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we have used the latest available shape model for gas and dust simulations of the inner coma of comet 67p/churyumov-gerasimenko for the period around may 2015 (equinox). we compare results from a purely insolation-driven model with a complementary set of observations made by rosina, virtis, miro, and osiris within the same period. the observations include - for the first time - inverted miro measurements of gas density, temperature and bulk velocity to constrain the model. the comparisons show that, as in november 2014 (marschall et al., 2016), insolation-driven activity does not provide an adequate fit to the data. both virtis and miro observations indicate that emissions from the hatmehit and imhotep regions of the nucleus are strongly depleted in total gas, h2o, and dust emissions in this case. the miro inversion provides a challenging constraint to the models as a consequence of the terminator orbit and nucleus pointing of the spacecraft. nonetheless a consistent picture with a dominance of outgassing from the hapi region, even at equinox, is clearly evident. an inhomogeneous model consistent with models proposed for the november 2014 time-frame was constructed and provides a better fit to the data. as far as we are aware this is the first time comae data from four rosetta instruments have been used to constrain within one self-contained model the emission distribution at the nucleus surface and study the dynamics of the gas and dust outflow. | a comparison of multiple rosetta data sets and 3d model calculations of 67p/churyumov-gerasimenko coma around equinox (may 2015) |
cometary activity is a manifestation of sublimation-driven processes at the surface of nuclei. however, cometary outbursts may arise from other processes that are not necessarily driven by volatiles. in order to fully understand nuclear surfaces and their evolution, we must identify the causes of cometary outbursts. in that context, we present a study of mini-outbursts of comet 46p/wirtanen. six events are found in our long-term lightcurve of the comet around its perihelion passage in 2018. the apparent strengths range from -0.2 to -1.6 mag in a 5″ radius aperture and correspond to dust masses between ~104 and 106 kg, but with large uncertainties due to the unknown grain size distributions. however, the nominal mass estimates are on the same order of magnitude as the mini-outbursts at comet 9p/tempel 1 and 67p/churyumov-gerasimenko, events that were notably lacking at comet 103p/hartley 2. we compare the frequency of outbursts at the four comets, and suggest that the surface of 46p has large-scale (~10-100 m) roughness that is intermediate to that of 67p and 103p, if not similar to the latter. the strength of the outbursts appear to be correlated with time since the last event, but a physical interpretation with respect to solar insolation is lacking. we also examine hubble space telescope images taken about two days following a near-perihelion outburst. no evidence for macroscopic ejecta was found in the image, with a limiting radius of about 2 m. | six outbursts of comet 46p/wirtanen |
measurements from the rosetta mission have shown a multitude of nonthermal electron distributions in the cometary environment, challenging the previously assumed plasma interaction mechanisms near a cometary nucleus. in this paper, we discuss electron trapping near a weakly outgassing comet from a fully kinetic (particle-in-cell) perspective. using the electromagnetic fields derived from the simulation, we characterize the trajectories of trapped electrons in the potential well surrounding the cometary nucleus and identify the distinguishing features in their respective velocity and pitch angle distributions. our analysis allows us to define a clear boundary in velocity phase space between the distributions of trapped and passing electrons. | electron trapping in the coma of a weakly outgassing comet |
we have detected h2o and o2 absorption against the far-uv continuum of stars located on lines of sight near the nucleus of comet 67p/churyumov-gerasimenko using the alice imaging spectrograph on rosetta. these stellar appulses occurred at impact parameters of ρ = 4-20 km, and heliocentric distances ranging from rh = - 1.8 to 2.3 au (negative values indicate pre-perihelion observations). the measured h2o column densities agree well with nearly contemporaneous values measured by virtis-h. the clear detection of o2 independently confirms the initial detection by the rosina mass spectrometer; however, the relative abundance of o2/h2o derived from the stellar spectra (11-68 per cent, with a median value of 25 per cent) is considerably larger than published values found by rosina. the cause of this difference is unclear, but potentially related to rosina measuring number density at the spacecraft position while alice measures column density along a line of sight that passes near the nucleus. | h2o and o2 absorption in the coma of comet 67p/churyumov-gerasimenko measured by the alice far-ultraviolet spectrograph on rosetta |
a cycle in the range of 26-30 myr has been reported in mass extinctions, and terrestrial impact cratering may exhibit a similar cycle of 31 ± 5 myr. these cycles have been attributed to the sun's vertical oscillations through the galactic disc, estimated to take from ∼30 to 42 myr between galactic plane crossings. near the galactic mid-plane, the solar system's oort cloud comets could be perturbed by galactic tidal forces, and possibly a thin dark matter (dm) disc, which might produce periodic comet showers and extinctions on the earth. passage of the earth through especially dense clumps of dm, composed of weakly interacting massive particles (wimps) in the galactic plane, could also lead to heating in the core of the planet through capture and subsequent annihilation of dm particles. this new source of periodic heating in the earth's interior might explain a similar ∼30 myr periodicity observed in terrestrial geologic activity, which may also be involved in extinctions. these results suggest that cycles of geological and biological evolution on the earth may be partly controlled by the rhythms of galactic dynamics. | disc dark matter in the galaxy and potential cycles of extraterrestrial impacts, mass extinctions and geological events |
comet is an experiment at j-parc, japan, which will search for neutrinoless conversion of muons into electrons in the field of a nucleus (μ- + n → e- + n); a lepton flavor violating process. the experimental sensitivity goal for this process is order of 10^-15 for phase-i and 10^-17 for phase-ii experiment, which is a factor of 100 to 10,000 improvements correspondingly over existing limits. recent progresses in facility and detector development are presented, along with comet phase-i and phase-ii experimental schedule. | comet muon conversion experiment in j-parc |
aims: cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma. we describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in the terminator plane.methods: we analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly using plasma moments). we propose a statistical approach over a period of one month.results: on average, two populations were observed, separated in phase space. the motion of the first is governed by its interaction with the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatible with an ambipolar electric field. both populations display a consistent anti-sunward velocity component.conclusions: cometary ions born in different regions of the coma are seen close to the nucleus of comet 67p/churyumov-gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative to the nucleus. a consistent anti-sunward component is observed for all cometary ions. an asymmetry is found in the average cometary ion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. there is no corresponding signature in the average magnetic field strength. | cometary ion dynamics observed in the close vicinity of comet 67p/churyumov-gerasimenko during the intermediate activity period |
using boltzmann–vlasov kinetic model, a currentless ion acoustic instability driven by stream of solar wind plasma is studied in a non‑thermal distributed electrons and ions. the non‑thermal distribution considered here is the generalized distribution which has low energetic flat‑top and velocity power law tail at higher energies. the instability threshold is found to be affected and depends upon the spectral indices r and q. it is found that the growth rate increases with the decrease in the value of r and increase with q. moreover, such kinetic instability has also been discussed for three species electron–ion–dust plasma using the generalized (r, q) distribution function. such case is of interest when the solar wind is streaming through the cometary plasma in the presence of interstellar dust and excites electrostatic instabilities. the dispersion properties and growth rates for ion‑acoustic and dust‑acoustic mode are calculated analytically and plotted for different values of the spectral indices r and q. | solar wind driven electrostatic instabilities with generalized (r , q ) distribution function |
gravitating systems surrounded by a dynamic sea of substructures experience fluctuations of the local tidal field which inject kinetic energy into the internal motions. this paper uses stochastic calculus techniques to describe `tidal heating' as a random walk of orbital velocities that leads to diffusion in a four-dimensional energy-angular momentum space. in spherical, static potentials, we derive analytical solutions for the green's propagators directly from the number density and velocity distribution of substructures with known mass and size functions without arbitrary cuts in forces or impact parameters. furthermore, a monte carlo method is presented, which samples velocity `kicks' from a probability function and can be used to model orbital scattering in fully generic potentials. for illustration, we follow the evolution of planetary orbits in a clumpy environment. we show that stochastic heating of (mass-less) discs in a keplerian potential leads to the formation, and subsequent `evaporation' of oort-like clouds, and derive analytical expressions for the escape rate and the fraction of comets on retrograde orbits as a function of time. extrapolation of the subhalo mass function of milky way-like haloes down to the wimp free-streaming length suggests that objects in the outer solar system experience repeated interactions with dark microhaloes on dynamical time-scales. | stochastic tidal heating by random interactions with extended substructures |
context. the mirror tracking system of the canadian automated meteor observatory (camo) can track meteors in real time, providing an effective angular resolution of 1 arc second and a temporal resolution of 100 frames per second. aims. we describe the upgraded hardware and give details of the data calibration and reduction pipeline. we investigate the influence of meteor morphology on radiant and velocity measurement precision, and use direct observations of meteoroid fragmentation to constrain their compressive strengths. methods. on july 21, 2017, camo observed a ~4 second meteor on a jfc orbit. it had a shallow entry angle ~8 deg and 12 fragments were visible in the narrow-field video. the event was manually reduced and the exact moment of fragmentation was determined. the aerodynamic ram pressure at the moment of fragmentation was used as a proxy for compressive strength, and strengths of an additional 19 fragmenting meteoroids were measured in the same way. the uncertainty in the atmosphere mass density was estimated to be +/-25% using navgem-ha data. results. we find that meteor trajectory accuracy significantly depends on meteor morphology. the camo radiant and initial velocity precision for non-fragmenting meteors with short wakes is ~0.5' and 1 m/s, while that for meteors with fragments or long wakes is similar to non-tracking, moderate field of view optical systems (5', ~50 m/s). measured compressive strengths of 20 fragmenting meteoroids (with less precise radiants due to their morphology) was in the range of 1-4 kpa, which is in excellent accord with rosetta in-situ measurements of 67p. fragmentation type and strength do not appear to be dependent on orbit. the mass index of the 12 fragments in the july 21 meteoroid was very high (s = 2.8), indicating possible progressive fragmentation. | high precision meteor observations with the canadian automated meteor observatory: data reduction pipeline and application to meteoroid mechanical strength measurements |
the distinctive cometary x-ray morphology of the recently discovered massive galaxy cluster "el gordo" (act-ct j0102-4915 z = 0.87) indicates that an unusually high-speed collision is ongoing between two massive galaxy clusters. a bright x-ray "bullet" leads a "twin-tailed" wake, with the sunyaev-zel'dovich (sz) centroid at the end of the northern tail. we show how the physical properties of this system can be determined using our flash-based, n-body/hydrodynamic model, constrained by detailed x-ray, sz, and hubble lensing and dynamical data. the x-ray morphology and the location of the two dark matter components and the sz peak are accurately described by a simple binary collision viewed about 480 million years after the first core passage. we derive an impact parameter of sime300 kpc, and a relative initial infall velocity of sime2250 km s-1 when separated by the sum of the two virial radii assuming an initial total mass of 2.15 × 1015 m ⊙ and a mass ratio of 1.9. our model demonstrates that tidally stretched gas accounts for the northern x-ray tail along the collision axis between the mass peaks, and that the southern tail lies off axis, comprising compressed and shock heated gas generated as the less massive component plunges through the main cluster. the challenge for λcdm will be to find out if this physically extreme event can be plausibly accommodated when combined with the similarly massive, high-infall-velocity case of the bullet cluster and other such cases being uncovered in new sz based surveys. | a hydrodynamical solution for the "twin-tailed" colliding galaxy cluster "el gordo" |
we present herschel space observatory pacs spectra of t tauri stars, in which we detect amorphous and crystalline water ice features. using irradiated accretion disk models, we determine the disk structure and ice abundance in each of the systems. combining a model-independent comparison of the ice feature strength and disk size with a detailed analysis of the model ice location, we estimate that the ice emitting region is at disk radii >30 au, consistent with a proto-kuiper belt. vertically, the ice emits most below the photodesorption zone, consistent with herschel observations of cold water vapor. the presence of crystallized water ice at a disk location (1) colder than its crystallization temperature and (2) where it should have been re-amorphized in ~1 myr suggests that localized generation is occurring; the most likely cause appears to be micrometeorite impact or planetesimal collisions. based on simple tests with uv models and different ice distributions, we suggest that the sed shape from 20 to 50 μm may probe the location of the water ice snowline in the disk upper layers. this project represents one of the first extra-solar probes of the spatial structure of the cometary ice reservoir thought to deliver water to terrestrial planets. | detections of trans-neptunian ice in protoplanetary disks |
the origin of the heavily fractionated reservoir of nitrogen in comets remains an issue in the theory of their formation and hence of the solar system. whether the fractionated reservoir traced by comets is inherited from the interstellar cloud or is the product of processes taking place in the protostar, or in the protoplanetary disc, remains unclear. so far, observations of nitrogen isotopic ratios in protostars or prestellar cores have not securely identified such a fractionated reservoir owing to the intrinsic difficulty of direct isotopic ratios measurements. in this paper, we report the detection of five rotational lines of hc_3n, including the weaker components of the hyperfine multiplets, and two rotational lines of its 15n isotopologue, towards the l1544 prestellar core. based on a mcmc/non-lte multiline analysis at the hyperfine level, we derive the column densities of hc_3n (8.0± 0.4{ × 10^{13}}{ cm^{-2}}) and hc_3^{15n} (2.0± 0.4{ × 10^{11}}{ cm^{-2}}) and derive an isotopic ratio of 400 ± 20(1σ). this value suggests that hc_3n is slightly depleted in 15n in l1544 with respect to the elemental 14n/15n ratio of ≈330 in the present-day local interstellar medium. our study also stresses the need for radiative calculations at the hyperfine level. finally, the comparison of the derived ratio with those obtained in cn and hcn in the same core seems to favour cn+c2h2 as the dominant formation route to hc3n. however, uncertainties in the isotopic ratios preclude definitive conclusions. | the nitrogen isotopic ratio of hc3n towards the l1544 prestellar core |
we investigated six bright swirls associated with magnetic anomalies of variable strength using chandrayaan-1 moon mineralogy mapper (m3) hyperspectral image data. we examined the 3 μm absorption band generally ascribed to solar wind-induced oh/h2o and spectral trends in the near-infrared wavelength range at on-swirl and off-swirl locations. we found that the 3 μm absorption band is weaker at on-swirl than at off-swirl locations and shows only weak variations with time-of-day. this result is consistent with magnetic anomaly shielding that reduces solar wind interaction with the surface. for a small swirl structure in mare moscoviense, we found the 3 μm absorption band to be similar to that of its surroundings due to the absence of strong magnetic shielding. our spectral analysis results at on-swirl and off-swirl locations suggest that the spectral trends at on-swirl and off-swirl locations cannot always be explained by reduced space-weathering alone. we propose that a combination of soil compaction possibly resulting from the interaction between the surface and cometary gas and subsequent magnetic shielding is able to explain all observed on-swirl vs. off-swirl spectral trends including the absorption band depth near 3 μm. our results suggest that an external mechanism of interaction between a comet and the uppermost regolith layer might play a significant role in lunar swirl formation. | processes governing the vis/nir spectral reflectance behavior of lunar swirls |
this paper presents results from our molecular characterization of comet 21p/giacobini-zinner during its 2018 apparition. we followed the comet during four observing runs, for a total of eight nights. the high-resolution spectra of 21p were acquired using ishell—the near-infrared high-resolution immersion echelle spectrograph on nasa/irtf (maunakea, hawaii). we detected many cometary emission lines across four customized ishell settings in the (2.9-5.2) μm range. co abundances relative to water displayed a relatively constant behavior during the observing campaign, suggesting a possible correlation between the outgassing of water and co. while co mixing ratios in 21p are consistent with the reference median value for jupiter family comets (jfcs), ethane was depleted relative to the reference median value for jfcs, except for one observing run (august 8 and 9) in which ethane appeared overabundant. we consider several possible causes: an ethane outburst, decreasing outgassing of water, or a seasonal effect owing to nucleus rotation. in the pre-perihelion runs, methanol was overabundant compared with the reference median value for jfcs, however it decreased steadily to a depleted value during 21p’s post-perihelion phase, suggesting a possible seasonal effect. we report 3σ upper limits for acetylene, formaldehyde, ammonia, and methane. the ratios of our measured 3σ upper limits for acetylene and detections of hydrogen cyanide are consistent with the depletion of c2 relative to cn in 21p observed at optical wavelengths. this result confirms that 21p is depleted in the carbon-chain primary volatile responsible for c2 production. | quantifying the evolution of molecular production rates of comet 21p/giacobini-zinner with ishell/nasa-irtf |
