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aims: the aim of this work is to characterise hcn and ch3oh emission from recent comets.methods: we used the onsala 20-m telescope to search for millimetre transitions of hcn towards a sample of 11 recent and mostly bright comets in the period from december 2016 to november 2019. also, ch3oh was searched for in two comets. the hcn sample includes the interstellar comet 2i/borisov. for the short-period comet 46p/wirtanen, we were able to monitor the variation of hcn emission over a time-span of about one month. we performed radiative transfer modelling for the observed molecular emission by also including time-dependent effects due to the outgassing of molecules.results: hcn was detected in six comets. two of these are short-period comets and four are long-period. six methanol transitions were detected in 46p/wirtanen, enabling us to determine the gas kinetic temperature. from the observations, we determined the molecular production rates using time-dependent radiative transfer modelling. for five comets, we were able to determine that the hcn mixing ratios lie near 0.1% using contemporary water production rates, {q{{{h}_2}{{o}}}}, taken from other studies. this hcn mixing ratio was also found to be typical in our monitoring observations of 46p/wirtanen but here we notice deviations of up to 0.2% on a daily timescale which could indicate short-time changes in outgassing activity. from our radiative transfer modelling of cometary comae, we find that time-dependent effects on the hcn level populations are of the order of 5-15% when {q{{{h}_2}{{o}}}} is around 2 × 1028 mol s−1. the effects may be stronger for comets with lower {q{{{h}_2}{{o}}}}. the exact details of the time-dependent effects depend on the amount of neutral and electron collisions, radiative pumping, and molecular parameters such as the spontaneous rate coefficient. | emission from hcn and ch3oh in comets. onsala 20-m observations and radiative transfer modelling |
the national toxicology program tested two common radiofrequency radiation (rfr) modulations emitted by cellular telephones in a 2‑year rodent cancer bioassay that included interim assessments of additional animals for genotoxicity endpoints. male and female hsd:sprague dawley sd rats and b6c3f1/n mice were exposed from gestation day 5 or postnatal day 35, respectively, to code division multiple access (cdma) or global system for mobile modulations over 18 hr/day, at 10‑min intervals, in reverberation chambers at specific absorption rates of 1.5, 3, or 6 w/kg (rats, 900 mhz) or 2.5, 5, or 10 w/kg (mice, 1,900 mhz). after 19 (rats) or 14 (mice) weeks of exposure, animals were examined for evidence of rfr‑associated genotoxicity using two different measures. using the alkaline (ph > 13) comet assay, dna damage was assessed in cells from three brain regions, liver cells, and peripheral blood leukocytes; using the micronucleus assay, chromosomal damage was assessed in immature and mature peripheral blood erythrocytes. results of the comet assay showed significant increases in dna damage in the frontal cortex of male mice (both modulations), leukocytes of female mice (cdma only), and hippocampus of male rats (cdma only). increases in dna damage judged to be equivocal were observed in several other tissues of rats and mice. no significant increases in micronucleated red blood cells were observed in rats or mice. in conclusion, these results suggest that exposure to rfr is associated with an increase in dna damage. environ. mol. mutagen. 61:276–290, 2020. | evaluation of the genotoxicity of cell phone radiofrequency radiation in male and female rats and mice following subchronic exposure |
partially ionized plasmas (pip) are essential constituents of many astrophysical environments, including the solar atmosphere, the interstellar medium, molecular clouds, accretion disks, planet ionospheres, cometary tails, etc., where the ionization degree may vary from very weak ionization to almost full ionization. the dynamics of pip is heavily affected by the interactions between the various charged and neutral species that compose the plasma. it has been shown that partial ionization effects influence the triggering and development of fluid instabilities as, e.g., kelvin-helmholtz, rayleigh-taylor, thermal, and magneto-rotational instabilities, among others. here we review the theory of some classic fluid instabilities that are present in pip and highlight the unique effects introduced by partial ionization. the main emphasis of the review is put on instabilities in the partially ionized solar atmospheric plasma, although other astrophysical applications are also mentioned. we focus on the mathematical and theoretical investigation of the onset and exponential growth of the instabilities. results of the nonlinear evolution obtained from full numerical simulations are also discussed. | theory of fluid instabilities in partially ionized plasmas: an overview |
in 2015 may, the southern hemisphere of comet 67p/churyumov-gerasimenko became visible by the osiris cameras on-board the rosetta spacecraft. the resolution was high enough to carry out a detailed analysis of the surface morphology, which is quite different from the northern hemisphere. previous works show that fine particle deposits are the most extensive geological unit in the northern hemisphere. in contrast, the southern hemisphere is dominated by outcropping consolidated terrain. in this work, we provide geomorphological maps of the southern hemisphere with the distinction of both geological units and linear features. the geomorphological maps described in this study allow us to gain a better understanding of the processes shaping the comet nucleus and the distribution of primary structures such as fractures and strata. | geomorphological mapping of comet 67p/churyumov-gerasimenko's southern hemisphere |
while the structural complexity of cometary comae is already recognizable from telescopic observations1, the innermost region, within a few radii of the nucleus, was not resolved until spacecraft exploration became a reality2,3. the dust coma displays jet-like features of enhanced brightness superposed on a diffuse background1,4,5. some features can be traced to specific areas on the nucleus, and result conceivably from locally enhanced outgassing and/or dust emission6-8. however, diffuse or even uniform activity over topographic concavity can converge to produce jet-like features9,10. therefore, linking observed coma morphology to the distribution of activity on the nucleus is difficult11,12. here, we study the emergence of dust activity at sunrise on comet 67p/churyumov-gerasimenko using high-resolution, stereo images from the osiris camera onboard the rosetta spacecraft, where the sources and formation of the jet-like features are resolved. we perform numerical simulations to show that the ambient dust coma is driven by pervasive but non-uniform water outgassing from the homogeneous surface layer. physical collimations of gas and dust flows occur at local maxima of insolation and also via topographic focusing. coma structures are projected to exhibit jet-like features that vary with the perspective of the observer. for an irregular comet such as 67p/churyumov-gerasimenko, near-nucleus coma structures can be concealed in the shadow of the nucleus, which further complicates the picture. | coma morphology of comet 67p controlled by insolation over irregular nucleus |
the highly varying plasma environment around comet 67p/churyumov-gerasimenko inspired an upgrade of the ion mass spectrometer (rosetta plasma consortium ion composition analyzer) with new operation modes, to enable high time resolution measurements of cometary ions. two modes were implemented, one having a 4 s time resolution in the energy range 0.3-82 ev/q and the other featuring a 1 s time resolution in the energy range 13-50 ev/q. comparing measurements made with the two modes, it was concluded that 4 s time resolution is enough to capture most of the fast changes of the cometary ion environment. the 1462 h of observations done with the 4 s mode were divided into hour-long sequences. it is possible to sort 84 per cent of these sequences into one of five categories, depending on their appearance in an energy-time spectrogram. the ion environment is generally highly dynamic, and variations in ion fluxes and energies are seen on time-scales of 10 s to several minutes. | investigating short-time-scale variations in cometary ions around comet 67p |
the aim of this study was to investigate preservation of biomolecular structures, particularly dna, in freeze-dried fibroblasts, after loading with trehalose via freezing-induced uptake. cells were freeze-dried with trehalose alone or in a mixture of albumin and trehalose. albumin was added to increase the glass transition temperature and storage stability. no viable cells were recovered after freeze-drying and rehydration. ftir studies showed that membrane phase behavior of freeze-dried cells resembles that of fresh cells. however, one day after rehydration membrane phase separation was observed, irrespective of the presence or absence of trehalose during freeze-drying. freeze-drying did not affect the overall protein secondary structure. analysis of dna damage via single cell gel electrophoresis (`comet assay') showed that dna damage progressively increased with storage duration and temperature. dna damage was prevented during storage at 4 °c. it is shown that trehalose reduces dna damage during storage, whereas addition of albumin did not seem to have an additional protective effect on storage stability (i.e. dna integrity) despite the fact that albumin increased the glass transition temperature. taken together, dna in freeze-dried somatic cells can be preserved using trehalose as protectant and storage at or below 4 °c. | freeze-drying of mammalian cells using trehalose: preservation of dna integrity |
the osiris camera onboard rosetta measured the phase function of both the coma dust and the nucleus. the two functions have a very different slope versus the phase angle. here, we show that the nucleus phase function should be adopted to convert the brightness to the size of dust particles larger than 2.5 mm only. this makes the dust bursts observed close to rosetta by osiris, occurring about every hour, consistent with the fragmentation on impact with rosetta of parent particles, whose flux agrees with the dust flux observed by giada. osiris also measured the antisunward acceleration of the fragments, thus providing the first direct measurement of the solar radiation force acting on the dust fragments and thus of their bulk density, excluding any measurable rocket effect by the ice sublimation from the dust. the obtained particle density distribution has a peak matching the bulk density of most cosima particles, and represents a subset of the density distribution measured by giada. this implies a bias in the elemental abundances measured by cosima, which thus are consistent with the 67p dust mass fractions inferred by giada, i.e. (38 ± 8) {per cent} of hydrocarbons versus the (62 ± 8) {per cent} of sulphides and silicates. | the phase function and density of the dust observed at comet 67p/churyumov-gerasimenko |
context. the mutual impedance probe (mip) of the rosetta plasma consortium (rpc) onboard the rosetta orbiter which was in operation for more than two years, between august 2014 and september 2016 to monitor the electron density in the cometary ionosphere of 67p/churyumov-gerasimenko. based on the resonance principle of the plasma eigenmodes, recent models of the mutual impedance experiment have shown that in a two-electron temperature plasma, such an instrument is able to separate the two isotropic electron populations and retrieve their properties.aims: the goal of this paper is to identify and characterize regions of the cometary ionized environment filled with a mix of cold and warm electron populations, which was observed by rosetta during the cometary operation phase.methods: to reach this goal, this study identifies and investigates the in situ mutual impedance spectra dataset of the rpc-mip instrument that contains the characteristics of a mix of cold and warm electrons, with a special focus on instrumental signatures typical of large cold-to-total electron density ratio (from 60 to 90%), that is, regions strongly dominated by the cold electron component.results: we show from the observational signatures that the mix of cold and warm cometary electrons strongly depends on the cometary latitude. indeed, in the southern hemisphere of 67p, where the neutral outgassing activity was higher than in northern hemisphere during post-perihelion, the cold electrons were more abundant, confirming the role of electron-neutral collisions in the cooling of cometary electrons. we also show that the cold electrons are mainly observed outside the nominal electron-neutral collision-dominated region (exobase), where electrons are expected to have cooled down. this which indicates that the cold electrons have been transported outward. finally, rpc-mip detected cold electrons far from the perihelion, where the neutral outgassing activity is lower, in regions where no electron exobase was expected to have formed. this suggests that the cometary neutrals provide a more frequent or efficient cooling of the electrons than expected for a radially expanding ionosphere. | observations of a mix of cold and warm electrons by rpc-mip at 67p/churyumov-gerasimenko |
radar observations of mercury and the mercury surface, space environment, geochemistry, and ranging (messenger) spacecraft data indicate the probable existence of water ice in the permanently shadowed polar regions. generally, water is accepted to be of exogenous origin through delivery via comets and meteoritic impact. however, a continuous water formation process that involves thermal transformation of chemically stable mineral-bound hydroxyl groups produced by implanted solar-wind protons is readily available on the surface of mercury. at typical temperatures prevailing on mercury's dayside surface, h2o can be produced from reactions involving oh groups on or within the h-saturated regolith grain interfaces. similar reactions will also occur due to micrometeorite impact events on both the dayside and nightside. once produced, h2o is released into the exosphere and then transported and processed via jeans escape, photodissociation, dissociative adsorption, or condensation. water reaching cold traps will be bound over geological periods. this simple water cycle will produce a highly chemically reduced surface and can deliver significant amounts of h2o to the permanently shadowed regions of mercury over geological time periods. the overall process is an important but hitherto unnoticed source term that will contribute to the accumulation of water in the cold traps and polar regions of mercury. | a new in situ quasi-continuous solar-wind source of molecular water on mercury |
in-situ measurements of individual dust grain parameters in the immediate vicinity of a cometary nucleus are being carried by the rosetta spacecraft at comet 67p/churyumov-gerasimenko. for the interpretations of these observational data, a model of dust grain motion as realistic as possible is requested. in particular, the results of the stardust mission and analysis of samples of interplanetary dust have shown that these particles are highly aspherical, which should be taken into account in any credible model. the aim of the present work is to study the dynamics of ellipsoidal shape particles with various aspect ratios introduced in a spherically symmetric expanding gas flow and to reveal the possible differences in dynamics between spherical and aspherical particles. their translational and rotational motion under influence of the gravity and of the aerodynamic force and torque is numerically integrated in a wide range of physical parameters values including those of comet 67p/churyumov-gerasimenko. the main distinctions of the dynamics of spherical and ellipsoidal particles are discussed. the aerodynamic characteristics of the ellipsoidal particles, and examples of their translational and rotational motion in the postulated gas flow are presented. | dynamics of aspherical dust grains in a cometary atmosphere: i. axially symmetric grains in a spherically symmetric atmosphere |
the galaxy cluster abell 3376 is a nearby (\bar{z}=0.046) dissociative merging cluster surrounded by two prominent radio relics and showing an x-ray comet-like morphology. the merger system is comprised of the subclusters a3376w and a3376e. based on new deep multiwavelength large-field images and published redshifts, we bring new insights about the history of this merger. despite the difficulty of applying the weak lensing technique at such low redshift, we successfully recovered the mass distribution in the cluster field. moreover, with the application of a two-body model, we have addressed the dynamics of this merging system. we have found the individual masses of m_{200}^w=3.0_{-1.7}^{+1.3}× 10^{14} m⊙ and m_{200}^e=0.9_{-0.8}^{+0.5}× 10^{14} m⊙. the cometary-shaped x-ray distribution shows only one peak spatially coincident with both eastern bcg and the a3376e mass peak whereas the gas content of a3376w seems to be stripped out. our data allowed us to confirm the existence of a third subcluster located at the north, 1147 ± 62 kpc apart from the neighbour subcluster a3376e and having a mass m_{200}^n=1.4_{-1.0}^{+0.7}× 10^{14} m⊙. from our dynamical analysis, we found the merging is taking place very close to the plane of the sky, with the merger axis just 10° ± 11° from it. the application of a two-body analysis code showed that the merging cluster is seen 0.9_{-0.3}^{+0.2} gyr after the pericentric passage and it is currently going to the point of maximum separation between the subclusters. | weak lensing and spectroscopic analysis of the nearby dissociative merging galaxy cluster abell 3376 |
the landing of the rosetta-mission lander philae on november 12th 2014 on comet 67 p/churyumov-gerasimenko was planned as a descent with passive landing and anchoring by harpoons at touch-down. actually the lander was not fixed at touch-down to the ground due to failing harpoons. the lander internal damper was actuated at touch-down for 42.6 mm with a speed of 0.08 m/s while the lander touch-down speed was 1 m/s. the kinetic energy before touch-down was 50 j, 45 j were dissipated by the lander internal damper and by ground penetration at touch-down, and 5 j kinetic energy are left after touch-down (0.325 m/s speed). most kinetic energy was dissipated by ground penetration (41 j) while only 4 j are dissipated by the lander internal damper. based on these data, a value for a constant compressive soil-strength of between 1.55 kpa and 1.8 kpa is calculated. this paper focuses on the reconstruction of the touch-down at agilkia over a period of around 20 s from first ground contact to lift-off again. after rebound philae left a strange pattern on ground documented by the osiris narrow angle camera (nac). the analysis shows, that the touch-down was not just a simple damped reflection on the surface. instead the lander had repeated contacts with the surface over a period of about 20 s±10 s. this paper discusses scenarios for the reconstruction of the landing sequence based on the data available and on computer simulations. simulations are performed with a dedicated mechanical multi-body model of the lander, which was validated previously in numerous ground tests. the simpack simulation software was used, including the option to set forces at the feet to the ground. the outgoing velocity vector is mostly influenced by the timing of the ground contact of the different feet. it turns out that ground friction during damping has strong impact on the lander outgoing velocity, on its rotation, and on its nutation. after the end of damping, the attitude of the lander can be strongly changed by the additional ground contacts even with the flywheel still running inside the lander. the simulation shows that the outbound velocity vector and the lander rotation were formed immediately at touch-down during the first 1.5 s. the outbound velocity vector is found to be formed by the ground slope and the lander damping characteristic, especially the nearly horizontal flight out. | rosetta lander philae: touch-down reconstruction |
