic map of asteroid (101955) bennu indicates heterogeneous resurfacing in the past 500,000\xa0years |
we successfully observed 191 near-earth asteroids using the arecibo observatory's s-band planetary radar system from 2017 december through 2019 december. we present radar cross sections for 167 asteroids; circular-polarization ratios for 112 asteroids based on doppler-echo-power spectra measurements; and radar albedos, constraints on size and spin periods, and surface-feature and shape evaluation for 37 selected asteroids using delay-doppler radar images with a range resolution of 75 m or finer. out of 33 asteroids with an estimated effective diameter of at least 200 m and sufficient image quality to give clues of the shape, at least 4 (~12%) are binary asteroids, including 1 equal-mass binary asteroid, 2017 ye5, and at least 10 (~30%) are contact-binary asteroids. for 5 out of 112 asteroids with reliable measurements in both circular polarizations, we measured circular-polarization ratios greater than 1.0, which could indicate that they are e-type asteroids, while the mean and the 1σ standard deviation were 0.37 ± 0.23. further, we find a mean opposite-sense circular-polarization radar albedo of 0.21 ± 0.11 for 41 asteroids (0.19 ± 0.06 for 11 s-complex asteroids). we identified two asteroids, 2011 wn15 and (505657) 2014 sr339, as possible metal-rich objects based on their unusually high radar albedos, and discuss possible evidence of water ice in 2017 ye5. | arecibo planetary radar observations of near-earth asteroids: 2017 december-2019 december |
it is speculated that some weakly active comets may be transitional objects between active and dormant comets. these objects are at a unique stage of the evolution of cometary nuclei, as they are still identifiable as active comets, in contrast to inactive comets that are observationally indistinguishable from low albedo asteroids. in this paper, we present a synthesis of comet and meteor observations of jupiter-family comet 209p/linear, one of the most weakly active comets recorded to-date. images taken by the xingming 0.35-m telescope and the gemini flamingo-2 camera are modeled by a monte carlo dust model, which yields a low dust ejection speed (1/10 of that of moderately active comets), dominance of large dust grains, and a low dust production of 0.4kgs-1 at 19 d after the 2014 perihelion passage. we also find a reddish nucleus of 209p/linear that is similar to d-type asteroids and most trojan asteroids. meteor observations with the canadian meteor orbit radar (cmor), coupled with meteoroid stream modeling, suggest a low dust production of the parent over the past few hundred orbits, although there are hints of a some temporary increase in activity in the 18th century. dynamical simulations indicate 209p/linear may have resided in a stable near-earth orbit for ∼104 yr, which is significantly longer than typical jfcs. all these lines of evidence imply that 209p/linear as an aging comet quietly exhausting its remaining near surface volatiles. we also compare 209p/linear to other low activity comets, where evidence for a diversity of the origin of low activity is seen. | when comets get old: a synthesis of comet and meteor observations of the low activity comet 209p/linear |
the yinggehai and qiongdongnan basins in the northwestern south china sea preserve a large volume of cenozoic sediments. however, their sources are still remain controversial and need a further research. this paper uses discriminant diagrams and bivariate plots of major, trace and rare earth elements, combined with heavy mineral data and detrital zircon u-pb ages to determine the provenance, source area weathering and tectonic setting of the upper miocene to pliocene sediments in the yinggehai and qiongdongnan basins, offshore south china sea. the sandstone samples used in this study are characterized by four features: (i) the studied sandstones are first-cycle deposits, no recycling processes are recorded in these sediments, and there is a low degree of weathering conditions in the source areas. (ii) the sandstones from the df fan, ld fan and central canyon system may have a similar source, being derived from an old upper continental crust mainly composed of felsic igneous source rocks. (iii) detrital zircon u-pb ages suggest that central vietnam is likely to be the dominant source of the df fan, ld fan and central canyon system. (iv) the tectonic setting of the sandstones in the df fan, ld fan and central canyon system belongs to the continental island arc (cia) or the active continental margin (acm) fields. | geochemistry and provenance of a multiple-stage fan in the upper miocene to the pliocene in the yinggehai and qiongdongnan basins, offshore south china sea |
aims: we carried out a spectroscopic survey in order to investigate the composition of 64 asteroids of the inner main belt, which are leftovers of the original planetesimals of our solar system (we call them inner main belt planetesimals or imbps). following published methods, we identified imbps in the inverse size versus semimajor axis (α) space, after the removal of all asteroids belonging to collisional families.methods: we conducted several ground-based observational campaigns of these imbps in the visible range at the 1.82 m asiago telescope, and in the near-infrared range at the telescopio nationale galileo, the lowell discovery telescope, and the nasa infrared telescope facility telescopes. as several of the identified planetesimals already have spectra published in the literature, we collected all the available data and focused the telescope time to investigate those never observed before, or to complete the 0.45-2.5 μm range spectrum for those for which there is only partial spectral coverage or data with poor signal-to-noise ratio. in this way, we obtained new spectra for 24 imbps. combining new and literature observations, we present spectra for 60 imbps in both the visible and near-infrared range, and 4 imbps in the visible only. all spectra were classified following well-established taxonomies. we also characterized their spectral absorption bands - when present -, their spectral slopes, and their mineralogy. in addition, we performed curve matching between astronomical and laboratory spectra in order to identify the closest meteorite analog using the relab database.results: the majority of the imbps belong to the s-complex; the latter are best matched with ordinary chondrite meteorites, and their olivine/(olivine and pyroxene) abundance ratio is not correlated with the semi-major axis. this result does not support the hypothesis that this ratio increases with heliocentric distance. furthermore, ~27% of the imbps belong to the c-complex, where ch/cgh types dominate, meaning that most of the carbonaceous-rich planetesimals were aqueously altered. these are best fitted by cm2 carbonaceous chondrite meteorites. finally, the remaining imbps (~20%) belong to the x-complex, and have various mineralogies and meteorite matches, while a few are end-member classes, including l-, k-, v-, and d- or t-types.conclusions: our spectroscopic investigation of imbps confirms that silicate-rich bodies dominated the inner main belt where temperature has permitted the condensation of silicate rocks. however, almost all the spectral types are found, with the notable exception of olivine-rich a-types and q-type asteroids. their absence, as well as the absence of the r- and o-types among planetesimals, might be due to the rarity of these types among large asteroids. however, the absence of q-types among primordial planetesimals is expected, as they have undergone surface rejuvenating processes. therefore, q-types have relatively young and less weathered surfaces compared to other types. our results support the hypothesis of compositional mixing in the early solar system. in particular, the fact that most of the c-complex planetesimals are aqueous altered, and the presence of three d- or t-type asteroids among them indicate that these bodies migrated from beyond 3 au to their current position. | composition of inner main-belt planetesimals |
context. landing on the surface of small bodies is particularly challenging, as the physical properties of the surface material are not well known and the mechanical response of this material in a low-gravity environment is not well understood.aims: in order to improve our understanding of low-speed impact processes on granular media and their outcome in low-gravity environments, we consider the landing of the package mascot, to be released by the jaxa asteroid sample return mission hayabusa2 on (162173) ryugu in october 2018. beyond addressing the theoretical aspects of the mechanical response of granular media in low gravity, this study also supports both engineering and scientific teams of hayabusa2 in the search for the lander and in the determination of ryugu's surface properties.methods: a campaign of hundreds of numerical simulations using the soft-sphere discrete element method implemented in the n-body code pkdgrav were performed to study the interaction between the lander and the low-gravity surface of the asteroid made of a granular medium representing the regolith. assuming a broad range of regolith properties, and the lander's trajectory and motion, we analyzed the outcomes of the landing (distance traveled by the lander, penetration depth, and shape of the traces left in the regolith surface) to determine the influence of the many parameters defining the properties of mascot and of the grains, and the ingoing motion of the lander.results: we identify well-marked trends for the fate of the lander and the traces left in the granular material. distances traveled by the lander are greater and penetrations are shallower for gravel-like media than for less frictional material. a similar trend is found for grazing impacts as opposed to vertical ones. different regolith properties also generate different traces on the ground after the impact. | numerical modeling of lander interaction with a low-gravity asteroid regolith surface. application to mascot on board hayabusa2 |
the world is entering a new era of exploring and exploiting outer space. the revolution in small, low-cost satellites, the recent initiatives from some countries to establish a legal framework, the increasing demand for technology metals and advances in space additive manufacturing have renewed the interest in space mining. biomining, the use of microorganisms to extract and recover valuable metals from minerals and wastes, could be used as alternative isru technology for harnessing space resources. this paper reviews in situ resources available on the moon, mars, and near-earth asteroids (neas) for implementing biomining processes in space, the effects of the space environment on biomining microbes, and space-based bioreactor designs that will enable leaching of metals from regoliths. a comparison between terrestrial and space biomining will also be presented, focusing on the differences in the composition of minerals on earth and space, the types of microorganisms used for leaching, and the parameters that need to be optimised in the space biomining processes. next steps to mature biomining approaches by combining knowledge from synthetic biology, systems biology, geomicrobiology and process engineering for space applications will also be explored. through an integrative effort of these fields, biomining processes commonly employed on earth can be harnessed for sustainable space exploration. | in situ resource utilisation: the potential for space biomining |