abundant mining and industrial activities located in the upper silesian coal basin (uscb) lead to large emissions of the potent greenhouse gas (ghg) methane (ch4). the strong localization of ch4 emitters (mostly confined to known coal mine ventilation shafts) and the large emissions of 448 and 720 kt ch4 yr−1 reported in the european pollutant release and transfer register (e-prtr 2017) and the emissions database for global atmospheric research (edgar v4.3.2), respectively, make the uscb a prime research target for validating and improving ch4 flux estimation techniques. high-precision observations of this ghg were made downwind of local (e.g., single facilities) to regional-scale (e.g., agglomerations) sources in the context of the comet 1.0 campaign in early summer 2018. a quantum cascade-interband cascade laser (qcl-icl)-based spectrometer adapted for airborne research was deployed aboard the german aerospace center (dlr) cessna 208b to sample the planetary boundary layer (pbl) in situ. regional ch4 emission estimates for the uscb are derived using a model approach including assimilated wind soundings from three ground-based doppler lidars. although retrieving estimates for individual emitters is difficult using only single flights due to sparse data availability, the combination of two flights allows for exploiting different meteorological conditions (analogous to a sparse tomography algorithm) to establish confidence on facility-level estimates. emission rates from individual sources not only are needed for unambiguous comparisons between bottom-up and top-down inventories but also become indispensable if (independently verifiable) sanctions are to be imposed on individual companies emitting ghgs. an uncertainty analysis is presented for both the regional-scale and facility-level emission estimates. we find instantaneous coal mine emission estimates of 451/423 ± 77/79 kt ch4 yr−1 for the morning/afternoon flight of 6 june 2018. the derived fuel-exploitation emission rates coincide (±6 %) with annual-average inventorial data from e-prtr 2017 although they are distinctly lower (−28 %/−32 %) than values reported in edgar v4.3.2. discrepancies in available emission inventories could potentially be narrowed down with sufficient observations using the method described herein to bridge the gap between instantaneous emission estimates and yearly averaged inventories. | estimating upper silesian coal mine methane emissions from airborne in situ observations and dispersion modeling |
the imprudent use of insecticides causes the development of resistance in insect pest populations, contamination of the environment, biological imbalance and human intoxication. the use of microbial pathogens combined with insecticides has been proposed as an alternative strategy for insect pest management. this ipm approach may offer effective ways to control pests, in addition to lowering the risk of chemical residues in the environment. spodoptera litura (fabricius) is a major pest of many crops like cotton, maize, tobacco, cauliflower, cabbage, and fodder crops globally. here, we evaluated the combined effects of new chemistry insecticides (chlorantraniliprole and emamectin benzoate) and entomopathogenic bacterial strains, shewanella sp. (ss4), thauera sp. (m9) and pseudomonas sp. (en4) against s. litura larvae inducing additive and synergistic interactions under laboratory conditions. both insecticides produced higher larval mortality when applied in combination with bacterial isolates having maximum mortality of 98 and 96% with lc50 of chlorantraniliprole and emamectin benzoate in combination with lc50 of pseudomonas sp. (en4) respectively. the lower concentration (lc20) of both insecticides also induced synergism when combined with the above bacterial isolates providing a valuable approach for the management of insect pests. the genotoxic effect of both the insecticides was also evaluated by conducting comet assays. the insecticide treatments induced significant dna damage in larval hemocytes that further increased in combination treatments. our results indicated that combined treatments could be a successful approach for managing s. litura while reducing the inappropriate overuse of insecticides. | synergistic and additive interactions of shewanella sp., pseudomonas sp. and thauera sp. with chlorantraniliprole and emamectin benzoate for controlling spodoptera litura (fabricius) |
in 2020, during the covid-19 pandemic, containment measures were applied inducing potential changes in air pollutant concentrations and thus in air toxicity. this study evaluates the role of restrictions on biological effects of particulate matter (pm) in different northwest italy sites: urban background, urban traffic, rural, and incinerator. daily pm samples collected in 2020 were pooled according to restrictions: january/february (no restrictions), march and april (first lockdown), may/june and july/august/september (low restrictions), october/november/december (second lockdown). the 2019 samples (pre-pandemic period) were pooled as 2020 for comparison. pools were extracted with organic solvents and extracts were tested to assess cytotoxicity (wst-1 assay) and genotoxicity (comet assay) on beas-2b cells, mutagenicity (ames test) on ta98 and ta100 salmonella typhimurium strains, and estrogenic activity (gene reporter assay) on meln cells. pollutant concentrations were also analyzed (pm10, pm2.5, polycyclic aromatic hydrocarbons). no difference was observed for pm and polycyclic aromatic hydrocarbon concentrations between 2020 and 2019. during lockdown months (2020), pm cytotoxicity/genotoxicity was significantly lower in some sites than during 2019, while considering pm mutagenicity/estrogenic activity some differences were detected but without statistical significance. pm extract effects decreased in some sites during 2020; this may be due to lockdowns that reduced/modified pollutant emissions and may be related also to complex pm origin/formation and to meteorological conditions. in conclusion, the study confirms that pm biological effects cannot be assessed considering only the pm concentration and suggests to include a battery of bioassay for air quality monitoring in order to protect human health from air pollution effects. graphical abstract | biological effects of particulate matter samples during the covid-19 pandemic: a comparison with the pre-lockdown period in northwest italy |
centaur 29p/schwassmann-wachmann 1 (sw1) is a highly active object orbiting in the transitional "gateway" region between the centaur and jupiter-family comet (jfc) regions. sw1 is unique among the centaurs in that it experiences quasi-regular major outbursts and produces co emission continuously; however, the source of the co is unclear. we argue that, due to its very large size (~32 km radius), sw1 is likely still responding, via amorphous water ice (awi) conversion to crystalline water ice (cwi), to the "sudden" change in its external thermal environment produced by its myrs-long dynamical migration from the kuiper belt to its current location at the inner edge of the centaur region. it is this conversion process that is the source of the abundant co and dust released from the object during its quiescent and outburst phases. if correct, these arguments have a number of important predictions testable via remote sensing and in situ spacecraft characterization, including the quick release on myr timescales of co from awi conversion for any few kilometer-scale scattered disk kuiper belt objects transiting into the inner system; that to date sw1 has only converted between 50% and 65% of its nuclear awi to cwi; that volume changes on awi conversion could have caused subsidence and cave-ins, but not significant mass wasting or crater loss; that sw1's coma should contain abundant amounts of cwi+co2 "dust" particles; and that when sw1 transits into the inner system within the next 10,000 yr, it will be a very different kind of jfc. | 29p/schwassmann-wachmann 1: a rosetta stone for amorphous water ice and co ↔ co2 conversion in centaurs and comets? |
the interstellar objects 1i/`oumuamua and 2i/borisov confirm the long-held expectation that bodies from one stellar system will be carried to another, allowing, in principle, interstellar panspermia. life might be transferred between stellar systems, depending on the nature of the bodies and how they escaped their systems. 2i/borisov appears to be a comet, with no more likelihood of carrying life than solar system comets. in contrast, the nature of 1i/`oumuamua has been difficult to determine. we review various hypotheses for its origin, including ejection of n2 ice from the surface of an exo-pluto, formation in a molecular cloud by freezing of h2, and a derelict solar sail of alien construction. of these, the n2 ice fragment hypothesis is uniquely falsifiable, plausible, and completely consistent with all observations. the possibility of interstellar panspermia would be made more probable if `oumuamua originated on a dwarf planet rather than a comet, although substantial challenges to transfer of life would remain. of proposed mechanisms for interstellar panspermia, transfer of life via rocky meteoroids is perhaps less improbable. | some pertinent issues for interstellar panspermia raised after the discovery of 1i/`oumuamua |
the paper presents experimental studies on the degassing of porous ice and porous mixtures of ice and sand in a vacuum. the study aims to find the relationship between the surface recession rate and the subsurface temperature gradient as well as the granulation and composition of the material. we propose an empirical equation tested on samples with a mass fraction of non-volatile material to ice in the range of 0-3.65. based on the proposed equation, calculations were carried out, which indicate the possibility of landslides on the inclined areas on the surface of comet 9p/tempel 1. | outgassing of selected possible cometary analogs: laboratory simulations |
having a nucleus darker than charcoal, comets are usually detected from earth through the emissions from their coma. the coma is an envelope of gas that forms through the sublimation of ices from the nucleus as the comet gets closer to the sun. in the far-ultraviolet portion of the spectrum, observations of comae have revealed the presence of atomic hydrogen and oxygen emissions. when observed over large spatial scales as seen from earth, such emissions are dominated by resonance fluorescence pumped by solar radiation. here, we analyse atomic emissions acquired close to the cometary nucleus by the rosetta spacecraft and reveal their auroral nature. to identify their origin, we undertake a quantitative multi-instrument analysis of these emissions by combining coincident neutral gas, electron and far-ultraviolet observations. we establish that the atomic emissions detected from rosetta around comet 67p/churyumov-gerasimenko at large heliocentric distances result from the dissociative excitation of cometary molecules by accelerated solar-wind electrons (and not by electrons produced from photo-ionization of cometary molecules). like the discrete aurorae at earth and mars, this cometary aurora is driven by the interaction of the solar wind with the local environment. we also highlight how the oxygen line o i at wavelength 1,356 å could be used as a tracer of solar-wind electron variability. | far-ultraviolet aurora identified at comet 67p/churyumov-gerasimenko |
some scenarios for planetesimal formation go through a phase of collapse of gravitationally bound clouds of millimeter- to centimeter-size pebbles. such clouds can form, for example, through the streaming instability in protoplanetary disks. we model the collapse process with a statistical model to obtain the internal structure of planetesimals with solid radii between 10 and 1000 km. during the collapse, pebbles collide, and depending on their relative speeds, collisions have different outcomes. a mixture of particle sizes inside a planetesimal leads to better packing capabilities and higher densities. in this paper we apply results from new laboratory experiments of dust aggregate collisions (presented in a companion paper) to model collision outcomes. we find that the internal structure of a planetesimal is strongly dependent on both its mass and the applied fragmentation model. low-mass planetesimals have no/few fragmenting pebble collisions in the collapse phase and end up as porous pebble piles. the number of fragmenting collisions increases with increasing cloud mass, resulting in wider particle size distributions and higher density. the collapse is nevertheless “cold” in the sense that collision speeds are damped by the high collision frequency. this ensures that a significant fraction of large pebbles survive the collapse in all but the most massive clouds. our results are in broad agreement with the observed increase in density of kuiper belt objects with increasing size, as exemplified by the recent characterization of the highly porous comet 67p/churyumov-gerasimenko. | the role of pebble fragmentation in planetesimal formation. ii. numerical simulations |
we present laboratory measurements of the phase functions and degree of linear polarization (dlp) curves of a selection of millimeter-sized cosmic dust analog particles. the set includes particles with similar sizes but diverse internal structure (compact and porous) and absorbing properties. the measured phase functions are found to be in all cases very different from those of micron-sized particles. they show a monotonic decrease with increasing phase angle from the back- to the side-scattering region, reaching a minimum at large phase angles before a steep increase of the forward peak. this is in stark contrast to the phase functions of micron-sized particles, which are rather flat at low and intermediate phase angles. the maximum of the dlp for millimeter-sized compact particles is shifted toward larger phase angles (∼130°) compared to that of micron-sized particles (∼90°). porosity plays an important role in the measured dlp curves: the maximum significantly decreases for increasing porosity as a result of multiple scattering within the particle. large porous particles with highly absorbing inclusions can reproduce both the osiris/rosetta phase functions and ground-based dlp observations of comet 67p/churyumov-gerasimenko. | experimental phase function and degree of linear polarization curves of millimeter-sized cosmic dust analogs |
the excessive use of metaldehyde in agriculture to combat mollusks endangers both the environment and non-target organisms. the aim of this study is to investigate the toxicity caused by metaldehyde in alliumcepa with the help of physiological, cytogenetic, biochemical and anatomical parameters. also, dna fragmentation caused by metaldehyde in root tip cells was measured by the "comet assay" method. the control group was germinated with tap water and the application groups were germinated with 20 mg/l metaldehyde, 40 mg/l metaldehyde, 100 mg/l metaldehyde and 200 mg/l metaldehyde for 72 h. the results of the physiological parameters showed that metaldehyde had a growth-limiting effect in a.cepa, depending on the application dose. according to root elongation levels, the ec50 (effective concentration) value for metaldehyde was 60.6 mg/l in a.cepa. as the treatment dose increased, the incidence of micronucleus and chromosomal aberrations gradually increased while mitotic index decreased. metaldehyde exposure induced damages such as sticky chromosome, fragment, unequal distribution of chromatin, reverse polarization, bridge, and multipolar anaphase. in addition, metaldehyde caused cell damage in epidermis and cortex, thickening of the cortex cell wall and flattened cell nucleus in root meristem. increasing doses of metaldehyde application also increased malondialdehyde levels, superoxide dismutase and catalase activities. as a result, it has been determined that the toxicity of metaldehyde in plants is versatile and the a.cepa test material is a suitable biological indicator to determine this toxicity. | assessing the combined toxic effects of metaldehyde mollucide |
chemical reactions and desorption processes are being triggered by incoming ionizing radiation over astrophysical ices in cold space environments. the quantification of these processes is crucial to achieve a detailed understanding of the underlying chemistry occurring within the ice. with this goal, we have upgraded the procoda code (pilling et al. 2022a) which solves a system of coupled differential equations and describes the evolution of the molecular abundances under processing by radiation, now including an effective rate constant (ercs) ordering by employing thermochemistry data taken from literature. this methodology helps to identify the most important reactions within the reaction network and therefore decreases the degeneracy of the solutions and enhancing the accuracy of the calculations. here, we described the chemical evolution of four irradiated pure co2 considering 11 different chemical species, 100 reaction routes and 11 radiation-induced desorption processes. the best-fit models provide the effective rate constants, several desorption parameters, as well as, the characterization of the chemical equilibrium (ce) phase. a comparison with previous code version was given and indicates that the ordering of rate constants by thermochemistry data is more important when more energy is deposited in the ice. the current work present more realistic values for the effective rate constants and a better characterization of the ce phase, such data can be used to refine astrochemical models to better describe cold space environments in the presence of incoming ionizing radiation field such molecular clouds and protoplanetary regions and the surface of comets and frozen moons and planets. | mapping the evolution of pure co2 ices irradiated by ions, uv, and electrons using the upgraded procoda code (employing an effective rate constant ordering by thermochemistry data) |
we analyze 2-5 μm spectroscopic observations of the dust coma of comet 67p/churyumov-gerasimenko obtained with the visible infrared thermal imaging spectrometer (virtis-h) instrument on board rosetta from 3 june to 29 october 2015 at heliocentric distances rh = 1.24-1.55 au. the 2-2.5 μm color, bolometric albedo, and color temperature were measured using spectral fitting. data obtained at α = 90° solar phase angle show an increase in bolometric albedo (0.05-0.14) with increasing altitude (0.5-8 km), accompanied by a possible marginal decrease in color and color temperature. possible explanations include dark particles on ballistic trajectories in the inner coma and radial changes in particle composition. in the phase angle range 50°-120°, phase reddening is significant (0.031%/100 nm deg-1) for a mean color of 2%/100 nm at α = 90°, which might be related to the roughness of the dust particles. moreover, a decrease in color temperature with decreasing phase angle is also observed at a rate of 0.3 k deg-1, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. comparing data acquired at fixed phase angle (α = 90°), a 20% increase in bolometric albedo is observed near perihelion. heliocentric variations in dust color are not significant in the time period we analyzed. the measured color temperatures vary from 260 to 320 k, and follow a rh-0.6 variation in the rh = 1.24-1.5 au range, which is close to the expected rh-0.5 value. | virtis-h observations of the dust coma of comet 67p/churyumov-gerasimenko: spectral properties and color temperature variability with phase and elevation |