volatile production rates, relative abundances, rotational temperatures, and spatial distributions in the coma were measured in c/2012 s1 (ison) using long-slit high-dispersion (λ/δλ ∼ 2.5 × 104) infrared spectroscopy as part of a worldwide observing campaign. spectra were obtained on ut 2013 october 26 and 28 with nirspec at the w.m. keck observatory, and ut 2013 november 19 and 20 with cshell at the nasa irtf. h2o was detected on all dates, with production rates increasing markedly from (8.7 ± 1.5) × 1027 molecules s-1 on october 26 (rh = 1.12 au) to (3.7 ± 0.4) × 1029 molecules s-1 on november 20 (rh = 0.43 au). short-term variability of h2o production is also seen as observations on november 19 show an increase in h2o production rate of nearly a factor of two over a period of about 6 h. c2h6, ch3oh and ch4 abundances in ison are slightly depleted relative to h2o when compared to mean values for comets measured at infrared wavelengths. on the november dates, c2h2, hcn and ocs abundances relative to h2o appear to be within the range of mean values, whereas h2co and nh3 were significantly enhanced. there is evidence that the abundances with respect to h2o increased for some species but not others between october 28 (rh = 1.07 au) and november 19 (rh = 0.46 au). the high mixing ratios of h2co/ch3oh and c2h2/c2h6 on november 19, and changes in the mixing ratios of some species with respect to h2o between october 28 to november 19, indicates compositional changes that may be the result of a transition from sampling radiation-processed outer layers in this dynamically new comet to sampling more pristine natal material as the outer processed layer was increasingly eroded and the thermal wave propagated into the nucleus as the comet approached perihelion for the first time. on november 19 and 20, the spatial distribution for dust appears asymmetric and enhanced in the antisolar direction, whereas spatial distributions for volatiles (excepting cn) appear symmetric with their peaks slightly offset in the sunward direction compared to the dust. spatial distributions for h2o, hcn, c2h6, c2h2, and h2co on november 19 show no definitive evidence for significant contributions from extended sources; however, broader spatial distributions for nh3 and ocs may be consistent with extended sources for these species. abundances of hcn and c2h2 on november 19 and 20 are insufficient to account for reported abundances of cn and c2 in ison near this time. differences in hcn and cn spatial distributions are also consistent with hcn as only a minor source of cn in ison on november 19 as the spatial distribution of cn in the coma suggests a dominant distributed source that is correlated with dust and not volatile release. the spatial distributions for nh3 and nh2 are similar, suggesting that nh3 is the primary source of nh2 with no evidence of a significant dust source of nh2; however, the higher production rates derived for nh3 compared to nh2 on november 19 and 20 remain unexplained. this suggests a more complete analysis that treats nh2 as a distributed source and accounts for its emission mechanism is needed for future work. | the compositional evolution of c/2012 s1 (ison) from ground-based high-resolution infrared spectroscopy as part of a worldwide observing campaign |
the fugin co survey revealed the three-dimensional structure of a galactic shock wave in the tangential direction of the 4 kpc molecular arm. the shock front is located at g30.5+00.0 + 95 km s-1 on the upstream (lower longitude) side of the star-forming complex w 43 (g30.8-0.03), and comprises a molecular bow shock (mbs) concave to w 43, exhibiting an arc-shaped molecular ridge perpendicular to the galactic plane with width ∼0.1°(10 pc) and vertical length ∼1° (100 pc). the mbs is coincident with the radio continuum bow of thermal origin, indicating association of ionized gas and similarity to a cometary bright-rimmed cloud. the upstream edge of the bow is sharp, with a growth width of ∼0.5 pc indicative of the shock front property. the velocity width is ∼10 km s-1, and the center velocity decreases by ∼15 km s-1 from the bottom to the top of the bow. the total mass of molecular gas in the mbs is estimated to be ∼1.2 × 106 m⊙, and ionized gas ∼2 × 104 m⊙. the vertical disk thickness has a step-like increase at the mbs by ∼2 times from lower to upper longitudes, which indicates hydraulic jump in the gaseous disk. we argue that the mbs was formed by the galactic shock compression of an accelerated flow in the spiral-arm potential encountering the w 43 molecular complex. a bow-shock theory can reproduce the bow morphology well. we argue that molecular bows are common in galactic shock waves, not only in the galaxy but also in galaxies, where mbss are associated with giant cometary h ii regions. we also analyzed the h i data in the same region to obtain a map of h i optical depth and molecular fraction. we found firm evidence of the h i to h2 transition in the galactic shock as revealed by a sharp molecular front at the mbs front. | forest unbiased galactic plane imaging survey with the nobeyama 45 m telescope (fugin). iv. galactic shock wave and molecular bow shock in the 4 kpc arm of the galaxy |
comets considered to be pristine objects contain key information about the early formation of the solar system. their volatile components can provide clues about the origin and evolution of gases and ices in the comets. measurements with rosina/rtof at 67p/churyumov-gerasimenko have now allowed, for the first time, a direct in situ high-time resolution measurement of the most abundant cometary molecules originating directly from a comet’s nucleus over a long time-period, much longer than any previous measurements at a close distance to a comet between 3.1 and 2.3 au. we determine the local densities of h2o, co2, and co, and investigate their variabilities. | high-time resolution in-situ investigation of major cometary volatiles around 67p/c-g at 3.1 - 2.3 au measured with rosina-rtof |
the cyano radical (cn) is one of the most frequently remotely observed species in space, and is also often observed in comets. data for the inner coma of comet 67p/churyumov-gerasimenko collected by the high-resolution double focusing mass spectrometer (dfms) on board the rosetta orbiter revealed an unexpected chemical complexity, and, recently, also more cn than expected from photodissociation of its most likely parent, hydrogen cyanide (hcn). here, we derive abundances relative to hcn of three cometary nitriles (including structural isomers) from dfms data. mass spectrometry of complex mixtures does not always allow isolation of structural isomers, and therefore in our analysis we assume the most stable and abundant (in similar environments) structure, that is hcn for chn, ch3cn for c2h3n, hc3n for c3hn, and nccn for c2n2. for cyanoacetylene (hc3n) and acetonitrile (ch3cn), the complete mission time-line was evaluated, while cyanogen (nccn) was often below the detection limit. by carefully selecting periods where cyanogen was above the detection limit, we were able to follow the abundance ratio between nccn and hcn from 3.16 au inbound to 3.42 au outbound. these are the first measurements of nccn in a comet. we find that neither nccn nor either of the other two nitriles is sufficiently abundant to be a relevant alternative parent to cn. | cyanogen, cyanoacetylene, and acetonitrile in comet 67p and their relation to the cyano radical |
pulsars traveling at supersonic speeds are often accompanied by cometary bow shocks seen in hα. we report on the first detection of a pulsar bow shock in the far-ultraviolet (fuv). we detected it in fuv images of the nearest millisecond pulsar j0437-4715 obtained with the hubble space telescope. the images reveal a bow-like structure positionally coincident with part of the previously detected hα bow shock, with an apex at 10″ ahead of the moving pulsar. its fuv luminosity, l(1250{--}2000 \mathringa )≈ 5 × {10}28 erg s-1, exceeds the hα luminosity from the same area by a factor of 10. the fuv emission could be produced by the shocked interstellar medium matter or, less likely, by relativistic pulsar wind electrons confined by strong magnetic field fluctuations in the bow shock. in addition, in the fuv images we found a puzzling extended (≃3″ in size) structure overlapping with the limb of the bow shock. if related to the bow shock, it could be produced by an inhomogeneity in the ambient medium or an instability in the bow shock. we also report on a previously undetected x-ray emission extending for about 5″ ahead of the pulsar, possibly a pulsar wind nebula created by shocked pulsar wind, with a luminosity l(0.5-8 kev) ∼ 3 × 1028 erg s-1. based on observations made with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. these observations are associated with programs go 12917 and go 10568. | first detection of a pulsar bow shock nebula in far-uv: psr j0437-4715 |
studies suggest that the pollution of white dwarf (wd) atmospheres arises from the accretion of minor planets, but the exact properties of polluting material, and in particular the evidence for water in some cases are not yet understood. several previous works studied the possibility of water surviving inside minor planets around evolving stars. however, they all focused on small, comet-sized to moonlet-sized minor planets, when the inferred mass inside the convection zones of he-dominated wds could actually be compatible with much more massive minor planets. here we explore for the first time, the water retention inside exoplanetary dwarf planets, or moderate-sized moons, with radii of the order of hundreds of kilometers. this paper concludes a series of papers that has now covered nearly the entire potential mass range of minor planets, in addition to the full mass range of their host stars. we find that water retention is (a) affected by the mass of the wd progenitor, and (b) it is on average at least 5%, irrespective of the assumed initial water composition, if it came from a single accretion event of an icy dwarf planet or moon. the latter prediction strengthens the possibility of habitability in wd planetary systems, and it may also be used in order to distinguish between pollution originating from multiple small accretion events and singular large accretion events. to conclude our work, we provide a code that calculates ice and water retention by interpolation and may be freely used as a service to the community. | post-main-sequence evolution of icy minor planets. iii. water retention in dwarf planets and exomoons and implications for white dwarf pollution |
we present the results of a molecular survey of comet 67p/churyumov-gerasimenko undertaken with the institut de radioastronomie millimétrique (iram) 30-m radio telescope in november-december 2021, when it had its most favourable apparition in decades. observations at iram 30-m during the 12-16 november period covered 8 ghz bandwidth at 3 mm, 16 ghz at 2 mm, and 60 ghz in the 1 mm window domain. these were completed by snapshots at 1 mm on 12-13 december and a short observation of the h2o line at 557 ghz with the odin sub-millimetre observatory on 17.0 november 2021, and with 18-cm observations of oh with the nançay radio telescope. less sensitive observations obtained at a previous perihelion passage on 18-22 september 2015 with iram and 9-12 november 2015 with odin are also presented. the gas outflow velocity, outgassing pattern, and temperature have been accurately constrained by the observations. they are perfectly consistent with those measured in situ with the rosetta/miro sub-millimetre instrument in 2015. in particular, the asymmetry of the line is well represented by a jet concentrating three-quarters of the outgassing in about π steradians. we derived abundances relative to water for seven molecules and significant upper limits for approximately five others. the retrieved abundances were compared to those measured in situ at the previous perihelion with rosetta. while those of hcn, ch3oh, and hnco are comparable, 67p is found to be depleted in h2s and relatively normal in cs (h2s/cs ≈ 3) in strong contradiction with the rosetta/rosina mass spectrometer measurement of the h2s/cs2 (≈100) abundance ratio. while the formaldehyde total abundance found with iram 30-m when assuming it to be mostly produced by a distributed source (haser parent scale length ≈8000 km) is similar to the one derived by rosetta/rosina, we find that the formaldehyde coming from the nucleus is one order of magnitude less abundant than measured in situ by rosetta/rosina. the radio spectra are only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/672/a170 | coma composition of comet 67p/churyumov-gerasimenko from radio-wave spectroscopy |
motion of many comets is affected by non-gravitational forces caused by outgassing from their surfaces. outgassing also produces reactive torques resulting in cometary spin evolution. we propose that the two processes are correlated and show that the change of cometary spin rate over its heliocentric orbit scales linearly with the amplitude of its non-gravitational acceleration. the proportionality constant depends on the comet size and orbital elements (semi-major axis and eccentricity) and on the (dimensionless) lever arm parameter $\zeta$ that relates the outgassing-induced torque and acceleration. we determine $\zeta$ for 7 comets for which both non-gravitational acceleration and change of spin period $\delta p$ were measured and verify this relation. this sample spanning almost 4 decades in $\delta p$ yields $\log\zeta=-2.21\pm 0.54$, surprisingly small value and spread. we then apply our framework to 209 comets with measured non-gravitational accelerations and determine the objects most likely to exhibit large spin period changes, $\delta p\gtrsim 20$ min per orbit assuming rotation period of 10 hr and $\zeta$ comparable to our control sample. these objects should be primary targets for future studies of cometary spin variability, further constraining distribution of $\zeta$. lack of comets with very high expected spin rate changes (which is not equivalent to having the highest non-gravitational acceleration) suggests that (1) cometary fission due to outgassing-driven spin-up must be an important process and (2) the distribution of $\zeta$ has a lower limit $\sim 10^{-3}$. | non-gravitational forces and spin evolution of comets |
the encounter of the meteoric material from 73p/schmassmann-wachmann 3 produced during the comet's 1995 outburst in may 2022 provides a rare and valuable opportunity to understand a fragmenting comet. here, we explore various ejection configurations and their impact on the meteor outburst detected in the early hours of ut 2022 may 31. we show that the dust must have been ejected ~4 to 5× faster than calculated by water-ice sublimation model to best match the observed meteor activity. as only a small subset of particles with a narrow range of cross-section is expected to have reached the earth, the large spread of meteor brightness likely indicates the presence of large but porous meteoroids in the trail. other effects such as an enhanced lunar sodium tail and a visible glow from the meteoroid trail may have also occurred during the encounter. | the 2022 encounter of the outburst material from comet 73p/schwassmann-wachmann 3 |
we investigate the role of secondary electron and ion emission from impact of gas molecules on the cassini langmuir probe (rpws-lp or lp) measurements in the ionosphere of saturn. we add a model of the emission currents, based on laboratory measurements and data from comet 1p/halley, to the equations used to derive plasma parameters from lp bias voltage sweeps. reanalysing several hundred sweeps from the cassini grand finale orbits, we find reasonable explanations for three open conundrums from previous lp studies of the saturn ionosphere. we find an explanation for the observed positive charging of the cassini spacecraft, the possibly overestimated ionospheric electron temperatures, and the excess ion current reported. for the sweeps analysed in detail, we do not find (indirect or direct) evidence of dust having a significant charge-carrying role in saturn's ionosphere. we also produce an estimate of h2o number density from the last six revolutions of cassini through saturn's ionosphere in greater detail than reported by the ion and neutral mass spectrometer. our analysis reveals an ionosphere that is highly structured in latitude across all six final revolutions, with mixing ratios varying with two orders of magnitude in latitude and one order of magnitude between revolutions and altitude. the result is generally consistent with an empirical photochemistry model balancing the production of h+ ions with the h+ loss through charge transfer with e.g. h2o, ch4, and co2, for which water vapour appears as the likeliest dominant source of the signal in terms of yield and concentration. | implications from secondary emission from neutral impact on cassini plasma and dust measurements |
context. on 12 november 2014, the european mission rosetta delivered the philae lander on the nucleus of comet 67p/churyumov-gerasimenko (67p). after the first touchdown, the lander bounced three times before finally landing at a site named abydos.aims: we provide a morphologically detailed analysis of the abydos landing site to support philae's measurements and to give context for the interpretation of the images coming from the comet infrared and visible analyser (civa) camera system onboard the lander.methods: we used images acquired by the osiris narrow angle camera (nac) on 6 december 2014 to perform the analysis of the abydos landing site, which provided the geomorphological map, the gravitational slope map, the size-frequency distribution of the boulders. we also computed the albedo and spectral reddening maps.results: the morphological analysis of the region could suggest that philae is located on a primordial terrain. the abydos site is surrounded by two layered and fractured outcrops and presents a 0.02 km2 talus deposit rich in boulders. the boulder size frequency distribution gives a cumulative power-law index of -4.0 + 0.3/-0.4, which is correlated with gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. the average value of the albedo is 5.8% at λ1 = 480.7 nm and 7.4% at λ2 = 649.2 nm, which is similar to the global albedos derived by osiris and civa, respectively. | characterization of the abydos region through osiris high-resolution images in support of civa measurements |
