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The paper considers the free molecular flow of gas through the dusty porous surface layer of a comet nucleus. The study is based on computer models of generation of a porous medium and Knudsen gas diffusion. We consider various types of homogeneous and heterogeneous layers constructed from nonintersecting spheres, including layers that contain microcracks or inner cavities. Using the test-particle method, we quantitatively estimate the free path distribution function, layer permeability, and effective kinetic characteristics of sublimation products passing through a nonisothermal porous layer. In addition, in this approach, we consider the volumetric absorption of visible solar radiation in the near-surface absorbing layer. Simple approximation expressions are obtained for all the transport characteristics under study, which makes it possible to estimate the characteristics with sufficient accuracy for practical applications in the physics of comets. The results will be used to construct new consistent models of energy transfer in the near-surface layer of a comet nucleus and, first of all, to analyze the results of the observations of comet 67P/Churyumov‒Gerasimenko.

In this work, we introduce a comet dust model that incorporates multiple dust morphologies along with inhomogeneous mixture of silicate minerals and carbonaceous materials under power-law size distribution, to replicate the standard polarization-phase curve observed in several comets in the narrow-band continuum. Following the results from Rosetta/MIDAS and COSIMA, we create high porosity Hierarchical Aggregates (HA) and low porosity (< 10$\%$) Solids in the form of agglomerated debris. We also introduce a moderate porosity structure with solids in the core, surrounded by fluffy aggregates called Fluffy Solids (FS). We study the mixing combinations, (HA and Solids), (HA and FS) and (HA, FS and Solids) for a range of power-law index n=2.0 to 3.0 for different sets of mixing percentage of silicate minerals and carbonaceous materials. Polarimetry of the short period comets 1P/Halley and 67P/Churyumov-Gerasimenko match best with the polarisation resulting from the combination of HA and Solids while the combinations (HA and FS) and (HA, FS and Solids) provide the best fit results for the long period comets C/1995 O1 (Hale-Bopp) and C/1996 B2 (Hyakutake). The best fit model results also recreate the observed wavelength dependence of polarization. Our dust model agree with the idea that the long period comets may have high percentage of loose particles (HA and FS) compared to those in the case of short period comets as the short period comets experience more frequent and/or higher magnitude of weathering., 16 Pages, 16 Figures, Accepted in MNRAS

The fine-structure detail of several comet dust tails is analysed from amateur and professional comet images using the Finson-Probstein mdoel. Given the date and time of the image taken, the comet’s position in the sky is calculated using an open source algorithm [1] and the comet’s dust tail is simulated for that position and time. This modeled dust tail structure is then projected and overlaid onto the comet image to directly compare and identify similarities and discrepancies between the model and the image. Using the novel analysis method of mapping the image to a dust grain beta against ejection time plot [2], tail structures can be more easily identified and analysed. This also allows for the tracking of tail structure over time, as images of a single comet from different times and observatories can be mapped onto the same plot. This method compensates for the difficulties of investigating tail structures in images as the comet moves across the image and as viewing geometry changes over time. This is a continuation of the work done previously on Comet C/2006 P1 (McNaught), which ultimately led to the observation of the formation processes of new fine-scale structure features in the comet’s dust tail [2]. This model is now applied to several other comets, including the recent Comet ATLAS (C/2019 Y4), to map their tail structures and to highlight this model’s utility in comet dust tail analysis. Finally, this work will be put into context as the first step in the development of an automated analysis method for cometary dust and ion tails. This automated method is in preparation for the upcoming opening of the Vera Rubin Observatory (LSST), and aims to automatically identify comet tail structures from the Observatory’s stream of comet images. The robustness of this analysis suite enables it to also be implemented on amateur comet images, making use of the abundant and valuable data from amateur astronomers. [1] Lang, Dustin, David W. Hogg, Keir Mierle, Michael Blanton, and Sam Roweis. 2010. "ASTROMETRY.NET: BLIND ASTROMETRIC CALIBRATION OF ARBITRARY ASTRONOMICAL IMAGES". The Astronomical Journal 139 (5): 1782-1800. doi:10.1088/0004-6256/139/5/1782. [2] Price, Oliver, Geraint H. Jones, Jeff Morrill, Mathew Owens, Karl Battams, Huw Morgan, Miloslav Drückmuller, and Sebastian Deiries. 2019. "Fine-Scale Structure In Cometary Dust Tails I: Analysis Of Striae In Comet C/2006 P1 (Mcnaught) Through Temporal Mapping". Icarus 319: 540-557. doi:10.1016/j.icarus.2018.09.013.