detailed morphological and photometric characterisation of comet 29p in the optical region is presented comprising: (a) multi-filter observations of the outburst coma in 2010-2012 with the 2.0-m faulkes telescopes (ft); (b) high-cadence, high-precision photometry in may-september 2014; and (c) hst observations in march 1996 (wfpc2/f702w filter). outbursts appear to be explosive in that: the rise to maximum light is short-lived; the expanding coma fits a model in which ejecta are produced in a singular event and expand into space with uniform velocity; and the motion of condensations within the outburst coma indicate a common onset time and origin. the bright outburst of 2010 february 2 generated a dust coma exhibiting expansion speeds up to 0.257 ± 0.013 km s-1 consistent with acceleration of cometary grains close to the nucleus driven by sublimating co ice and n2 ice at 24 ± 6 k. material ejected ∼1 d after this outburst exhibited a v-r colour gradient: redder towards the main outflow, bluer in the opposite sense; potentially arising from differences in spectral emission (from gas), light scattering (particle size), and spectral reflectance (composition). b-v, v-r and r-i colour images revealed colour/compositional differences in near-nucleus structures and the evolution of the expanding coma, which brightened by ∼30% within 5-6 days of the outburst. broadband photometry indicated a general reddening coma with time (change in b-v from +0.76 to +0.83; v-sdss-r‧ from 0.25 to +0.31 in 14 d). sdss-r‧-sdss-i‧ photometry indicated gradual spectral attenuation at >700 nm. asymmetric, fan-shaped comae, characteristic of 29p, potentially form when the expanding cloud from an outburst is shielded by the nucleus. rotational-gradient filtered hst and ft images show unusual 2-fold and 4-fold symmetry involving oppositely-directed radial outflows moving at up to 0.15 km s-1: possibly an indication of material escaping from fissures along the perimeter of a crustal 'plate' when dislodged by pressure build-up in the subsurface. pairs of outbursts separated in time by 52-65 d took place in 2010, 2011, and 2012 exhibiting similar coma outflow patterns indicative of outbursts repeating a second time from the same source, and suggesting a nuclear rotation period of 59 ± 4 (s.e.) d. the escape velocity of the nucleus is sufficiently high (0.013-0.023 km s-1) that a significant fraction of ejecta falls back onto its surface, the action of which, we suggest, re-forms the crust and may trigger outbursts from nearby sites (e.g. triple events of february 2010, and may 2014). a short-lived (<1 d) anomalous brightening of 0.36 ± 0.12 mag observed on 2014 july 21 during quiescence may have arisen from an especially weak mini-outburst in which most of the ejected material failed to reach escape velocity. during quiescence in 2014, comet 29p fluctuated in brightness over time-scales of 2-10 d by up to ±0.25 mag, probably via local jet activity continuing to feed the faint persistent inner coma. 29p also exhibited weak outbursts of <1 mag amplitude during quiescence and these will generally be missed by observers. image analysis methodology tracking the locus of the coma photocentre with increasing photometric aperture size is used to quantify the directional motion of cometary haloes within 1-2 d of an outburst. | anatomy of outbursts and quiescent activity of comet 29p/schwassmann-wachmann |
merging galaxy clusters with radio relics provide rare insights to the merger dynamics as the relics are created by the violent merger process. we demonstrate one of the first uses of the properties of the radio relic to reduce the uncertainties of the dynamical variables and determine the three-dimensional (3d) configuration of a cluster merger, act-cl j0102-4915, nicknamed el gordo. from the double radio relic observation and the x-ray observation of a comet-like gas morphology induced by motion of the cool core, it is widely believed that el gordo is observed shortly after the first core passage of the subclusters. we employ a monte carlo simulation to investigate the 3d configuration and dynamics of el gordo. using the polarization fraction of the radio relic, we constrain the estimate of the angle between the plane of the sky and the merger axis to be α = 21° ± ^9_{11}. we find the relative 3d merger speed of el gordo to be 2400± ^{400}_{200} km s^{-1} at pericentre. the two possible estimates of the time since pericentre (tsp) are 0.46± ^{0.09}_{0.16} and 0.91± ^{0.22}_{0.39} gyr for the outgoing and returning scenario, respectively. we put our estimates of the tsp into context by showing that if the time-averaged shock velocity is approximately equal to or smaller than the pericentre velocity of the corresponding subcluster in the centre-of-mass frame, the two subclusters are more likely to be moving towards, rather than away, from each other, post apocentre. we compare and contrast the merger scenario of el gordo with that of the bullet cluster, and show that this late-stage merging scenario explains why the south-east (se) dark matter lensing peak of el gordo is closer to the merger centre than the se cool core. | the return of the merging galaxy subclusters of el gordo? |
we have utilized the nasa/irtf 3 m spex instrument’s high-resolution spectral mode to observe and characterize the near-infrared flux emanating from the unusual kepler light curve system kic 8462852. by comparing the resulting 0.8-4.2 μm spectrum to a mesh of model photospheric spectra, the 6 emission line analyses of the rayner et al. catalog, and the 25 system collections of debris disks we have observed to date using spex under the near infrared debris disk survey, we have been able to additionally characterize the system. within the errors of our measurements, this star looks like a normal solar abundance main-sequence f1v to f3v dwarf star without any obvious traces of significant circumstellar dust or gas. using connelley & greene’s emission measures, we also see no evidence of significant ongoing accretion onto the star nor any stellar outflow away from it. our results are inconsistent with large amounts of static close-in obscuring material or the unusual behavior of a yso system, but are consistent with the favored episodic giant comet models of a gyr old stellar system favored by boyajian et al. we speculate that kic 8462852, like the ∼1.4 gyr old f2v system η corvi, is undergoing a late heavy bombardment, but is only in its very early stages. | irtf/spex observations of the unusual kepler light curve system kic8462852 |
combining dynamical models of dust from jupiter-family comets and halley-type comets, we demonstrate that the seasonal variation of the dust/meteoroid environment at mercury is responsible for producing the dawn-dusk asymmetry in mercury’s exosphere observed by the messenger spacecraft. our latest models, calibrated recently from ground-based and space-borne measurements, provide unprecedented statistics that enable us to study the longitudinal and latitudinal distribution of meteoroids impacting mercury’s surface. we predict that the micrometeoroid impact vaporization source is expected to undergo significant motion on mercury’s surface toward the nightside during mercury’s approach to aphelion and toward the dayside when the planet is approaching the sun. | reconciling the dawn-dusk asymmetry in mercury’s exosphere with the micrometeoroid impact directionality |
the localized delivery of new long-lived species to jupiter's stratosphere by comet shoemaker-levy 9 in 1994 opened a window to constrain jovian chemistry and dynamics by monitoring the evolution of their vertical and horizontal distributions. however, the spatial distributions of co and hcn, two of these long-lived species, had never been jointly observed at high latitudinal resolution. atacama large millimeter/submillimeter array observations of hcn and co in march 2017 show that co was meridionally uniform and restricted to pressures lower than 3 ± 1 mbar. hcn shared a similar vertical distribution in the low- to mid-latitudes, but was depleted at pressures between 2−1+2 and 0.04−0.03+0.07 mbar in the aurora and surrounding regions, resulting in a drop by two orders of magnitude in column density. we propose that heterogeneous chemistry bonds hcn on large aurora-produced aerosols at these pressures in the jovian auroral regions causing the observed depletion. | evidence for auroral influence on jupiter's nitrogen and oxygen chemistry revealed by alma |
in august 2019, a second interstellar object 2i/borisov was discovered 2 years after the discovery of the first known interstellar object, 1i/'oumuamua. can we send a spacecraft to this object, using existing technologies? in this paper we assess the technical feasibility of a near-term mission to 2i/borisov. we apply the optimum interplanetary trajectory software (oits) tool to generate trajectories to 2i/borisov. as results, we get the minimal $\delta v$ trajectory with a launch date in july 2018. for this trajectory, a falcon heavy launcher could have hauled an 8 ton spacecraft to 2i/borisov. for a later launch date, results for a combined powered jupiter flyby with a solar oberth maneuver are presented. for a launch in 2027, we could reach 2i/borisov in 2052, using the space launch system (sls), up-scaled parker probe heat shield technology, and solid propulsion engines. using a sls a spacecraft with a mass of 765 kg could be sent to 2i/borisov. a falcon heavy could deliver 202 kg to 2i/borisov. arrival times sooner than 2052 can potentially be achieved but with higher $\delta v$ requirements and lower spacecraft payload masses. 2i/borisov's discovery shortly after the discovery of 1i/'oumuamua implies that the next interstellar object might be discovered in the near future. the feasibility of a mission to both, 1i/'oumuamua and 2i/borisov using existing technologies indicates that missions to at least some future interstellar objects are feasible as well. | sending a spacecraft to interstellar comet 2i/borisov |
in this chapter, we provide a review of radiative processes in cometary atmospheres spanning a broad range of wavelengths, from radio to x-rays. we focus on spectral modeling, observational opportunities, and anticipated challenges in the interpretation of new observations, based on our current understanding of the atomic and molecular processes occurring in the atmospheres of small, icy bodies. close to the surface, comets possess a thermalized atmosphere that traces the irregular shape of the nucleus. gravity is too low to retain the gas, which flows out to form a large, collisionless exosphere (coma) that interacts with the heliospheric radiation environment. as such, cometary comae represent conditions that are familiar in the context of planetary atmosphere studies. however, the outer comae are tenuous, with densities lower than those found in vacuum chambers on earth. comets, therefore, provide us with unique natural laboratories that can be understood using state-of-the-art theoretical treatments of the relevant microphysical processes. radiative processes offer direct diagnostics of the local physical conditions, as well as the macroscopic coma properties.these can be used to improve our understanding of comets and other astrophysical environments such as icy moons and the interstellar medium. | radiative processes as diagnostics of cometary atmospheres |
we carry out a population study of magnetized radio filaments in the galactic centre using meerkat data by focusing on the spacing between the filaments that are grouped. the morphology of a sample of 43 groupings containing 174 magnetized radio filaments are presented. many grouped filaments show harp-like, fragmented cometary tail-like, or loop-like structures in contrast to many straight filaments running mainly perpendicular to the galactic plane. there are many striking examples of a single filament splitting into two prongs at a junction, suggestive of a flow of plasma along the filaments. spatial variations in spectral index, brightness, bending, and sharpening along the filaments indicate that they are evolving on a 105-6-yr time-scale. the mean spacings between parallel filaments in a given grouping peaks at ~16 arcsec. we argue by modeling that the filaments in a grouping all lie on the same plane and that the groupings are isotropically oriented in 3d space. one candidate for the origin of filamentation is interaction with an obstacle, which could be a compact radio source, before a filament splits and bends into multiple filaments. in this picture, the obstacle or sets the length scale of the separation between the filaments. another possibility is synchrotron cooling instability occurring in cometary tails formed as a result of the interaction of cosmic ray driven galactic centre outflow with obstacles such as stellar winds. in this picture, the mean spacing and the mean width of the filaments are expected to be a fraction of a parsec, consistent with observed spacing. | statistical properties of the population of the galactic centre filaments - ii. the spacing between filaments |
we analyzed the bvr photometry of comet c/2012 j1 (catalina) taken between march 2013 and may 2014 with telescopes ranging from 0.20 to 2.0 m aperture in australia, europe, and the united states. we found an absolute magnitude in the r‑band of h0 = 7.2 ± 0.1 measured with a photometric aperture radius ρ of 42.4 arcsec, corresponding to projected distances in the sky of 7.2 × 104–1.5 × 105 km. comet c/2012 j1 (catalina) shows an asymmetric secular light curve, which is typical for comets. the nucleus has a minimum radius of 3.3 km admitting an albedo of 0.04. the inner coma exhibited radial pulsations before perihelion related to the dust rate proxy afρ. the afρ parameter was inversely proportional to the photometric aperture radius ρ because the angular diameter of the coma was small compared with the aperture radii used. the comet had three outbursts with brightness variations between 0.2 and 2.99 magnitudes per event. the median normalized reflectivity gradient s′ is 4.4 with an amplitude of 22.9%/100 nm in the spectral range between 440 and 647 nm. the dispersion of the gradient s′ means that 20% of the measurements are bluer than the solar color. | photometric bvr observations of comet c/2012 j1 (catalina) before and after perihelion |
context. comet 46p/wirtanen is a near-earth object (neo) for which no associated meteor shower has ever been reported.aims: this study is aimed at improving our understanding of why there has been no observed shower activity for this neo to date, as well as to consider whether any past activity could be uncovered from the post-prediction results.methods: the usual dynamic tools for meteoroid streams were used to describe the behavior of the particles ejected by the comet. the resulting modeled meteoroid stream was thoroughly inspected for collisions between the stream and the earth.results: the results show a possible encounter forecast for december 12, 2023, between 8:00 and 12:30 ut. the slow entry velocity is typically known to cause dim meteors. the activity level of the shower is highly uncertain due to the absence of reported past showers.conclusions: overall, the most optimal observations on the forecasted day would be achieved from eastern australia, new zealand, and oceania. these observations will help constrain the size distribution of meteoroids from comet 46p/wirtanen in the millimeter range. | a new meteor shower from comet 46p/wirtanen expected in december 2023 |
the proposed cosmic-induced conflagration of the black mat (bm), at the end of the allerød interstade, dated to the 12.8 ka—younger dryas boundary (ydb), has been variably related to multiple airburst events following earth's encounter with the encke comet. evidence for the bm, as on mt. viso in the western alps of europe, and in the high northwestern venezuelan andes, relies upon variably distributed rock clasts, paleosols, and sediment resident in late glacial (lg) moraines, mass wasted deposits, and glaciolacustrine sediment. it is the age correlation of these two cosmic-affected sites—viso-andes—correlated with the 12,737 ± 41 cal yr bp upper yd age glaciolacustrine sediment of kråkenes, norway, and readjused pollen sites to 12,820 yr bp that has not been discussed in terms of contemporaneity—cosmic-terrestrial. the cosmic theory termed the yd impact hypothesis—ydih—has witnessed slow acceptance by the scientific community, compared with century-long attention paid to the yd terrestrially oriented hypotheses. the cosmic-affected lg sediment (viso), with ams c14 dated glaciofluvial sediment in the northern andes, place the upper yd aligned with black mat dated sediment on several continents. as well, the cosmic hypothesis supporting the yd covers wider spatial ground compared with terrestrial arguments and is likely a progenitor of this one major climatic shift of the neogene. previous workers on the yd climatic shift, as outlined here, may have overlooked, or overreached to explain, the bm occurrence. firming up the ydih to the ydb parallels similar past struggles with continental drift to plate tectonics, crater age chronology theories on mars, agassiz's ice age theory, and human-induced climatic warming. time perhaps, to bring the terrestrially driven explanation for the ydb to the ydih, the latter was continually supported by a number of independent studies. | the younger dryas boundary (ydb): terrestrial, cosmic, or both? |
context. during its two-year mission at comet 67p, rosetta nearly continuously monitored the inner coma plasma environment for gas production rates varying over three orders of magnitude, at distances to the nucleus ranging from a few to a few hundred kilometres. to achieve the best possible measurements, cross-calibration of the plasma instruments is needed.aims: our goal is to provide a consistent plasma density dataset for the full mission, while in the process providing a statistical characterisation of the plasma in the inner coma and its evolution.methods: we constructed physical models for two different methods to cross-calibrate the spacecraft potential and the ion current as measured by the rosetta langmuir probes (lap) to the electron density as measured by the mutual impedance probe (mip). we also described the methods used to estimate spacecraft potential, and validated the results with the ion composition analyser (ica).results: we retrieve a continuous plasma density dataset for the entire cometary mission with a much improved dynamical range compared to any plasma instrument alone and, at times, improve the temporal resolution from 0.24−0.74 hz to 57.8 hz. the physical model also yields, at a three-hour time resolution, ion flow speeds and a proxy for the solar euv flux from the photoemission from the langmuir probes.conclusions: we report on two independent mission-wide estimates of the ion flow speed that are consistent with the bulk h2o+ ion velocities as measured by the ica. we find the ion flow to consistently be much faster than the neutral gas over the entire mission, lending further evidence that the ions are collisionally decoupled from the neutrals in the coma. measurements of ion speeds from rosetta are therefore not consistent with the assumptions made in previously published plasma density models of the comet 67p's ionosphere at the start and end of the mission. also, the measured euv flux is perfectly consistent with independently derived values previously published from lap and lends support for the conclusions drawn regarding an attenuation of solar euv from a distant nanograin dust population, when the comet activity was high. the new density dataset is consistent with the existing mip density dataset, but it facilitates plasma analysis on much shorter timescales, and it also covers long time periods where densities were too low to be measured by mip. | plasma densities, flow, and solar euv flux at comet 67p. a cross-calibration approach |