context. the giotto and rosetta missions gave us the unique opportunity of probing the close environment of cometary ionospheres of 1p/halley (1p) and 67p/churyumov-gerasimenko (67p). the plasma conditions encountered at these two comets were very different from each other, which mainly stem from the different heliocentric distances, which drive photoionization rates, and from the outgassing activities, which drive the neutral densities.aims: we asses the relative contribution of different plasma processes that are ongoing in the inner coma: photoionization, transport, photoabsorption, and electron-ion dissociative recombination. the main goal is to identify which processes are at play to then quantitatively assess the ionospheric density.methods: we provide a set of analytical formulas to describe the ionospheric number density profile for cometary environments that take into account some of these processes. we discuss the validity of each model in the context of the rosetta and giotto missions.results: we show that transport is the dominant loss process at large cometocentric distances and low outgassing rates. chemical plasma loss through e--ion dissociative recombination matters around 67p near perihelion and at 1p during the giotto flyby: its effects increase as the heliocentric distance decreases, that is, at higher outgassing activity and higher photoionization frequency. photoabsorption is of importance for outgassing rates higher than 1028 s-1 and only close to the cometary nucleus, well below the location of both spacecraft. finally, regardless of the processes we considered, the ion number density profile always follows a 1/r law at large cometocentric distances. | comparative study of photo-produced ionosphere in the close environment of comets |
we measure the photometric color in the inner coma of comet 29p/schwassmann-wachmann 1 on nine nights in august and october, 2018. we see variations in the color slope from s′ = (19.72 ± 1.72)% per 0 . 1 μm to s′ = -(6.88 ± 1.72)% per 0 . 1 μm . the blue color is accompanied with increasing brightness suggesting that it is caused by mild outburst activity. we model the extreme values of s′ using agglomerated debris particles. the reddest color suggests a coma dominated by fe-mg silicate particles or organic particles obeying a differential power-law size distribution with power index n ≈ 2.6 ± 0.3. the bluest color is indicative of a high abundance of either water-ice having a power index n ≤ 2 or mg-rich silicate particles having n ≈ 2.5 ± 0.3. from these properties we compute an instantaneous dustload of the inner coma ranging from as low as 1450 ± 150 m3 when there was sporadic activity to 5,900 - 26,300 m3 when there was mild activity. such a dustload is one-two orders of magnitude larger compared to other comets. we perform simulation of the dust motion within the coma to estimate the number of particles leaving our aperture to constrain the dust production rate. we find a dust production rate of qdust ≈ 4.6 ± 2.3 kg/s during the quiescent period, and qdust ≈ 17.6 ± 2.8 kg/s during a mild outburst. such values appear at the lower limit of what has been calculated previously. | color variations of comet 29p/schwassmann-wachmann 1 in 2018 |
the relative fractions of fe in metal, sulfide, or oxide—the fe oxidation state—in the interstellar medium (ism) can provide constraints on the processes that operated on material in the protosolar disk. we used synchrotron-based x-ray absorption spectra of three mineral standards and two kinds of primitive extraterrestrial materials to constrain the oxidation state and mineralogy of the host phase of ism fe as measured by x-ray observations of fe-l ism absorption from the chandra x-ray observatory. oxidation of cometary material appears to have taken place in the nebula, before incorporation into cometary nuclei, although the mechanism is unknown. we also test the hypothesis of ishii et al. that ism solids consist largely of glass with embedded metals and sulfides (gems), enigmatic components of primitive interplanetary dust particles. the hypothesis is not consistent with observations. using fe l-edge absorption spectra of comet 81p/wild 2 samples returned by the stardust mission, we also find that chandra observations are inconsistent with the hypothesis the cometary fine-grained material consists of unaltered interstellar dust. | measurement of the oxidation state of fe in the ism using x-ray absorption spectroscopy |
primitive solar system materials, such as certain types of meteorites, interplanetary dust particles and cometary matter, contain small quantities of refractory dust grains that are older than our solar system. these `presolar grains' condensed in the winds of evolved stars and in the ejecta of stellar explosions, and they were part of the interstellar gas and dust cloud from which our solar system formed 4.57 billion years ago1. interstellar dust is not only stardust but forms in the interstellar medium as well, predominantly as silicates, and, to a lesser extent, as carbonaceous dust and iron particles2. presolar grains represent a sample of stardust, and their abundances in primitive solar system materials can be used to constrain the fraction of stardust among interstellar dust. here we show that the size distribution of presolar silicates follows that observationally derived for interstellar dust, at least in the diameter range 100-500 nm, that current estimates of presolar grain abundances (mass fractions) are at least a factor of 2 too low, and that several per cent of the interstellar dust in the interstellar cloud pre-dating our solar system was stardust, making it a minor but still important ingredient of the starting material from which our solar system formed. | the stardust abundance in the local interstellar cloud at the birth of the solar system |
from the operation of the mupus thermal probe spohn et al. (2015) concluded that the material of the nucleus of 67p/churyumov-gerasimenko is likely to have a high strength, at least locally at the philae landing site. in this work we consider the derived strength of the material in order to constrain its granulation. for this purpose we performed numerical simulations of the long-term sintering of ice-dust granular mixtures of different granulation, covered by a dust mantle. the dust mantle has a thickness of 0-16 cm, and a (pore size and temperature-dependent) thermal conductivity. according to our simulations a hardened layer at least a meter thick forms beneath the dust only when the grains are tens of microns in radius, or smaller. | comet 67p/churyumov-gerasimenko: hardening of the sub-surface layer |
{\tilde{x}}2a\prime\prime hss has yet to be observed in the gas phase in the interstellar medium (ism). hss has been observed in cometary material and in high abundance. however, its agglomeration to such bodies or dispersal from them has not been observed. similarly, hso and hos have not been observed in the ism, either, even though models support their formation from reactions of known sulfur monoxide and hydrogen molecules, among other pathways. consequently, this work provides high-level, quantum chemical rovibrational spectroscopic constants and vibrational frequencies in order to assist in interstellar searches for these radical molecules. furthermore, the hso-hos isomerization energy is determined to be 3.63 kcal mol-1, in line with previous work, and the dipole moment of hos is 36% larger at 3.87 d than hso, making the less stable isomer more rotationally intense. finally, the s-s bond strength in hss is shown to be relatively weak at 30% of the typical disulfide bond energy. consequently, hss may degrade into sh and sulfur atoms, making any ism abundance of hss likely fairly low, as recent interstellar surveys have observed. | on the detectability of the x 2a" hss, hso, and hos radicals in the interstellar medium |
aims: the morphology of cometary surfaces can provide important information to constrain the composition and evolution of comets. in this work, we investigate the sublimation behavior of comet analog materials and how the sample composition affects the evolution of morphological features in laboratory experiments. in our experiments, we used dust ice mixtures as analog material to form observed cometary morphologies.methods: we used ice-dust mixtures in different mixing ratios as cometary analog material. in order to obtain realistic results, we scaled the expected cohesive and gravitational forces on comets to laboratory conditions. the samples were placed in a vacuum sublimation chamber and permanently cooled down to temperatures below 150 k to simulate the space environment. in the experiment, the samples were insolated with a light source from two different directions and alterations on the surface were recorded with a camera.results: we find that the morphology of sublimation residues of ice-dust mixtures is strongly dependent on the ice-dust ratio as well as the insolation direction. high amounts of ice cause constant surface alteration and lead to exotic morphologies. low amounts cause fewer and more episodic surface changes during its sublimation. collapse events resulting in irregular and very rough surfaces occur during horizontal insolation. movies associated to figs 6 and 8 are available at https://www.aanda.org | sublimation of ice-dust mixtures in cooled vacuum environments to reproduce cometary morphologies |
the daytime arietid meteor shower is active from mid-may to late june and is amongst the strongest of the annual meteor showers, comparable in activity and duration to the perseids and the geminids. due to the daytime nature of the shower, the arietids have mostly been constrained by radar studies. the arietids exhibit a long-debated discrepancy in the semi-major axis and the eccentricity of meteoroid orbits as measured by radar and optical surveys. radar studies yield systematically lower values for the semi-major axis and eccentricity, where the origin of these discrepancies remain unclear. the proposed parent bodies of the stream include comet 96p/machholz [mcintosh, b.a., 1990. comet p/machholz and the quadrantid meteor stream. icarus 86, 894 299-304. doi:10.1016/0019-1035(90)90219-y.] and more recently a member of the marsden group of sun-skirting comets, p/1999 j6 [sekanina, z., chodas, p.w., 2005. origin of the marsden and kracht groups of sunskirting 922 comets. i. association with comet 96p/machholz and its interplanetary complex. apjs 923 161, 551-586. doi:10.1086/497374.]. in this work, we present detailed numerical modelling of the daytime arietid meteoroid stream, with the goal to identifying the parent body and constraining the age of the stream. we use observational data from an extensive survey of the arietids by the canadian meteor orbit radar (cmor), in the period of 2002-2013, and several optical observations by the sonotaco meteor network and the cameras for all-sky meteor surveillance (cams). we find the most plausible scenario to be that the age and the formation mechanism of the arietids is consistent with continuous cometary activity of 96p/machholz over a time interval of ≈12,000 years. the sun-skirting comet p/1999 j6 suggested by [sekanina, z., chodas, p.w., 2005. origin of the marsden and kracht groups of sunskirting 922 comets. i. association with comet 96p/machholz and its interplanetary complex. apjs 923 161, 551-586. doi:10.1086/497374.] may contribute to the shower, but the comet break up prior to 950 ce they propose does not reproduce all the characteristics of the observed shower. | the age and the probable parent body of the daytime arietid meteor shower |
spectral parameters measured by the rosetta/virtis imaging spectrometer on the nucleus of comet 67p/churyumov-gerasimenko were studied as a function of incidence, emission and phase angles. a statistical analysis was undertaken for a number of spectral parameters: reflectance at seven wavelengths (0.55, 0.75, 1.2, 1.7, 2.0, 2.8 and 4.0 μm), the depth and centre of the 3.2 μm organics band, and the visible and infrared slopes. different photometric behaviours were assessed over the entire comet surface, on the four different comet macro-regions (head, neck, body and bottom) and for different local solar times. phase functions are on average both spatially and temporally constant, indicating an overall homogeneity of optical properties. comparison between phase functions of 67p/churyumov-gerasimenko and of other comets explored by space missions indicates a variation of phase curve steepness among comets, larger than expected for objects having similar albedo. this can be ascribed to different surface roughness, in turn due to different levels of surface erosion. band depth appears to be independent of phase angle, which may help in constraining the surface composition. however, its band centre slightly moves to longer wavelengths with increasing incidence angle, possibly due to exposure of low amounts of water ice due to a weak cometary activity at increasing temperatures. water ice abundance is also the main driver of the photometric behaviour of the visible and infrared slope, since larger water ice abundance causes a slope decrease and a phase reddening increase in the neck region and during the nighttime. | photometric behaviour of 67p/churyumov-gerasimenko and analysis of its pre-perihelion diurnal variations |
submillimeter/far-ir spectroscopy was used to detect and quantify organic molecules sublimated after the ultraviolet photolysis (at 12 k) and warm-up (up to 300 k) of a methanol (ch3oh) ice sample. eleven sublimated photoproducts were uniquely identified: carbon monoxide (co), formaldehyde (h2co), ketene (c2h2o), acetaldehyde (ch3cho), ethylene oxide (ch2och2), vinyl alcohol (ch2choh), ethanol (ch3ch2oh), dimethyl ether (ch3och3), methyl formate (hcooch3), glycolaldehyde (hoch2cho), and acetone ((ch3)2co). two additional products were detected in the photolyzed ice by fourier-transform infrared (ftir) spectroscopy: carbon dioxide (co2) and methane (ch4). the rotational temperatures and gas densities were calculated for the organics containing two or more c atoms via a rotation diagram analysis, and the gas-phase submillimeter/far-ir technique was used in tandem with mass spectrometry and ftir spectroscopy of the ice during photolysis. the abundance ratios of the sublimated species (normalized to methanol) were compared to those observed in hot cores (orion-kl, sagittarius b2(n), and iras 16293-2422(b)) and in comets c/2014 q2 (lovejoy) and 67p/churyumov-gerasimenko. | sublimation of laboratory ices millimeter/submillimeter experiment (sublime): structure-specific identifications of products from uv-photolyzed methanol ice |
explanation of the observed gas activity based on the parameters of the comet's nucleus is not an obvious matter. solutions based on certain thermal models can be obtained, but the use of arbitrary values for poorly known model parameters is always required. in this work, we carry out a study of the dependence of gas activity on these parameters and assess the importance of each of them. we consider model porous dust layers of diverse structures. solid state and gas thermal conductivities are examined to estimate the possible range of effective thermal conductivity. the simulation results are embedded in a thermal model, explicitly including a radiative thermal conductivity and a resistance of the dust layer against the gas flow. sublimation of water ice and supervolatiles (co2 and co) is tested at different heliocentric distances. it is shown that when sublimation is the main energy sink, the role of uncertainties in the structure of the layer is small. as the relative contribution of sublimation decreases, the scatter of solutions reaches tens of per cent. the expected large uncertainties in the effective thermal conductivity can also significantly change the gas production. the analysis performed shows that, in spite of the parameter range having been narrowed down by results from the rosetta mission, the unavoidable uncertainty in the values of some model parameters (e.g. thermal conductivity) blurs the theoretical simulation estimates. instead of presenting a narrow set of specific solutions, it is desirable to analyse the entire range of possible solutions. | sensitivity of modelled cometary gas production on the properties of the surface layer of the nucleus |
aims: we theoretically investigated the dimerization of methanimine, ch2=nh, a process that has been invoked to explain the formation of haze in the atmosphere of titan and nitrogen organic compounds in interstellar/cometary ice analogs.methods: we used density functional theory to characterize the minima and transition states of the investigated processes, while we computed the energetics with the more accurate coupled cluster method. we then obtained rate coefficients via combination of capture theory and statistical calculations.results: the process involving two neutral molecules is characterized by significant energy barriers and cannot occur under the low temperature conditions of titan or interstellar/cometary ices unless an external energy source is provided. on the contrary, the processes involving one molecule of either ionized or protonated methanimine are barrierless reactions and can therefore contribute to the formation of larger ions. in particular, the reaction involving ionized methanimine can also be efficient in the very low temperature conditions of the interstellar medium, leading to products of general formula c2n2h5+.conclusions: the present work suggests that polymerization of methanimine is not an efficient process in space unless an ionization/protonation or a significant energy source is available. | dimerization of methanimine and its charged species in the atmosphere of titan and interstellar/cometary ice analogs |
we present a global geomorphological map of comet 67p/churyumov-gerasimenko (67p/c-g) using data acquired by the rosetta orbiter's osiris narrow angle camera. the images used in our study were acquired between 2014 august and 2015 may, before 67p/c-g passed through perihelion. imagery of the southern hemisphere was included in our study, allowing us to compare the contrasting hemispheres of 67p/c-g in a single study. our work also puts into greater context the morphologies studied in previous works, and also the morphologies observed on previously visited cometary nuclei. relative to other nuclei, 67p/c-g appears most similar to 81p/wild 2, with a topographically heterogeneous surface dominated by smooth-floored pits. our mapping describes the landscapes of 67p/c-g when they were first observed by rosetta, and our map can be used to detect changes in surface morphologies after its perihelion passage. our mapping reveals strong latitudinal dependences for emplaced units and a highly heterogeneous surface. layered bedrock units that represent the exposed nucleus of 67p/c-g are dominant at southern latitudes, while topographically smooth, dust covered regions dominate the northern hemisphere. equatorial latitudes are dominated by smooth terrain units that show evidence for flow structures. we observe no obvious differences between the comet's two lobes, with the only longitudinal variations being the imhotep and hatmehit basins. these correlations suggest a strong seasonal forcing on the surface evolution of 67p/c-g, where materials are transported from the southern hemisphere to northern hemisphere basins over multiple orbital time-scales. | geomorphology of comet 67p/churyumov-gerasimenko |
downward fluxes of fe and na, measured near the mesopause with the university of colorado lidars near boulder, and a chemical ablation model developed at the university of leeds, are used to constrain the velocity/mass distribution of the meteoroids entering the atmosphere and to derive an improved estimate for the global influx of cosmic dust. we find that the particles responsible for injecting a large fraction of the ablated material into the earth's upper atmosphere enter at relatively slow speeds and originate primarily from the jupiter family of comets. the global mean na influx is 17,200 ± 2800 atoms/cm2/s, which equals 298 ± 47 kg/d for the global input of na vapor and 150 ± 38 t/d for the global influx of cosmic dust. the global mean fe influx is 102,000 ± 18,000 atoms/cm2/s, which equals 4.29 ± 0.75 t/d for the global input of fe vapor. | measurements of the vertical fluxes of atomic fe and na at the mesopause: implications for the velocity of cosmic dust entering the atmosphere |