the elemental and isotopic compositions of meteorites are expected to reflect several key processes that occurred in the early solar system, including the migration of gas and dust throughout the protoplanetary disk, the formation of chondrules, and the accretion of the first planetary bodies. however, the specific origins of the various compositions measured among these rocks are currently poorly constrained, limiting our understanding of these processes. here, we use previously measured elemental and isotopic compositions of chondrites and iron meteorites to identify that carbonaceous (cc) meteorites are mixtures of noncarbonaceous (nc) material, calcium-aluminum-rich inclusion (cai) material, and ci (ivuna-like) material, in varying proportions. these trends indicate that chondrules in co (ornans-like), cm (mighei-like), cv (vigarano-like), and tl (tagish lake) chondrites share near-identical average proportions of ci material, arguing that they were generated through the remelting of preexisting nc chondrules all in the same disk environment. because this proportion likely evolved over space and time throughout the disk, this similarity argues that these chondrules originate from a restricted spatial region and time interval, favoring their generation through a localized event. moreover, the compositions of cr (renazzo-like) chondrites indicate that their constituents formed through mechanisms different from those in co, cm, cv, and tl chondrites. the recovered proportions of ci material in cc iron meteorites and chondrites together also argue for evolution in either the predominant direction of dust and gas motion in the first ∼10 au of the disk or the radial distance of planetesimal accretion throughout the cc reservoir. | constraints on chondrule generation, disk dynamics, and asteroid accretion from the compositions of carbonaceous meteorites |
determining the timescales of the accretion and chemical differentiation of meteorite parent bodies provides some of the most direct constraints on the formation of planetesimals and the earliest stages of planet formation. we present high-precision hf-w isotope data for a comprehensive set of ureilites, ultramafic mantle restites derived from a partially melted and incompletely differentiated asteroid. all samples are characterized by strong 182w deficits, indicating that silicate melt extraction on the ureilite parent body at 3.3 ± 0.7 ma after cai formation postdated core formation in iron meteorite parent bodies by ∼2-3 ma. thermal modeling of planetesimal heating by 26al-decay combined with the new hf-w data indicates that the ureilite parent body accreted at ∼1.6 ma after cai formation and, therefore, more than ∼1 ma later than iron meteorite parent bodies, but more than ∼0.5 ma earlier that most chondrite parent bodies. due to its relatively 'late' accretion, the ureilite parent body contained too little 26al to cause complete melting and, therefore, would have probably remained incompletely differentiated even without exhaustion of 26al by silicate melt segregation. our results show that both in terms of degree of differentiation and accretion timescale the ureilite parent body is intermediate between fully differentiated and undifferentiated bodies, implying that there is an inverse correlation between extent of melting and metal-silicate separation versus time of accretion and differentiation. | planetesimal differentiation revealed by the hf-w systematics of ureilites |
asteroid (16) psyche is a unique, metal-rich object belonging to the "m" taxonomic class. it may be a remnant protoplanet that has been stripped of most silicates by a hit-and-run collision. because psyche offers insight into the planetary formation process, it is the target of nasa's psyche mission, set to launch in 2023. in order to constrain psyche's surface properties, we have carried out a mid-infrared (5-14 μm) spectroscopic study using data collected with the spitzer space telescope's infrared spectrograph. our study includes two observations covering different rotational phases. using thermophysical modeling, we find that psyche's surface is smooth and likely has a thermal inertia γ = 5-25 j/m2/k/s1/2 and bolometric emissivity ɛ = 0.9, although a scenario with ɛ = 0.7 and thermal inertia up to 95 j/m2/k/s1/2 is possible if psyche is somewhat larger than previously determined. the smooth surface is consistent with the presence of a metallic bedrock, which would be more ductile than silicate bedrock, and thus may not readily form boulders upon impact events. from comparisons with laboratory spectra of silicate and meteorite powders, psyche's 7-14 μm emissivity spectrum is consistent with the presence of fine-grained (< 75 μm) silicates on psyche's surface. we conclude that psyche is likely covered in a fine silicate regolith, which may also contain iron grains, overlying an iron-rich bedrock. | asteroid (16) psyche: evidence for a silicate regolith from spitzer space telescope spectroscopy |
about 66 million years ago, an asteroid about 10 km in diameter struck the yucatan peninsula creating the chicxulub crater. the crater has been dated and found to be coincident with the cretaceous-paleogene (k-pg) mass extinction event, one of six great mass extinctions in the last 600 million years. this event precipitated one of the largest episodes of rapid climate change in earth's history, yet no modern three-dimensional climate calculations have simulated the event. similarly, while there is an ongoing effort to detect asteroids that might hit earth and to develop methods to stop them, there have been no modern calculations of the sizes of asteroids whose impacts on land would cause devastating effects on earth. here, we provide the information needed to initialize such calculations for the k-pg impactor and for a 1 km diameter impactor. there is considerable controversy about the details of the events that followed the chicxulub impact. we proceed through the data record in the order of confidence that a climatically important material was present in the atmosphere. the climatic importance is roughly proportional to the optical depth of the material. spherules with diameters of several hundred microns are found globally in an abundance that would have produced an atmospheric layer with an optical depth around 20, yet their large sizes would only allow them to stay airborne for a few days. they were likely important for triggering global wildfires. soot, probably from global or near-global wildfires, is found globally in an abundance that would have produced an optical depth near 100, which would effectively prevent sunlight from reaching the surface. nanometer-sized iron particles are also present globally. theory suggests these particles might be remnants of the vaporized asteroid and target that initially remained as vapor rather than condensing on the hundred-micron spherules when they entered the atmosphere. if present in the greatest abundance allowed by theory, their optical depth would have exceeded 1000. clastics may be present globally, but only the quartz fraction can be quantified since shock features can identify it. however, it is very difficult to determine the total abundance of clastics. we reconcile previous widely disparate estimates and suggest the clastics may have had an optical depth near 100. sulfur is predicted to originate about equally from the impactor and from the yucatan surface materials. by mass, sulfur is less than 10 % of the observed mass of the spheres and estimated mass of nanoparticles. since the sulfur probably reacted on the surfaces of the soot, nanoparticles, clastics, and spheres, it is likely a minor component of the climate forcing; however, detailed studies of the conversion of sulfur gases to particles are needed to determine if sulfuric acid aerosols dominated in late stages of the evolution of the atmospheric debris. numerous gases, including co2, so2 (or so3), h2o, co2, cl, br, and i, were likely injected into the upper atmosphere by the impact or the immediate effects of the impact such as fires across the planet. their abundance might have increased relative to current ambient values by a significant fraction for co2, and by factors of 100 to 1000 for the other gases. for the 1 km impactor, nanoparticles might have had an optical depth of 1.5 if the impact occurred on land. if the impactor struck a densely forested region, soot from the forest fires might have had an optical depth of 0.1. only s and i would be expected to be perturbed significantly relative to ambient gas-phase values. one kilometer asteroids impacting the ocean may inject seawater into the stratosphere as well as halogens that are dissolved in the seawater. for each of the materials mentioned, we provide initial abundances and injection altitudes. for particles, we suggest initial size distributions and optical constants. we also suggest new observations that could be made to narrow the uncertainties about the particles and gases generated by large impacts. | designing global climate and atmospheric chemistry simulations for 1 and 10 km diameter asteroid impacts using the properties of ejecta from the k-pg impact |
most bodies in the solar system do not have a homogeneous structure. understanding the outcome of an impact into regolith layers of different properties is especially important for nasa's double asteroid redirection test (dart) and esa's hera missions. here we used the isale shock physics code to simulate the dart impact into three different target scenarios in the strength regime: a homogeneous porous half-space; layered targets with a porous weak layer overlying a stronger bedrock; and targets with exponentially decreasing porosity with depth. for each scenario we determined the sensitivity of crater morphology, ejecta mass-velocity distribution and momentum transferred from the impact for deflection, β - 1 , to target properties and structure. we found that for a homogeneous porous half-space, cohesion and porosity play a significant role and the dart impact is expected to produce a β - 1 between 1 and 3. in a two-layer target scenario, the presence of a less porous, stronger lower layer close to the surface can cause both amplification and reduction of ejected mass and momentum relative to the homogeneous upper-layer case. for the case of dart, the momentum enhancement can change by up to 90%. impacts into targets with an exponentially decreasing porosity with depth only produced an enhancement in the ejected mass and momentum for sharp decreases in porosity that occur within 6 m of the asteroid surface. together with measurements of the dart crater by the hera mission, these results can be used to test the predictive capabilities of numerical models of asteroid deflection. | the effects of asteroid layering on ejecta mass-velocity distribution and implications for impact momentum transfer |
all-sky meteor orbit system (amos) is a semi-autonomous video observatory for detection of transient events on the sky, mostly the meteors. its hardware and software development and permanent placement on several locations in slovakia allowed the establishment of slovak video meteor network (svmn) monitoring meteor activity above the central europe. the data reduction, orbital determination and additional results from amos cameras - the svmn database - as well as from observational expeditions on canary islands and in canada provided dynamical and physical data for better understanding of mutual connections between parent bodies of asteroids and comets and their meteoroid streams. we present preliminary results on exceptional and rare meteor streams such as september ɛ perseids (spe) originated from unknown long periodic comet on a retrograde orbit, suspected asteroidal meteor stream of april α comae berenicids (aco) in the orbit of meteorites příbram and neuschwanstein and newly observed meteor stream camelopardalids (cam) originated from jupiter family comet 209p/linear. | all-sky meteor orbit system amos and preliminary analysis of three unusual meteor showers |
photographs of the asteroid itokawa reveal unexpectedly strong size segregation between lowlands populated almost entirely by small pebbles and highlands consisting of larger boulders. we propose that this segregation may be caused by a simple and unexplored effect: pebbles accreting onto the asteroid rebound from boulders, but sink into pebbly regions. by number, overwhelmingly more particles on itokawa are pebbles, and collisions involving these pebbles must unavoidably cause pebbly regions to grow. we carry out experiments and simulations that demonstrate that this mechanism of size sorting based on simple counting of grains produces strong lateral segregation that reliably obeys an analytic formula. | size sorting on the rubble-pile asteroid itokawa |