the retrieval of turbulence parameters with profiling doppler wind lidars (dwls) is of high interest for boundary layer meteorology and its applications. dwls provide wind measurements above the level of meteorological masts while being easier and less expensive to deploy. velocity-azimuth display (vad) scans can be used to retrieve the turbulence kinetic energy (tke) dissipation rate through a fit of measured azimuth structure functions to a theoretical model. at the elevation angle of 35.3∘ it is also possible to derive tke. modifications to existing retrieval methods are introduced in this study to reduce errors due to advection and enable retrievals with a low number of scans. data from two experiments are utilized for validation: first, measurements at the meteorological observatory lindenberg-richard-aßmann observatory (mol-rao) are used for the validation of the dwl retrieval with sonic anemometers on a meteorological mast. second, distributed measurements of three dwls during the comet campaign with two different elevation angles are analyzed. for the first time, the ground-based dwl vad retrievals of tke and its dissipation rate are compared to in situ measurements of a research aircraft (here: dlr cessna grand caravan 208b), which allows for measurements of turbulence above the altitudes that are in range for sonic anemometers. from the validation against the sonic anemometers we confirm that lidar measurements can be significantly improved by the introduction of the volume-averaging effect into the retrieval. we introduce a correction for advection in the retrieval that only shows minor reductions in the tke error for 35.3∘ vad scans. a significant bias reduction can be achieved with this advection correction for the tke dissipation rate retrieval from 75∘ vad scans at the lowest measurement heights. successive scans at 35.3 and 75∘ from the comet campaign are shown to provide tke dissipation rates with a good correlation of r>0.8 if all corrections are applied. the validation against the research aircraft encourages more targeted validation experiments to better understand and quantify the underestimation of lidar measurements in low-turbulence regimes and altitudes above tower heights. | towards improved turbulence estimation with doppler wind lidar velocity-azimuth display (vad) scans |
cometary nuclei are considered to most closely reflect the composition of the building blocks of our solar system. as such, comets carry important information about the prevalent conditions in the solar nebula before and after planet formation. recent measurements of the time variation of major and minor volatile species in the coma of the jupiter family comet 67p/churyumov-gerasimenko (67p) by the rosina (rosetta orbiter spectrometer for ion and neutral analysis) instrument onboard rosetta provide insight into the possible origin of this comet. the observed outgassing pattern indicates that the nucleus of 67p contains crystalline ice, clathrates, and other ices. the observed outgassing is not consistent with gas release from an amorphous ice phase with trapped volatile gases. if the building blocks of 67p were formed from crystalline ices and clathrates, then 67p would have agglomerated from ices that were condensed and altered in the protosolar nebula closer to the sun instead of more pristine ices originating from the interstellar medium or the outskirts of the disc, where amorphous ice may dominate. | the presence of clathrates in comet 67p/churyumov-gerasimenko |
the intensive measurement campaign comet 1.0 (carbon dioxide and methane mission) took place during may and june 2018, with a focus on greenhouse gases over europe. comet 1.0 aimed at characterising the distribution of ch4 and co2 over significant regional sources with the use of a fleet of research aircraft as well as validating remote sensing measurements from state-of-the-art instrumentation installed on board against a set of independent in situ observations. here we present the results of over 55 h of accurate and precise in situ measurements of co2, ch4 and co mole fractions made during comet 1.0 flights with a cavity ring-down spectrometer aboard the german research aircraft halo (high altitude and long range research aircraft), together with results from analyses of 96 discrete air samples collected aboard the same platform. a careful in-flight calibration strategy together with post-flight quality assessment made it possible to determine both the single-measurement precision as well as biases against respective world meteorological organization (wmo) scales. we compare the result of greenhouse gas observations against two of the available global modelling systems, namely jena carboscope and cams (copernicus atmosphere monitoring service). we find overall good agreement between the global models and the observed mole fractions in the free tropospheric range, characterised by very low bias values for the cams ch4 and the carboscope co2 products, with a mean free tropospheric offset of 0 (14) nmol mol−1 and 0.8 (1.3) µmol mol−1 respectively, with the numbers in parentheses giving the standard uncertainty in the final digits for the numerical value. higher bias is observed for cams co2 (equal to 3.7 (1.5) µmol mol−1), and for co the model-observation mismatch is variable with height (with offset equal to −1.0 (8.8) nmol mol−1). we also present laboratory analyses of air samples collected throughout the flights, which include information on the isotopic composition of ch4, and we demonstrate the potential of simultaneously measuring δ13c−ch4 and δ2h−ch4 from air to determine the sources of enhanced methane signals using even a limited number of discrete samples. using flasks collected during two flights over the upper silesian coal basin (uscb, southern poland), one of the strongest methane-emitting regions in the european union, we were able to use the miller-tans approach to derive the isotopic signature of the measured source, with values of δ2h equal to −224.7 (6.6) ‰ and δ13c to −50.9 (1.1) ‰, giving significantly lower δ2h values compared to previous studies in the area. | in situ observations of greenhouse gases over europe during the comet 1.0 campaign aboard the halo aircraft |
we compute partial photoionization frequencies of h2o, co2, and co, the major molecules in the coma of comet 67p/churyumov-gerasimenko, the target comet of the ongoing esa rosetta mission. values are computed from thermosphere ionosphere mesosphere energy and dynamics/solar euv experiment solar euv spectra for 2014 august 1, 2015 march 1, and for perihelion (2015 august, as based on prediction). from the varying total photoionization frequency of h2o, as computed from 2014 august 1 to 2015 may 20, we derive a simple analytical expression for the electron-to-neutral number density ratio as a function of cometocentric and heliocentric distance. the underlying model assumes radial movement of the coma constituents and does not account for chemical loss or the presence of electric fields. we discuss various effects/processes that can cause deviations between values from the analytical expression and actual electron-to-neutral number density ratios. the analytical expression is thus not strictly meant as predicting the actual electron-to-neutral number density ratio, but is useful in comparisons with observations as an indicator of processes at play in the cometary coma. | on the electron-to-neutral number density ratio in the coma of comet 67p/churyumov-gerasimenko: guiding expression and sources for deviations |
titan's thick n2-ch4 atmosphere is unlike any in the solar system, and its origin has been shrouded in mystery for over half a century. here, i perform a detailed analysis of chemical and isotopic data from the cassini-huygens mission to develop the hypothesis that titan's (non-photochemical) atmospheric gases came from deep within. it is suggested that titan's ch4, n2, and noble gases originated in a rocky core buried inside the giant satellite, and hydrothermal and cryovolcanic processes were critical to the creation of titan's atmosphere. mass balance and chemical equilibrium calculations demonstrate that all aspects of this hypothesis can be considered geochemically plausible with respect to contemporary observational, experimental, and theoretical knowledge. specifically, i show that a rocky core with a bulk noble gas content similar to that in ci carbonaceous meteorites would contain sufficient 36ar and 22ne to explain their reported abundances. i also show that henry's law constants for noble gases in relevant condensed phases can be correlated with the size of their atoms, which leads to expected mixing ratios for 84kr (∼0.2 ppbv) and 132xe (∼0.01 ppbv) that can explain why these species have yet to be detected (huygens upper limit <10 ppbv). the outgassing of volatiles into titan's atmosphere may be restricted by the stability of clathrate hydrates in titan's interior. the noble gas geochemistry also provides significant new insights into the origin of n2 and ch4 on titan, as i find that ar and n2, and kr and ch4 should exhibit similar phase partitioning behavior on titan. one implication is that over 95% of titan's n2 may still reside in the interior. another key result is that the upper limit from the huygens gc-ms on the kr/ch4 ratio in titan's atmosphere is far too low to be consistent with accretion of primordial ch4 clathrate, which motivates me to consider endogenic production of ch4 from co2 as a result of geochemical reactions between liquid water and anhydrous rock (i.e., serpentinization). i show that sufficient ch4 can be produced to replenish titan's atmosphere many times over in the face of irreversible photolysis and escape of ch4, which is consistent with the favored model of episodic cryovolcanic outgassing. there should also have been enough nh3 inside titan so that its thermal decomposition in a hot rocky core can generate the observed atmospheric n2, and if correct this model would imply that titan's interior has experienced vigorous hydrothermal processing. the similarity in 14n/15n between cometary nh3 and titan's n2 is consistent with this picture. as for the isotopes in ch4, i show that their observed relative abundances can be explained by low-temperature (∼20 °c) equilibria with liquid water (d/h) and the expected aqueous alteration mineral calcite (12c/13c), provided that nickel was present to catalyze isotopic exchange over geologic timescales. the present hypothesis is chemically and isotopically consistent with the cassini-huygens data, and it implies that the formation of titan's atmosphere would have been an unavoidable consequence of volatile processing that was driven by the geophysical evolution of the interior. if all of the atmospheric n2 and ch4 have an endogenic origin, then no more than ∼1.6 times the present amount of n2 can be lost by photochemistry and escape over the history of the atmosphere; and the d/h ratio in titan's water should be much lower than that in enceladus' plume. given its important implications to the origin and evolution of volatiles in the outer solar system, we must go back to titan to acquire additional isotopic data that will allow more rigorous tests of models of the origin of its atmosphere. i predict the following isotopic ratios: 20ne/22ne ≈ 8.9, 36ar/38ar ≈ 5.3, (14n/15n)nh3 ≈ 130-170 , (12c/13c)co2 ≈ 84 , (d/h)h2o ≈ 1.7 ×10-4 ; and recommend that future in situ instrumentation have the capability to measure the rare isotopologues of n2 and ch4, which represent previously unconsidered but potentially valuable sources of geochemical information on the origin and evolution of titan's atmosphere. | noble gases, nitrogen, and methane from the deep interior to the atmosphere of titan |
we interpret recent observations of the secondary dust ejecta cloud around the moon from the lunar dust experiment (ldex) on board the nasa lunar atmosphere and dust environment explorer (ladee) spacecraft with help from dynamical models of meteoroids. results suggest that in order to match the spatial structure of observed ejecta profiles, the flux of meteoroids on the moon must be primarily provided by short-period comets with an excess ratio of at least 1.3:1 compared to long-period comets. this ratio increases significantly if the dependence of the ejecta yield on impactor velocity is stronger than generally believed. the model accounts for the orbital geometry of ladee and shows no indication of a large asymmetry in the meteoroid flux impacting from the helion and anti-helion directions. | constraining the ratio of micrometeoroids from short- and long-period comets at 1 au from ladee observations of the lunar dust cloud |
context. detection of molecular oxygen and prediction of its abundance have long been a challenge for astronomers. the low abundances observed in few interstellar sources are well above the predictions of current astrochemical models. during the rosetta mission, an unexpectedly high abundance of o2 was discovered in the comet 67p/churyumov-gerasimenko's coma. a strong correlation between o2 and h2o productions is observed, whereas no such correlation is observed between o2 and either of co or n2.aims: we suggest that the o2 molecule may be formed during the evaporation of water ice. we propose a possible reaction: the dismutation of h2o2 (2 h2o2-→ 2 h2o + o2), a molecule which should be co-produced during the water ice mantle growth on dust grains. we aim to test this hypothesis under realistic experimental conditions.methods: we performed two sets of experiments. they consist of producing a mixture of d2o and d2o2 via the reaction of o2 and d on a surface held at 10 k. the first set is made on a silicate substrate, and explores the limit of thin films, in order to prevent any complication due to trapping during the desorption. the second set is performed on a pre-deposited h2o ice substrate and mimics the desorption of mixed ice.results: in thin films, o2 is produced by the dismutation of h2o2, even at temperatures as low as 155 k. mixed with water, h2o2 desorbs after the water ice sublimation and even more desorption of o2 is observed.conclusions: h2o2, synthesised during the growth of interstellar ices (or by later processing), desorbs at the latest stage of the water sublimation and undergoes the dismutation reaction. therefore an o2 release in the gas phase should occur at the end of the evaporation of ice mantles. temperature gradients along the geometry of clouds, or interior of comets, should blend the different stages of the sublimation. averaged along the whole process, a mean value of the o2/h2o ratio of a few percent in the gas phase seems plausible. | production of o2 through dismutation of h2o2 during water ice desorption: a key to understanding comet o2 abundances |
comet 103p/hartley 2 has diurnally controlled, co2-driven activity on the tip of the small lobe of its bilobate nucleus. such activity is unique among the comet nuclei visited by spacecraft, and suggests that co2 ice is very near the surface, which is inconsistent with our expectations of an object that thermophysically evolved for ∼45 million years prior to entering the jupiter family of comets. here we explain this pattern of activity by showing that a very plausible recent episode of rapid rotation (rotation period of ∼11 [10-13] h) would have induced avalanches in hartley 2's currently active regions that excavated down to co2-rich ices and activated the small lobe of the nucleus. at hartley 2's current rate of spindown about its principal axis, the nucleus would have been spinning fast enough to induce avalanches ∼3-4 orbits prior to the dixi flyby (∼1984-1991). this coincides with hartley 2's discovery in 1986, and implies that the initiation of co2 activity facilitated the comet's discovery. during the avalanches, the sliding material would either be lofted off the surface by gas activity, or possibly gained enough momentum moving downhill (toward the tip of the small lobe) to slide off the tip of the small lobe. much of this material would have failed to reach escape velocity, and would reimpact the nucleus, forming debris deposits. the similar size frequency distribution of the mounds observed on the surface of hartley 2 and chunks of material in its inner coma suggest that the 20-40 m mounds observed by the dixi mission on the surface of hartley 2 are potentially these fallback debris deposits. as the nucleus spun down (rotation period increased) from a period of ∼11-18.34 h at the time of the dixi flyby, the location of potential minima, where materials preferentially settle, migrated about the surface, allowing us to place relative ages on most of the terrains on the imaged portion of the nucleus. | rotationally induced surface slope-instabilities and the activation of co2 activity on comet 103p/hartley 2 |
we present analysis of high spectral resolution nir spectra of co and h2o in comet c/2009 p1 (garradd) taken during its 2011-2012 apparition with the cshell instrument on nasa's infrared telescope facility (irtf). we also present analysis of observations of atomic oxygen in comet garradd obtained with the arces echelle spectrometer mounted on the arc 3.5-m telescope at apache point observatory and the tull coude spectrograph on the harlan j. smith 2.7-m telescope at mcdonald observatory. the observations of atomic oxygen serve as a proxy for h2o and co2. we confirm the high co abundance in comet garradd and the asymmetry in the co/h2o ratio with respect to perihelion reported by previous studies. from the oxygen observations, we infer that the co2/h2o ratio decreased as the comet moved towards the sun, which is expected based on current sublimation models. we also infer that the co2/h2o ratio was higher pre-perihelion than post-perihelion. we observe evidence for the icy grain source of h2o reported by several studies pre-perihelion, and argue that this source is significantly less abundant post-perihelion. since h2o, co2, and co are the primary ices in comets, they drive the activity. we use our measurements of these important volatiles in an attempt to explain the evolution of garradd's activity over the apparition. | evolution of h2o, co, and co2 production in comet c/2009 p1 garradd during the 2011-2012 apparition |
we report on initial results from 20 days’ worth of transiting exoplanet survey satellite spacecraft observations of comet 46p/wirtanen. the long-duration, high-cadence measurements show a 2018 september 26 outburst that exhibited a two-phase, 0.5 mag brightening profile, and may be the best temporally characterized natural outburst ever recorded. gas velocities from the outburst peaked at 800 {{m}} {{{s}}}-1, while dust expanded at only 10s of {{m}} {{{s}}}-1. coadded images also revealed a previously unreported dust trail that extends beyond the 24° field of view. | first results from tess observations of comet 46p/wirtanen |
ice sintering is a form of metamorphism that drives the microstructural evolution of an aggregate of grains through surface and volume diffusion. this leads to an increase in the grain-to-grain contact area (neck) and density of the aggregate over time, resulting in the evolution of its strength, porosity, thermal conductivity, and other properties. this process plays an important role in the evolution of icy planetary surfaces, though its rate and nature are not well constrained. in this study, we explore the model of swinkels and ashby (1981, https://doi.org/10.1016/0001-6160(81)90154-1) and assess the extent to which it can be used to quantify sintering timescales for water ice. we compare predicted neck growth rates to new and historical observations of ice sintering and find agreement to some studies at the order of magnitude level. first-order estimates of neck growth timescales on planetary surfaces show that ice may undergo significant modification over geologic timescales, even in the outer solar system. densification occurs over much longer timescales, suggesting that some surfaces may develop cohesive, but porous, crusts. sintering rates are extremely sensitive to temperature and grain size, occurring faster in warmer aggregates of smaller grains. this suggests that the microstructural evolution of ices may vary not only throughout the solar system but also spatially across the surface and in the near surface of a given body. our experimental observations of complex grain growth and mass redistribution in ice aggregates point to components of the model that may benefit from improvement and areas where additional laboratory studies are needed. | the microstructural evolution of water ice in the solar system through sintering |