Images and low-resolution spectra of the near-Earth Jupiter family comet (JFC) 249P/LINEAR in the visible range obtained with the instrument OSIRIS in the 10.4m Gran Telescopio Canarias on January 3, 4, 6 and February 6, 2016 are presented, together with a series of images obtained with the 0.4m telescope of the Great Shefford Observatory. The reflectance spectrum of 249P is similar to that of a B-type asteroid. The comet has an absolute (visual) nuclear magnitude $H_V=17.0\pm 0.4$, which corresponds to a radius of about 1-1.3 km for a geometric albedo $\sim 0.04-0.07$. From the analysis of GTC images using a Monte Carlo dust tail code we find that the time of maximum dust ejection rate was around 1.6 days before perihelion. We may be in front of a new class of near-Earth JFC whose source region is not the distant trans-neptunian population, but much closer in the asteroid belt. Therefore, 249P/LINEAR may be a near-Earth counterpart of the so-called main-belt comets or active asteroids., Paper accepted in Icarus (now in Press)

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 ...

International audience; Rosetta has detected the presence of the hydrogen halides HF, HCl, and HBr in the coma of comet 67P/Churyumov-Gerasimenko. These species are known to freeze out on icy grains in molecular clouds. Analysis of the abundances of HF and HCl as a function of cometocentric distance suggests that these hydrogen halides are released both from the nucleus surface and off dust particles in the inner coma. We present three lines of evidence. First, the abundances of HF and HCl relative to the overall neutral gas in the coma appear to increase with distance, indicating that a net source must be present; since there is no hint at any possible parent species with sufficient abundances that could explain the observed levels of HF or HCl, dust particles are the likely origin. Second, the amplitude of the daily modulation of the halide-to-water density due to the rotation and geometry of 67P's nucleus and the corresponding surface illumination is observed to progressively diminish with distance and comet dust activity; this can be understood from the range of dust particle speeds well below the neutral gas expansion speed, which tends to smooth the coma density profiles. Third, strong halogen abundance changes detected locally in the coma cannot be easily explained from composition changes at the surface, while they can be understood from differences in local gas production from the dust particles.

The timing and extent to which the initial interstellar material was thermally processed provide fundamental constraints for models of the formation and early evolution of the solar protoplanetary disk. We argue that the nonsolar (solar Δ17O ≈ −29‰) and near-terrestrial (Δ17O ≈ 0‰) O-isotopic compositions of the Earth and most extraterrestrial materials (Moon, Mars, asteroids, and comet dust) were established very early by heating of regions of the disk that were modestly enriched (dust/gas ≥ 5–10 times solar) in primordial silicates (Δ17O ≈ −29‰) and water-dominated ice (Δ17O ≈ 24‰) relative to the gas. Such modest enrichments could be achieved by grain growth and settling of dust to the midplane in regions where the levels of turbulence were modest. The episodic heating of the disk associated with FU Orionis outbursts were the likely causes of this early thermal processing of dust. We also estimate that at the time of accretion the CI chondrite and interplanetary dust particle parent bodies were composed of ~5–10% of pristine interstellar material. The matrices of all chondrites included roughly similar interstellar fractions. Whether this interstellar material avoided the thermal processing experienced by most dust during FU Orionis outbursts or was accreted by the disk after the outbursts ceased to be important remains to be established.

On June 12 1996 UT, three 11–12 R magnitude stars were occulted by comet Hale–Bopp. The passage of these stars through the cometary atmosphere was monitored at the Observatorio do Pico dos Dias (Brazil) using a 0.6 m telescope. We detected an absorption of starlight by the comet dust implying in a drop of $$(6\pm 1) \times 10^{-2}$$ magnitude of occulted star XPM 152-0898466 at a minimum distance of ( $$4.3 \pm 0.2)\times 10^{4}$$ km from the central condensation. This result, combined with magnitude variations of other stars, suggests the detection of a jet in the coma. From our measurement of extinction, we infer that the opacity of the nucleus surface was $$\tau \sim 3$$ . The mean geometric albedo p of dust grains is $$(4.5 \pm 0.7) \times 10^{-3}$$ . This low albedo may suggest a difference in the grain population associated to coma and jets.