trojan asteroids are small bodies orbiting around the l4 or l5 lagrangian points of a sun-planet system. due to their peculiar orbits, they provide key constraints to the solar system evolution models. despite numerous dedicated observational efforts in the last decade, asteroid 2010 tk7 has been the only known earth trojan thus far. here we confirm that the recently discovered 2020 xl5 is the second transient earth trojan known. to study its orbit, we used archival data from 2012 to 2019 and observed the object in 2021 from three ground-based observatories. our study of its orbital stability shows that 2020 xl5 will remain in l4 for at least 4 000 years. with a photometric analysis we estimate its absolute magnitude to be hr=18.5 8−0.15+0.16?, and color indices suggestive of a c-complex taxonomy. assuming an albedo of 0.06 ± 0.03, we obtain a diameter of 1.18 ± 0.08 km, larger than the first known earth trojan asteroid. | orbital stability analysis and photometric characterization of the second earth trojan asteroid 2020 xl5 |
the leading source of uncertainty to predict the orbital motion of asteroid (99942) apophis is a non-gravitational acceleration arising from the anisotropic thermal re-emission of absorbed radiation, known as the yarkovsky effect. previous attempts to obtain this parameter from astrometry for this object have only yielded marginally small values, without ruling out a pure gravitational interaction. here we present an independent estimation of the yarkovsky effect based on optical and radar astrometry which includes observations obtained during 2021. our numerical approach exploits automatic differentiation techniques. we find a non-zero yarkovsky parameter, a2 = (−2.899 ± 0.025) × 10−14 au d−2, with induced semi-major axis drift of (−199.0 ± 1.5) m yr−1 for apophis. our results provide definite collision probability predictions for the close approaches in 2029, 2036, and 2068. | non-zero yarkovsky acceleration for near-earth asteroid (99942) apophis |
when planetesimals grow via collisions in a turbulent disk, stirring through density fluctuation caused by turbulence effectively increases the relative velocities between planetesimals, which suppresses the onset of runaway growth. we investigate the onset of runaway growth in a turbulent disk through simulations that calculate the mass and velocity evolution of planetesimals. when planetesimals are small, the average relative velocity between planetesimals, {v}{{r}}, is much greater than their surface escape velocity, {v}{{esc}}, so that runaway growth does not occur. as planetesimals become large via collisional growth, {v}{{r}} approaches {v}{{esc}}. when {v}{{r}}≈ 1.5{v}{{esc}}, runaway growth of the planetesimals occurs. during the oligarchic growth subsequent to runaway growth, a small number of planetary embryos produced via runaway growth become massive through collisions with planetesimals with radii of that at the onset of runaway growth, {r}{{p,run}}. we analytically derive {r}{{p,run}} as a function of the turbulent strength. growing ∼ 10 {m}\oplusembryos that are suitable to become the cores of jupiter and saturn requires {r}{{p,run}}∼ 100 km, which is similar to the proposed fossil feature in the size distribution of main belt asteroids. in contrast, the formation of mars as quickly as suggested from hf-w isotope studies requires small planetesimals at the onset of runaway growth. thus, the conditions required to form mars, jupiter, and saturn and the size distribution of the main-belt asteroids indicate that the turbulence increased in amplitude relative to the sound speed with increasing distance from the young sun. | from planetesimals to planets in turbulent protoplanetary disks. i. onset of runaway growth |
despite the hazards of asteroids, utilization of their resources and useful materials have been raised recently. in some scenarios, capturing and controlling asteroids are essential for asteroid mining. to this end, a reliable detumbling mission using a swarm of cubesats, each equipped with a low-thrust thruster, is proposed in this paper. the landing location and the orientation of each cubesat on an ellipsoidal asteroid are determined by designing optimal cubesat (thruster) configuration according to a minimum number of required cubesats for maximizing reliability and minimizing fuel consumption with a specific level of redundancy using a genetic algorithm. the feasibility of the configuration is examined using the geometric method. examining the proposed configuration through a simulation shows acceptable performance with the desired reliability and level of redundancy. | designing reliable detumbling mission for asteroid mining |
astronomical solutions provide insight into the solar system's dynamical evolution and are indispensable tools in cyclostratigraphy and astrochronology. constructing an absolute, fully calibrated astronomical time scale (ats) has hitherto been hindered beyond ∼50 ma because orbital calculations disagree before that age due to solar system chaos. we have recently developed a new approach that allows extending the fully calibrated astronomical time scale to ∼58 ma. here, we present geologic data and new astronomical solutions, extending our approach across the paleocene epoch (∼66 to ∼56 ma). new astronomical solutions were generated using numerical solar system integrations following our earlier work, which now provides geologically constrained astronomical solutions for the cenozoic era (66-0 ma). the orbital solutions are available to 300 ma - we caution, however, that the time interval 300-66 ma is unconstrained due to dynamical chaos in the solar system. we have tested the sensitivity of our new solutions to various parameters, including numerical stepsize, solar quadrupole moment, number of asteroids included, initial positions, and tidal dissipation. we demonstrate that our new solutions yield improved agreement with the geologic record across the paleocene epoch, compared to previously available astronomical solutions for that period. furthermore, we discuss implications of our results for solar system chaos and resonance transitions. we have also obtained k/t boundary (ktb) ages based on our new solutions, which suggest slightly younger ktb ages than those inferred from most recent 40ar/39ar radiometric dating. | geologically constrained astronomical solutions for the cenozoic era |
context. it is well known that hydrogen cyanide and formamide can universally be considered as key molecules in prebiotic synthesis. despite the fact that formamide has been detected in interplanetary and interstellar environments, other prebiotic species are far more abundant, including, for example, formaldehyde. however, several results indicate that formamide can play the role of important intermediate as well as that of a feedstock molecule in chemical abiogenesis. diverse recently proposed scenarios of the origins of the first biopolymers show that liquid formamide environments could have been crucial for the formation of nucleobases, nucleosides, and for phosphorylation reactions, which lead to nucleotides.aims: here we report on a wide exploration of the formaldehyde reaction network under plasma conditions mimicking an asteroid descent in an earth-like atmosphere and its impact.methods: dielectric breakdown using a high-power kj-class laser system (pals - prague asterix laser system) along with quantum mechanical, ab initio molecular dynamics, and enhanced sampling simulations have been employed in order to mimic an asteroid impact plasma.results: being more abundant than formamide both in interstellar and interplanetary environments, during the era of early and late heavy bombardment of earth and other planets, formaldehyde might have been delivered on asteroids to young planets. in the presence of nitrogen-bearing species, this molecule has been reprocessed under plasma conditions mimicking the local environment of an impacting body. we show that plasma reprocessing of formaldehyde leads to the formation of several radical and molecular species along with formamide. conclusion. all the canonical nucleobases, the simplest amino acid (i.e., glycine), and the sugar ribose, have been detected after treatment of formaldehyde and nitrogen gas with dielectric breakdown. our results, supported by quantum mechanical and enhanced sampling simulations, show that formaldehyde - by producing inter alia formamide - may have had the role of starting substance in prebiotic synthesis. | prebiotic synthesis initiated in formaldehyde by laser plasma simulating high-velocity impacts |
the direction in which a planetary core solidifies has fundamental implications for the feasibility and nature of dynamo generation. although earth's core is outwardly solidifying, the cores of certain smaller planetary bodies have been proposed to inwardly solidify due to their lower central pressures. however, there have been no unambiguous observations of inwardly solidified cores or the relationship between this solidification regime and planetary magnetic activity. to address this gap, we present the results of complimentary paleomagnetic techniques applied to the matrix metal and silicate inclusions within the iva iron meteorites. this family of meteorites has been suggested to originate from a planetary core that had its overlaying silicate mantle removed by collisions during the early solar system. this process is thought to have produced a molten ball of metal that cooled rapidly and has been proposed to have inwardly solidified. recent thermal evolution models of such a body predict that it should have generated an intense, multipolar and time-varying dynamo field. this field could have been recorded as a remanent magnetisation in the outer, cool layers of a solid crust on the iva parent core. we find that the different components in the iva iron meteorites display a range of paleomagnetic fidelities, depending crucially on the cooling rate of the meteorite. in particular, silicate inclusions in the quickly cooled são joão nepomuceno meteorite are poor paleomagnetic recorders. on the other hand, the matrix metal and some silicate subsamples from the relatively slowly cooled steinbach meteorite are far better paleomagnetic recorders and provide evidence of an intense (≳100 μt) and directionally varying (exhibiting significant changes on a timescale ≲200 kyr) magnetic field. this is the first demonstration that some iron meteorites record ancient planetary magnetic fields. furthermore, the observed field intensity, temporal variability and dynamo lifetime are consistent with thermal evolution models of the iva parent core. because the acquisition of remanent magnetisation by some iva iron meteorites require that they cooled below their curie temperature during the period of dynamo activity, the magnetisation carried by steinbach also provides strong evidence favouring the inward solidification of its parent core. | paleomagnetic evidence for dynamo activity driven by inward crystallisation of a metallic asteroid |
context. the available set of spin and shape modelled asteroids is strongly biased against slowly rotating targets and those with low lightcurve amplitudes. this is due to the observing selection effects. as a consequence, the current picture of asteroid spin axis distribution, rotation rates, radiometric properties, or aspects related to the object's internal structure might be affected too.aims: to counteract these selection effects, we are running a photometric campaign of a large sample of main belt asteroids omitted in most previous studies. using least chi-squared fitting we determined synodic rotation periods and verified previous determinations. when a dataset for a given target was sufficiently large and varied, we performed spin and shape modelling with two different methods to compare their performance.methods: we used the convex inversion method and the non-convex sage algorithm, applied on the same datasets of dense lightcurves. both methods search for the lowest deviations between observed and modelled lightcurves, though using different approaches. unlike convex inversion, the sage method allows for the existence of valleys and indentations on the shapes based only on lightcurves.results: we obtain detailed spin and shape models for the first five targets of our sample: (159) aemilia, (227) philosophia, (329) svea, (478) tergeste, and (487) venetia. when compared to stellar occultation chords, our models obtained an absolute size scale and major topographic features of the shape models were also confirmed. when applied to thermophysical modelling (tpm), they provided a very good fit to the infrared data and allowed their size, albedo, and thermal inertia to be determined.conclusions: convex and non-convex shape models provide comparable fits to lightcurves. however, some non-convex models fit notably better to stellar occultation chords and to infrared data in sophisticated thermophysical modelling (tpm). in some cases tpm showed strong preference for one of the spin and shape solutions. also, we confirmed that slowly rotating asteroids tend to have higher-than-average values of thermal inertia, which might be caused by properties of the surface layers underlying the skin depth. the photometric data is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/610/a7 | photometric survey, modelling, and scaling of long-period and low-amplitude asteroids |