measurements of the nitrogen isotopic ratio in solar system comets show a constant value, ≈140, which is three times lower than the protosolar ratio, a highly significant difference that remains unexplained. observations of static starless cores at early stages of collapse confirm the theoretical expectation that nitrogen fractionation in interstellar conditions is marginal for most species. yet, observed isotopic ratios in n2h+ are at variance with model predictions. these gaps in our understanding of how the isotopic reservoirs of nitrogen evolve, from interstellar clouds to comets, and, more generally, to protosolar nebulae, may have their origin in missing processes or misconceptions in the chemistry of interstellar nitrogen. so far, theoretical studies of nitrogen fractionation in starless cores have addressed the quasi-static phase of their evolution such that the effect of dynamical collapse on the isotopic ratio is not known. in this paper, we investigate the fractionation of 14n and 15n during the gravitational collapse of a pre-stellar core through gas-phase and grain adsorption and desorption reactions. the initial chemical conditions, which are obtained in steady state after typically a few myr, show low degrees of fractionation in the gas phase, in agreement with earlier studies. however, during collapse, the differential rate of adsorption of 14n- and 15n-containing species onto grains results in enhanced 15n:14n ratios, in better agreement with the observations. furthermore, we find differences in the behavior, with increasing density, of the isotopic ratio in different species. we find that the collapse must take place on approximately one free-fall timescale, based on the co abundance profile in l183. various chemical effects that bring models into better agreement with observations are considered. thus, the observed values of 14n2h+:n15nh+ and 14n2h+:15nnh+ could be explained by different temperature dependences of the rates of dissociative recombination of these species. we also study the impact of the isotopic sensitivity of the charge-exchange reaction of n2 with he+ on the fractionation of ammonia and its singly deuterated analog and find significant depletion in the 15n variants. however, these chemical processes require further experimental and theoretical investigations, especially at low temperature. these new findings, such as the depletion-driven fractionation, may also be relevant to the dense, uv-shielded regions of protoplanetary disks. | depletion and fractionation of nitrogen in collapsing cores |
magnetic fields inconsistent with draped interplanetary magnetic fields and crustal fields have been observed on mars. considering the discovery of a global looping magnetic field around the venusian magnetotail and the similarities in the solar wind interactions between mars and venus, we use mars atmosphere and volatile evolution observations to investigate the global looping field on mars and its formation mechanism. it is found that a global looping field also exists on mars; therefore, this type of global looping field is a common feature of unmagnetized planetary bodies with ionospheres, and therefore should also exist on titan and near-sun comets. the comparison of the looping fields on mars and venus shows that the looping field is stronger on mars. solar wind azimuthal flows around the magnetotail toward the -{\boldsymbol{e}} magnetotail polar region ({x}mse}< 0,{y}mse}=0,{z}mse}< -1{r}m) are observed. we illustrate that the looping field can be formed by bending the draped field lines with these azimuthal flows, and that these azimuthal flows are associated with heavy ion plumes along the +{\boldsymbol{e}} direction that are expected to be stronger on mars than venus. the current system associated with the looping field and its possible connection with the nightside ionosphere formations and ion escapes on mars and venus are discussed. | the induced global looping magnetic field on mars |
dunes, dune fields, and ripples are unique and useful records of the interaction between wind and granular materials - finding such features on a planetary surface immediately suggests certain information about climate and surface conditions (at least during the dunes' formation and evolution). additionally, studies of dune characteristics under non-earth conditions allow for "tests" of aeolian process models based primarily on observations of terrestrial features and dynamics, and refinement of the models to include consideration of a wider range of environmental and planetary conditions. to-date, the planetary aeolian community has found and studied dune fields on mars, venus, and the saturnian moon titan. additionally, we have observed candidate "aeolian bedforms" on comet 67p/churyumov-gerasimenko, the jovian moon io, and - most recently - pluto. in this paper, we hypothesize that the progression of investigations of aeolian bedforms and processes on a particular planetary body follows a consistent sequence - primarily set by the acquisition of data of particular types and resolutions, and by the maturation of knowledge about that planetary body. we define that sequence of generated knowledge and new questions (within seven investigation phases) and discuss examples from all of the studied bodies. the aim of such a sequence is to better define our past and current state of understanding about the aeolian bedforms of a particular body, to highlight the related assumptions that require re-analysis with data acquired during later investigations, and to use lessons learned from planetary and terrestrial aeolian studies to predict what types of investigations could be most fruitful in the future. | our evolving understanding of aeolian bedforms, based on observation of dunes on different worlds |
a severe reduction of greenhouse gas emissions is necessary to reach the objectives of the paris agreement. the implementation and continuous evaluation of mitigation measures requires regular independent information on emissions of the two main anthropogenic greenhouse gases, carbon dioxide (co2) and methane (ch4). our aim is to employ an observation-based method to determine regional-scale greenhouse gas emission estimates with high accuracy. we use aircraft- and ground-based in situ observations of ch4, co2, carbon monoxide (co), and wind speed from two research flights over the upper silesian coal basin (uscb), poland, in summer 2018. the flights were performed as a part of the carbon dioxide and methane (comet) mission above this european ch4 emission hot-spot region. a kriging algorithm interpolates the observed concentrations between the downwind transects of the trace gas plume, and then the mass flux through this plane is calculated. finally, statistic and systematic uncertainties are calculated from measurement uncertainties and through several sensitivity tests, respectively. for the two selected flights, the in-situ-derived annual ch4 emission estimates are 13.8±4.3 and 15.1±4.0 kg s-1, which are well within the range of emission inventories. the regional emission estimates of co2, which were determined to be 1.21±0.75 and 1.12±0.38 t s-1, are in the lower range of emission inventories. co mass balance emissions of 10.1±3.6 and 10.7±4.4 kg s-1 for the uscb are slightly higher than the emission inventory values. the ch4 emission estimate has a relative error of 26 %-31 %, the co2 estimate of 37 %-62 %, and the co estimate of 36 %-41 %. these errors mainly result from the uncertainty of atmospheric background mole fractions and the changing planetary boundary layer height during the morning flight. in the case of co2, biospheric fluxes also add to the uncertainty and hamper the assessment of emission inventories. these emission estimates characterize the uscb and help to verify emission inventories and develop climate mitigation strategies. | estimating ch4, co2 and co emissions from coal mining and industrial activities in the upper silesian coal basin using an aircraft-based mass balance approach |
we present an extensive data set of ground-based observations and models of the dust environment of comet 67p/churyumov-gerasimenko covering a large portion of the orbital arc from about 4.5 au pre-perihelion through 3.0 au post-perihelion, acquired during the current orbit. in addition, we have also applied the model to a dust trail image acquired during this orbit, as well as to dust trail observations obtained during previous orbits, in both the visible and the infrared. the results of the monte carlo modelling of the dust tail and trail data are generally consistent with the in situ results reported so far by the rosetta instruments optical, spectroscopic, and infrared remote imaging system (osiris) and grain impact analyser and dust accumulator (giada). we found the comet nucleus already active at 4.5 au pre-perihelion, with a dust production rate increasing up to ∼3000 kg s-1 some 20 d after perihelion passage. the dust size distribution at sizes smaller than r = 1 mm is linked to the nucleus seasons, being described by a power law of index -3.0 during the comet nucleus southern hemisphere winter but becoming considerably steeper, with values between -3.6 and -4.3, during the nucleus southern hemisphere summer, which includes perihelion passage (from about 1.7 au inbound to 2.4 au outbound). this agrees with the increase of the steepness of the dust size distribution found from giada measurements at perihelion showing a power index of -3.7. the size distribution at sizes larger than 1 mm for the current orbit is set to a power law of index -3.6, which is near the average value of insitu measurements by osiris on large particles. however, in order to fit the trail data acquired during past orbits previous to the 2009 perihelion passage, a steeper power-law index of -4.1 has been set at those dates, in agreement with previous trail modelling. the particle sizes are set at a minimum of r = 10 μm, and a maximum size, which increases with decreasing heliocentric distance, in the 1-40 cm radius domain. the particle terminal velocities are found to be consistent with the in situ measurements as derived from the instrument giada on board rosetta. | the dust environment of comet 67p/churyumov-gerasimenko: results from monte carlo dust tail modelling applied to a large ground-based observation data set |
we present a detailed study of the cometary ionospheric response to a cometary brightness outburst using in situ measurements for the first time. the comet 67p/churyumov-gerasimenko (67p) at a heliocentric distance of 2.4 au from the sun, exhibited an outburst at ~1000 ut on 19 february 2016, characterized by an increase in the coma surface brightness of two orders of magnitude. the rosetta spacecraft monitored the plasma environment of 67p from a distance of 30 km, orbiting with a relative speed of ~0.2 m s-1. the onset of the outburst was preceded by pre-outburst decreases in neutral gas density at rosetta, in local plasma density, and in negative spacecraft potential at ~0950 ut. in response to the outburst, the neutral density increased by a factor of ~1.8 and the local plasma density increased by a factor of ~3, driving the spacecraft potential more negative. the energetic electrons (tens of ev) exhibited decreases in the flux of factors of ~2 to 9, depending on the energy of the electrons. the local magnetic field exhibited a slight increase in amplitude (~5 nt) and an abrupt rotation (~36.4°) in response to the outburst. a weakening of 10-100 mhz magnetic field fluctuations was also noted during the outburst, suggesting alteration of the origin of the wave activity by the outburst. the plasma and magnetic field effects lasted for about 4 h, from ~1000 ut to 1400 ut. the plasma densities are compared with an ionospheric model. this shows that while photoionization is the main source of electrons, electron-impact ionization and a reduction in the ion outflow velocity need to be accounted for in order to explain the plasma density enhancement near the outburst peak. | impact of a cometary outburst on its ionosphere. rosetta plasma consortium observations of the outburst exhibited by comet 67p/churyumov-gerasimenko on 19 february 2016 |
as rosetta was orbiting comet 67p/churyumov-gerasimenko, the ion and electron sensor detected negative particles with angular distributions like those of the concurrently measured solar wind protons but with fluxes of only about 10% of the proton fluxes and energies of about 90% of the proton energies. using well-known cross sections and energy-loss data, it is determined that the fluxes and energies of the negative particles are consistent with the production of h- ions in the solar wind by double charge exchange with molecules in the coma. | charge exchange in cometary coma: discovery of h- ions in the solar wind close to comet 67p/churyumov-gerasimenko |
according to current theories of the formation of stellar systems, comets belong to the oldest and most pristine class of bodies to be found around a star. when approaching the sun, the nucleus shows increasing activity and a pressure increase inside the material causes sublimated and trapped gas molecules to stream away from their regions of origin towards the surface. the present work studies two essential mechanisms of gas transport through a porous layer, namely the darcy and the knudsen flow. gas flow measurements are performed in the laboratory with several analogue materials, which are mimicking dry cometary surface properties. in this first series of measurements, the aim was to separate gas transport properties from internal sources like local sublimation or release of trapped gases. therefore, only dry granular materials were used and maintaining a low temperature environment was unnecessary. the gas permeability and the knudsen diffusion coefficient of the sample materials are obtained, thereby representing the relative importance of the respective flow mechanism. the experiments performed with air at a stable room temperature show that the grain size distribution and the packing density of the sample play a major role for the permeability of the sample. the larger the grains, the bigger the permeability and the knudsen diffusion coefficient. from the latter, we estimated effective pore diameters. finally, we explain how these parameters can be adapted to obtain the gas flow properties of the investigated analogue materials under the conditions to be expected on the comet. | viscous and knudsen gas flow through dry porous cometary analogue material |
a detailed exploration of the potential energy surface of quinoline cation (c9h7n·+) is carried out to extend the present understanding of its fragmentation mechanisms. density functional theory calculations have been performed to explore new fragmentation schemes, giving special attention to previously unexplored pathways, such as isomerization and elimination of hnc. the isomerization mechanisms producing five- to seven-membered ring intermediates are described and are found to be a dominant channel both energetically and kinetically. energetically competing pathways are established for the astrochemically important hnc-loss channel, which has hitherto never been considered in the context of the loss of a 27 amu fragment from the parent ions. elimination of acetylene was also studied in great detail. overall, the computational results are found to complement the experimental observations from the concurrently conducted pepico investigation. these could potentially open the doors for rich and interesting vacuum ultraviolet radiation-driven chemistry on planetary atmospheres, meteorites, and comets. | photodissociation of quinoline cation: mapping the potential energy surface |
since their formation in the protosolar nebula some ∼4.5 billion years ago, comets are in storage in cold distant regions of the solar system, the kuiper belt/scattered disk or oort cloud. therefore, they have been considered as mostly unaltered samples of the protosolar nebula. however, a significant dose of energy is deposited by galactic cosmic rays (gcrs) into the outermost tens of meters of cometary nuclei during their stay in the oort cloud or kuiper belt. we investigate the impact of energy deposition by gcrs on cometary nuclei. we use experimental results from laboratory experiments and the energy deposition by gcrs estimated by gronoff et al. (2020), to discuss the depth down to which the cometary nucleus is altered by gcrs. we show that gcrs do not significantly change the isotopic composition of cometary material but modify the chemical composition and the ice structure in the outer layers of the nucleus, which cannot be considered as pristine solar nebula material. we discuss the effect of the collisional history of comets on the distribution of processed material inside the nucleus and its implication on the observation of comets. | the effect of cosmic rays on cometary nuclei. ii. impact on ice composition and structure |
context. formamide (nh2hco) and isocyanic acid (hnco) have been observed as gaseous species in several astronomical environments such as cometary comae and pre- and proto-stellar objects. a debate is open on the formation route of those molecules, in particular if they are formed by chemical reactions in the gas phase and/or on grains. in this latter case it is relevant to understand if the formation occurs through surface reactions or is induced by energetic processing.aims: we present arguments that support the formation of formamide in the solid phase by cosmic-ion-induced energetic processing of ices present as mantles of interstellar grains and on comets. formamides, along with other molecules, are expelled in the gas phase when the physical parameters are appropriate to induce the desorption of ices.methods: we have performed several laboratory experiments in which ice mixtures (h2o:ch4:n2, h2o:ch4:nh3, and ch3oh:n2) were bombarded with energetic (30-200 kev) ions (h+ or he+). ftir spectroscopy was performed before, during, and after ion bombardment. in particular, the formation of hnco and nh2hco was measured quantiatively.results: energetic processing of ice can quantitatively reproduce the amount of nh2hco observed in cometary comae and in many circumstellar regions. hnco is also formed, but additional formation mechanisms are requested to quantitatively account for the astronomical observations.conclusions: we suggest that energetic processing of ices in the pre- and proto-stellar regions and in comets is the main mechanism to produce formamide, which, once it is released in the gas phase because of desorption of ices, is observed in the gas phase in these astrophysical environments. | synthesis of formamide and isocyanic acid after ion irradiation of frozen gas mixtures |
one of the scientific objectives of the rosetta mission is to investigate the diamagnetic cavity of comet 67p/churyumov-gerasimenko. we employed combined data of several instruments of the rosetta plasma consortium to identify and study diamagnetic cavity crossing events. using electron data from the ion electron sensor to complement the magnetometer data enabled us to work out a search criterion for the cavity crossing events based on a unique signature we identified in the electron spectrum. although this search criterion is insufficient to find all the cavity events, we were able to find an abundance of more than one hundred cavity crossings in the data obtained in the summer of 2015. this unexpectedly high number of events allowed us to study their common features, as well as the shape and extent of the diamagnetic cavity in the terminator plane. the results suggest that in the summer of 2015 there was a cavity around comet 67p, which had a highly variable outer boundary. we present the effects of the diamagnetic cavity on the thermal and suprathermal electron and suprathermal ion content of the plasma, and also the probable mechanisms responsible for these charged particle signatures. | charged particle signatures of the diamagnetic cavity of comet 67p/churyumov-gerasimenko |
aims: we use four observational data sets, mainly from the rosetta mission, to constrain the activity pattern of the nucleus of comet 67p/churyumov-gerasimenko (67p).methods: we developed a numerical model that computes the production rate and non-gravitational acceleration of the nucleus of comet 67p as a function of time, taking into account its complex shape with a shape model reconstructed from osiris imagery. we used this model to fit three observational data sets: the trajectory data from flight dynamics; the rotation state as reconstructed from osiris imagery; and the water production measurements from rosina of 67p. the two key parameters of our model, adjusted to fit the three data sets all together, are the activity pattern and the momentum transfer efficiency (i.e., the so-called η parameter of the non-gravitational forces).results: we find an activity pattern that can successfully reproduce the three data sets simultaneously. the fitted activity pattern exhibits two main features: a higher effective active fraction in two southern super-regions ( 10%) outside perihelion compared to the northern regions (<4%), and a drastic rise in effective active fraction of the southern regions ( 25-35%) around perihelion. we interpret the time-varying southern effective active fraction by cyclic formation and removal of a dust mantle in these regions. our analysis supports moderate values of the momentum transfer coefficient η in the range 0.6-0.7; values η ≤ 0.5 or η ≥ 0.8 significantly degrade the fit to the three data sets. our conclusions reinforce the idea that seasonal effects linked to the orientation of the spin axis play a key role in the formation and evolution of dust mantles, and in turn, they largely control the temporal variations of the gas flux. | constraining models of activity on comet 67p/churyumov-gerasimenko with rosetta trajectory, rotation, and water production measurements |