hyperactive comets have high water production rates, with inferred sublimation areas of order the surface area of the nucleus. comets 46p/wirtanen and 103p/hartley 2 are two examples of this cometary class. based on observations of comet hartley 2 by the deep impact spacecraft, hyperactivity appears to be caused by the ejection of water-ice grains and/or water-ice-rich chunks of nucleus into the coma. these materials increase the sublimating surface area and yield high water production rates. the historic close approach of comet wirtanen to earth in 2018 afforded an opportunity to test hartley 2-style hyperactivity in a second jupiter-family comet. we present high spatial resolution, near-infrared spectroscopy of the inner coma of wirtanen. no evidence for the 1.5 or 2.0 μm water-ice absorption bands is found in six 0.8-2.5 μm spectra taken around perihelion and closest approach to earth. in addition, the strong 3.0 μm water-ice absorption band is absent in a 2.0-5.3 μm spectrum taken near perihelion. using spectroscopic and sublimation lifetime models, we set constraints on the physical properties of the ice grains in the coma, assuming they are responsible for the comet's hyperactivity. we rule out pure water-ice grains of any size, given their long lifetime. instead, the hyperactivity of the nucleus and lack of water-ice absorption features in our spectra can be explained either by icy grains on the order of 1 μm in size with a small amount of low-albedo dust (greater than 0.5% by volume) or by large chunks containing significant amounts of water ice. | nondetection of water-ice grains in the coma of comet 46p/wirtanen and implications for hyperactivity |
aims: we investigate the influence of three basic factors on water production rate as a function of heliocentric distance: nucleus shape, the spin axis orientation, and the distribution of activity on a comet's surface.methods: we used a basic water sublimation model driven by solar insolation to derive total production rates for different nuclei shapes and spin axis orientations using the orbital parameters of 67p/churyumov-gerasimenko. we used known shape models derived from prior missions to the jupiter family and short period comets. the slopes of production rates versus heliocentric distance were calculated for the different model setups.results: the standard (homogeneous) outgassing model confirms the well-known result regarding the heliocentric dependence of water production rate that remains invariant for different nuclei shapes as long as the rotation axis is perpendicular to the orbital plane. when the rotation axis is not perpendicular, the nucleus shape becomes a critically important factor in determining the water production curves as the illuminated cross section of the nucleus changes with heliocentric distance. shape and obliquity can produce changes in the illuminated cross section of up to 50% over an orbit. in addition, different spin axis orientations for a given shape can dramatically alter the pre- and post-perihelion production curves, as do assumptions about the activity distribution on the surface. if, however, the illuminated cross section of the nucleus is invariant, then the dependence on the above parameters is weak, as demonstrated here with the 67p/churyumov-gerasimenko shape. the comets hartley 2 and wild 2 are shown to yield significantly different production curve shapes for the same orbit and orientation as 67p/cg, varying by as much as a factor of three as a result of only changing the nucleus shape. finally, we show that varying just three basic parameters, shape, spin axis orientation, and active spots distribution on the surface can lead to arbitrary deviations from the expected inverse square law dependence of water production rates near 1 au.conclusions: with the results obtained, we cannot avoid the conclusion that, without prior knowledge of basic parameters (shape, spin axis orientation, activity locations), it is difficult to reveal the nature of cometary outgassing from the heliocentric water production rates. similarly, the inter-comparison of water production curves of two such comets may not be meaningful. | interpretation of heliocentric water production rates of comets |
aims: we present a study of the meteor complex of the short-period comet 2p/encke.methods: for five perihelion passages of the parent comet in the past, we modeled the associated theoretical stream. specifically, each of our models corresponds to a part of the stream characterized with a single value of the evolutionary time and a single value of the strength of the poynting-robertson effect. in each model, we follow the dynamical evolution of 10 000 test particles via a numerical integration. the integration was performed from the time when the set of test particles was assumed to be ejected from the comet's nucleus up to the present. at the end of the integration, we analyzed the mean orbital characteristics of those particles that approached the earth's orbit, and thus created a meteor shower or showers. using the mean characteristics of the predicted shower, we attempted to select its real counterpart from each of five considered databases (one photographic, three video, and one radio-meteor). if at least one attempt was successful, the quality of the prediction was evaluated.results: the modeled stream of 2p approaches the earth's orbit in several filaments with the radiant areas grouped in four cardinal directions of ecliptical showers. these groups of radiant areas are situated symmetrically with respect to the apex of the earth's motion around the sun. specifically, we found that showers #2, #17, #156, #172, #173, #215, #485, #624, #626, #628, #629, #632, #634, #635, #636, and #726 in the iau-mdc list of all showers are dynamically related to 2p. in addition, we found five new 2p-related showers in the meteor databases considered. | meteoroid-stream complex originating from comet 2p/encke |
context. thanks to our expanding knowledge of the galactic and stellar neighborhood of the solar system, modern long-period comet motion studies must take into account both stellar perturbations and the overall galactic potential.aims: our aim is to propose algorithms and methods that aid in performing numerical integrations of equations of motion for a small body of the solar system that are much faster and with greater precision.methods: we propose a new formulation of the equations of motion formulated in the solar system barycentric frame, but one that accurately accounts for the differential perturbations caused by the galactic potential. to make certain these equations are applied effectively, we provide numerical ephemerides of the galactic positions of the sun and a set of potential stellar perturbers.results: the proposed methods raise the precision by several orders of magnitude and, simultaneously, greatly reduce the necessary cpu time. the application of this approach is presented with the example of a detailed dynamical study of the past motion of comet c/2015 xy1. | galactic and stellar perturbations of long-period comet motion. practical considerations |
we consider the stochastic heat equation on $\mathbb r^d$ with multiplicative space-time white noise noise smoothed in space. for $d\geq 3$ and small noise intensity, the solution is known to converge to a strictly positive random variable as the smoothing parameter vanishes. in this regime, we study the rate of convergence and show that the pointwise fluctuations of the smoothened solutions as well as that of the underlying martingale of the brownian directed polymer converge to a gaussian limit. | fluctuation and rate of convergence for the stochastic heat equation in weak disorder |
comet interceptor is an esa f-class mission expected to launch in 2028 on the same launcher as esa's ariel mission. comet interceptor's science payload consists of three spacecraft, a primary spacecraft that will carry two smaller probes to be released at the target. the three spacecraft will fly-by the target along different chords, providing multiple simultaneous perspectives of the comet nucleus and its environment. each of the spacecraft will be equipped with different but complementary instrument suites designed to study the far and near coma environment and surface of a comet or interstellar object (iso). the primary spacecraft will perform a fly-by at ~1000 km from the target. the two smaller probes will travel deeper into the coma, closer to the nucleus. the mission is being designed and launched without a specific comet designated as its main target. comet interceptor will travel to the sun-earth l2 lagrangian point with ariel and wait in hibernation until a suitable long-period comet (lpc) is found that will come close enough to the sun for the spacecraft to maneuver to an encounter trajectory. to prepare for all eventualities, the science team has assembled a preliminary set of backup targets from the known jupiter family comets, where a suitable fly-by trajectory can be achieved during the nominal mission timeline (including the possibility of some launch delay). to better prioritize this list, we are releasing our potential backup targets in order to solicit the planetary community's help with observations of these objects over future apparitions and to encourage publication of archival data on these objects. | potential backup targets for comet interceptor |
in its 16 years of scientific measurements, the spitzer space telescope performed ground-breaking and key infrared measurements of solar system objects near and far. targets ranged from the smallest planetesimals to the giant planets; spitzer helped us to reshape our understanding of these objects while also laying the groundwork for future infrared space-based observations like those to be undertaken by the james webb space telescope in the 2020s. in this review article, we describe how spitzer advanced our knowledge of solar system formation and evolution through observations of small outer solar system planetesimals—that is, comets, centaurs and kuiper belt objects (kbos). relics from the early formation era of our solar system, these objects hold important information about the processes that created them.we group spitzer's key contributions into three broad classes: characterization of new solar system objects (comets d/ison 2012 s1, c/2016 r2 and 1i/`oumuamua); large population surveys of known objects (comets, centaurs and kbos); and compositional studies through spectral measurements of body surfaces and emitted materials. | spitzer's solar system studies of comets, centaurs and kuiper belt objects |
the plasma environment near comet 67p/churyumov-gerasimenko (67p/cg) is dynamically affected by various factors, including the incident solar wind and outgassing from the nucleus. the rosetta spacecraft magnetometer (mag) instrument observations near perihelion showed crossing events into a magnetic field-free region at about 170 km from the nucleus in 2015 july at 1.26 au from the sun. at each crossing, the magnitude of the magnetic field dropped by more than 20 nt to near zero. we compared the ion and electron sensor (ies) electron differential flux energy spectrum inside and outside the crossing boundaries. the ies observations show a modest but consistent drop in electron flux for energies between 40 ev and a few hundred ev at each cavity crossing event. this drop in the electron spectra might be due to the absence or attenuation of solar wind electrons inside the observed diamagnetic regions, which might or might not be a diamagnetic cavity. there is no apparent simple linear correlation between the electron count rate measured by the ies at different energies and the magnitude of the magnetic field, however; at all energies, the highest electron count rates are recorded at the highest magnetic field magnitudes. from model-data comparisons it seems that inside diamagnetic regions, pure coma photoelectrons are not sufficient to explain the observations and that a trapping mechanism and/or infused solar wind electrons are necessary to explain the observed electron fluxes. | plasma environment around comet 67p/churyumov-gerasimenko at perihelion: model comparison with rosetta data |
models of the solar system evolution show that almost all the primitive material leftover from the formation of the planets was ejected to the interstellar space as a result of dynamical instabilities. accordingly, minor bodies should also be ejected from other planetary systems and should be abundant in the interstellar space. the number density of such objects, and prospects for their detection as they penetrate through the solar system, were speculated about for decades, recently rising high hopes with the pan-starrs and lsst surveys. these expectations materialized on 18 october 2017 with the pan-starrs's discovery of 1i/'oumuamua. here we report homogeneous photometric observations of this body from gemini north, which densely cover a total of 8 hr over two nights. a combined ultra-deep image of 1i/'oumuamua shows no signs of cometary activity, confirming the results from earlier, less sensitive searches. our data also show an enormous range of brightness variations > 2.5 mag, larger than ever observed in the population of solar system objects, suggesting a very elongated shape of the body. but most significantly, the light curve does not repeat exactly from one rotation cycle to another and its double-peaked periodicity of 7.5483 $\pm$ 0.0073 hr from our data is inconsistent with earlier determinations. these are clear signs of a tumbling motion, a remarkable characteristic of 1i/'oumuamua's rotation, consistent with a catastrophic collision in the distant past. this first example of an impacted minor body of exosolar origin indicates that collisional evolution of minor body populations in other planetary systems is not uncommon. | tumbling motion of 1i/'oumuamua reveals body's violent past |
context. the origin of water in the stratospheres of giant planets has been an outstanding question ever since its first detection by the infrared space observatory some 20 years ago. water can originate from interplanetary dust particles, icy rings and satellites, and large comet impacts. analyses of herschel space observatory observations have proven that the bulk of jupiter's stratospheric water was delivered by the shoemaker-levy 9 impacts in 1994. in 2006, the cassini mission detected water plumes at the south pole of enceladus, which made the moon a serious candidate for saturn's stratospheric water. further evidence was found in 2011 when herschel demonstrated the presence of a water torus at the orbital distance of enceladus that was fed by the moon's plumes. finally, water falling from the rings onto saturn's uppermost atmospheric layers at low latitudes was detected during the final orbits of cassini's end-of-mission plunge into the atmosphere.aims: in this paper, we use herschel mapping observations of water in saturn's stratosphere to identify its source.methods: we tested several empirical models against the herschel-hifi and -pacs observations, which were collected on december 30, 2010, and january 2, 2011, respectively.results: we demonstrate that saturn's stratospheric water is not uniformly mixed as a function of latitude, but peaks at the equator and decreases poleward with a gaussian distribution. we obtain our best fit with an equatorial mole fraction 1.1 ppb and a half width at half maximum of 25°, when accounting for a temperature increase in the two warm stratospheric vortices produced by saturn's great storm of 2010-2011.conclusions: this work demonstrates that enceladus is the main source of saturn's stratospheric water. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa. | herschel map of saturn's stratospheric water, delivered by the plumes of enceladus |
to test a technique to be used on the white-light imager onboard the recently launched parker solar probe mission, we performed a numerical differentiation of the brightness profiles along the photometric axis of the f-corona models that are derived from stereo ahead sun earth connection heliospheric investigation observations recorded with the hi-1 instrument between 2007 december and 2014 march. we found a consistent pattern in the derivatives that can be observed from any s/c longitude between about 18° and 23° elongation with a maximum at about 21°. these findings indicate the presence of a circumsolar dust density enhancement that peaks at about 23° elongation. a straightforward integration of the excess signal in the derivative space indicates that the brightness increase over the background f-corona is on the order of 1.5%-2.5%, which implies an excess dust density of about 3%-5% at the center of the ring. this study has also revealed (1) a large-scale azimuthal modulation of the inner boundary of the pattern, which is in clear association with mercury’s orbit; and (2) a localized modulation of the inner boundary that is attributable to the dust trail of comet 2p/encke, which occurs near ecliptic longitudes corresponding to the crossing of encke’s and mercury’s orbital paths. moreover, evidence of dust near the s/c in two restricted ranges of ecliptic longitudes has also been revealed by this technique, which is attributable to the dust trails of (1) comet 73p/schwassmann-wachmann 3, and (2) 169p/neat. | evidence for a circumsolar dust ring near mercury’s orbit |
we measure the degree of linear polarization of comet 46p/wirtanen during two months, embracing the perihelion passage in 2018 december with phase angles ranging from α = 18.1° to 46.4°. the polarimetric response pq obtained resembles what was previously found in comet c/1975 v1 (west). this suggests 46p/wirtanen belongs to a group of comets with high maximum positive polarization. in the first half of 2019 february, we conducted bvri photometry of 46p/wirtanen and found either neutral or blue colour of its dust, which is in good accordance with measurements of c/1975 v1 (west). while aperture-averaged polarimetry of 46p/wirtanen reveals a nearly zero polarization pq at the lowest phase angle α = 18.1°, simultaneous imaging polarimetry suggests that the negative polarization (pq < 0) arises in a region of within 5000 km of the nucleus, where the negative polarization could be as strong as pq = -(1.44 ± 0.15) per cent. this observation suggests the existence of the circumnucleus halo and that the coma is populated by at least two types of dust particles. one of those reveals a low positive polarization at side scattering and high negative polarization near backscattering. both polarimetric features are simultaneously produced by weakly absorbing mg-rich silicate particles. another type of dust produces solely positive polarization that could be attributed to carbonaceous particles. this composition of 46p/wirtanen coma appears to be similar with what was previously found in comet c/1975 v1 (west). | monitoring polarization in comet 46p/wirtanen |