the microwave cathode was developed as a neutralizer for the microwave ion thrusters of the japanese asteroid explorers hayabusa and hayabusa2. since it emits hundreds of ma of electron current, ion currents collect at the wall of the cathode, which causes fatal destruction due to sputtering. in an effort to reduce the sputtering voltage, this study investigates the effect of the strength of the magnetic field at the nozzle on the anode voltage. firstly, a magnetic field is applied at the nozzle by a coil. using the coil, decreasing the magnetic field intensity increases the electron density at the exit of the nozzle. it is presumed that the applied magnetic field facilitates the detachment of magnetic lines by the electrons inside the microwave cathode, resulting in a reduction of the anode voltage. by weakening the nozzle magnetic field, trapped electrons are reduced and the transportability to the outside is improved. secondly, to realize the same magnetic field intensity achieved in the first experiment without any additional power consumption, the author proposes the use of a magnetic shield. the magnetic shield reduces the anode voltage from 37 v to 32 v at 180 ma, the nominal current of the flight model. since the sputtering rate exponentially increases with the anode voltage, reducing the anode voltage through these techniques is effective in increasing the lifetime of the cathode. | effect of nozzle magnetic field on microwave discharge cathode performance |
electrostatic dust levitation is the phenomenon where dust grains hover above the surface of an airless body due to the approximate balancing of the forces attracting the grain to and repelling the grain from the body. the dynamics of levitating grains have been investigated previously for the case where the grain's motion is constrained to one dimension. additionally, other prior investigations have observed the 2d motion of grains near surface features (e.g. craters). in this work, we systematically investigate the 2d motion of electrostatically levitating grains about a circular asteroid cross section. we find that solar radiation pressure strongly depresses the altitudes of grain levitation leading to more strongly damped altitude oscillations. we show that a dynamical systems approximation can provide useful information about the grain dynamics, especially over short timescales. we also demonstrate that grains are able to levitate in a spatially inhomogeneous plasma environment. these results are significant for assessing the feasibility of global dust transport through electrostatic levitation on asteroids. | dynamics of 2d electrostatic dust levitation at asteroids |
we present an analysis of the blank-sky spectra observed with the faint object spectrograph on board the hubble space telescope. we study the diffuse sky emission from ultraviolet to optical wavelengths, which is composed of zodiacal light (zl), diffuse galactic light (dgl), and residual emission. the observations were performed towards 54 fields distributed widely over the sky, with spectral coverage from 0.2 to 0.7 μm. in order to avoid contaminating light from earthshine, we use the data collected only in orbital nighttime. the observed intensity is decomposed into the zl, dgl, and residual emission, in eight photometric bands spanning our spectral coverage. we found that the derived zl reflectance spectrum is flat in the optical, which indicates major contribution of c-type asteroids to the interplanetary dust (ipd). in addition, the zl reflectance spectrum has an absorption feature at ∼0.3 μm. the shape of the dgl spectrum is consistent with those found in earlier measurements and model predictions. while the residual emission contains a contribution from the extragalactic background light, we found that the spectral shape of the residual looks similar to the zl spectrum. moreover, its optical intensity is much higher than that measured from beyond the ipd cloud by pioneer 10/11, and also than that of the integrated galaxy light. these findings may indicate the presence of an isotropic zl component, which is missed in the conventional zl models. | ultraviolet to optical diffuse sky emission as seen by the hubble space telescope faint object spectrograph |
this paper presents a quantitative study of the evolution of the ejecta cloud released from a hypervelocity impact on a binary asteroid. the asteroid impact & deflection assessment (aida) mission project in collaboration between nasa and esa aims to perform an asteroid deflection demonstration, using a half-ton projectile that will perform a hypervelocity impact on the surface of the secondary of the binary near-earth asteroid (65803) didymos, called hereafter didymoon. we performed numerical simulations of the post-impact dynamics of the ejecta cloud in the framework of the current mission scenario of aida. our analysis relies on a classification of the orbits as a function of the ejecta fates, e.g., a collision with one of the binary components or the escape from the region of influence of the system. a grid search of launching sites of ejecta was defined over the globe of didymoon, and considering a wide range of possible ejection speeds, we determined the dependency of ejecta fate on launching sites (projectile impact sites) and speeds. this range enables us to track all the complex cases that include different types of dynamical fates. the results reveal the detailed proportions of the ejecta that are either orbiting, escaping or re-accreting on the primary/secondary at the end of the considered timescale, as a function of the ejection speed, which allows us to explore the global characteristics of the ejecta dynamical fates. two major mechanisms are found to be working broadly during the post-ejection evolution of the ejecta cloud: 1) ejecta on mean motion resonance orbits with didymoon produce long-term quasi-periodic showers onto didymoon over at least a couple of weeks after the projectile impact, 2) ejecta on non-resonant orbits produce a rapid and high re-accretion flux. this rapid and high flux occurs just once because ejecta on such orbits leave the system unless they experience a collision during their first encounter. for both mechanisms, swing-bys of didymoon are found to occur. these swing-bys are a source of chaotic motion because the outcome of the swing-by is extremely sensitive to the ejecta initial conditions. moreover, for all ejecta speeds, a zone free of ejecta is noticed to emerge around the mid-latitude zone of the celestial sphere about two months after the projectile impact. also, the extent of this zone depends on the ejecta speed. for the second part of this study, we performed full-scale simulations of the ejecta cloud released from 6 hypothetical impact sites. to define the initial conditions of the ejecta based on cratering scaling laws, we considered two kinds of material composing didymoon's subsurface and then combined a power-law size distribution of the ejecta with an ejection speed distribution. we find that the ejecta cloud evolution can be divided in two periods. it starts with a first violent period (<10 h) with fast re-accretion or ejection of the ejecta from the system. a second period is found to be more sensitive to the launching site than the first one. during this second period, ejecta will either re-accrete or being ejected from the system, depending both on their sizes and on their average survival time in close proximity of the binary components. there is thus a size-sorting effect dictated by the solar radiation pressure, which proves to be efficient to move out of the system the dust-size ejecta (<1 mm) for all considered launching sites and material types. on the other hand, the larger ejecta, being less or not affected by the solar radiation pressure, can survive longer in the system. | ejecta cloud from the aida space project kinetic impact on the secondary of a binary asteroid: ii. fates and evolutionary dependencies |
eos family was created during a catastrophic impact about 1.3 gyr ago. rotation states of individual family members contain information about the history of the whole population. we aim to increase the number of asteroid shape models and rotation states within the eos collision family, as well as to revise previously published shape models from the literature. such results can be used to constrain theoretical collisional and evolution models of the family, or to estimate other physical parameters by a thermophysical modeling of the thermal infrared data. we use all available disk-integrated optical data (i.e., classical dense-in-time photometry obtained from public databases and through a large collaboration network as well as sparse-in-time individual measurements from a few sky surveys) as input for the convex inversion method, and derive 3d shape models of asteroids together with their rotation periods and orientations of rotation axes. we present updated shape models for 15 asteroids and new shape model determinations for 16 asteroids. together with the already published models from the publicly available damit database, we compiled a sample of 56 eos family members with known shape models that we used in our analysis of physical properties within the family. rotation states of asteroids smaller than ∼ 20 km are heavily influenced by the yorp effect, whilst the large objects more or less retained their rotation state properties since the family creation. moreover, we also present a shape model and bulk density of asteroid (423) diotima, an interloper in the eos family, based on the disk-resolved data obtained by the near infrared camera (nirc2) mounted on the w.m. keck ii telescope. | spin states of asteroids in the eos collisional family |
(modified from published version) twelve years ago the catalina sky survey discovered earth's first known natural geocentric object other than the moon, a few-meter diameter asteroid designated 2006 rh120. despite significant improvements in ground-based telescope and detector technology in the past decade the asteroid surveys have not discovered another temporarily-captured orbiter (tco; colloquially known as minimoons). within a few years the large synoptic survey telescope (lsst) will either begin to regularly detect tcos or force a re-analysis of the creation and dynamical evolution of small asteroids in the inner solar system. the first studies of the provenance, properties, and dynamics of earth's minimoons suggested that there should be a steady state population with about one 1- to 2-meter diameter captured objects at any time. that model was then improved and extended to include the population of temporarily-captured flybys (tcfs), objects that fail to make an entire revolution around earth while energetically bound to the earth-moon system. several different techniques for discovering tcos have been considered but their small diameters, proximity, and rapid motion make them challenging targets for existing ground-based optical, meteor, and radar surveys. we expect that if the tco population is confirmed, and new objects are frequently discovered, they can provide new opportunities for 1) studying the dynamics of the earth-moon system, 2) testing models of the production and dynamical evolution of small asteroids from the asteroid belt, 3) rapid and frequent low delta-v missions to multiple minimoons, and 4) evaluating in-situ resource utilization techniques on asteroidal material. here we review the past decade of minimoon studies in preparation for capitalizing on the scientific and commercial opportunities of tcos in the first decade of lsst operations. | earth's minimoons: opportunities for science and technology. |