"the supernova of 1604 marks a major turning point in the cosmological crisis of the sixteenth and seventeenth centuries. capturing the eyes and imagination of europe, it ignited an explosion of ideas that forever changed the face of science. variously interpreted as a comet or star, the new luminary brought together a broad network of scholars who debated the nature of the novelty and its origins in the universe. at the heart of the interdisciplinary discourse was johannes kepler, whose book on the new star (1606) assessed the many disputes of the day. beginning with several studies about kepler's book, the authors of the present volume explore the place of kepler and the 'new star' in early modern culture and religion, and how contemporary debate shaped the course of science down to the present day. contributors are: (1) dario tessicini, (2) christopher m. graney, (3) javier luna, (4) patrick j. boner, (5) jonathan regier, (6) aviva rothman, (7) miguel á. granada, (8) pietro daniel omodeo, (9) matteo cosci, and (10) william p. blair" | kepler's new star (1604): context and controversy |
hcn is a commonly observed molecule in solar system bodies and in interstellar environments. its abundance with respect to cn is a proposed tracer of uv exposure. hcn is also frequently used to probe the thermal history of objects, by measuring its degree of nitrogen fractionation. to address the utility of hcn as a probe of disks, we present atacama large (sub-) millimeter array observations of cn, hcn, h13cn, and hc15n toward the protoplanetary disk around herbig ae star mwc 480, and of cn and hcn toward the disk around t tauri star dm tau. emission from all molecules is clearly detected and spatially resolved, including the first detection of hc15n in a disk. toward mwc 480, cn emission extends radially more than 1″ exterior to the observed cut-off of hcn emission. quantitative modeling further reveals very different radial abundance profiles for cn and hcn, with best-fit outer cut-off radii of >300 au and 110 ± 10 au, respectively. this result is in agreement with model predictions of efficient hcn photodissociation into cn in the outer-part of the disk where the vertical gas and dust column densities are low. no such difference in cn and hcn emission profiles are observed toward dm tau, suggestive of different photochemical structures in herbig ae and t tauri disks. we use the hcn isotopologue data toward the mwc 480 disk to provide the first measurement of the 14n/15n ratio in a disk. we find a low disk averaged 14n/15n ratio of 200 ± 100, comparable to what is observed in cloud cores and comets, demonstrating interstellar inheritance and/or efficient nitrogen fractionation in this disk. | cyanide photochemistry and nitrogen fractionation in the mwc 480 disk |
imidacloprid (imid), a systemic neonicotinoid insecticide, is broadly used worldwide. it is reported to contaminate aquatic systems. this study was proposed to evaluate oxidative stress and genotoxicity of imid on nile tilapia (oreochromis niloticus) and the protective effect of ascorbic acid (asc). o. niloticus juveniles (30.4 ± 9.3 g, 11.9 ± 1.3 cm) were divided into six groups (n = 10/replicate). for 21 days, two groups were exposed to sub-lethal concentrations of imid (8.75 ppm, 1/20 of 72 h-lc50 and 17.5 ppm, 1/10 of 72 h-lc50); other two groups were exposed to asc (50 ppm) in combination with imid (8.75 and 17.5 ppm); one group was exposed to asc (50 ppm) in addition to a group of unexposed fish which served as controls. oxidative stress was assessed in the liver where the level of enzymatic activities including superoxide dismutase (sod), catalase (cat) and glutathione peroxidase (gpx) in addition to mrna transcripts and, lipid peroxidation (lpo) were evaluated. moreover, mitotic index (mi) and comet assay were performed, in addition, the erythrocytic micronucleus (mn), and nuclear abnormalities (na) were observed to assess genotoxicity in fish. imid exposure induced significant (p ˂ 0.05) changes in the antioxidant profile of the juveniles' liver by increasing the activities and gene expression of sod, cat and gpx as well as elevating the levels of lpo. dna strand breaks in gill cells, erythrocytes and hepatocytes along with erythrocytic mn and na were also significantly elevated in imid-exposed groups. mi showed a significant (p ˂ 0.05) decrease associated with imid exposure. asc administration induced a significant amelioration towards the imid toxicity (8.75 and 17.5 ppm). a significant protective potency against the genotoxic effects of imid was evidenced in asc co-treated groups. collectively, results highlight the importance of asc as a protective agent against imid-induced oxidative stress and genotoxicity in o. niloticus juveniles. | the role of ascorbic acid combined exposure on imidacloprid-induced oxidative stress and genotoxicity in nile tilapia |
this study provides the first observations of plutogenic ions and their unique interaction with the solar wind. we find ~20% solar wind slowing that maps to a point only ~4.5 rp upstream of pluto and a bow shock most likely produced by comet-like mass loading. the pluto obstacle is a region of dense heavy ions bounded by a "plutopause" where the solar wind is largely excluded and which extends back >100 rp into a heavy ion tail. the upstream standoff distance is at only ~2.5 rp. the heavy ion tail contains considerable structure, may still be partially threaded by the interplanetary magnetic field (imf), and is surrounded by a light ion sheath. the heavy ions (presumably ch4+) have average speed, density, and temperature of ~90 km s-1, ~0.009 cm-3, and ~7 × 105 k, with significant variability, slightly increasing speed/temperature with distance, and are n-s asymmetric. density and temperature are roughly anticorrelated yielding a pressure ~2 × 10-2 ppa, roughly in balance with the interstellar pickup ions at ~33 au. we set an upper bound of <30 nt surface field at pluto and argue that the obstacle is largely produced by atmospheric thermal pressure like venus and mars; we also show that the loss rate down the tail (~5 × 1023 s-1) is only ~1% of the expected total ch4 loss rate from pluto. finally, we observe a burst of heavy ions upstream from the bow shock as they are becoming picked up and tentatively identify an imf outward sector at the time of the nh flyby. | pluto's interaction with the solar wind |
we simulate the stresses induced by temperature changes in a putative hard layer near the surface of comet 67p/churyumov-gerasimenko with a thermo-viscoelastic model. such a layer could be formed by the recondensation or sintering of water ice (and dust grains), as suggested by laboratory experiments and computer simulations, and would explain the high compressive strength encountered by experiments on board the philae lander. changes in temperature from seasonal insolation variation penetrate into the comet's surface to depths controlled by the thermal inertia, causing the material to expand and contract. modelling this with a maxwellian viscoelastic response on a spherical nucleus, we show that a hard, icy layer with similar properties to martian permafrost will experience high stresses: up to tens of mpa, which exceed its material strength (a few mpa), down to depths of centimetres to a metre. the stress distribution with latitude is confirmed qualitatively when taking into account the comet's complex shape but neglecting thermal inertia. stress is found to be comparable to the material strength everywhere for sufficient thermal inertia (≳50 j m-2 k-1 s-1/2) and ice content (≳45% at the equator). in this case, stresses penetrate to a typical depth of 0.25 m, consistent with the detection of metre-scale thermal contraction crack polygons all over the comet. thermal fracturing may be an important erosion process on cometary surfaces which breaks down material and weakens cliffs. | thermal fracturing on comets. applications to 67p/churyumov-gerasimenko |
context. because comets are part of the most primitive bodies of our solar system, establishing their chemical composition and comparing them to other astrophysical bodies gives new constraints on the formation and evolution of organic matter throughout the solar system. for two years, the time-of-flight secondary ion mass spectrometer cometary secondary ion mass analyzer (cosima) on board the rosetta orbiter performed in situ analyses of the dust particles ejected from comet 67p/churyumov-gerasimenko (67p).aims: the aim is to determine the h/c elemental ratio of the refractory organic component contained in cometary particles of 67p.methods: we analyzed terrestrial and extraterrestrial calibration samples using the cosima ground-reference model. exploiting these calibration samples, we provide calibration lines in both positive and negative ion registration modes. thus, we are now able to measure the cometary h/c elemental ratio.results: the mean h/c value is 1.04 ± 0.16 based on 33 different cometary particles. consequently, the h/c atomic ratio is on average higher in cometary particles of 67p than in even the most primitive insoluble organic matter extracted from meteorites.conclusions: these results imply that the refractory organic matter detected in dust particles of 67p is less unsaturated than the material in meteorites. | h/c elemental ratio of the refractory organic matter in cometary particles of 67p/churyumov-gerasimenko |
aims: we provide a measurement of the seasonal evolution of the dust deposit erosion and accretion in the hapi region of comet 67p/churyumov-gerasimenko with a vertical accuracy of 0.2-0.9 m.methods: we used osiris narrow angle camera images with a spatial scale of lower than 1.30 m px-1 and developed a tool to monitor the time evolution of 22 boulder heights with respect to the surrounding dust deposit. the tool is based on the measurement of the shadow length projected by the boulder on the surrounding pebble deposit. assuming the position of the boulders does not change during the observational period, boulder height variations provide an indication of how the thickness of the surrounding dust layer varies over time through erosion and accretion phenomena.results: we measured an erosion of the dust deposit of 1.7 ± 0.2 m during the inbound orbit until 12 december, 2014. this value nearly balances the fallout from the southern hemisphere during perihelion cometary activity. during the perihelion phase, the dust deposit then increased by 1.4 ± 0.8 m. this is interpreted as a direct measurement of the fallout thickness. by comparing the erosion rate and dust volume loss rate at the hapi region measured in the coma, the fallout represents ~96% in volume of the ejecta. the amount of the eroded pristine material from the southern hemisphere, together with its subsequent transport and fallout on the nucleus, led us to discuss the pristine water ice abundance in comet 67p. we determine that the refractory-to-ice mass ratio ranges from 6 to 110 in the perihelion-eroded pristine nucleus, providing a pristine ice mass fraction of (8 ± 7)% in mass. | time evolution of dust deposits in the hapi region of comet 67p/churyumov-gerasimenko |
context. the landing and rebound of the philae lander, which was part of the esa rosetta mission, enabled us to study the mechanical properties of the surface of comet 67p/churyumov-gerasimenko, because we could use philae as an impact probe.aims: the aim is to approximate the descent and rebound trajectory of the philae lander and use this information to derive the compressive strength of the surface material from the different surface contacts and scratches created during the final touchdown. combined with laboratory measurements, this can give an insight into what comets are made of and how they formed.methods: we combined observations from the romap magnetometer on board philae with observations made by the rosetta spacecraft, particularly by the osiris camera system and the rpc-mag magnetometer. additionally, ballistic trajectory and collision modeling was performed. these results are placed in context using laboratory measurements of the compressibility of different materials.results: it was possible to reconstruct possible trajectories of philae and determine that a pressure of 100 pa is enough to compress the surface material up to a depth of 20 cm. considering all errors, the derived compressive strength shows little dependence on location, with an overall upper limit for the surface compressive strength of 800 pa. | compressive strength of comet 67p/churyumov-gerasimenko derived from philae surface contacts |
recent models find that nuclei of comets are a mixture of water-rich and water-poor cm-sized pebbles. we aim to fit the correlation of the deuterium-to-hydrogen ratio, d/h, with the nucleus active area fraction. pebble parameters, constrained by the rosetta mission data, depend on where pebbles accreted in the protoplanetary disc. the diversity of comets depends on the fraction of water-rich versus water-poor pebbles in each nucleus. our model explains why the d/h values correlate to the nucleus active area fraction, and also implies that: (i) the seasonal colour cycle of the nucleus is opposite to the dust coma one; (ii) the perihelion dust size distribution is steeper than the average; (iii) water-ice content is anticorrelated with the amount of supervolatiles and with the d/h ratio. (iv) the fallout is composed of supervolatiles-depleted water-poor pebbles, whose d/h ratio was measured by the rosetta mission; (v) the d/h average in nuclei may be different than that measured in comae and cannot be retrieved by local sample-return missions; (vi) mixing of pebbles in the outer protoplanetary disc excludes any correlation of the water content, of the d/h ratio and of the nucleus size with the disc location where comets were born. | water and deuterium-to-hydrogen ratio in comets |
aims: the tensile strength of granular matter is of great importance to our understanding of the evolution of comets and to our attempts to reproduce processes on cometary surfaces in laboratory experiments. in this work, we investigate the tensile strength of three different materials and their mixtures, which can be used as cometary analog materials in the laboratory.methods: we used two types of siliceous dusts and granular water ice whose polydisperse particles were either angular or spherical. our samples were cooled to below 150 k to better simulate the conditions of a cometary surface and to avoid thermal alteration of the material. we used the brazilian disk test method to exert stress on the cooled samples and determine the tensile strength at the moment the samples broke.results: we find that the tensile strength of two component mixtures is strongly dominated by the component with the higher tensile strength. the materials made of mostly angular dust particles have a lower filling fraction, but a higher tensile strength compared to materials made of spherical particles. furthermore, the tensile strength of the cooled components is substantially lower than the tensile strength of the same components at room temperature. this implies that the surface energy of the investigated materials at low temperatures is significantly lower than previously assumed. | tensile strength of dust-ice mixtures and their relevance as cometary analog material |
remote sensing observations of dust particles ejected from comets provide important hints on the intimate nature of the materials composing these primitive objects. the measurement of dust coma backscattering ratio, bsr, defined as the ratio of the reflectance at phase angle 0° and 30°, helps tuning theoretical models aimed at solving the inverse scattering problem deriving information on the nature of the ejected particles. the rosetta/osiris camera sampled the coma phase function of comet 67p, with four series acquired at low phase angles from 2015 january to 2016 may. we also added previously published data to our analysis to increase the temporal resolution of our findings. we measured a bsr in the range ∼ [1.7-3.6], broader than the range found in literature from ground-based observations of other comets. we found that during the post-perihelion phase, the bsr is systematically larger than the classical cometary dust values only for nucleocentric distances smaller than ∼100 km. we explain this trend in terms of a cloud of chunks orbiting the nucleus at distances <100 km ejected during perihelion and slowly collapsing on the nucleus over a few months because of the coma gas drag. this also implies that the threshold particle size for the dust phase function to become similar to the nucleus phase function is between 2.5 mm and 0.1 m, taking into account previous rosetta findings. | the backscattering ratio of comet 67p/churyumov-gerasimenko dust coma as seen by osiris onboard rosetta |
the rosetta orbiter spectrometer for ion and neutral analysis (rosina) instrument onboard the rosetta spacecraft has measured molecular oxygen (o2) in the coma of comet 67p/churyumov-gerasimenko (67p/c-g) in surprisingly high abundances. these measurements mark the first unequivocal detection of o2 in a cometary environment. the large relative abundance of o2 in 67p/c-g despite its high reactivity and low interstellar abundance poses a puzzle for its origin in comet 67p/c-g, and potentially other comets. since its detection, there have been a number of hypotheses put forward to explain the production and origin of o2 in the comet. these hypotheses cover a wide range of possibilities from various in situ production mechanisms to protosolar nebula and primordial origins. here, we review the o2 formation mechanisms from the literature, and provide a comprehensive summary of the current state of knowledge of the sources and origin of cometary o2. | origin of molecular oxygen in comets: current knowledge and perspectives |
ex lup is the prototype of a class of pre-main-sequence eruptive stars defined by their repetitive outbursts lasting several months. in 2008 january-september ex lup underwent its historically largest outburst, brightening by about 4 mag in visual light. in previous studies we discovered ongoing silicate crystal formation in the inner disk during the outburst, but also noticed that the measured crystallinity fraction started decreasing after the source returned to the quiescent phase. here we present new observations of the 10 μm silicate feature, obtained with the midi and visir instruments at paranal observatory. the observations demonstrate that within five years practically all crystalline forsterite disappeared from the surface of the inner disk. we reconstruct this process by presenting a series of parametric axisymmetric radiative transfer models of an expanding dust cloud that transports the crystals from the terrestrial zone to outer disk regions where comets are supposed to form. it is possible the early sun also experienced similar flare-ups, and the forming planetesimals might have incorporated crystalline silicate material produced by such outbursts. finally, we discuss how far the location of the dust cloud could be constrained by future james webb space telescope observations. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programmes 091.c-0668 and 097.c-0639. | spectral evolution and radial dust transport in the prototype young eruptive system ex lup |