SUISEI is a suite of computational tools that has been developed over the past three decades and successfully applied to comets; including ComChem, a global, multi-fluid gas dynamics simulation with detailed chemical kinetics of the cometary coma; ComDust, a model of comet dust evolution and interaction with gas; and ComNuc, a 3-D simulation of gas and heat flow within the comet nucleus porous subsurface layers. The combination of these tools have resulted in an improved knowledge of chemical species in the comet’s coma and their relationship to native molecules in the nucleus ices by analyzing space- and ground-based observations and in situ measurements from spacecraft missions. A review of SUISEI is presented and applications are made to two cases: chemical recycling of HCN in comets and the physical conditions of the near-Sun object, 3200 Phaethon.

In the last two decades, experimental hypervelocity impacts (HVI) using light gas gun (LGG) shots have answered numerous questions about how comet dust can be captured, and have repeatedly provided explanations for phenomena encountered during study of samples returned from comet Wild 2 by the NASA JPL-Caltech Stardust mission. LGG experiments were carried out in several laboratories, especially in NASA, in Japan, and at the University of Kent (Canterbury, UK). Analogue materials were produced for testing and calibration of novel and diverse microanalysis methods in research institutions around the world. Impact tracks on low density silica aerogel and craters on Al alloy foils gave calibration in determination of size and composition for Wild 2 particles, and experimental HVI features revealed how internal grain size and structure of comet dust grains can be interpreted from detailed shapes of impact structures. Firing of analogue mineral materials helped us to understand how specific mineral components are preserved, how crystal structure and composition are altered during capture, and how this may limit interpretation of collected grains. In this review, I explain the range of studies performed so far, and suggest new experiments are needed to help understand: preservation, alteration and loss of subtle internal grain structures; modification of elemental and isotopic signatures in relatively fragile materials (e.g. organic matter); and the size of particles making bulbous aerogel tracks.

The article presents the description of possible activity from the comet 46P/Wirtanen meteor shower. The proximity of this comet to the Earth orbit in 1984–2042 increases probabily for the Earth to encounter meteoroid particles released by this comet. For the nearest years two cases of such activity are found—in 2017 and 2019 and their characteristics and circumstances are presented.

This work is a part of a more global effort aimed at understanding and interpreting in situ and remote sensing data acquired by instruments on board Rosetta. This study aims at deriving the dust mass source rate and the location of the dust jet source observed by Rosetta VIRTIS-M on 2015 April 12. The analysis is performed by means of the coupled kinetic modelling of gas and dust in the coma of comet 67P/Churyumov-Gerasimenko, which were used for calculating the coma brightness as it would be seen from the Rosetta spacecraft. The dust mass production rate and a possible location of the jet origin needed to explain the Rosetta VIRTIS-M dust brightness image were inferred by comparing the calculated brightness with VIRTIS-M data. Our analysis suggests that the dust mass production rate needed to maintain the observed jet is about 1.9 kg s-1. According to our analysis, the location of the observed jet surface footprint is outside of the nucleus area characterized by the highest gas production rate, which suggests that gas and dust source rates are not necessarily proportional to each other across the entire nucleus surface. The inferred location of the possible jet origin is consistent with that of the observed active pits. In this paper, we show that the jet intensity is variable in time, and has a lifetime of at least 10 h.

International audience; Remote observations of the light scattered by dust particles in comet 67P/Churyumov–Gerasimenko (67P/C-G) (photometry and imaging polarimetry) allow us to compare the deduced physical properties of these particles with in situ measurements provided by the Rosetta mission. Onboard experiments on the dust confirm properties inferred from polarimetric observations and from laboratory experiments, namely the existence of large dark particles in the size range 10–500 μm, which could be fluffy and compact aggregates of smaller grains (submicron- to micron-sized) and possibly of compact particles. The 2008–2009 apparition of comet 67P/C-G allowed us to observe the comet with two telescopes under a French–Indian collaboration. From the photometric and polarimetric observations, we inferred the presence of slow-moving, large compact particles in the coma before perihelion and eventually after. The additional ejection of fluffy aggregates of submicron-sized grains was consistent with observations after perihelion. In 2014–2015, as part of a worldwide campaign, observations of 67P/C-G were carried out in order to follow the evolution of the dust coma during the Rosetta mission. The campaign included observations with the Hubble Space Telescope, and photometric observations with the Himalayan Chandra Telescope in India. The comet was very active for about three months after perihelion, showing collimated jets, the structure of which changed over time, and a long dust tail. Using new published polarization values for observations in 2010, we were able to compare pre- and post-perihelion data and also to build partial phase curves for 67P/C-G (limited to phase angles smaller than 40°).