pillars and globules are the best examples of the impact of the radiation and wind from massive stars on the surrounding interstellar medium. we mapped the g287.84-0.82 cometary globule (with the treasure chest cluster embedded in it) in the south pillars region of carina (i) in [c ii], 63 μm [o i], and co(11-10) using the heterodyne receiver array upgreat on sofia and (ii) in j = 2-1 transitions of co, 13co, c18o, and j = 3-2 transitions of h2co using the apex telescope in chile. we used these data to probe the morphology, kinematics, and physical conditions of the molecular gas and the photon-dominated regions (pdrs) in g287.84-0.82. the velocity-resolved observations of [c ii] and [o i] suggest that the overall structure of the pillar (with red-shifted photoevaporating tails) is consistent with the effect of fuv radiation and winds from η car and o stars in trumpler 16. the gas in the head of the pillar is strongly influenced by the embedded cluster, whose brightest member is an o9.5 v star, cpd -59°2661. the emission of the [c ii] and [o i] lines peak at a position close to the embedded star, while all the other tracers peak at another position lying to the northeast consistent with gas being compressed by the expanding pdr created by the embedded cluster. the molecular gas inside the globule was probed with the j = 2-1 transitions of co and isotopologs as well as h2co, and analyzed using a non-local thermodynamic equilibrium model (escape-probability approach), while we used pdr models to derive the physical conditions of the pdr. we identify at least two pdr gas components; the diffuse part ( 104 cm-3) is traced by [c ii], while the dense (n 2-8 × 105 cm-3) part is traced by [c ii], [o i], and co(11-10). using the f = 2-1 transition of [13c ii] detected at 50 positions in the region, we derived optical depths (0.9-5), excitation temperatures (80-255 k) of [c ii], and n(c+) of 0.3-1 × 1019 cm-2. the total mass of the globule is 1000 m⊙, about half of which is traced by [c ii]. the dense pdr gas has a thermal pressure of 107-108 k cm-3, which is similar to the values observed in other regions. a copy of the reduced datacubes (fits files) is available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/626/a131 | opening the treasure chest in carina |
we review the development of dust science from the first ground-based astronomical observations of dust in space to compositional analysis of individual dust particles and their source objects. a multitude of observational techniques is available for the scientific study of space dust: from meteors and interplanetary dust particles collected in the upper atmosphere to dust analyzed in situ or returned to earth. in situ dust detectors have been developed from simple dust impact detectors determining the dust hazard in earth orbit to dust telescopes capable of providing compositional analysis and accurate trajectory determination of individual dust particles in space. the concept of dust astronomy has been developed, recognizing that dust particles, like photons, carry information from remote sites in space and time. from knowledge of the dust particles' birthplace and their bulk properties, we learn about the remote environment out of which the particles were formed. dust observatory missions like cassini, stardust, and rosetta study saturn's satellites and rings and the dust environments of comet wild 2 and comet churyumov-gerasimenko, respectively. supplemented by simulations of dusty processes in the laboratory we are beginning to understand the dusty environments in space. | the dawn of dust astronomy |
a 2000-2017 set of long-period comets with high-quality orbits of perihelion distance <1 au is used to show that the objects that perish shortly before perihelion are nearly exclusively the oort cloud comets, especially those with perihelia within 0.6 au of the sun, intrinsically fainter, and dust poor. their propensity for disintegration is much higher than predicted by bortle's perihelion survival rule, prompting the author to propose a new synoptic index to be tested in future prognostication efforts. by their susceptibility to demise near the sun, the nuclei of oort cloud comets differ dramatically from the nuclei of other long-period comets that almost always survive. in this scenario, `oumuamua -- discovered after perihelion -- is in all probability a major piece of debris of an interstellar comet that was bound to perish near perihelion if it was similar to, though much fainter than, the known oort cloud comets. the nondetection of `oumuamua by the spitzer space telescope is compatible with optical data for pancake shape, but not for cigar shape, with the maximum dimension not exceeding 160 m (at an 0.1 albedo). although the solar radiation pressure induced nongravitational acceleration requires very high porosity, `oumuamua's estimated mass is orders of magnitude greater than for a cloud of unbound submicron-sized dust grains of equal cross section. the acceleration could have displaced `oumuamua by 250,000 km in 50 days, scattering other potential debris over a large volume of space. | 1i/`oumuamua and the problem of survival of oort cloud comets near the sun |
context. the large and vertically non-uniform abundance of co in neptune's atmosphere has been interpreted as the result of past cometary impact(s), either single or distributed in size and time, which could also be at the origin of neptune's hcn.aims: we aim to provide observational support for this scenario by searching for other comet-induced species, in particular carbon sulfide (cs) which has been observed continuously in jupiter since the 1994 shoemaker-levy 9 impacts.methods: in april 2016 we used the alma interferometer to search for cs(7-6) at 342.883 ghz in neptune.results: we report on the detection of cs in neptune's atmosphere, the first unambiguous observation of a sulfur-bearing species in a giant planet beyond jupiter. carbon sulfide appears to be present only at submillibar levels, with a column density of (2.0-3.1) × 1012 cm-2, and a typical mixing ratio of (2-20) × 10-11 that depends on its precise vertical location. the favoured origin of cs is deposition by a putative large comet impact several centuries ago, and the strong depletion of cs with respect to co - compared to the jupiter case - is likely due to the cs sticking to aerosols or clustering to form polymers in neptune's lower stratosphere.conclusions: the cs detection, along with recent analyses of the co profile, reinforces the presumption of a large comet impact into neptune ~1000 yr ago, that delivered co, cs, and hcn at the same time. | detection of cs in neptune's atmosphere from alma observations |
in this work, we present the results of an observational study of 2i/borisov carried out with the 10.4-m gran telescopio canarias (gtc) and the 3.6-m telescopio nazionale galileo (tng), both telescopes located at the roque de los muchachos observatory, in the island of la palma (spain). the study includes images in the visible and near-infrared, as well as visible spectra in the 3600-9200 å wavelength range. n-body simulations were also performed to explore its orbital evolution and galactic kinematic context. the comet's dust continuum and near-infrared colours are compatible with those observed for solar system comets. from its visible spectrum on the nights of 2019 september 24 and 26, we measured cn gas production rates q(cn) = (2.3 ± 0.4) × 1024 mol s-1 and q(cn) = (9.5 ± 0.2) × 1024 mol s-1, respectively, in agreement with measurements reported by other authors on similar nights. we also obtained an upper limit for the c2 production rate of q(c2) < (4.5 ± 0.1) × 1024 mol s-1. dust modelling results indicate a moderate dust production rate of ∼50 kg s-1 at heliocentric distance rh = 2.6 au, with a differential power-law dust size distribution of index ∼-3.4, within the range reported for many comet comae. our simulations show that the galactic velocity of 2i/borisov matches well that of known stars in the solar neighbourhood and also those of more distant regions of the galactic disc. | visible and near-infrared observations of interstellar comet 2i/borisov with the 10.4-m gtc and the 3.6-m tng telescopes |
a new experimental setup, interstellar ice-dust experiment (inside), was designed for studying cosmic grain analogs represented by ice-coated carbon- and silicate-based dust grains. with the new instrument, we can simulate the physical and chemical conditions prevailing in interstellar and circumstellar environments. the setup combines ultrahigh vacuum and low-temperature conditions with infrared spectroscopy and mass spectrometry. using inside, we plan to investigate physical and chemical processes, such as adsorption, desorption, molecule formation, on the surface of dust/ice samples. first experiments on the photodesorption of water ice molecules from the surface of silicate and carbon grains by uv photons revealed a strong influence of the surface properties on the desorption yield, in particular in the monolayer regime. in the second experiment, the thermal desorption of cometary ice analogs composed of six molecular components was studied for the first time. codesorption of co2 and ch3oh with o2 indicates that at high o2 concentrations in cometary or interstellar ices, “heavy” ice molecules can be partly trapped in o2 and enter the gas phase much earlier than expected. this effect could explain astronomical detections of complex organic molecules in cold dense interstellar clouds. | photodesorption of water ice from dust grains and thermal desorption of cometary ices studied by the inside experiment |
we present the results of millimetre-wave spectroscopic and continuum observations of the comet c/2020 f3 (neowise) undertaken with the institut de radioastronomie millimétrique (iram) 30-m and the northern extended millimeter array (noema) telescopes on 22, 25-27 july, and 7 august 2020. production rates of hcn, hnc, ch3oh cs, h2co, ch3cn, h2s, and co were determined with upper limits on six other species. the comet shows abundances within the range observed for other comets. the co abundance is low (3.2% relative to water), while h2s is relatively abundant (1.1% relative to water). the h2co abundance shows a steep variation with heliocentric distance, possibly related to a distributed production from the dust or macro-molecular source. the ch3oh and h2s production rates show a slower decrease post-perihelion than water. there was no detection of the nucleus point source contribution based on the interferometric map of the continuum (implying a size of r < 4.7 km), but this yielded an estimate of the dust production rate, leading to a relatively low dust-to-gas ratio of 0.7 ± 0.3 on 22.4 july 2020. the radio spectra are available only at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/668/a171 | observations of comet c/2020 f3 (neowise) with iram telescopes |
we review the recent observations of protoplanetary disks together with relevant theoretical studies with an emphasis on the evolution of volatiles. in the last several years atacama large millimeter/submillimeter array (alma) provided evidence of grain growth, gas-dust decoupling, and sub-structures such as rings and gaps in the dust continuum. molecular line observations revealed radial and vertical distributions of molecular abundances and also provided significant constraints on the gas dynamics such as turbulence. while sub-millimeter and millimeter observations mainly probe the gas and dust outside the radius of several au, ice and inner warm gas are investigated at shorter wavelengths. gas and dust dynamics are key to connecting these observational findings. one of the emerging trends is inhomogeneous distributions of elemental abundances, most probably due to dust-gas decoupling. | the physical and chemical processes in protoplanetary disks: constraints on the composition of comets |
discovery of nine populations in a set of 193 select soho kreutz sungrazers (sekanina 2021) is confirmed for the first time via a histogram of the true longitudes of the ascending node, constructed for a revised set of 220 select sungrazers imaged exclusively by the soho's c2 coronagraph. marsden's orbits are approximately corrected for effects of the out-of-plane nongravitational force. population i displays two peaks in the histogram, one presumably belonging to a side branch alike to population pe, but with no related naked-eye sungrazer known. swarms/clusters of objects are commonplace, providing evidence on cascading fragmentation proceeding throughout the orbit. augmentation to all c2-only soho kreutz comets, aimed at removing deliberate bias against populations i and pe, reduces the appearance of populations ia and pre-i to bulges along the slope of the histogram because of the swollen wings of populations i and pe, respectively. populations ii through iv change very little or not at all. the high population i-to-ii abundance ratio, of 14:1, may be a product of temporal limitations in fragment release. a drop in the number of fragments toward the ends of the nodal-longitude distribution, especially from population ii to iv, is in line with the contact-binary model. | populations of the kreutz sungrazer system in a soho database |
using visible multiobject spectrograph (vimos)-integral field unit (ifu) observations, we study the interstellar medium (ism) of two star-forming dwarf galaxies, um 461 and mrk 600. our aim was to search for the existence of metallicity inhomogeneities that might arise from infall of nearly pristine gas feeding ongoing localized star formation. the ifu data allowed us to study the impact of external gas accretion on the chemical evolution as well as the ionized gas kinematics and morphologies of these galaxies. both systems show signs of morphological distortions, including cometary-like morphologies. we analysed the spatial variation of 12 + log(o/h) abundances within both galaxies using the direct method (te), the widely applied hii-chi-mistry code, as well as by employing different standard calibrations. for um 461, our results show that the ism is fairly well mixed, at large scales; however, we find an off-centre and low-metallicity region with 12 + log(o/h) < 7.6 in the sw part of the brightest h ii region, using the direct method. this result is consistent with the recent infall of a metal-poor h i cloud into the region now exhibiting the lowest metallicity, which also displays localized perturbed neutral and ionized gas kinematics. mrk 600 in contrast, appears to be chemically homogeneous on both large and small scales. the intrinsic differences in the spatially resolved properties of the ism in our analysed galaxies are consistent with these systems being at different evolutionary stages. | detecting metal-poor gas accretion in the star-forming dwarf galaxies um 461 and mrk 600 |
context. the study of distant comets, which are active at large heliocentric distances, is important for a better understanding of their physical properties and mechanisms of long-lasting activity.aims: we analyzed the dust environment of the distant comet c/2014 a4 (sonear), with a perihelion distance near 4.1 au, using comprehensive observations obtained by different methods.methods: we present an analysis of spectroscopy, photometry, and polarimetry of comet c/2014 a4 (sonear), which were performed on november 5-7, 2015, when its heliocentric distance was 4.2 au and phase angle was 4.7°. long-slit spectra and photometric and linear polarimetric images were obtained using the focal reducer scorpio-2 attached to the prime focus of the 6 m telescope bta (sao ras, russia). we simulated the behavior of color and polarization in the coma presenting the cometary dust as a set of polydisperse polyshapes rough spheroids.results: no emission features were detected in the 3800-7200 å wavelength range. the continuum showed a reddening effect with the normalized gradient of reflectivity 21.6 ± 0.2% per 1000 å within the 4650-6200 å wavelength region. the fan-like structure in the sunward hemisphere was detected. the radial profiles of surface brightness differ for r-sdss and g-sdss filters, indicating a predominance of submicron and micron-sized particles in the cometary coma. the dust color (g-r) varies from 0.75 ± 0.05m to 0.45 ± 0.06m along the tail. for an aperture radius near 20 000 km, the dust productions in various filters were estimated as afρ = 680 ± 18 cm (r-sdss) and 887 ± 16 cm (g-sdss). the polarization map shows spatial variations in polarization over the coma from about -3% near the nucleus to -8% at a cometocentric distance of about 150 000 km. our simulations show that the dust particles are dominated (or covered) by ice and tholin-like organics. spatial changes in the color and polarization can be explained by particle fragmentation. | photometry, spectroscopy, and polarimetry of distant comet c/2014 a4 (sonear) |
the mineralogy of comet 81p/wild 2 particles, collected in aerogel by the stardust mission, has been determined using synchrotron fe-k x-ray absorption spectroscopy with in situ transmission xrd and x-ray fluorescence, plus complementary microraman analyses. our investigation focuses on the terminal grains of eight stardust tracks: c2112,4,170,0,0; c2045,2,176,0,0; c2045,3,177,0,0; c2045,4,178,0,0; c2065,4,187,0,0; c2098,4,188,0,0; c2119,4,189,0,0; and c2119,5,190,0,0. three terminal grains have been identified as near pure magnetite fe3o4. the presence of magnetite shows affinities between the wild 2 mineral assemblage and carbonaceous chondrites, and probably resulted from hydrothermal alteration of the coexisting feni and ferromagnesian silicates in the cometary parent body. in order to further explore this hypothesis, powdered material from a cr2 meteorite (nwa 10256) was shot into the aerogel at 6.1 km s-1, using a light-gas gun, and keystones were then prepared in the same way as the stardust keystones. using similar analysis techniques to the eight stardust tracks, a cr2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel. | magnetite in comet wild 2: evidence for parent body aqueous alteration |
chondrules are sub-millimetre spherical metal-sulphide-silicate objects which formed from the solar protoplanetary disk material, and as such provide an important record of the chronology and conditions of the solar system in pre-planetary times. chondrules are a major constituent of chondritic meteorites; however, despite being recognised for over 200 years their origins remain enigmatic. this comprehensive review describes state-of-the-art research into chondrules, bringing together leading cosmochemists and astrophysicists to review the properties of chondrules and their possible formation mechanisms based on careful observations of their chemistry, mineralogy, petrology and isotopic composition, as well as laboratory experiments and theoretical modelling. current and upcoming space missions returning material from chondritic asteroids and cometary bodies have invigorated research in this field, leading to new models and observations, and providing new insight into the conditions and timescales of the solar protoplanetary disk. presenting the most recent advances, this book is an invaluable reference for researchers and graduate students interested in meteorites, asteroids, planetary accretion and solar system dynamics. | chondrules: records of protoplanetary disk processes |