asteroid (514107) ka`epaoka`awela is the first example of an object in the 1/1 mean motion resonance with jupiter with retrograde motion around the sun. its orbit was shown to be stable over the age of the solar system, which implies that it must have been captured from another star when the sun was still in its birth cluster. ka`epaoka`awela orbit is also located at the peak of the capture probability in the coorbital resonance. identifying the periodic orbits that ka`epaoka`awela and similar asteroids followed during their evolution is an important step towards precisely understanding their capture mechanism. here, we find the families of periodic orbits in the two-dimensional retrograde coorbital problem and analyse their stability and bifurcations into three-dimensional periodic orbits. our results explain the radical differences observed in 2d and 3d coorbital capture simulations. in particular, we find that analytical and numerical results obtained for planar motion are not always valid at infinitesimal deviations from the plane. | periodic orbits of the retrograde coorbital problem |
in the restricted problem of three bodies when the primaries are triaxial rigid bodies, the necessary and sufficient conditions to find the locations of the three libration collinear points are stated. in addition, the linear stability of these points is studied for the case of the euler angles of rotational motion being θi = 0, ψi + φi = π/2, i = 1, 2 accordingly. we underline that the model studied in this paper has special importance in space dynamics when the third body moves in gravitational fields of planetary systems and particularly in a jupiter model or a problem including an irregular asteroid. | on the libration collinear points in the restricted three - body problem |
both asteroids and comets can come close to the earth's orbit. any dust released from any them will form a meteoroid stream whose orbit may allow the earth to pass through it. if this takes place, the ablation of the meteoroids in the earth's atmosphere will be observed as meteors. the various ways in which both showers and the related stream can be identified from these observations are described. in this region, orbital evolution is rapid due to a number of effects, so that orbits will progressively diverge from the original orbit and the showers become weaker, making the identification of the stream and its parent more tenuous. catalogues of recognized showers and streams are listed together with the updated orbital characteristics of all the streams. eventually a stream will lose its identity and the meteoroids merge into the sporadic background. methods for determining whether the sporadic meteors originate from comets or asteroids based on their orbits are discussed. finally, they merge into the zodiacal dust clouds and the observations of these clouds are discussed together with an overview of their main characteristics. | minor meteor showers and the sporadic background |
in the framework of the circular restricted three body problem we show that the numerically computed strength sr(e, i, ω) is a good indicator of the strength and width of the mean-motion resonances in the full space (e, i, ω). we present a survey of strengths in the space (e, i) for typical interior and exterior resonances. the resonance strength is highly dependent on (e, i, ω) except for exterior resonances of the type 1:k for which the dependence with (i, ω) is softer. such resonances are thus strong even for retrograde orbits. all other resonances are weaker at very-high eccentricities for ω ∼ 90° or 270° and 60° ≲ i ≲ 120°. we explore the resonance structure in the space (a, i) by means of dynamical maps and we find structures similar to those of space (a, e). | strength, stability and three dimensional structure of mean motion resonances in the solar system |
two narrow and dense rings (called c1r and c2r) were discovered around the centaur object (10199) chariklo during a stellar occultation observed on 2013 june 3. following this discovery, we planned observations of several occultations by chariklo’s system in order to better characterize the physical properties of the ring and main body. here, we use 12 successful occulations by chariklo observed between 2014 and 2016. they provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. our new observations are currently consistent with the circular ring solution and pole position, to within the ±3.3 km formal uncertainty for the ring radii derived by braga-ribas et al. the six resolved c1r profiles reveal significant width variations from ∼5 to 7.5 km. the width of the fainter ring c2r is less constrained, and may vary between 0.1 and 1 km. the inner and outer edges of c1r are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. no constraint on the sharpness of c2r’s edges is available. a 1σ upper limit of ∼20 m is derived for the equivalent width of narrow (physical width < 4 km) rings up to distances of 12,000 km, counted in the ring plane. | the structure of chariklo’s rings from stellar occultations |
we report photometry and spectroscopy of the outburst of the young stellar object eso-hα99. the outburst was first noticed in gaia alert gaia18dvc and later by the asteroid terrestrial-impact last alert system (atlas). we have established the outburst light curve with archival atlas orange filter photometry, gaia data, new v-band photometry, and j, h, and ksphotometry from the infrared imaging system (iris) and the united kingdom infrared telescope (ukirt). the brightness has fluctuated several times near the light curve maximum. the transiting exoplanet survey satellite (tess) satellite observed eso-hα 99 with high cadence during one of these minor minima and found brightness fluctuations on timescales of days and hours. imaging with ukirt shows the outline of an outflow cavity, and we find one knot of {{{h}}}2 1-0 s(1) emission, now named mho 1520, on the symmetry axis of this nebula, indicating recent collimated outflow activity from eso-hα 99. its pre-outburst sed shows a flat far-infrared spectrum, confirming its early evolutionary state and its similarity to other deeply embedded objects in the broader exor class. the pre-outburst luminosity is 34 l ⊙, a much higher luminosity than typical exors, indicating that eso-hα 99 may be a star of intermediate mass. infrared and optical spectroscopy show a rich emission-line spectrum, including h i lines, strong red ca ii emission, as well as infrared co bandhead emission, all characteristic exors in the broadest sense. comparison of the present spectra with an optical spectrum obtained in 1993, presumably in the quiescent state of the object, shows that during the present outburst the continuum component of the spectrum has increased notably more than the emission lines. the hα equivalent width during the outburst is down to one-half of its 1993 level, and shock-excited emission lines are much less prominent. | the new exor outburst of eso-hα 99 observed by gaia atlas and tess |
the lifetime of a planetary disc that orbits a white dwarf represents a crucial input parameter into evolutionary models of that system. here we apply a purely analytical formalism to estimate lifetimes of the debris phase of these discs, before they are ground down into dust or are subject to sublimation from the white dwarf. we compute maximum lifetimes for three different types of white dwarf discs, formed from (i) radiative yorp break-up of exo-asteroids along the giant branch phases at 2-100 au, (ii) radiation-less spin-up disruption of these minor planets at ${\sim} 1.5\!-\!4.5\, \mathrm{r}_{\odot }$ , and (iii) tidal disruption of minor or major planets within about $1.3\, \mathrm{r}_{\odot }$ . we display these maximum lifetimes as a function of disc mass and extent, constituent planetesimal properties, and representative orbital excitations of eccentricity and inclination. we find that yorp discs with masses of up to 1024 kg live long enough to provide a reservoir of surviving cm-sized pebbles and m- to km-sized boulders that can be perturbed intact to white dwarfs with cooling ages of up to 10 gyr. debris discs formed from the spin or tidal disruption of these minor planets or major planets can survive in a steady state for up to, respectively, 1 or 0.01 myr, although most tidal discs would leave a steady state within about 1 yr. our results illustrate that dust-less planetesimal transit detections are plausible, and would provide particularly robust evolutionary constraints. our formalism can easily be adapted to individual systems and future discoveries. | the lifetimes of planetary debris discs around white dwarfs |
sn 2018hti is a type i superluminous supernova (slsn i) with an absolute g-band magnitude of -22.2 at maximum brightness, discovered by the asteroid terrestrial-impact last alert system in a metal-poor galaxy at a redshift of 0.0612. we present extensive photometric and spectroscopic observations of this supernova, covering the phases from ∼-35 d to more than +340 d from the r-band maximum. combining our bvgri-band photometry with swift uvot optical/ultraviolet photometry, we calculated the peak luminosity as ∼3.5 × 1044 erg s-1. modelling the observed light curve reveals that the luminosity evolution of sn 2018hti can be produced by an ejecta mass of 5.8 m⊙ and a magnetar with a magnetic field of b = 1.8 × 1013 g having an initial spin period of p0 = 1.8 ms. based on such a magnetar-powered scenario and a larger sample, a correlation between the spin of the magnetar and the kinetic energy of the ejecta can be inferred for most slsne i, suggesting a self-consistent scenario. like for other slsne i, the host galaxy of sn 2018hti is found to be relatively faint (mg = -17.75 mag) and of low metallicity (z = 0.3 z⊙), with a star formation rate of 0.3 m⊙ yr-1. according to simulation results of single-star evolution, sn 2018hti could originate from a massive, metal-poor star with a zero-age main sequence (zams) mass of 25-40 m⊙, or from a less massive rotating star with mzams ≈ 16-25 m⊙. for the case of a binary system, its progenitor could also be a star with $m_\mathrm{zams} \gtrsim 25\, \mathrm{ m}_\odot$ . | sn 2018hti: a nearby superluminous supernova discovered in a metal-poor galaxy |
various properties of jovian trojan asteroids such as composition, rotation periods, and photometric amplitudes, or the rate of binarity in the population, can provide information and constraints on the evolution of the group and of the solar system itself. here we present new photometric properties of 45 jovian trojans from the k2 mission of the kepler space telescope, and present phase-folded light curves for 44 targets, including (11351) leucus, one of the targets of the lucy mission. we extend our sample to 101 asteroids with previous k2 trojan measurements, then compare their combined amplitude and frequency distributions to other ground-based and space data. we show that there is a dichotomy in the periods of trojans with a separation at ∼100 hr. we find that 25% of the sample are slow rotators (p ≥ 30 hr), an excess that can be attributed to binary objects. we also show that 32 systems can be classified as potential detached binary systems. finally, we calculate density and rotation constraints for the asteroids. both the spin barrier and fits to strengthless ellipsoid models indicate low densities and thus compositions similar to populations of comets and trans-neptunian objects throughout the sample. this supports the scenario of outer solar system origin for jovian trojans. | 101 trojans: a tale of period bimodality, binaries, and extremely slow rotators from k2 photometry |
neptunian trojans (nts), trans-neptunian objects in 1:1 mean-motion resonance with neptune, are generally thought to have been captured from the original trans-neptunian protoplanetary disc into co-orbital resonance with the ice giant during its outward migration. it is possible, therefore, that the colour distribution of nts is a constraint on the location of any colour transition zones that may have been present in the disc. in support of this possible test, we obtained g, r, and i-band observations of 18 nts, more than doubling the sample of nts with known visible colours to 31 objects. out of the combined sample, we found ≈4 objects with g -i colours of >1.2 mags placing them in the very red (vr) category as typically defined. we find, without taking observational selection effects into account, that the nt g - i colour distribution is statistically distinct from other trans-neptunian dynamical classes. the optical colours of jovian trojans and nts are shown to be less similar than previously claimed with additional vr nts. the presence of vr objects among the nts may suggest that the location of the red to vr colour transition zone in the protoplanetary disc was interior to 30 - 35 au. | keck, gemini, and palomar 200-inch visible photometry of red and very-red neptunian trojans |