Comets have been invoked in numerous studies as a potentially important source of dust and gas around stars, but none has studied the thermo-physical evolution, out-gassing rate, and dust ejection of these objects in such stellar systems. We investigate the thermo-physical evolution of comets in exo-planetary systems in order to provide valuable theoretical data required to interpret observations of gas and dust. We use a quasi 3D model of cometary nucleus to study the thermo-physical evolution of comets evolving around a single star from 0.1 to 50 AU, whose homogeneous luminosity varies from 0.1 to 70 solar luminosities. This paper provides mass ejection, lifetimes, and the rate of dust and water gas mass productions for comets as a function of the distance to the star and stellar luminosity. Results show significant physical changes to comets at high stellar luminosities. The models are presented in such a manner that they can be readily applied to any planetary system. By considering the examples of the Solar System, Vega and HD 69830, we show that dust grains released from sublimating comets have the potential to create the observed (exo)zodiacal emission. We show that observations can be reproduced by 1 to 2 massive comets or by a large number of comets whose orbits approach close to the star. Our conclusions depend on the stellar luminosity and the uncertain lifetime of the dust grains. We find, as in previous studies, that exozodiacal dust disks can only survive if replenished by a population of typically sized comets renewed from a large and cold reservoir of cometary bodies beyond the water ice line. These comets could reach the inner regions of the planetary system following scattering by a (giant) planet., Comment: 21 pages, 10 figures

International audience; Because of the diurnal thermal cycle and the irregular shape of the nucleus, gas outflow of comet 67P/Churyumov–Gerasimenko could be highly anisotropic as indicated by the colliminated dust jet structures on the sunlit side. Based on the OSIRIS imaging observations of the outgassing effect, a simple model of surface sublimation can be constructed by taking into account the dependence on the solar insolation. With preliminary information on the time variability of the global gas production rate, a sequence of gas coma models can be generated at different epochs before and after perihelion. We also investigate different patterns of dust particle dynamics under the influences of nuclear rotation and gas drag. From these considerations, a consistent picture of the spatial distribution of dusty materials across the surface of comet 67P as it moves around the perihelion can be developed. It is found that because of the redeposition of the ejected dust from the Southern hemisphere to the Northern hemisphere during the southern summer season the Hapi region could gain up to 0.4 m while the Wosret region would lose up to 1.8 m of dust mantle per orbit.

The aim of this paper is to contribute to the characterization of the general properties of the Long Period Comets (LPCs) family, and in particular to report on the dust environment of comet C/2009 P1 (Garradd).The comet was observed at two epochs pre-perihelion, at ~6 AU and at ~2.5 AU: broad-band images have been used to investigate its coma morphology and properties and to model the dust production rate.Comet C/2009 P1 (Garradd) is one of the most active and "dust producing" LPCs ever observed, even at the large heliocentric distance rh~6 AU. Its coma presents a complex morphology, with subtle structures underlying the classical fan-shaped tail, and, at rh~2.5 AU, also jet-like structures and spiralling outflows. In the reference aperture of radius ρ=5°×104 km, the R-Afρ is 3693±156 cm and 6368±412 cm, in August 2010 (rh~6 AU) and July 2011 (rh~2.5 AU), respectively. The application of a first order photometric model, under realistic assumptions on grain geometric albedo, power-law dust size distribution, phase darkening function and grain dust outflow velocity, yielded a measure of the dust production rate for the two epochs of observation of Qd=7.27×102 kg/s and Qd=1.37×103 kg/s, respectively, for a reference outflow dust velocity of vsmall=25 m/s for small (0.1-10 μm) grains and vlarge=1 m/s for large (10 μm-1 cm) grains.These results suggest that comet Garradd is one of the most active minor bodies observed in recent years, highly contributing to the continuous replenishment of the Interplanetary Dust Complex also in the outer Solar System, and pose important constraints on the mechanism(s) driving the cometary activity at large heliocentric distances. Fil: Mazzotta Epifani, C.. Istituto Nazionale Di Astrofisica; Italia. Osservatorio Astronomico di Roma; Italia Fil: Snodgrass, C.. The Open University; Reino Unido Fil: Perna, D.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Dall’Ora, M.. Osservatorio Astronomico di Capodimonte; Italia Fil: Palumbo, P.. Università Parthenope; Italia Fil: Della Corte, V.. Istituto di Astrofisica e Planetologia Spaziale; Italia Fil: Alvarez Candal, A.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil Fil: Melita, Mario Daniel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Rotundi, A.. Università Parthenope; Italia