copper oxide nanoparticles (cuo nps) are known to exhibit toxic effects on a variety of cell types and organs. to determine the oxidative impact of cuo nps on hepatocellular carcinoma (hcc) cells, well-differentiated (hepg2) and poorly differentiated (sk-hep-1) cells were exposed to cuo nps. cell viability assay showed that the median inhibition concentration (ic50) for sk-hep-1 and hepg2 cells was 25 μg ml-1 and 85 μg ml-1, respectively. cellular fluorescence intensity using dcfh-da staining analysis revealed significant intracellular reactive oxygen species (ros) generation of up to 242% in sk-hep-1 cells, compared with 86% in hepg2 cells. hplc analysis demonstrated that a cuo np treatment caused cellular gsh depletion of 58% and a gsh/gssg ratio decrease to ~0.1 in sk-hep-1 cells. the oxidative stress caused by enhanced superoxide anion production was observed in both hepg2 (146%) and sk-hep-1 (192%) cells. the griess assay verified that cuo nps induced no production (170%) in sk-hep-1 cells. comet assay and western blot further demonstrated that cuo nps induced severe dna strand breakage (70%) in sk-hep-1 cells and caused dna damage via increased γ-h2ax levels. these results suggest that well-differentiated hepg2 cells possess a robust antioxidant defense system against cuo np-induced ros stress and exhibit more tolerance to oxidative stress. conversely, poorly differentiated sk-hep-1 cells exhibited a deregulated antioxidant defense system that allowed accumulation of cuo np-induced ros and resulted in severe cytotoxicity.copper oxide nanoparticles (cuo nps) are known to exhibit toxic effects on a variety of cell types and organs. to determine the oxidative impact of cuo nps on hepatocellular carcinoma (hcc) cells, well-differentiated (hepg2) and poorly differentiated (sk-hep-1) cells were exposed to cuo nps. cell viability assay showed that the median inhibition concentration (ic50) for sk-hep-1 and hepg2 cells was 25 μg ml-1 and 85 μg ml-1, respectively. cellular fluorescence intensity using dcfh-da staining analysis revealed significant intracellular reactive oxygen species (ros) generation of up to 242% in sk-hep-1 cells, compared with 86% in hepg2 cells. hplc analysis demonstrated that a cuo np treatment caused cellular gsh depletion of 58% and a gsh/gssg ratio decrease to ~0.1 in sk-hep-1 cells. the oxidative stress caused by enhanced superoxide anion production was observed in both hepg2 (146%) and sk-hep-1 (192%) cells. the griess assay verified that cuo nps induced no production (170%) in sk-hep-1 cells. comet assay and western blot further demonstrated that cuo nps induced severe dna strand breakage (70%) in sk-hep-1 cells and caused dna damage via increased γ-h2ax levels. these results suggest that well-differentiated hepg2 cells possess a robust antioxidant defense system against cuo np-induced ros stress and exhibit more tolerance to oxidative stress. conversely, poorly differentiated sk-hep-1 cells exhibited a deregulated antioxidant defense system that allowed accumulation of cuo np-induced ros and resulted in severe cytotoxicity. electronic supplementary information (esi) available. see doi: 10.1039/c4nr05843g | enhanced reactive oxygen species overexpression by cuo nanoparticles in poorly differentiated hepatocellular carcinoma cells |
the micro-imaging dust analysis system (midas) atomic force microscope (afm) onboard the rosetta orbiter was the first such instrument launched into space in 2004. designed only a few years after the technique was invented, midas is currently orbiting comet 67p churyumov-gerasimenko and producing the highest resolution 3d images of cometary dust ever made in situ. after more than a year of continuous operation much experience has been gained with this novel instrument. coupled with operations of the flight spare and advances in terrestrial afm a set of "lessons learned" has been produced, cumulating in recommendations for future spaceborne atomic force microscopes. the majority of the design could be reused as-is, or with incremental upgrades to include more modern components (e.g. the processor). key additional recommendations are to incorporate an optical microscope to aid the search for particles and image registration, to include a variety of cantilevers (with different spring constants) and a variety of tip geometries. | midas: lessons learned from the first spaceborne atomic force microscope |
observations by the messenger spacecraft during its flyby and orbital observations of mercury in 2008-2015 indicated the presence of cold icy materials hiding in permanently-shadowed craters in mercury's north polar region. these icy condensed volatiles are thought to be composed of water ice and frozen organics that can persist over long geologic timescales and evolve under the influence of the mercury space environment. polar ices never see solar photons because at such high latitudes, sunlight cannot reach over the crater rims. the craters maintain a permanently cold environment for the ices to persist. however, the magnetosphere will supply a beam of ions and electrons that can reach the frozen volatiles and induce ice chemistry. mercury's magnetic field contains magnetic cusps, areas of focused field lines containing trapped magnetospheric charged particles that will be funneled onto the mercury surface at very high latitudes. this magnetic highway will act to direct energetic protons, ions and electrons directly onto the polar ices. the radiation processing of the ices could convert them into higher-order organics and dark refractory materials whose spectral characteristics are consistent with low-albedo materials observed by messenger laser altimeter (mla) and radar instruments. galactic cosmic rays (gcr), scattered uv light and solar energetic particles (sep) also supply energy for ice processing. cometary impacts will deposit h2o, ch4, co2 and nh3 raw materials onto mercury's surface which will migrate to the poles and be converted to more complex csbnd hsbnd nsbnd osbnd s-containing molecules such as aldehydes, amines, alcohols, cyanates, ketones, hydroxides, carbon oxides and suboxides, organic acids and others. based on lab experiments in the literature, possible specific compounds produced may be: h2co, hcooh, ch3oh, hco, h2co3, ch3c(o)ch3, c2o, cxo, c3o2, cxoy, ch3cho, ch3och2ch2och3, c2h6, cxhy, no2, hno2, hno3, nh2oh, hno, n2h2, n3, hcn, na2o, naoh, ch3nh2, so, so2, so3, ocs, h2s, ch3sh, even bxhy. three types of radiation processing mechanisms may be at work in the ices: (1) impact/dissociation, (2) ion implantation and (3) nuclear recoil (hot atom chemistry). magnetospheric energy sources dominate the radiation effects. total energy fluxes of photons, seps and gcrs are all around two or more orders of magnitude less than the fluxes from magnetospheric energy sources (in the focused cusp particles). however, seps and gcrs cause chemical processing at greater depths than other particles leading to thicker organic layers. processing of polar volatiles on mercury would be somewhat different from that on the moon because mercury has a magnetic field while the moon does not. the channeled flux of charged particles through these magnetospheric cusps is a chemical processing mechanism unique to mercury as compared to other airless bodies. | ices on mercury: chemistry of volatiles in permanently cold areas of mercury's north polar region |
water ice exists on many objects in space. the most abundant icy species, among them water, are present in the icy satellites of the outer solar system giant planets. the nuclei of comets, which are mainly composed of water ice, give another example of its abundance. in the interstellar medium (ism), ice mantles, formed by molecular species sticking on dust grains, consist mainly of water ice. all these objects are exposed to ionizing radiation like ions, uv photons, and electrons. sputtering of atoms, molecules, ions, and radicals from icy surfaces may populate and maintain exospheres of icy objects in the solar system. in other respects, ionized hydrides such as oh+, h2o+, and h3o+ have been detected in the gas phase in star-forming regions. interactions with cosmic rays could be an additional explanation to the current models for the formation of those species. in fact, laboratory simulations showed that the main components of the sputtered ionic species from water ice are oxygen hydrides. in this work, water ice targets were irradiated at several temperatures (10-200 k) by 90 kev o6+ ions, yielding an electronic stopping power of about 12 ev/å, when the nuclear stopping power is comparable to the electronic stopping power. sputtering of secondary ions after bombardment of the ice target was analyzed by time-of-flight mass spectrometry (tof-sims). besides hydrogen ions (h+, h2+, h3+), also o+, o2+, oh+, (h2o)+, and clusters of (h2o)nh+ with n = 1-8 are emitted. our results show a progressive yield decrease with increasing temperature of all of the detected species. this is related to the structure of the ice: the ionic sputtering yield for crystalline ice is much lower than for an amorphous ice. for instance, amorphous ice at 10 k exhibits a yield of the order of 2 × 10-6 secondary (h2o)nh+ hydride ions/projectile (with n = 1-8). as the temperature is increasing toward the phase transition to crystalline ice, the yields decrease by about one order of magnitude. | production of hydronium ion (h3o)+ and protonated water clusters (h2o)nh+ after energetic ion bombardment of water ice in astrophysical environments |
the european space agency's rosetta spacecraft, with the rosetta orbiter spectrometer for ion and neutral analysis (rosina) onboard, has been following and observing comet 67p/churyumov-gerasimenko since summer 2014. prior to this period, and due to a technical failure also during this period, optimization and calibration campaigns have been conducted on ground with the reflectron-type time of flight (rtof) mass spectrometer as a preparatory work for the analysis of data recorded during the science phase of the mission. in this work, we show the evolution of the performance of rtof, and demonstrate and quantify the sensitivity and functionality of rtof onboard rosetta. we also present a fragmentation and sensitivity database for the most abundant molecules observed around the comet such as h2o, co, co2, as well as the noble gases. | sensitivity and fragmentation calibration of the time-of-flight mass spectrometer rtof on board esa's rosetta mission |
soon after the rosetta orbiter rendezvoused with comet 67p/churyumov-gerasimenko at a solar distance of ~3.5 au and began to fly in triangular-shaped trajectories around it, the ion and electron sensor detected negative particles at energies from about 100 ev/q to over 18 kev/q. the lower energy particles came from roughly the direction of the comet; the higher-energy particles came from approximately the solar direction. these particles are interpreted as clusters of molecules, most likely water, which we refer to as nanograins because their inferred diameters are less than 100 nm. acceleration of the grains away from the comet is through gas drag by the expanding cometary atmosphere, while acceleration back to the vicinity of the comet is caused partly by solar radiation pressure but mainly by the solar wind electric field. these observations represent the first measurements of energetic charged submicron-sized dust or ice grains (nanograins) in a cometary environment. | observation of charged nanograins at comet 67p/churyumov-gerasimenko |
as part of the european space agency's rosetta mission the lander philae touched down on comet 67p/churyumov-gerasimenko on november 12, 2014. the magnetic field has been measured onboard the orbiter and the lander. the orbiter's tri-axial fluxgate magnetometer rpc-mag is one of five sensors of the rosetta plasma consortium. the lander is also equipped with a tri-axial fluxgate magnetometer as part of the rosetta lander magnetometer and plasma-monitor package (romap). this unique setup makes a two point measurement between the two spacecrafts in a relatively small distance of less than 50 km possible. both magnetometers were switched on during the entire descent, the initial touchdown, the bouncing between the touchdowns and after the final touchdown. we describe a method for attitude determination by correlating magnetic low-frequency waves, which was tested under different conditions and finally used to reconstruct philae's attitude during descent and after landing. in these cases the attitude could be determined with an accuracy of better than ± 5 °. these results were essential not only for philae operations planning but also for the analysis of the obtained scientific data, because nominal sources for this information, like solar panel currents and camera pictures could not provide sufficient information due to the unexpected landing position. | attitude reconstruction of rosetta's lander philae using two-point magnetic field observations by romap and rpc-mag |
the onset of the paleocene-eocene thermal maximum (petm) and associated carbon isotope excursion (cie; approx. 56 mya) was geologically abrupt, but it is debated whether it took thousands of years or was effectively instantaneous. wright and schaller (2013) published a significant new record of the onset of the cie, and claimed that it could be resolved across 13 annual layers in a drill core through the marlboro clay at millville, new jersey (ocean drilling program (odp) leg 174x). supporting evidence for similar layering was reported from another new jersey drill site, wilson lake b, and a photograph of the marlboro clay in outcrop (wright and schaller, 2014). such a short duration would imply an instantaneous perturbation of the atmosphere and surface ocean and the impact of a comet or asteroid as the likely cause. however, pearson and nicholas (2014) suggested, based on the published core photographs, that the layers in the marlboro clay cores could be artifacts of drilling disturbance, so-called biscuiting, wherein the formation is fractured into layers or biscuits and drilling mud is injected in between the layers. (we now prefer the term core discing following kidd, 1978.) here we report new observations on the cores which support that interpretation, including concentric grooves on the surfaces of the core discs caused by spinning in the bit, micro-fracturing at their edges, and injected drilling mud. we re-interpret the limited outcrop evidence as showing joints rather than sedimentary layers. we argue that foraminifer concentrations in the sediments are far too high for the layers to have been annually deposited in turbid waters at depths of 40-70 m, indicating that the onset of the cie in the marlboro clay likely took on the order of millennia, not years (zeebe et al., 2014). re-coring of millville aimed at minimizing drilling disturbance to allow a higher-resolution study of the carbon isotope excursion is highly desirable. | drilling disturbance and constraints on the onset of the paleocene-eocene boundary carbon isotope excursion in new jersey |
the in situ cometary dust particle instrument cosima (cometary secondary ion mass analyser) onboard esa's rosetta mission has collected about 31 000 dust particles in the inner coma of comet 67p/churyumov-gerasimenko since august 2014. the particles are identified by optical microscope imaging and analysed by time-of-flight secondary ion mass spectrometry. after dust particle collection by low speed impact on metal targets, the collected particle morphology points towards four families of cometary dust particles. cosima is an in situ laboratory that operates remotely controlled next to the comet nucleus. the particles can be further manipulated within the instrument by mechanical and electrostatic means after their collection by impact. the particles are stored above 0°c in the instrument and the experiments are carried out on the refractory, ice-free matter of the captured cometary dust particles. an interesting particle morphology class, the compact particles, is not fragmented on impact. one of these particles was mechanically pressed and thereby crushed into large fragments. the particles are good electrical insulators and transform into rubble pile agglomerates by the application of an energetic indium ion beam during the secondary ion mass spectrometry analysis. this article is part of the themed issue 'cometary science after rosetta'. | mechanical and electrostatic experiments with dust particles collected in the inner coma of comet 67p by cosima onboard rosetta |
anthropogenic point sources, such as coal-fired power plants, produce a major share of global co2 emissions. international climate agreements demand their independent monitoring. due to the large number of point sources and their global spatial distribution, the implementation of a satellite-based observation system is convenient. airborne active remote sensing measurements demonstrate that the deployment of lidar is promising in this respect. the integrated path differential absorption lidar charm-f is installed on board an aircraft in order to detect weighted column-integrated dry-air mixing ratios of co2 below the aircraft along its flight track. during the carbon dioxide and methane mission (comet) in spring 2018, airborne greenhouse gas measurements were performed, focusing on the major european sources of anthropogenic co2 emissions, i.e., large coal-fired power plants. the flights were designed to transect isolated exhaust plumes. from the resulting enhancement in the co2 mixing ratios, emission rates can be derived via the cross-sectional flux method. on average, our results roughly correspond to reported annual emission rates, with wind speed uncertainties being the major source of error. we observe significant variations between individual overflights, ranging up to a factor of 2. we hypothesize that these variations are mostly driven by turbulence. this is confirmed by a high-resolution large eddy simulation that enables us to give a qualitative assessment of the influence of plume inhomogeneity on the cross-sectional flux method. our findings suggest avoiding periods of strong turbulence, e.g., midday and afternoon. more favorable measurement conditions prevail during nighttime and morning. since lidars are intrinsically independent of sunlight, they have a significant advantage in this regard. | determination of the emission rates of co2 point sources with airborne lidar |
comets are constantly interacting with the solar wind. when the comet activity is high enough, this leads to the creation of a magnetic field free region around the nucleus known as the diamagnetic cavity. it has been suggested that the ion-neutral drag force is balancing the magnetic pressure at the cavity boundary, but after the visit of rosetta to comet 67p/churyumov-gerasimenko the coupling between ions and neutrals inside the cavity has been debated, at least for moderately active comets. in this study, we use data from the ion composition analyser to determine the bulk speeds and temperatures of the low-energy ions in the diamagnetic cavity of comet 67p. the low-energy ions are affected by the negative spacecraft potential, and we use the spacecraft plasma interaction software to model the resulting influence on the detected energy spectra. we find bulk speeds of 5-10 km s-1 with a most probable speed of 7 km s-1, significantly above the velocity of the neutral particles. this indicates that the collisional coupling between ions and neutrals is not strong enough to keep the ions at the same speed as the neutrals inside the cavity. the temperatures are in the range 0.7-1.6 ev, with a peak probability at 1.0 ev. we attribute the major part of the temperature to the fact that ions are born at different locations in the coma, and hence are accelerated over different distances before reaching the spacecraft. | ion bulk speeds and temperatures in the diamagnetic cavity of comet 67p from rpc-ica measurements |