we present observations from the rosetta plasma consortium of the effects of stormy solar wind on comet 67p/churyumov-gerasimenko. four corotating interaction regions (cirs), where the first event has possibly merged with a coronal mass ejection, are traced from earth via mars (using mars express and mars atmosphere and volatile evolution mission) to comet 67p from october to december 2014. when the comet is 3.1-2.7 au from the sun and the neutral outgassing rate ∼1025-1026 s-1, the cirs significantly influence the cometary plasma environment at altitudes down to 10-30 km. the ionospheric low-energy (∼5 ev) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. the spacecraft potential drops below -20 v upon impact when the flux of electrons increases. the increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. during all events, the fluxes of suprathermal (∼10-100 ev) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. at impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around the comet. during two cir impact events, we observe possible plasma boundaries forming, or moving past rosetta, as the strong solar wind compresses the cometary plasma environment. we also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events. | solar wind interaction with comet 67p: impacts of corotating interaction regions |
the solar system's oort cloud can be perturbed by the galactic tide and by individual passing stars. these perturbations can inject oort cloud objects into the inner parts of the solar system, where they may be observed as the long-period comets (periods longer than 200 yr). using dynamical simulations of the oort cloud under the perturbing effects of the tide and 61 known stellar encounters, we investigate the link between long-period comets and encounters. we find that past encounters were responsible for injecting at least 5 per cent of the currently known long-period comets. this is a lower limit due to the incompleteness of known encounters. although the galactic tide seems to play the dominant role in producing the observed long-period comets, the non-uniform longitude distribution of the cometary perihelia suggests the existence of strong - but as yet unidentified - stellar encounters or other impulses. the strongest individual future and past encounters are probably hip 89825 (gliese 710) and hip 14473, which contribute at most 8 and 6 per cent to the total flux of long-period comets, respectively. our results show that the strength of an encounter can be approximated well by a simple proxy, which will be convenient for quickly identifying significant encounters in large data sets. our analysis also indicates a smaller population of the oort cloud than is usually assumed, which would bring the mass of the solar nebula into line with planet formation theories. | finding the imprints of stellar encounters in long-period comets |
context. mainly for historical reasons, nearly all of the current thermophysical models of dust activity rely on the poorly justified assumption of cohesionless dust lifted by a gas drag force against the weak nucleus gravity. the interpretation of rosetta data and our understanding of comet activity is particularly sensitive to this assumption.aims: we investigate the role that cohesion forces among the dust grains play in the evolution of temperature and pressure at the ice-dust interface and the resulting dust activity (lifting).methods: we used a 1d thermophysical numerical model that provides a realistic description of cohesion forces among dust aggregates. several conditions of solar illumination on the nucleus are investigated for the h2o, co, and co2 ices below the dust layer. we examine a wide range of dust grain sizes.results: the simulations confirm an increase in temperature and pressure at the ice boundary between the two model layers with respect to exposed pure ice. furthermore, we show that a non-monotonic behavior of temperature and pressure versus layer thickness is expected at the ice-dust interface for fine aggregates (of sizes ≤30 μm), but not for the larger grains. the ratio of vapor pressure to the physically determined tensile strength for various agglomerate sizes and layer thicknesses provides further evidence that the gas drag is not sufficient to remove dust grains of sizes <1 mm, which is a result of taking cohesion forces among the particles into account.conclusions: in the framework of the presented model, which can be considered common in terms of assumptions and physical parameters in the cometary community, the dust removal by a gas drag force is not a plausible physical mechanism. the sublimation of not only water ice, but also of super-volatile ice (i.e., co) is unable to remove dust grains for illumination conditions corresponding to 1.3 au. a way out of this impasse requires revision of the most common model assumption employed by the cometary community. | is near-surface ice the driver of dust activity on 67p/churyumov-gerasimenko |
context. first results based on gaia data show that the well-known star gliese 710 will be the closest flyby star in the next several myrs and its minimum distance from the sun will be almost five times smaller than that suggested by pre-gaia solution.aims: the aim of this work is to investigate the proximity parameters and the influence of the close approach of gliese 710 on the basis of gaia dr1. furthermore, we compare new results with previous works based on hip2 and tycho 2 catalogues to demonstrate how gaia improves the accuracy of determination of such phenomena.methods: using a numerical integration in an axisymmetric galactic model, we determine new parameters of the close encounter for gliese 710. adding ten thousand clones drawn with the use of a covariance matrix, we estimate the most probable position and velocity of this star at the minimum distance from the sun.results: our calculations show that gliese 710 will pass 13365 au from the sun in 1.35 myr from now. at this proximity it will have the brightness of -2.7 mag and a total proper motion of 52.28 arcsec per year. after the passage of gliese 710 we will observe a large flux of new long-period comets. thanks to the gaia mission, the uncertainties of the minimum distance and time of the close approach are several times smaller than suggested by previous works based on data from earlier observations. | gliese 710 will pass the sun even closer. close approach parameters recalculated based on the first gaia data release |
context. the n2 and co-rich and water-depleted comet c/2016 r2 (pan-starrs) - hereafter "c/2016 r2" - is a unique comet for detailed spectroscopic analysis.aims: we aim to explore the associated photochemistry of parent species, which produces different metastable states and forbidden emissions, in this cometary coma of peculiar composition.methods: we reanalyzed the high-resolution spectra of comet c/2016 r2 obtained in february 2018 using the uves spectrograph of the european southern observatory very large telescope. various forbidden atomic emission lines of [ci], [ni], and [oi] were observed in the optical spectrum of this comet when it was at 2.8 au from the sun. the observed forbidden emission intensity ratios are studied in the framework of a couple-chemistry emission model.results: the model calculations show that co2 is the major source of both atomic oxygen green and red doublet emissions in the coma of c/2016 r2 (while for most comets it is generally h2o), whereas, co and n2 govern the atomic carbon and nitrogen emissions, respectively. our modeled oxygen green-to-red-doublet and carbon-to-nitrogen emission ratios are higher by a factor of three than what is found from observations. these discrepancies could be due to uncertainties associated with photon cross sections or unknown production and/or loss sources. our modeled oxygen green-to-red-doublet emission ratio is close to what is seen in observations when we consider an o2 abundance with a production rate of 30% relative to the co production rate. we constrained the mean photodissociation yield of co, producing c(1s) at about 1%, a quantity which has not been measured in the laboratory. the collisional quenching is not a significant loss process for n(2d) though its radiative lifetime is significant (~10 h). hence, the observed [ni] doublet-emission ratio ([ni] 5198/5200) of 1.22, which is smaller than the terrestrial measurement by a factor 1.4, is mainly due to the characteristic radiative decay of n(2d). | forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet c/2016 r2 (pan-starrs) |
we present an analysis of transient events observed by the visible infrared thermal imaging spectrometer, instrument aboard rosetta, for the dates of 2015 august 10, september 13 and 14, during the two months surrounding the comet perihelion passage of the rosetta spacecraft. we detected and characterized events with life-times ranging from 26 min down to 6 min. the temporal evolution of the outburst shows a sudden increase of radiance from quiescent coma to the maximum in a few minutes. this rapid onset is correlated with a change of the visible dust colour from red, 15-18± 3 {{ per cent}}/100 nm, to bluer with values of 7-10± 0.3 {{ per cent}}/100 nm. the dust morphology of these outbursts can be classified into two main types: narrow and collimated plumes (august 10, september 13) and broad blobs (september 14). the observations suggest that there are localized regions on the surface that are more prone to outbursts than the rest of the nucleus. the projected dust velocity during the outburst events ranges between 22.2 ± 2.2 m s-1 and 64.9 ± 10.6 m s-1. the total ejected mass during an outburst event is estimated to be between 10 and 500 tons for a duration of 6-26 min assuming size distribution indices between -2.5 and -3. | summer outbursts in the coma of comet 67p/churyumov-gerasimenko as observed by rosetta-virtis |
saturn’s rings are rock-poor, containing 90%-95% ice by mass. as a group, saturn’s moons interior to and including tethys are also about 90% ice. tethys itself contains < 6 % rock by mass, in contrast to its similar-mass outer neighbor dione, which contains > 40 % rock. here we simulate the evolution of a massive primordial ice-rich ring and the production of satellites as ring material spreads beyond the roche limit. we describe the roche-interior ring with an analytic model, and use an n-body code to describe material beyond the roche limit. we track the accretion and interactions of spawned satellites, including tidal interaction with the planet, assuming a tidal dissipation factor for saturn of q∼ {10}4. we find that ring torques and capture of moons into mutual resonances produce a system of ice-rich inner moons that extends outward to approximately tethys’s orbit in 109 years, even with relatively slow orbital expansion due to tides. the resulting mass and semimajor axis distribution of spawned moons resembles that of mimas, enceladus, and tethys. we estimate the mass of rock delivered to the moons by external cometary impactors during a late heavy bombardment. we find that the inner moons receive a mass in rock comparable to their current total rock content, while dione and rhea receive an order-of-magnitude less rock than their current rock content. this suggests that external contamination may have been the primary source of rock in the inner moons, and that dione and rhea formed from much more rock-rich source material. reproducing the distribution of rock among the current inner moons is challenging, and appears to require large impactors stochasticity and/or the presence of some rock in the initial ring. | accretion of saturn’s inner mid-sized moons from a massive primordial ice ring |
the recent discovery of the first confirmed interstellar objects (isos) passing through the solar system on clearly hyperbolic objects opens the potential for near term iso missions, either to the two known objects, or to similar objects found in the future. such isos are the only exobodies we have a chance of accessing directly in the near future. this white paper focuses on the science possible from in situ spacecraft exploration of nearby isos. such spacecraft missions are technically possible now and are suitable potential missions in the period covered by the 2023-2032 decadal survey. spacecraft missions can determine the structure and the chemical and isotopic composition of iso in a close flyby coupled with a small sub-probe impactor and either a mass spectrometer or a high resolution uv spectrometer; this technology will also be useful for fast missions to transneptune objects (tnos) and long period comets. iso exploration holds the potential of providing considerable improvements in our knowledge of galactic evolution, of planetary formation, and of the cycling of astrobiologically important materials through the galaxy. | exobodies in our back yard: science from missions to nearby interstellar objects |
we review the history of spacecraft encounters with comets, concentrating on those that took place in the recent past, since the publication of the comets ii book. this includes the flyby missions stardust and deep impact, and their respective extended missions, the rosetta rendezvous mission, and serendipitous encounters. while results from all of these missions can be found throughout this book, this chapter focuses on the questions that motivated each mission, the technologies that were required to answer these questions, and where each mission opened new areas to investigate. there remain a large number of questions that will require future technologies and space missions to answer; we also describe planned next steps and routes forward that may be pursued by missions that have yet to be selected, and eventually lead to cryogenic sample return of nucleus ices for laboratory study. | past and future comet missions |
the coma of comet c/2016 r2 (panstarrs) is one of the most chemically peculiar ever observed, in particular due to its extremely high co/h2o and ${{\rm{n}}}_{2}^{+}$ /h2o ratios, and unusual trace volatile abundances. however, the complex shape of its co emission lines, as well as uncertainties in the coma structure and excitation, has lead to ambiguities in the total co production rate. we performed high-resolution, spatially, spectrally, and temporally resolved co observations using the james clerk maxwell telescope and submillimeter array to elucidate the outgassing behavior of c/2016 r2. results are analyzed using a new, time-dependent, three-dimensional radiative transfer code (sublimating gases in lime; sublime, based on the open-source version of the line modeling engine), incorporating for the first time, accurate state-to-state collisional rate coefficients for the co-co system. the total co production rate was found to be in the range of (3.8 - 7.6) × 1028 s-1 between 2018 january 13 and february 1 (at r h = 2.8-2.9 au), with a mean value of (5.3 ± 0.6) × 1028 s-1. the emission is concentrated in a near-sunward jet, with a half-opening angle of ~62° and an outflow velocity of 0.51 ± 0.01 km s-1, compared to 0.25 ± 0.01 km s-1 in the ambient (and nightside) coma. evidence was also found for an extended source of co emission, possibly due to icy grain sublimation around 1.2 × 105 km from the nucleus. based on the coma molecular abundances, we propose that the nucleus ices of c/2016 r2 can be divided into a rapidly sublimating apolar phase, rich in co, co2, n2, and ch3oh, and a predominantly frozen (or less abundant), polar phase containing more h2o, ch4, h2co, and hcn. | a sublime 3d model for cometary coma emission: the hypervolatile-rich comet c/2016 r2 (panstarrs) |
the disk midplane temperature is potentially affected by the dust traps/rings. the dust depletion beyond the water snowline will cast a shadow. in this study, we adopt a detailed gas-grain chemical reaction network, and investigate the radial gas and ice abundance distributions of dominant carbon-, oxygen-, and nitrogen-bearing molecules in disks with shadow structures beyond the water snowline around a proto-solar-like star. in shadowed disks, the dust grains at r ~ 3-8 au are predicted to have more than ~5-10 times the amount of ices of organic molecules such as h2co, ch3oh, and nh2cho, saturated hydrocarbon ices such as ch4 and c2h6, in addition to h2o, co, co2, nh3, n2, and hcn ices, compared with those in non-shadowed disks. in the shadowed regions, we find that hydrogenation (especially of co ice) is the dominant formation mechanism of complex organic molecules. the gas-phase n/o ratios show much larger spatial variations than the gas-phase c/o ratios; thus, the n/o ratio is predicted to be a useful tracer of the shadowed region. n2h+ line emission is a potential tracer of the shadowed region. we conclude that a shadowed region allows for the recondensation of key volatiles onto dust grains, provides a region of chemical enrichment of ices that is much closer to the star than within a non-shadowed disk, and may explain to some degree the trapping of o2 ice in dust grains that formed comet 67p/churyumov-gerasimenko. we discuss that, if formed in a shadowed disk, jupiter does not need to have migrated vast distances. | the molecular composition of shadowed proto-solar disk midplanes beyond the water snowline |
context. 29p/schwassmann-wachmann 1 is a distant centaur/comet, showing persistent co-driven activity and frequent outbursts.aims: we aim to better characterize its gas and dust activity from multiwavelength observations performed during outbursting and quiescent states.methods: we used the hifi, pacs and spire instruments of the herschel space observatory on several dates in 2010, 2011, and 2013 to observe the h2o 557 ghz and nh3 573 ghz lines and to image the dust coma in the far-infrared. observations with the iram 30 m telescope were undertaken in 2007, 2010, 2011, and 2021 to monitor the co production rate through the 230 ghz line, and to search for hcn at 89 ghz. the 70 and 160 µm pacs images were used to measure the thermal flux from the nucleus and the dust coma. modeling was performed to constrain the size of the sublimating icy grains and to derive the dust production rate.results: hcn is detected for the first time in comet 29p (at 5σ in the line area). h2o is detected as well, but not nh3. h2o and hcn line shapes differ strongly from the co line shape, indicating that these two species are released from icy grains. co production rates are in the range (2.9-5.6) × 1028 s−1 (1400-2600 kg s−1). a correlation between the co production rate and coma brightness is observed, as is a correlation between co and h2o production. the correlation obtained between the excess of co production and excess of dust brightness with respect to the quiescent state is similar to that established for the continuous activity of comet hale-bopp. the measured q(h2o)/q(co) and q(hcn)/q(co) production rate ratios are 10.0 ± 1.5 % and 0.12 ± 0.03 %, respectively, averaging the april-may 2010 measurements (q(h2o) = (4.1 ± 0.6) × 1027 s−1, q(hcn) = (4.8 ± 1.1) × 1025 s−1). we derive three independent and similar values of the effective radius of the nucleus, ~31 ± 3 km, suggesting an approximately spherical shape. the inferred dust mass-loss rates during quiescent phases are in the range 30-120 kg s−1, indicating a dust-to-gas mass ratio <0.1 during quiescent activity. we conclude that strong local heterogeneities exist on the surface of 29p, with quenched dust activity from most of the surface, but not in outbursting regions.conclusions: the volatile composition of the atmosphere of 29p strongly differs from that of comets observed within 3 au from the sun. the observed correlation between co, h2o and dust activity may provide important constraints for the outburst-triggering mechanism. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important contribution from nasa. based on observations carried out under project numbers 243-07, 151-09, d22-09, 144-10 and 001-21 with the iram 30 m telescope. iram is supported by insu/cnrs (france), mpg (germany) and ign (spain). | water, hydrogen cyanide, carbon monoxide, and dust production from distant comet 29p/schwassmann-wachmann 1 |