we report on the implemented design of a two-colour instrument based on electron-multiplying ccd (emccd) detectors. this instrument is currently installed at the danish 1.54 m telescope at eso's la silla observatory in chile, and will be available at the song (stellar observations network group) 1m telescope node at tenerife and at other song nodes as well. we present the software system for controlling the two-colour instrument and calibrating the high frame-rate imaging data delivered by the emccd cameras. an analysis of the performance of the two-colour instrument at the danish telescope shows an improvement in spatial resolution of up to a factor of two when doing shift-and-add compared with conventional imaging, and the possibility of doing high-precision photometry of emccd data in crowded fields. the danish telescope, which was commissioned in 1979, is limited by a triangular coma at spatial resolutions below 0.5 arcsec, and better results will thus be achieved at the near diffraction-limited optical system on the song telescopes, where spatial resolutions close to 0.2 arcsec have been achieved. regular emccd operations have been running at the danish telescope for several years and produced a number of scientific discoveries, including microlensing detected exoplanets, detecting previously unknown variable stars in dense globular clusters, and discovering two rings around the small asteroid-like object (10199) chariklo. based on data collected with the danish 1.54m telescope at eso's la silla observatory. | the two-colour emccd instrument for the danish 1.54 m telescope and song |
recent dynamical analyses suggest that some jupiter family comets (jfcs) may originate in the main asteroid belt instead of the outer solar system. this possibility is particularly interesting given evidence that icy main-belt objects are known to be present in the themis asteroid family. we report results from dynamical analyses specifically investigating the possibility that icy themis family members could contribute to the observed population of jfcs. numerical integrations show that such dynamical evolution is indeed possible via a combination of eccentricity excitation apparently driven by the nearby 2:1 mean-motion resonance with jupiter, gravitational interactions with planets other than jupiter, and the yarkovsky effect. we estimate that, at any given time, there may be tens of objects from the themis family on jfc-like orbits with the potential to mimic active jfcs from the outer solar system, although not all, or even any, may necessarily be observably active. we find that dynamically evolved themis family objects on jfc-like orbits have semimajor axes between 3.15 and 3.40 au for the vast majority of their time on such orbits, consistent with the strong role that the 2:1 mean-motion resonance with jupiter likely plays in their dynamical evolution. we conclude that a contribution from the themis family to the active jfc population is plausible, although further work is needed to better characterize this contribution. | potential themis-family asteroid contribution to the jupiter-family comet population |
there are only a few known main belt (mb) asteroid families with ages greater than 2 gyr (brož et al., 2013; spoto et al., 2015). estimates based on the family producing collision rate suggest that the lack of > 2 gyr-old families may be due to a selection bias in current techniques used to identify families. family fragments disperse in their orbital elements, semi-major axis, a, eccentricity, e, and inclination, i, due to secular resonances, close encounters with massive asteroids and the non-gravitational yarkovsky force. this causes the family fragments to be indistinguishable from the background of the main belt making them more difficult to identify with the hierarchical clustering method (hcm) with increasing family age. the discovery of the eulalia and new polana families in the inner belt relied on new techniques because yarkovsky spreading made them too disperse to be identified using the classical hcm. the techniques used to discover the new polana and eulalia families are modified here to identify asteroid families by searching for correlations between a and asteroid diameter, d, or absolute magnitude, h. a group of asteroids is identified as a collisional family if its boundary in the a vs. 1/d or a vs. h planes has a characteristic v-shape which is due to the size dependent yarkovsky spreading. the v-shape boundary is identified with two separate techniques. the first technique identifies a border by measuring a steep drop between the number of objects inside and outside of the border. the second technique identifies the v-shape border by measuring a peak in the number density of objects in a vs. 1/d , h space. families are identified with just one or both v-shape identifying techniques. the v-shape techniques are demonstrated on the known families of erigone, vesta, koronis, and families difficult to identify by hcm such as flora, baptistina, new polana, eulalia and karin. future applications of the technique, such as in a large scale search for > 2 gyr-old families throughout the mb, are discussed. | yarkovsky v-shape identification of asteroid families |
the asteroid 4 vesta is the second most massive planetesimal in the solar system and a rare example of a planetary object that possibly can be linked to a specific group of differentiated meteorites, the howardite-eucrite-diogenite suite. the 182hf-182w chronometry of individual zircon grains from six basaltic eucrites revealed distinct growth episodes ranging from 4532 - 11 / + 6 ma to 4565.0 ± 0.9 ma and constrains the early thermal history of 4 vesta, indicating that its mantle generated basaltic melts for at least 35 million years (myr). initially, the energy needed for melting was provided by decay of short-lived isotopes, mostly 26al. the long duration of magmatism despite the short lifetime of 26al implies that the asteroid must have accreted within the first ∼4 myr of solar system formation, similar to the formation of iron meteorite parent bodies, and that its interior must have been thermally well insulated by an early-formed crust that prevented heat loss. | prolonged magmatism on 4 vesta inferred from hf-w analyses of eucrite zircon |
ureilite meteorites are achondrites that are debris of the mantle of a now disrupted differentiated asteroid rich in carbon. they provide a unique opportunity to study the differentiation processes of such a body. we analyzed the iron isotopic compositions of 30 samples from the ureilite parent body (upb) including 29 unbrecciated ureilites and one ureilitic trachyandesite (alm-a) which is at present the sole large crustal sample of the upb. the δ56fe of the whole rocks fall within a restricted range, from 0.01 to 0.11‰, with an average of + 0.056 ± 0.008‰, which is significantly higher than that of chondrites. we show that this difference can be ascribed to the segregation of s-rich metallic melts at low degrees of melting at a temperature close to the fe-fes eutectic, and certainly before the onset of the melting of the silicates (< 1100 °c), in agreement with the marked s depletions, and the siderophile element abundances of the ureilites. these results point to an efficient segregation of s-rich metallic melts during the differentiation of small terrestrial bodies. | early stages of core segregation recorded by fe isotopes in an asteroidal mantle |
missions to asteroids are now an important component of the space exploration program of major space agencies in the world, with the goal of better understanding the formation of the solar system and learn about their dynamics to be able to react in case of a possible collision with the earth. as binary asteroids compose approximately 16% of near earth asteroids, they are getting more attention from researchers. one mission is currently being planned to binary asteroid system 65803 didymos. this mission motivates research on the dynamics of a spacecraft near a binary asteroid. since the primary bodies of these binary systems have small masses, perturbations like the solar radiation pressure (srp) or the shape of the primary bodies have a great influence on the dynamics of a spacecraft in their vicinity. studies that already exist on the effect of the srp on the dynamics of a spacecraft near binary asteroid systems have mostly used low-fidelity srp acceleration models, such as the cannonball model or simple flat plate model with a purely reflecting spacecraft. this study shows how the choice of the model influences the strength of the srp acceleration acting on the spacecraft and how it is possible to take advantage of the choice of the nominal attitude of the spacecraft to influence how the srp affects the spacecraft dynamics when using a more complex srp acceleration model. various types of trajectories are studied, with different results and conclusions. | impact of solar radiation pressure modeling on orbital dynamics in the vicinity of binary asteroids |
context. the rotation state of small asteroids is affected by the yarkovsky-o'keefe-radzievskii-paddack (yorp) effect, which is a net torque caused by solar radiation directly reflected and thermally reemitted from the surface. due to this effect, the rotation period slowly changes, which can be most easily measured in light curves because the shift in the rotation phase accumulates over time quadratically.aims: by new photometric observations of selected near-earth asteroids, we want to enlarge the sample of asteroids with a detected yorp effect.methods: we collected archived light curves and carried out new photometric observations for asteroids (10115) 1992 sk, (1620) geographos, and (1685) toro. we applied the method of light curve inversion to fit observations with a convex shape model. the yorp effect was modeled as a linear change of the rotation frequency υ ≡ dω∕dt and optimized together with other spin and shape parameters.results: we detected the acceleration υ = (8.3 ± 0.6) × 10−8 rad d−2 of the rotation for asteroid (10115) 1992 sk. this observed value agrees well with the theoretical value of yorp-induced spin-up computed for our shape and spin model. for (1685) toro, we obtained υ = (3.3 ± 0.3) × 10−9 rad d−2, which confirms an earlier tentative yorp detection. for (1620) geographos, we confirmed the previously detected yorp acceleration and derived an updated value of υ with a smaller uncertainty. we also included the effect of solar precession into our inversion algorithm, and we show that there are hints of this effect in geographos' data.conclusions: the detected change of the spin rate of (10115) 1992 sk has increased the total number of asteroids with yorp detection to ten. in all ten cases, the dω∕dt value is positive, so the rotation of these asteroids is accelerated. it is unlikely to be just a statistical fluke, but it is probably a real feature that needs to be explained. | rotation acceleration of asteroids (10115) 1992 sk, (1685) toro, and (1620) geographos due to the yorp effect |
the near-earth asteroid (162173) ryugu, the target of hayabusa2 space mission, was observed via both orbiter and the lander instruments. the infrared radiometer on the mascot lander (mara) is the only instrument providing spectrally resolved mid-infrared (mir) data, which is crucial for establishing a link between the asteroid material and meteorites found on earth. earlier studies revealed that the single boulder investigated by the lander belongs to the most common type found on ryugu. here we show the spectral variation of ryugu's emissivity using the complete set of in-situ mir data and compare it to those of various carbonaceous chondritic meteorites, revealing similarities to the most aqueously altered ones, as well as to asteroid (101955) bennu. the results show that ryugu experienced strong aqueous alteration prior to any dehydration. | mid-infrared emissivity of partially dehydrated asteroid (162173) ryugu shows strong signs of aqueous alteration |