in order to improve our understanding of landing on small bodies and of asteroid evolution, we use our novel drop tower facility to perform low-velocity (2-40 cm s-1), shallow impact experiments of a 10 cm diameter aluminum sphere into quartz sand in low effective gravities (∼0.2-1 m s-2). using in situ accelerometers, we measure the acceleration profile during the impacts and determine the peak accelerations, collision durations and maximum penetration depth. we find that the penetration depth scales linearly with the collision velocity but is independent of the effective gravity for the experimental range tested, and that the collision duration is independent of both the effective gravity and the collision velocity. no rebounds are observed in any of the experiments. our low-gravity experimental results indicate that the transition from the quasi-static regime to the inertial regime occurs for impact energies two orders of magnitude smaller than in similar impact experiments under terrestrial gravity. the lower energy regime change may be due to the increased hydrodynamic drag of the surface material in our experiments, but may also support the notion that the quasi-static regime reduces as the effective gravity becomes lower. | an experimental study of low-velocity impacts into granular material in reduced gravity |
the australasian tektite strewn field is exceptional, not only as the largest and most recent, but also as the only strewn field without an identified source impact crater. therefore, scenarios without the formation of an impact crater, such as a low altitude cometary airburst, have proven hard to discard. here, new geochemical evidence is presented for mixing of projectile and target material, which implies the formation of an australasian tektite-related impact crater. first, ninety-two australasian tektites were grouped according to their cr, co and ni concentrations. based on this data, australasian tektites with the highest ni contents (>200 μg/g) occur more than 1500 km south-southeast (sse) of the northern indochina region, with the highest concentration of ni-rich tektites in south vietnam, the islands of borneo, belitung, and java, and reports in literature for ni-rich tektites in central australia. the tektites with the highest cr and ni abundances often also show highly siderophile element (hse) enrichments of up to 4 ng/g ir. the most ni-rich samples exhibit broadly chondrite-relative hse proportions. however, a chondritic impactor contribution appears to be inconsistent with the observed ni/cr, ni/co, and cr/co ratios. a previously suggested significant terrestrial mantle contribution can also not explain the siderophile element enrichments in combination with relatively low feotot (<7 wt.%) and mgo (<4 wt.%) contents. elemental fractionation during impact cratering or tektite formation by an impactor with a chondritic signature may explain these observations. alternatively, a projectile component from a primitive achondrite may be advocated, with contribution from a mafic to ultramafic extraterrestrial lithology with a relatively unfractionated hse signature and ni/cr ratio distinctly higher than those of earth's mantle. element distribution maps obtained from individual australasian tektites document complex mingling processes of chemically distinct melt batches, each exhibiting variable contributions from distinct endmember compositions. these texturally recorded mingling processes are consistent with high-resolution numerical models of impact cratering processes that resolve the growth of kelvin-helmholtz instabilities at the projectile/target interface during impact, when both materials co-occur at high pressure. these numerical models indicate that ni-rich tektite populations across the central part of the australasian tektite strewn field could represent projectile-enriched material preferentially ejected downrange. continued tracing of this ni-rich component across the strewn field may help to constrain the location of the yet to be identified source crater of the australasian (micro)tektites. | on the nature of the ni-rich component in splash-form australasian tektites |
we have designed and built a laboratory facility to investigate the spectro-photometric and morphologic properties of different types of ice-bearing planetary surface analogs and follow their evolution upon exposure to a low pressure and low temperature environment. the results obtained with this experiment are used to verify and improve our interpretations of current optical remote-sensing datasets. they also provide valuable information for the development and operation of future optical instruments. the simulation chamber for imaging the temporal evolution of analogue samples (sciteas) is a small thermal vacuum chamber equipped with a variety of ports and feedthroughs that permit both in-situ and remote characterizations as well as interacting with the sample. a large quartz window located directly above the sample is used to observe its surface from outside with a set of visible and near-infrared cameras. the sample holder can be easily and quickly inserted and removed from the chamber and is compatible with the other measurement facilities of the laboratory for outflow studies of sublimating materials (lossy) at the university of bern. we report here on the results of two of the first experiments performed in the sciteas chamber. in the first experiment, fine-grained water ice mixed with dark organic and mineral matter was left to sublime in vacuum and at low temperature, simulating the evolution of the surface of a comet nucleus approaching the sun. we observed and characterized the formation and evolution of a crust of refractory organic and mineral matter at the surface of the sample and linked the evolution of its structure and texture to its spectro-photometric properties. in the second experiment, a frozen soil was prepared by freezing a mixture of smectite mineral and water. the sample was then left to sublime for 6 h to simulate the loss of volatiles from icy soil at high latitudes on mars. colour images were produced using the definitions of the filters foreseen for the cassis imager of the exomars/tgo mission in order to prepare future science operations. | the sciteas experiment: optical characterizations of sublimating icy planetary analogues |
airless bodies in the solar system are continually bombarded by meteoroids, sustaining impact ejecta clouds. while large bodies like the moon retain a significant fraction of ejecta, small asteroids shed this material into the interplanetary dust complex. measurements of the lunar impact ejecta cloud found it was sustained by the known sporadic meteoroid sources. here, we extend those measurements using a model of the idp environment at 1 au to investigate the structure of an ejecta cloud at an eccentric airless body, asteroid 3200 phaethon. due to phaethon's large eccentricity, its ejecta cloud is highly asymmetric. at 1 au, the cloud is canted towards the asteroid's apex direction and its density varies by five orders of magnitude. compared to a body in a circular orbit at 1 au, phaethon's peak ejecta density at 1 au is approximately 30 times higher, largely due to enhanced ejecta production from meteoroids shed from jupiter family comets. such asymmetric ejecta production suggests phaethon experiences significantly different meteoroid-specific space weathering processes than a body with a similar semi-major axis on a circular orbit. we estimate impact ejecta processes at phaethon shed approximately 1 ton per year, which is not sufficient to appreciably contribute to the geminids meteoroid complex. these estimates most likely represent a lower limit, as phaethon is expected to have a higher ejecta yield than the moon. additionally, we calculate predicted impact counts for a dust detector on close flybys of phaethon in preparation for the destiny+ mission and find the large majority of impacts would be detected on the morning-side sunlit hemisphere. these results suggest eccentric asteroids shed more material than those on near-circular orbits, and are suitable candidates for in-situ dust detection and chemical characterization due to their amplified asymmetric ejecta production. | impact ejecta environment of an eccentric asteroid: 3200 phaethon |
cosmic dust particles are mostly responsible for polarization of the light that we observe from astrophysical objects. they also lead to color-extinction, thermal re-emission and other scattering related phenomena. micrometric dust particles are often made of smaller constituent (nanometric grains). they are characterized by their size (average radius), chemical composition and morphology (including porosity). in the present work, we address the question of the role of the dust particle porosity on light polarization and color, using discrete dipole approximation (dda) light scattering code. to this purpose, we develop an algorithm to generate dust particles of arbitrary values of porosity. in brief, starting from a compact spherical ensemble of dipoles,randomly the dipoles are removed one by one, such that the remaining dipoles remain connected within their neighbours. we stop the removal process when the desired porosity is obtained. then we compute and study the optical properties of the porous dust particle.the main objective of this paper is to develop a tool to generate dust particles with an arbitrary value of porosity and to study the effect of porosity on their light scattering properties. as a possible application, we simulate cometary polarization and color values which grossly match with the observed ones for the comet 1p/halley, leaving scope for future work. | the effect of porosity of dust particles on polarization and color with special reference to comets |
we outline the key questions about comets that must be answered in order to understand cometary formation in the context of the protoplanetary disc and the role of comets in the formation and evolution of the solar system. we then discuss the new understanding of comets from rosetta and from other recent advances, including work presented by others at the discussion meeting. finally, we suggest some key directions for future projects to better address the above questions. this article is part of the themed issue 'cometary science after rosetta'. | comets: looking ahead |
disintegrating planets allow for the unique opportunity to study the composition of the interiors of small, hot, rocky exoplanets because the interior is evaporating and that material is condensing into dust, which is being blown away and then transiting the star. their transit signal is dominated by dusty effluents forming a comet-like tail trailing the host planet (or leading it, in the case of k2-22b), making these good candidates for transmission spectroscopy. to assess the ability of such observations to diagnose the dust composition, we simulate the transmission spectra from 5 to 14 μm for the planet tail assuming an optically thin dust cloud comprising a single dust species with a constant column density scaled to yield a chosen visible transit depth. we find that silicate resonant features near 10 μm can produce transit depths that are at least as large as those in the visible. for the average transit depth of 0.55% in the kepler band for k2-22b, the features in the transmission spectra can be as large as 1%, which is detectable with the james webb space telescope (jwst) miri low-resolution spectrograph in a single transit. the detectability of compositional features is easier with an average grain size of 1 μm despite features being more prominent with smaller grain sizes. we find most features are still detectable for transit depths of ∼0.3% in the visible range. if more disintegrating planets are found with future missions such as the space telescope tess, follow-up observations with jwst can explore the range of planetary compositions. | inferring the composition of disintegrating planet interiors from dust tails with future james webb space telescope observations |
in the solar system, extra-terrestrial organic molecules have been found on cometary primitive objects, on titan and enceladus icy moons and on mars. identification could be achieved for simple organic species by remote sensing based on spectroscopic methods. however in situ mass spectrometry is a key technology to determine the nature of more complex organic matter. a large panel of mass spectrometers has already been developed for space exploration combining different types of analysers and ion sources. up to now the highest mass resolution reached with a space instrument is 9000 at m/z 28 and corresponds to the dfms-rosina instrument (balsiger et al., 2007) dedicated to the study of the comet 67p/churyumov-gerasimenko's atmosphere and ionosphere, in a low pressure environment. a new concept of mass analyser offering ultra-high mass resolving power of more than 50,000 at m/z 56 (under high vacuum condition about 10-9 mbar) is currently being developed for space applications: the cosmorbitrap (briois et al., 2016), based on the orbitrap™ technology. this work challenges the use of lab-cosmorbitrap, a space instrument prototype combining laser ablation ionisation and the cosmorbitrap mass analyser, to identify solid organic molecules of relevance to the future space exploration. for this purpose a blind test was jointly organised by the jaxa-hrms team (japan aerospace exploration agency-high resolution mass spectrometry) and the cosmorbitrap consortium. the jaxa team provided two organic samples, whereas the cosmorbitrap consortium analysed them without prior information. thanks to the high analytical performances of the prototype and our hrms data post-processing, we successfully identified the two molecules as hobt, hydroxybenzotriazole (c6h5n3o) and bbot, 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (c26h26n2o2s), with a mass resolving power of, respectively, 123 540 and 69 219. the success of this blind test on complex organic molecules shows the strong potential of lab-cosmorbitrap for future space applications. | identification of organic molecules with a laboratory prototype based on the laser ablation-cosmorbitrap |
using in situ measurements from different instruments on board the rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67p/churyumov-gerasimenko. these waves are thought to be generated by a modified ion-weibel instability that grows due to a beam of water ions created by water molecules that outgass from the comet. we take advantage of a cometary outburst event that occurred on 2016 february 19 to probe this generation mechanism. we analyze the 3d magnetic field waveforms to infer the properties of the magnetic oscillations of the cometary ion waves. they are observed in the typical frequency range ( 50 mhz) before the cometary outburst, but at 20 mhz during the outburst. they are also observed to be elliptically right-hand polarized and to propagate rather closely ( 0-50°) to the background magnetic field. we also construct a density dataset with a high enough time resolution that allows us to study the plasma contribution to the ion cometary waves. the correlation between plasma and magnetic field variations associated with the waves indicates that they are mostly in phase before and during the outburst, which means that they are compressional waves. we therefore show that the measurements from multiple instruments are consistent with the modified ion-weibel instability as the source of the singing comet wave activity. we also argue that the observed frequency of the singing comet waves could be a way to indirectly probe the strength of neutral plasma coupling in the 67p environment. | properties of the singing comet waves in the 67p/churyumov-gerasimenko plasma environment as observed by the rosetta mission |
we use laboratory experiments to derive information on the chemistry occurring during the evolution of astrophysical ices from dense molecular clouds to interplanetary objects. through a new strategy that consists of coupling very high resolution mass spectrometry and infrared spectroscopy (ft-ir), we investigate the molecular content of the organic residues synthesized from different initial ice compositions. we also obtain information on the evolution of the soluble part of the residues after their over-irradiation. the results give insight into the role of water ice as a trapping and diluting agent during the chemical evolution. they also give information about the importance of the amount of ammonia in such ices, particularly regarding its competition with the carbon chemistry. all of these results allow us to build a first mapping of the evolution of soluble organic matter based on its chemical and physical history. furthermore, our results suggest that interstellar ices should lead to organic materials enriched in heteroatoms that present similarities with cometary materials but strongly differ from meteoritic organic material, especially in their c/n ratios. | cometary materials originating from interstellar ices: clues from laboratory experiments |
1. introduction; 2. dynamics; 3. solar heating and energy transport; 4. planetary atmospheres; 5. planetary surfaces; 6. planetary interiors; 7. magnetic fields and plasmas; 8. meteorites; 9. minor planets; 10. comets; 11. planetary rings; 12. extrasolar planets; 13. planet formation; 14. planets and life; appendixes; references; index. | planetary sciences |
planetary impact events eject large volumes of surface material. crater excavation processes are difficult to study, and in particular the details of individual ejecta fragments are not well understood. a related, enduring issue in planetary mapping is whether a given crater resulted from a primary impact (asteroid or comet) or instead is a secondary crater created by an ejecta fragment. with mapping and statistical analyses of six lunar secondary crater fields (including orientale, copernicus, and kepler) we provide three new constraints on these issues: (1) estimation of the maximum secondary crater size as a function of distance from a primary crater on the moon, (2) estimation of the size and velocity of ejecta fragments that formed these secondaries, and (3) estimation of the fragment size ejected at escape velocity. through this analysis, we confirmed and extended a suspected scale-dependent trend in ejecta size-velocity distributions. maximum ejecta fragment sizes fall off much more steeply with increasing ejection velocity for larger primary impacts (compared to smaller primary impacts). specifically, we characterize the maximum ejecta sizes for a given ejection velocity with a power law and find that the velocity exponent varies between approximately -0.3 and -3 for the range of primary craters investigated here (0.83-660 km in diameter). data for the jovian moons europa and ganymede confirm similar trends for icy surfaces. this result is not predicted by analytical theories of formation of grady-kipp fragments or spalls during impacts and suggests that further modeling investigations are warranted to explain this scale-dependent effect. | lunar secondary craters and estimated ejecta block sizes reveal a scale-dependent fragmentation trend |