9 years in the saturn system, the cassini spacecraft finally observed titan in the supersonic and super-alfvénic solar wind. these unique observations reveal that titan's interaction with the solar wind is in many ways similar to unmagnetized planets mars and venus and active comets in spite of the differences in the properties of the solar plasma in the outer solar system. in particular, cassini detected a collisionless, supercritical bow shock and a well-defined induced magnetosphere filled with mass-loaded interplanetary magnetic field lines, which drape around titan's ionosphere. although the flyby altitude may not allow the detection of an ionopause, cassini reports enhancements of plasma density compatible with plasma clouds or streamers in the flanks of its induced magnetosphere or due to an expansion of the induced magnetosphere. because of the upstream conditions, these observations may be also relevant to other bodies in the outer solar system such as pluto, where kinetic processes are expected to dominate. | titan's interaction with the supersonic solar wind |
context. a new type of low-frequency wave was detected by the magnetometer of the rosetta plasma consortium at the comet during the initial months after the arrival of the rosetta spacecraft at comet 67p/churyumov-gerasimenko. this large-amplitude, nearly continuous wave activity is observed in the frequency range from 30 mhz to 80 mhz where 40 mhz to 50 mhz is the dominant frequency. this type of low frequency is not closely related to the gyrofrequency of newborn cometary ions, which differs from previous wave activity observed in the interaction region of comets with the solar wind.aims: this work aims to reveal a global view on the wave activity region using simulations of the comet-solar wind interaction region. parameters, such as wavelength, propagation direction, and propagation patterns, are within the focus of this study. while the rosetta observations only provide local information, numerical simulations provide further information on the global wave properties.methods: standard hybrid simulations were applied to the comet-solar wind interaction scenario. in the model, the ions were described as particles, which allows us to describe kinetic processes of the ions. the electrons were described as a fluid.results: the simulations exhibit a threefold wave structure of the interaction region. a mach cone and a whistler wing are observed downstream of the comet. the third kind of wave activity found are low-frequency waves at 97 mhz, which corresponds to the waves observed by richter et al. (2015, ann. geophys., 33, 1031). these waves are caused by the initial pick-up of the cometary ions that are perpendicular to the solar wind flow and in the interplanetary magnetic field direction. the associated electric current becomes unstable. the simulations show that wave activity is only detectable in the + e hemisphere and that the mach cone and whistler wings need to be distinguished from the newly found instability driven wave activity. the movie associated to fig. 10 is available at http://www.aanda.org | low-frequency waves at comet 67p/churyumov-gerasimenko. observations compared to numerical simulations |
recent meerkat radio continuum observations of the galactic centre at 20 cm show a large population of non-thermal radio filaments (nrfs) in the inner few hundred pc of the galaxy. we have selected a sample of 57 radio sources, mainly compact objects, in the meerkat mosaic image that appear to be associated with nrfs. the selected sources are about four times the number of radio point sources associated with filaments than would be expected by random chance. furthermore, an apparent correlation between bright ir stars and nrfs is inferred from their similar latitude distributions, suggesting that they both co-exist within the same region. to examine if compact radio sources are related to compact ir sources, we have used archival 2mass, and spitzer data to make spectral energy distribution of individual stellar sources coincident or close to radio sources. we provide a catalogue of radio and ir sources for future detailed observations to investigate a potential three-way physical association between nrfs, compact radio and ir stellar sources. this association is suggested by models in which nrfs are cometary tails produced by the interaction of a large-scale nuclear outflow with stellar wind bubbles in the galactic centre. | the population of galactic centre filaments - iii. candidate radio and stellar sources |
sintering is a process driven by mass transport that leads to the formation of a sinter neck between neighbouring particles. the temporal growth of the neck area can lead to an increase of the mechanical strength and increased heat conductivity of granular icy surfaces on solar system bodies. for water ice, sublimation is closely connected to the sinter process, because it drives the mass transport from the particles in contact to their neck region. here, we report on novel experiments conducted to investigate the sinter and the sublimation processes of micrometre-sized water-ice particles with the help of a cryogenically cooled scanning electron microscope. based on these experiments, we developed a sinter model based on which the sintering influence on the tensile strength, the compressive strength, and the thermal conductivity of icy surfaces on solar system objects can be derived. applied to comets, we find that the sinter process is faster than the typical erosion rates of cometary surfaces, implying that the uppermost icy surface layers are thermally processed. the surface of jupiter's moon europa is warm enough to experience sintering during its lifetime, whereas the sinter time-scale of saturn's moon enceladus is longer than the age of our solar system. | sintering and sublimation of micrometre-sized water-ice particles: the formation of surface crusts on icy solar system bodies |
aims: we calculate the size-frequency distribution of the boulders on the southern hemisphere of comet 67p churyumov-gerasimenko (67p), which was in shadow before the end of april 2015. we compare the new results with those derived from the northern hemisphere and equatorial regions of 67p, highlighting the possible physical processes that lead to these boulder size distributions.methods: we used images acquired by the osiris narrow angle camera (nac) on 2 may 2015 at a distance of 125 km from the nucleus. the scale of this dataset is 2.3 m/px; the high resolution of the images, coupled with the favorable observation phase angle of 62°, provided the possibility to unambiguously identify boulders ≥7 m on the surface of 67p and to manually extract them with the software arcgis. we derived the size-frequency distribution of the illuminated southern hemisphere.results: we found a power-law index of -3.6 ± 0.2 for the boulders on the southern hemisphere with a diameter range of 7-35 m. the power-law index is equal to the one previously found on northern and equatorial regions of 67p, suggesting that similar boulder formation processes occur in both hemispheres. the power-law index is related to gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. in addition, the presence of a larger number of boulders per km2 in the southern hemisphere, which is a factor of 3 higher with respect to the northern hemisphere, suggests that the southernmost terrains of 67p are affected by a stronger thermal fracturing and sublimating activity, hence possibly causing larger regressive erosion and gravitational events. | the southern hemisphere of 67p/churyumov-gerasimenko: analysis of the preperihelion size-frequency distribution of boulders ≥7 m |
we numerically model the dynamics of the enceladus plume ice grains and define our nominal plume model as having a particle size distribution n(r) ~ r-q with q = 4 and a total particulate mass rate of 16 kg s-1. this mass rate is based on average plume brightness observed by cassini across a range of orbital positions. the model predicts sample volumes of ~1600 µg for a 1 m2 collector on a spacecraft making flybys at 20-60 km altitudes above the enceladus surface. we develop two scenarios to predict the concentration of amino acids in the plume based on these assumed sample volumes. we specifically consider glycine, serine, α-alanine, α-aminoisobutyric acid and isovaline. the first `abiotic' model assumes that enceladus has the composition of a comet and finds abundances between 2 × 10-6 to 0.003 µg for dissolved free amino acids and 2 × 10-5 to 0.3 µg for particulate amino acids. the second `biotic' model assumes that the water of enceladus's ocean has the same amino acid composition as the deep ocean water on earth. we compute the expected captured mass of amino acids such as glycine, serine, and α-alanine in the `biotic' model to be between 1 × 10-5 to 2 × 10-5 µg for dissolved free amino acids and dissolved combined amino acids and about 0.0002 µg for particulate amino acids. both models consider enhancements due to bubble bursting. expected captured mass of amino acids is calculated for a 1 m2 collector on a spacecraft making flybys with a closest approach of 20 km during mean plume activity for the given nominal particle size distribution. | collecting amino acids in the enceladus plume |
context. near- and mid-infrared observations have revealed the presence of organic refractory materials in the solar system, in cometary nuclei and on the surface of centaurs, kuiper-belt and trans-neptunian objects. in these astrophysical environments, organic materials can be formed because of the interaction of frozen volatile compounds with cosmic rays and solar particles, and favoured by thermal processing. the analysis of laboratory analogues of such materials gives information on their properties, complementary to observations.aims: we present new experiments to contribute to the understanding of the chemical composition of organic refractory materials in space.methods: we bombard frozen water, methanol and ammonia mixtures with 40 kev h+ and we warmed the by-products up to 300 k. the experiments enabled the production of organic residues that we analysed by means of infrared spectroscopy and by very high resolution mass spectrometry to study their chemical composition and their high molecular diversity, including the presence of hexamethylenetetramine and its derivatives.results: we find that the accumulated irradiation dose plays a role in determining the composition of the residue.conclusions: based on the laboratory doses, we estimate the astrophysical timescales to be short enough to induce an efficient formation of organic refractory materials at the surface of icy bodies in the outer solar system. | irradiation dose affects the composition of organic refractory materials in space. results from laboratory analogues |
context. the swan lyman α photometer onboard soho monitored the hydrogen cloud around comet 67p/churyumov-gerasimenko (67p) postperihelion at the three last perihelions in 1996, 2002, and 2009.aims: combining the swan results with some new rosetta data allows estimating the erosion rate of the comet, quantified by the thickness of a layer that is disposed of at each orbit.methods: by integrating the production rates measured with swan in time and adding some estimates for periods that are not covered by swan, we estimate the total h2o mass loss per orbit to be 2.7 ± 0.4 × 109 kg. we also tried to explain the observed change in the rotation rate during the 2009 orbit (period decrease of 1285 s) and the change observed by rosetta from june 2014 to february 2015 (period increase of 32 s and 98 s up to 17 may 2015) with three different mechanisms: sublimation-induced torque, thermal dilatation, and separation between the two lobes.results: the total ejected mass depends on dust-to-gas mass ratios (4 ± 2) determined from rosetta. this means that a layer of 1.0 ± 0.5 m thickness is lost at each orbit. the outgassing-induced torque may explain the observed changes in the rotation rate around perihelion in 2009 and recent changes. the torque decelerated the rotation from august 2014 to 17 may 2015, at which time it changed sign and began to accelerate the rotation, consistent with the average behavior observed for the 2009 apparition.conclusions: the thickness of lost material needs to be kept in mind when interpreting all surface features. at 1 m ± 0.5 m, the erosion rate per orbit is high and supports the idea that the composition of the material that is measured in the coma (gas and solid) is indeed representative of the bulk material of the nucleus. we also argued that monitoring the rotation rate yields a very accurate and precious indicator of the global activity of the comet with which other activity measurements can be compared. | estimate of the erosion rate from h2o mass-loss measurements from swan/soho in previous perihelions of comet 67p/churyumov-gerasimenko and connection with observed rotation rate variations |
experimental simulations in the laboratory may provide important information about the chemical evolution occurring in various astrophysical objects such as extraterrestrial ices. interstellar or (pre)cometary ice analogues made of h2o, ch3oh, and nh3 at 77 k, when subjected to an energetic process (vuv photons, electrons or ions) and then warmed-up to room temperature, lead, in the laboratory, to the formation of an organic residue. in this paper we expand our previous analysis of the residues in order to obtain a better insight into their molecular content. data analyses show that three different chemical groups are present in the residue in the negative electrospray ionization (esi) mode: chn, cho and chnosbnd whereas only two groups are detected in the positive esi mode: chn and chno. in both cases, the chno group is the most abundant. the application of specific data treatment shows that residue mainly contains aliphatic linear molecules or cyclic structures connected to unsaturated chemical functions such as esters, carboxylic acids, amides or aldehydes. in lower abundances, some molecules do present aromatic structures. the comparison of our residue with organic compounds detected in the murchison meteorite gives an interesting match, which suggests that laboratory simulation of interstellar ice chemistry is relevant to understand astrophysical organic matter evolution. | insight into the molecular composition of laboratory organic residues produced from interstellar/pre-cometary ice analogues using very high resolution mass spectrometry |
electric field measurements from cometary environments are very rare but can provide important information on how plasma waves help fashion the plasma environment. the long dwelling time of the rosetta spacecraft close to comet 67p/churyumov-gerasimenko promises to improve this state. we here present the first electric field measurements from 67p, performed by the rosetta dual langmuir probe instrument lap. measurements of the electric field from cometocentric distances of 149 and 348 km are presented together with estimates of plasma density changes. persistent wave activity around the local h2o+ lower hybrid frequency is observed, with the largest amplitudes observed at sharp plasma gradients. we demonstrate that the necessary requirements for the lower hybrid drift instability to be operating are fulfilled. we suggest that lower hybrid waves are responsible for the creation of a warm electron population, the origins of which have been unknown so far, by heating ambient electrons in the magnetic field-parallel direction. | rosetta measurements of lower hybrid frequency range electric field oscillations in the plasma environment of comet 67p |
saprolegniosis is a worldwide fungal-like infection affecting freshwater fishes and their eggs. reports show high mortalities and subsequent economic losses annually from saprolegnia infections. most therapeutants against saprolegnia spp. infections are inefficient and some have negative impact on the environment. in this study, we have investigated the ability of boric acid (ba) to prevent saprolegnia infection in nile tilapia (oreochromis niloticus). ba inhibited radial growth of saprolegnia hyphae in vitro. complete in vitro growth inhibition was found at a concentration of ≥0.6 g/l. inhibitory effects were also observed in vivo when nile tilapia were experimentally challenged with saprolegnia spores and followed over 10 days post challenge and under continuous exposure to different ba concentrations. no signs of saprolegniosis were observed in fish treated with ba at concentrations of 0.4 g/l and above. comet assay revealed that ba has low toxicity in tilapia continuously exposed to concentrations of 0.2-0.6 g/l for 96 h. additionally, no significant histomorphological changes were observed in ba-treated fish compared to non-treated controls. alanine aminotransferase (alt) and aspartate aminotransferase (ast) enzyme levels indicated reduction in systemic tissue damage associated with saprolegnia infection. this study demonstrates the potential of ba as a prophylactic measure against saprolegnia infection in tilapia, and we recommend additional studies on environmental impact. | efficacy and safety of boric acid as a preventive treatment against saprolegnia infection in nile tilapia (oreochromis niloticus) |
this paper is a continuation of miles et al. (2015) [icarus] and miles (2015b) [icarus], which detail new observations of comet 29p/schwassmann−wachmann, characterise its rotational period (∼57 d), and identify the presence of discrete sources of outburst on its nucleus: the latter ruling out amorphous-to-crystalline h2o ice transitions as the cause of its outbursts. summary data are presented for 29p and a further 16 non-fragmenting comets which exhibit outbursts of >2 magnitudes. a comprehensive physicochemical mechanism is postulated to account for major outbursts based on melting of cometary ices and the exothermic dissolution of gases, especially co and co2 at pressures of 10−200 kpa. the thermodynamics of enthalpy heating are described and heats of solution are calculated from gas-liquid solubility data yielding -6 kj mol-1 for co in ch4, and -15 kj mol-1 for co2 in ch3oh close to their freezing point. heats of solution are ∼6 times greater (per mole) than the enthalpy of fusion of the pure ch4 and ch3oh ices, enabling gas pressures of >∼80 kpa to continually melt these ices. supervolatile o2 and n2 gases may also participate by dissolving exothermically in liquid ch4 and other hydrocarbons potentially reaching high mixing ratios. h2s and nh3 gases dissolve exothermically in ch3oh liberating up to 20 kj mol-1 and 13 kj mol-1, respectively, and all three hydrophilic species facilitate sintering of h2o ice in the near-surface of comets. localised melting and consolidation is favoured in slowly-rotating cometary nuclei of intermediate dust/gas ratios, at pressures of ∼1 kpa, and temperatures as low as 50−65 k where o2 and n2 are abundant. nyctogenic processes on the night-time side of the nucleus restock desiccated surface layers, reseal the crust, enabling fractionation of solutes in sub-crustal liquid phases via fractional sublimation/distillation of non-polar, hydrophobic ch4 and other hydrocarbons; and by fractional crystallisation of polar, hydrophilic phases rich in aqueous ch3oh and other organic oxygenates, e.g. ch2o, able to form low melting point eutectic mixtures. a generalised outburst mechanism is described involving the containment of gases as solutes in cryomagma beneath consolidated surface crustal regions. disruption of the crust and associated pressure loss render the cryomagma supersaturated, and the concomitant explosive exsolution of gases provokes a cometary outburst. the co gas-exsolution mechanism operates at ∼65 to 95 k and accounts for activity of 29p and other distant comets up to rh = ∼15 au. a similar mechanism can operate at ∼150 to 200 k driven by co2 in aqueous ch3oh and may account for rare outbursts of jupiter-family comets such as 17p/holmes. at least 10-15% of all periodic comets may be subject to gas-exsolution outbursts, the majority of which are weak and go undetected. possible surface morphologies of the nucleus of comet 29p are discussed. the mechanism may also explain the phenomenon of strong cometary outbursts triggering secondary events, as observed for 17p, 29p and 41p. | heat of solution: a new source of thermal energy in the subsurface of cometary nuclei and the gas-exsolution mechanism driving outbursts of comet 29p/schwassmann−wachmann and other comets |
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