using the s-band radar at arecibo observatory, we observed thirteen x/m-class asteroids; nine were previously undetected and four were re-observed, bringing the total number of tholen x/m-class asteroids observed with radar to 29. of these 29m-class asteroids, 13 are also w-class, defined as m-class objects that also display a 3-μm absorption feature which is often interpreted as the signature of hydrated minerals (jones, t.d., lebofsky, l.a., lewis, j.s., marley, m.s. [1990]. icarus 88, 172-192; rivkin, a.s., howell, e.s., britt, d.t., lebofsky, l.a., nolan, m.c., branston, d.d. [1995]. icarus 117, 90-100; rivkin, a.s., howell, e.s., lebofsky, l.a., clark, b.e., britt, d.t. [2000]. icarus 145, 351-368). consistent with our previous work (shepard, m.k. et al. [2008]. icarus 195, 184-205; shepard, m.k., harris, a.w., taylor, p.a., clark, b.e., ockert-bell, m., nolan, m.c., howell, e.s., magri, c., giorgini, j.d., benner, l.a.m. [2011]. icarus 215, 547-551), we find that 38% of our sample (11 of 29) have radar albedos consistent with metal-dominated compositions. with the exception of 83 beatrix and 572 rebekka, the remaining objects have radar albedos significantly higher than the mean s- or c-class asteroid (magri, c., nolan, m.c., ostro, s.j., giorgini, j.d. [2007]. icarus 186, 126-151). seven of the eleven high-radar-albedo asteroids, or 64%, also display a 3-μm absorption feature (w-class) which is thought to be inconsistent with the formation of a metal dominated asteroid. we suggest that the hydration absorption could be a secondary feature caused by low-velocity collisions with hydrated asteroids, such as ci or cm analogs, and subsequent implantation of the hydrated minerals into the upper regolith. there is recent evidence for this process on vesta (reddy, v. et al. [2012]. icarus 221, 544-559; mccord, t.b. et al. [2012]. nature 491, 83-86; prettyman, t.h. et al. [2012]. science 338, 242-246; denevi, b.w. et al. [2012]. science 338, 246-249). eleven members of our sample show bifurcated radar echoes at some rotation phases; eight of these are high radar albedo targets. one interpretation of a bifurcated echo is a contact binary, like 216 kleopatra, and several of our sample are contact binary candidates. however, evidence for other targets indicates they are not contact binaries. instead, we hypothesize that these asteroids may have large-scale variations in surface bulk density, i.e. isolated patches of metal-rich and silicate-rich regions at the near-surface, possibly the result of collisions between metal and silicate-rich asteroids. | a radar survey of m- and x-class asteroids. iii. insights into their composition, hydration state, & structure |
this paper describes the guidance and navigation technique used by hayabusa2 for the asteroid rendezvous operation to reach ryugu. the operation results, including the achieved guidance and navigation performance, are also summarized. multiple assessment and navigation teams worked closely to provide reliable navigation solutions with a short solution delivery cycle. although the uncertainty of the ryugu's ephemeris was considerable before hayabusa2's arrival, a combination of radiometric-optical hybrid navigation and a stochastic-constrained optimum guidance method was able to achieve an accuracy of less than 100 m and 1 cm/s, and the arrival was precisely timed. | rendezvous to asteroid with highly uncertain ephemeris: hayabusa2's ryugu-approach operation result |
an impact experiment was performed on the surface of the c-type asteroid (162173) ryugu using an instrument called the small carry-on impactor (sci) carried by the japan aerospace exploration agency spacecraft hayabusa2. using a small camera separated from the spacecraft, we observed the development of the ejecta curtain formed by the sci impact in situ. based on the patterns appearing in the ejecta curtain, we evaluated the physical properties of large boulders and regolith grains on ryugu. we found that the large boulders on the surface near the sci impact point had a compressive strength consistent with the previous estimation of a tensile strength based on low thermal inertia observed for boulders on ryugu. furthermore, the ejecta curtain consisted of the boulders with a maximum size of several decimeters. moreover, the filament structure was formed in the sci ejecta curtain, strongly suggesting that the sci impact ejecta curtain particles had a size range greater than one order of magnitude; a characteristic size of the regolith grains in the curtain was estimated to be several centimeters. these regolith grains primarily originated from the subsurface layer. we propose three different hypotheses for the geological process that formed the subsurface structure at the sci impact point consistent with the above observations. because these hypotheses have different predictions for materials in sci ejecta, the samples obtained from the second touchdown will be able to constrain which hypothesis is the most likely. | impact experiment on asteroid (162173) ryugu: structure beneath the impact point revealed by in situ observations of the ejecta curtain |
the one‑step synthesis and characterization of a new and robust titanium‑based metal–organic framework, acm‑1, is reported. in this structure, which is based on infinite ti−o chains and 4,4′,4′′,4′′′‑(pyrene‑1,3,6,8‑tetrayl) tetrabenzoic acid as a photosensitizer ligand, the combination of highly mobile photogenerated electrons and a strong hole localization at the organic linker results in large charge‑separation lifetimes. the suitable energies for band gap and conduction band minimum (cbm) offer great potential for a wide range of photocatalytic reactions, from hydrogen evolution to the selective oxidation of organic substrates. | a titanium metal–organic framework with visible‑light‑responsive photocatalytic activity |
the very wide diversity of asteroid compositions in the main belt suggests significant material transport in the solar protoplanetary disk and hints at the presence of interstellar ices in hydrated bodies. however, only a few quantitative estimations of the contribution of interstellar ice in the inner solar system have been reported, leading to considerable uncertainty about the extent of radial inward mixing in the solar protoplanetary disk 4.56 ga ago. we show that the pristine cm chondrite paris contains primary ca-carbonates whose o-isotopic compositions require an 8%-35% contribution from interstellar water. the presence of interstellar water in paris is confirmed by its bulk d/h isotopic composition that shows significant d enrichment (d/h = (167 ± 0.2) × 10-6) relative to the mean d/h of cm chondrites ((145 ± 3) × 10-6) and the putative d/h of local cm water ((82 ± 1.5) × 10-6). these results imply that (i) efficient radial mixing of interstellar ices occurred from the outer zone of the solar protoplanetary disk inward and that (ii) chondrites accreted water ice grains from increasing heliocentric distances in the solar protoplanetary disk. | inward radial mixing of interstellar water ices in the solar protoplanetary disk |
we explore experimentally possible explanations of the polarization curves of the sunlight reflected by the barbarian asteroids. their peculiar polarization curves are characterized by a large-inversion angle, around 30°, which could be related to the presence of feo-bearing spinel embedded in calcium-aluminum inclusions. in order to test this hypothesis, we have measured the phase function and degree of linear polarization of six samples of mg-rich olivine and spinel. for each material, we have analysed the light scattering properties of a millimeter-sized grain and of two powdered samples with size distributions in the micrometer size range. the three spinel samples show a well-defined negative polarization branch with an inversion phase angle located around 24°-30°. in contrast, in the case of the olivine samples, the inversion angle is highly dependent on particle size and tends to decrease for larger sizes. we identify the macroscopic geometries as a possible explanation for the evident differences in the polarization curves between olivine and spinel millimeter samples. although the polarization behaviour in near backscattering of the barbara asteroid is similar to that of our spinel mm-sized sample in random orientation, this similarity could result in part from crystal retro-reflection rather than composition. this is part of an ongoing experimental project devoted to test separately several components of cv3-like meteorites, representative of the barbarians composition, to disentangle their contributions to the polarization behaviour of these objects. | experimental phase function and degree of linear polarization curve of olivine and spinel and the origin of the barbarian polarization behaviour |
the terrestrial planets endured a phase of bombardment following their accretion, but the nature of this late accreted material is debated, preventing a full understanding of the origin of inner solar system volatiles. we report the discovery of nucleosynthetic chromium isotope variability (μ 54 cr) in martian meteorites that represent mantle-derived magmas intruded in the martian crust. the μ 54 cr variability, ranging from −33.1 ± 5.4 to +6.8 ± 1.5 parts per million, correlates with magma chemistry such that samples having assimilated crustal material define a positive μ 54 cr endmember. this compositional endmember represents the primordial crust modified by impacting outer solar system bodies of carbonaceous composition. late delivery of this volatile-rich material to mars provided an exotic water inventory corresponding to a global water layer >300 meters deep, in addition to the primordial water reservoir from mantle outgassing. this carbonaceous material may also have delivered a source of biologically relevant molecules to early mars. early mars was bombarded by carbonaceous asteroids that delivered water and organics to the planet's surface. | late delivery of exotic chromium to the crust of mars by water-rich carbonaceous asteroids |
the mars-moon exploration with gamma rays and neutrons (megane) investigation will use gamma-ray and neutron spectroscopy to measure the elemental composition of mars' moon phobos. megane is part of the japanese martian moons exploration (mmx) mission that will make comprehensive remote sensing measurements of both of mars' moons phobos and deimos. mmx will also return to earth regolith samples of phobos. the science goals of the megane investigation mirror those of the mmx mission. megane will use elemental composition measurements to determine if phobos is a captured asteroid or the end result of a giant impact event on mars, study phobos surface processes, provide reconnaissance to support the sample site selection, and supply compositional context for the returned samples. to accomplish its measurements, megane will use a high-purity ge gamma-ray spectrometer (grs), and a neutron spectrometer (ns) that consists of two 3he gas proportional neutron sensors. the grs derives heritage from similar instruments from nasa's mercury surface, space environment, geochemistry, and ranging mission and the psyche mission that is currently in development; the ns is based on similar instruments used for nasa's lunar prospector and psyche missions. | measuring the elemental composition of phobos: the mars-moon exploration with gamma rays and neutrons (megane) investigation for the martian moons exploration (mmx) mission |