solar system objects with perihelia beyond the orbit of jupiter (q > 5 au) are too cold for water ice to generate an appreciable coma via sublimation. despite this, numerous high-perihelion objects (hpos) including many comets and recently escaped kuiper belt objects (centaurs) are observed to be active out at least to the orbit of saturn (q ∼ 10 au). peak equilibrium temperatures at 10 au (∼125 k), while far too low to sublimate water ice, are sufficient to sublimate supervolatiles such as co and co2 ice. temperatures at 10 au are also high enough to trigger the rapid crystallization of exposed amorphous ice, thus constituting another possible driver of distant activity. while supervolatile ices can sublimate strongly (as ${r}_{{\rm{h}}}^{-2} ) to at least kuiper belt (30 au) distances, crystallization is an exponential function of temperature that cannot be sustained much beyond ∼10 au. the heliocentric dependence of the activity thus suggests an observational test. if activity in high-perihelion objects is triggered by crystallization, then no examples of activity should be found with perihelia of q ≫ 10 au. if, on the other hand, activity is due to free sublimation of exposed supervolatile ices, or another cause, then distant activity might be detected. we obtained sensitive, high-resolution hubble space telescope observations of hpos to search for activity beyond the crystallization zone. no examples of activity were detected in 53 objects with q > 15 au, consistent with the crystallization trigger hypothesis. however, sensitivity limits are such that we cannot reject the alternative hypothesis that mass loss is driven by the sublimation of supervolatile ices. we also searched for binary companions in our sample, finding none and setting an empirical 3σ limit to the binary fraction of <8%. | hubble space telescope search for activity in high-perihelion objects |
during its 1989 flyby, the voyager 2 spacecraft imaged six small moons of neptune, all with orbits well interior to that of the large, retrograde moon triton1. along with a set of nearby rings, these moons are probably younger than neptune itself; they formed shortly after the capture of triton and most of them have probably been fragmented multiple times by cometary impacts1-3. here we report hubble space telescope observations of a seventh inner moon, hippocamp. it is smaller than the other six, with a mean radius of about 17 kilometres. we also observe naiad, neptune's innermost moon, which was last seen in 1989, and provide astrometry, orbit determinations and size estimates for all the inner moons, using an analysis technique that involves distorting consecutive images to compensate for each moon's orbital motion and that is potentially applicable to searches for other moons and exoplanets. hippocamp orbits close to proteus, the outermost and largest of these moons, and the orbital semimajor axes of the two moons differ by only ten per cent. proteus has migrated outwards because of tidal interactions with neptune. our results suggest that hippocamp is probably an ancient fragment of proteus, providing further support for the hypothesis that the inner neptune system has been shaped by numerous impacts. | the seventh inner moon of neptune |
this paper provides a brief summary and overview of the astrochemistry associated with the formation of stars and planets. it is aimed at new researchers in the field to enable them to obtain a quick overview of the landscape and key literature in this rapidly evolving area. the journey of molecules from clouds to protostellar envelopes, disks and ultimately exoplanet atmospheres is described. the importance of the close relation between the chemistry of gas and ice and the physical structure and evolution of planet-forming disks, including the growth and drift of grains and the locking up of elements at dust traps, is stressed. using elemental abundance ratios like c/o, c/n, o/h in exoplanetary atmospheres to link them to their formation sites is therefore not straightforward. interesting clues come from meteorites and comets in our own solar system, as well as from the composition of earth. a new frontier is the analysis of the kinematics of molecular lines to detect young planets in disks. a number of major questions to be addressed in the coming years are formulated, and challenges and opportunities are highlighted. | astrochemistry associated with planet formation |
this chapter focuses mainly on recent results obtained from observations on the mars express (mex) and venus express (vex) spacecraft. remote observations of cometary tails, which have also an induced origin, provide a lot of examples of sudden cometary tail disconnection that appear as a detachment of a very large plasma cloud from the coma. a signature of reconnection is plasma jets streaming in the opposite directions from the reconnection site. magnetotails of mars and venus are the main channels through which solar wind scavenges planetary atmospheric/ionospheric material. such an erosion of atmospheres of non-magnetized planets can be an important factor for evolution of their atmosphere and water inventory. the strong variability inherent to induced magnetospheres calls for a continuous solar wind monitoring and multispacecraft observations of our planetary neighbors. | magnetotails of mars and venus |
we present observations using the baade magellan and canada-france-hawaii telescopes showing that main-belt comet 324p/la sagra, formerly known as p/2010 r2, has become active again for the first time since originally observed to be active in 2010-2011. the object appears point-source-like in 2015 march and april as it approached perihelion (true anomaly of ν ∼ 300°), but was ∼1 mag brighter than expected if inactive, suggesting the presence of unresolved dust emission. activity was confirmed by observations of a cometary dust tail in 2015 may and june. we find an apparent net dust production rate of {dot{m}_d}≲ 0.1 kg s-1 during these observations. 324p is now the fourth main-belt comet confirmed to be recurrently active, a strong indication that its activity is driven by sublimation. it now has the largest confirmed active range of all likely main-belt comets, and also the most distant confirmed inbound activation point at r ∼ 2.8 au. further observations during the current active period will allow direct comparisons of activity strength with 324p's 2010 activity. | the reactivation of main-belt comet 324p/la sagra (p/2010 r2) |
it has long been hypothesised that the jupiter-family comets (jfcs) come from the scattered disc, an unstable planetesimal population beyond neptune. this viewpoint has been widely accepted, but a few issues remain, the most prominent of which are the total number of visible jfcs with a perihelion distance q < 2.5 au and the corresponding number of objects in the scattered disc. in this work we give a robust estimate of the number of visible jfcs with q < 2.5 au and diameter d> 2.3 km based on recent observational data. this is combined with numerical simulations that use a simple fading law applied to jfcs that come close to the sun. for this we numerically evolve thousands of comets from the scattered disc through the realm of the giant planets and keep track of their number of perihelion passages with perihelion distance q < 2.5 au, below which the activity is supposed to increase considerably. we can simultaneously fit the jfc inclination and semi-major axis distribution accurately with a delayed power law fading function of the form φm ∝ (m2 + m2)- k/ 2, where φm is the visibility, m is the number of perihelion passages with q < 2.5 au, m is an integer constant, and k is the fading index. we best match both the inclination and semi-major axis distributions when k ~ 1.4, m = 40, and the maximum perihelion distance below which the observational data is complete is qm ~ 2.3 au. from observational data we calculate that a jfc with diameter d = 2.3 km has a typical total absolute magnitude ht = 10.8, and the steady-state number of active jfcs with diameter d > 2.3 km and q < 2.5 au is of the order of 300 (but with large uncertainties), approximately a factor two higher than earlier estimates. the increased jfc population results in a scattered disc population of 6 billion objects and decreases the observed oort cloud to scattered disc population ratio to 13, virtually the same as the value of 12 obtained with numerical simulations. | an updated estimate of the number of jupiter-family comets using a simple fading law |
high-resolution infrared spectra of jupiter-family comet 45p/honda-mrkos-pajdušáková were obtained with nirspec at the w. m. keck observatory on two post-perihelion dates (ut 2017 february 13 and 19), when the comet was at heliocentric distances of 1.01 and 1.10 au, respectively. on ut february 13, h2o was measured simultaneously with six trace parent molecules: ch3oh, c2h6, hcn, nh3, c2h2, and h2co. on ut february 19, ch4 and co were also targeted in addition to the species measured on ut february 13. abundances of co, ch4, and c2h2 relative to h2o are consistent with values obtained from irtf/ishell observations of 45p in early january 2017 just after perihelion when the heliocentric distance was 0.55-0.56 au. differences are seen in h2co/h2o, c2h6/h2o, ch3oh/h2o, and hcn/h2o in february compared to january. additionally, nh3 abundances appear highly variable during the february measurements, suggesting possible fluctuations of a factor of ten; however, there is significant uncertainty in quantifying nh3 owing to the marginal detections of only one or two lines on each of the two dates. combining all infrared spectroscopic observations of 45p in january and february 2017, a post-perihelion relationship of q(h2o) = (2.81 ± 0.25) × 1027 [rh(-3.83±0.18)] molecules s-1 is derived. however, all measurements suggest significant variability in h2o production on timescales of hours and days. compared to other comets, volatile abundances relative to h2o in 45p are as follows: co (depleted relative to all measured comets), ch3oh (enriched/all comets), ch4 and c2h6 (typical/all comets, enriched/jupiter-family comets), c2h2 (depleted/all comets, typical/jupiter-family comets), h2co (january: typical, february depleted/all comets), hcn (january: severely depleted, february: typical/jupiter-family comets). the small geocentric distances of the comet in february 2017 provide high spatial resolution in the coma of 45p (~12 and 19 km/pixel on february 13 and 19, respectively). overall, the spatial distributions of volatiles and dust suggest a relatively symmetric and uniform coma during the ut february 13 and 19 observations, with small spatial differences noted between some volatile species. measured c2h2 and hcn abundances are consistent with hcn as the primary parent of cn and c2h2 as a significant but not primary parent for c2, based on c2 and cn production rate measurements from the 2017 and previous apparitions. extracted spectra show an increase in the dust-to-gas ratio in 45p from february 13 to 19 in agreement with contemporaneous narrowband optical measurements. | post-perihelion volatile production and release from jupiter-family comet 45p/honda-mrkos-pajdušáková |
the collisional evolution of solid material in protoplanetary disks is a crucial step in the formation of planetesimals, comets, and planets. although dense protoplanetary environments favor fast dust coagulation, there are several factors that limit the straightforward pathway from interstellar micron-size grains to pebble-size aggregates. apart from the grain bouncing, fragmentation, and fast drift to the central star, a notable limiting factor is the electrostatic repulsion of like-charged grains. in this study we aim at theoretical modeling of the dust coagulation coupled with the dust charging and disk ionization calculations. we show that the electrostatic barrier is a strong restraining factor to the coagulation of micrometer-size dust in dead zones of the disk (where the turbulence is suppressed). while the sustained turbulence helps to overcome the electrostatic barrier, low fractal dimensions of dust aggregates can potentially block their further coagulation even in this case. coulomb repulsion may keep a significant fraction of small dust in the disk atmosphere and outer regions. | inhibited coagulation of micron-size dust due to the electrostatic barrier |
the dynamics near the lagrange equilibria $l_1$ and $l_2$ of the circular restricted three-body problem has gained attention in the last decades due to its relevance in some topics such as the temporary captures of comets and asteroids and the design of trajectories for space missions. in this paper we investigate the temporary captures using the tube manifolds of the horizontal lyapunov orbits originating at $l_1$ and $l_2$ of the cr3bp at energy values which have not been considered so far. after showing that the radius of convergence of any hamiltonian normalization at $l_1$ or $l_2$ computed with the cartesian variables is limited in amplitude by $\|1-\mu-x_{l_1}\|$ ($\mu$ denoting the reduced mass of the problem), we investigate if regularizations allow us to overcome this limit. in particular, we consider the hamiltonian describing the planar three-body problem in the levi-civita regularization and we compute its normalization for the sun-jupiter reduced mass for an interval of energy which overcomes the limit of cartesian normalizations. as a result, for the largest values of the energy that we consider, we notice a transition in the structure of the tubes manifolds emanating from the lyapunov orbit, which can contain orbits that collide with the secondary body before performing one full circulation around it. we discuss the relevance of this transition for temporary captures. | a study of temporary captures and collisions in the circular restricted three-body problem with normalizations of the levi-civita hamiltonian |
we examine the dynamics of small bodies in orbits similar to that of comet 29p/schwassmann-wachmann 1, i.e. near-circular orbits between jupiter and saturn. as of late 2019, there are 14 other known bodies in this region that lie in similar orbits. previous research has shown that this region of the solar system, which in this work we call the "near centaur region" (ncr), is not stable, suggesting that any bodies found in it would have very short lifetimes. we performed 20 myr high-precision numerical simulations of the evolution of massless particles, initially located in the kuiper belt but close to neptune, with perihelia slightly below 33 au ("neptune crossers"). some of these particles quickly migrate inward, passing through the ncr before becoming jupiter family comets. we find that objects in the ncr do indeed generally travel through it very quickly. however, our simulations reveal that resonant behavior in this region is somewhat common and can trap objects for up to 100 kyr. we summarize the dynamics of 29p and other observed bodies in the region-two of which seem to be clearly exhibiting resonant behavior-and use our simulations to put limits on the reservoir size of the neptune crossers, which at its time determines the reservoir size of the kuiper belt. finally, we put some constraints on the current population of centaurs and particularly of the ncr population, based on the injection rates required to keep the observed population of jupiter family comets in steady-state. | dynamics of small bodies in orbits between jupiter and saturn |
context. the esa rosetta probe has not seen direct evidence of a fully formed bow shock at comet 67p/churyumov-gerasimenko (67p). ion spectrometer measurements of cometary pickup ions measured in the vicinity of the nucleus of 67p are available and may contain signatures of the large-scale plasma environment.aims: the aim is to investigate the possibility of using pickup ion signatures to infer the existence or nonexistence of a bow shock-like structure and possibly other large-scale plasma environment features.methods: a numerical plasma model in the hybrid plasma description was used to model the plasma environment of a comet. simulated pickup ion spectra were generated for different interplanetary magnetic field conditions. the results were interpreted through test particle tracing in the hybrid simulation solutions.results: features of the observed pickup ion energy spectrum were reproduced, and the model was used to interpret the observation to be consistent with a shock-like structure. we identify (1) a spectral break related to the bow shock, (2) a mechanism for generating the spectral break, and (3) a dependency of the energy of the spectral break on the interplanetary magnetic field magnitude and bow shock standoff distance. | hybrid modeling of cometary plasma environments. ii. remote-sensing of a cometary bow shock |
the present understanding of cometary atmospheres is based on whipple's "dirty iceball" idea in which the nucleus consists of a mixture of frozen volatiles and non-volatile dust. the atmospheres of comets, commonly referred to as comas, are different in a number of important ways from planetary atmospheres. this chapter presents a very simple, spherically symmetric description of the innermost region of active comet atmospheres that captures most of the basic physics without going into too much detail. cometary magnetotails are formed by the draping of the interplanetary magnetic field (imf) around the diamagnetic cavity boundary. since cometary magnetotails are essentially draped imf lines, they are very sensitive to changes in the solar wind. the goal of the chapter is to summarize the pre-rosetta mission understanding of cometary magnetospheres. this understanding is based on ground-based observations and a small number of short-duration flyby missions. | physics of cometary magnetospheres |
despite the long escort by the esa rosetta mission, direct observations of a fully developed bow shock around 67p/churyumov-gerasimenko have not been reported. expanding on our previous work on indirect observations of a shock, we model the large-scale features in cometary pickup ions, and compare the results with the esa rosetta plasma consortium ion composition analyser ion spectrometer measurements over the pre-perihelion portion of the escort phase. using our hybrid plasma simulation, an empirical, asymmetric outgassing model for 67p, and varied interplanetary magnetic field (imf) clock angles, we model the evolution of the large-scale plasma environment. we find that the subsolar bow shock standoff distance is enhanced by asymmetric outgassing with a factor of 2 to 3, reaching up to $18\,000\, \rm {km}$ approaching perihelion. we find that distinct spectral features in simulated pickup ion distributions are present for simulations with shock-like structures, with the details of the spectral features depending on shock standoff distance, heliocentric distance, and imf configuration. asymmetric outgassing along with imf clock angle is found to have a strong effect on the location of the spectral features, while the imf clock angle causes no significant effect on the bow shock standoff distance. these dependences further complicate the interpretation of the ion observations made by rosetta. our data-model comparison shows that the large-scale cometary plasma environment can be probed by remote sensing the pickup ions, at least when the comet's activity is comparable to that of 67p, and the solar wind parameters are known. | remote sensing of cometary bow shocks: modelled asymmetric outgassing and pickup ion observations |
there was a color gradient of the coma along the radius r, approximately described by b-v=(0.3+/-0.2)+(0.2+/-0.2)*log10(r) for 4.1 =< r =< 9.6 arcsec. this indicates that the coma had a uniform color that was bluer than that of the sun regardless of the aperture radius r, or that the coma became redder with increasing distance from the optocenter. the relationship between the v-brightnesses and the same aperture radius range gives v=(17.4+/-0.4)+(-3.9+/-0.5)*log10(r). the exponent m < 1, which results from the fitted curve, indicates that the dust is pushed into the tail by the solar radiation and fills up the anti-solar regions. | erratum of atel #16315: observations of comet 12p/pons-brooks after the july 19, 2023 outburst |
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