a significant fraction of white dwarfs (wds) exhibit signs of ongoing accretion of refractory elements at rates ~103-107 kg s-1, among which, 37 wds were detected to harbor dusty debris disks. such a concurrence requires not only fertile reservoirs of planetary material but also a high duty cycle of metal delivery. it has been commonly suggested that this material could be supplied by solar system analogs of main belt asteroids or kuiper belt objects. here we consider the primary progenitors of wd pollutants as a population of residual high-eccentricity planetesimals, devolatilized during the stellar giant phases. equivalent to the solar system's long-period comets, they are scattered to the proximity of wds by perturbations from remaining planets, galactic tides, passing molecular clouds, and nearby stars. these objects undergo downsizing when they venture within the tidal disruption limit. we show quantitatively how the breakup condition and fragment sizes are determined by material strength and gravity. thereafter, the fragments' semimajor axes need to decay by at least ~6 orders of magnitude before their constituents are eventually accreted onto the surface of wds. we investigate the orbital evolution of these fragments around wds and show that wds' magnetic fields induce an alfvén-wave drag during their periastron passages and rapidly circularize their orbits. this process could be responsible for the observed accretion rates of heavy elements and the generation of circum-wd debris disks. speculative implications are that giant planets may be common around wds' progenitors and that they may still be bound to some wds today. | orbital migration and circularization of tidal debris by alfvén-wave drag: circumstellar debris and pollution around white dwarfs |
variations in the abundances of moderately volatile elements (mve) are one of the most fundamental geochemical differences between the terrestrial planets. whether these variations are the consequence of nebular processes, planetary volatilization, differentiation or late accretion is still unresolved. the element mercury is the most volatile of the mve and is a strongly chalcophile element. it is one of the few elements that exhibit large mass-dependent (mdf) and mass-independent (mif) isotopic fractionations for both odd (odd-mif, δ199hg and δ201hg) and even (even-mif, δ200hg) hg isotopes in nature, which is traditionally used to trace hg biogeochemical cycling in surface environments. however, the hg isotopic composition of earth and meteorites is not well constrained. here, we present hg isotopic data for terrestrial basaltic, trachytic and granitic igneous samples. these rocks are isotopically lighter (δ202hg = -3.3 ± 0.9‰; 1 standard deviation) than sedimentary rocks that have previously been considered to represent the terrestrial hg isotope composition (δ202 hg = - 0.7 ± 0.5 ‰; 1 standard deviation). we show degassing during magma emplacement induces mif that are consistent with kinetic fractionation in these samples. also presented is a more complete dataset for chondritic (carbonaceous, ordinary and enstatite) meteorites, which are consistent with previous work for carbonaceous chondrites (positive odd-mif) and ordinary chondrites (no mif), and demonstrate that some enstatite chondrites exhibit positive odd-mif, similar to carbonaceous chondrites. the terrestrial igneous rocks fall within the range of chondritic compositions for both mif and mdf. given the fact that planetary differentiation (core formation, evaporation) would contribute to hg loss from the silicate portion of earth and would likely fractionate hg isotopes from chondritic compositions, we suggest that the budget of the mantle hg is dominated by late accretion of chondritic materials to earth, as also suggested for other volatile chalcophile elements (s, se, te). considering the hg isotopic signatures, materials with compositions similar to co chondrites or ordinary chondrites are the most likely late accretion source candidates. finally, eucrite meteorites, which are highly depleted in volatile elements, are isotopically heavier than chondrites and exhibit negative odd-mif. the origin of volatile depletion in eucrites has been vigorously debated. we show that δ199hg versus δ201hg relationships point toward an equilibrium nuclear field shift effect, suggesting that volatile loss occurred during a magma ocean phase at the surface of the eucrite parent body, likely the asteroid 4-vesta. | chondritic mercury isotopic composition of earth and evidence for evaporative equilibrium degassing during the formation of eucrites |
in early 2019, the osiris-rex spacecraft discovered small particles being ejected from the surface of the near-earth asteroid bennu.sww although they were seen to be ejected at slow speeds, on the order of tens of cm/s, a number of particles were surprisingly seen to orbit for multiple revolutions and days, which requires a dynamical mechanism to quickly and substantially modify the orbit to prevent re-impact upon their first periapse passage. this paper demonstrates that, based on simulations constrained by the conditions of the observed events, the combined effects of gravity, solar radiation pressure, and thermal radiation pressure from bennu can produce many sustained orbits for ejected particles. furthermore, the simulated populations exhibit two interesting phenomena that could play an important role in the geophysical evolution of bodies such as bennu. first, small particles (<1 cm radius) are preferentially removed from the system, which could lead to a deficit of such particles on the surface. second, re-impacting particles preferentially land near or on the equatorial bulge of bennu. over time, this can lead to crater in-filling and growth of the equatorial radius without requiring landslides. | dynamical evolution of simulated particles ejected from asteroid bennu |
influences of morphology on the optical properties of soot particles have gained increasing attentions. however, studies on the effect of the way primary particles are coated on the optical properties is few. aimed to understand how the primary particles are coated affect the optical properties of soot particles, the coated soot particle was simulated using the acentric core-shell monomers model (acm), which was generated by randomly moving the cores of concentric core-shell monomers (ccm) model. single scattering properties of the ccm model with identical fractal parameters were calculated 50 times at first to evaluate the optical diversities of different realizations of fractal aggregates with identical parameters. the results show that optical diversities of different realizations for fractal aggregates with identical parameters cannot be eliminated by averaging over ten random realizations. to preserve the fractal characteristics, 10 realizations of each model were generated based on the identical 10 parent fractal aggregates, and then the results were averaged over each 10 realizations, respectively. the single scattering properties of all models were calculated using the numerically exact multiple-sphere t-matrix (mstm) method. it is found that the single scattering properties of randomly coated soot particles calculated using the acm model are extremely close to those using ccm model and homogeneous aggregate (ha) model using maxwell-garnett effective medium theory. our results are different from previous studies. the reason may be that the differences in previous studies were caused by fractal characteristics but not models. our findings indicate that how the individual primary particles are coated has little effect on the single scattering properties of soot particles with acentric core-shell monomers. this work provides a suggestion for scattering model simplification and model selection. | a model study of aggregates composed of spherical soot monomers with an acentric carbon shell |
context. asteroid (16) psyche is the largest m-type asteroid in the main belt and the target of the nasa psyche mission. it is also the only asteroid of this size (d > 200 km) known to be metal rich. although various hypotheses have been proposed to explain the rather unique physical properties of this asteroid, a perfect understanding of its formation and bulk composition is still missing.aims: we aim to refine the shape and bulk density of (16) psyche and to perform a thorough analysis of its shape to better constrain possible formation scenarios and the structure of its interior.methods: we obtained disk-resolved vlt/sphere/zimpol images acquired within our eso large program (id 199.c-0074), which complement similar data obtained in 2018. both data sets offer a complete coverage of psyche's surface. these images were used to reconstruct the three-dimensional (3d) shape of psyche with two independent shape modeling algorithms (mpcd and adam). a shape analysis was subsequently performed, including a comparison with equilibrium figures and the identification of mass deficit regions.results: our 3d shape along with existing mass estimates imply a density of 4.20 ± 0.60 g cm-3, which is so far the highest for a solar system object following the four telluric planets. furthermore, the shape of psyche presents small deviations from an ellipsoid, that is, prominently three large depressions along its equator. the flatness and density of psyche are compatible with a formation at hydrostatic equilibrium as a jacobi ellipsoid with a shorter rotation period of ∼3h. later impacts may have slowed down psyche's rotation, which is currently ∼4.2 h, while also creating the imaged depressions.conclusions: our results open the possibility that psyche acquired its primordial shape either after a giant impact while its interior was already frozen or while its interior was still molten owing to the decay of the short-lived radionuclide 26al. the reduced images are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/638/l15 based on observations made with eso telescopes at the paranal observatory under programme id 199.c-0074 (pi: p. vernazza). | asteroid (16) psyche's primordial shape: a possible jacobi ellipsoid |
nitrogen-doped porous activated carbon monoliths (ndp-acms) have long been the most desirable materials for supercapacitors. unique to the conventional template based lewis acid/base activation methods, herein, we report on a simple yet practicable novel approach to production of the three-dimensional ndp-acms (3d-ndp-acms). polyacrylonitrile (pan) contained carbon nanotubes (cnts), being pre-dispersed into a tubular level of dispersions, were used as the starting material and the 3d-ndp-acms were obtained via a template-free process. first, a continuous mesoporous pan/cnt based 3d monolith was established by using a template-free temperature-induced phase separation (ttps). second, a nitrogen-doped 3d-acm with a surface area of 613.8 m2/g and a pore volume 0.366 cm3/g was obtained. a typical supercapacitor with our 3d-ndp-acms as the functioning electrodes gave a specific capacitance stabilized at 216 f/g even after 3000 cycles, demonstrating the advantageous performance of the pan/cnt based 3d-ndp-acms. | nitrogen-doped porous carbon monoliths from polyacrylonitrile (pan) and carbon nanotubes as electrodes for supercapacitors |
a recent report by nasa identified dust/particulate mitigation techniques as a highly relevant study for future long-term planetary exploration missions (nasa, 2015). the deleterious effects of lunar dust on spacesuits discovered during the apollo missions has compelled nasa to identify dust mitigation as a critical path for potential future lunar, asteroid and mars missions. the complexity of spacesuit design has however constrained integrating existing dust cleaning technologies, formerly demonstrated on rigid surfaces, into the spacesuit system. accordingly, this research is investigating novel methods to integrate dust mitigation technologies for use on spacesuits. we examine utilizing a novel combination of active and passive technologies integrated into the spacesuit outerlayer to alleviate dust contamination. leveraging two specific technologies, the electrodynamics dust shield (eds) active technology and work function matching coating (wfm) passive technology, developed by nasa for rigid surfaces, we apply new high performance materials such as the carbon nanotube (cnt) flexible fibers to develop a spacesuit-integrated dust cleaning system. through experiments conducted using jsc-1a lunar dust simulant on coupons made of spacesuit outerlayer material, feasibility of integrating the proposed dust cleaning system and its performance were assessed. results from these preliminary experiments show that the integrated dust cleaning system is capable of removing 80-95% of dust from the spacesuit material demonstrating proof of concept. this paper describes the techniques and results from the experiments. future challenges of implementing the proposed approach into fight suits are identified. | proof of concept demonstration of novel technologies for lunar spacesuit dust mitigation |
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