International audience; Comet 67P/Churyumov-Gerasimenko (hereafter, 67P) was observed on 12 December 2015, from 2 m Himalayan Chandra Telescope in India in photometry to study its dust properties, using Bessell R and I filters. We study the photometric images to highlight coma structures and jets. The radial decrease in intensity in the different coma structures are compared to the azimuthally integrated intensities. The observations of the slopes show a quasi-steady-state coma to an optocentric distance of about 20 000 km. The change in the slopes in the structures indicates changing properties of the dust particles and/or change in their local size distributions. Comparison of the radial decrease in the two wavelengths suggests a change in the local colour-index. Based on the absolute photometry carried out in the present work, we calculate the reddening of the comet dust which helps to characterize variations in the size and the materials of the particles. The colour-index is calculated for different apertures and regions in the coma (0.40 ± 0.07 mag) for a 22000 diameter aperture. A colour map is constructed showing the variation of the colour-index through the coma. Changes appear at the transition between the coma and the tail with a low colour-index (< 0.3 mag) close to the optocentre and further away increasing up in the tail direction (about 0.45 mag at 10 000 km). We interpret these changes in terms of dust properties and we compare our results to other remote observations of 67P including in situ Rosetta observations.

Приведены результаты исследования сезонного хода аэрозольной оптической толщи (АОТ) атмосферы в районе Уссурийска. Широкий максимум АОТ наблюдается в марте–июле и два минимума – в феврале и сентябре. Обсуждается вопрос о возможном влиянии метеорных потоков (пылевых следов комет) на измеряемую оптическую толщу атмосферы., The results of study of the seasonal distribution of the aerosol optical depth (AOD) in the Earth atmosphere near Ussuriysk are given. The wide maximum of AOD is detected during March–July, whereas two minimums of AOD are found in February and September. A possible influence of the meteor shower (dusty traces of comets) on the measured AOD is discussed., №202(6) (2018)

This work is intended to answer the question, whether on comet 67P/Churyumov–Gerasimenko pristine, not hardened material can be locally preserved close to the surface. Simulated is the thermally driven sintering of ice-dust grains underlying the dust mantle. Considered is the Ma׳at region located at the north side of the small lobe Head. It is shown that locally thermal conditions can allow preservation of a not thermally hardened ice-dust material.

Observations of Comet C/2010 X1 (Elenin) in August 2011 showed a pattern of evolution of coma morphology into an expanding, amorphous cloud of rapidly decreasing surface brightness shortly before perihelion passage, similar to C/1999 S4 (LINEAR) in 2000. However, the comet’s difficult viewing geometry at the time of disruption made it impossible to study the event using high-resolution imaging techniques and, in particular, to measure the ratio of dust to cometessimals which gives information on the internal structure of the nucleus before disruption. We report Herschel/PACS observations of the defunct Comet C/2010 X1 (Elenin), aimed at detecting its infrared ghost: the debris cloud and any remaining inert, or low-activity cometessimals that may have been released in the break-up of the nucleus, taking advantage of the comet’s close pass to Earth in mid-October 2011. These observations would have allowed us to detect, potentially, both individual surviving inert fragments of the nucleus of ≈260 m diameter (and significantly smaller, active cometessimals) and the expanding dust cloud, being particularly sensitive to coarse dust and boulders in the millimetre to metre size range. No discrete bodies were detected by Herschel to this limiting size.

The principle of habitable planets creation of near stars in our galaxy was developed. It was shown that the Earth and the Moon formed as a result of thermal nuclear explosion (TNE) after a collision with a small comet. The comet has broken through the proto-Earth crust, and created conditions for liquid-drop division into the Earth and the Moon. It is shown that the comet impact on the proto-Earth led to formation of continents as well as to formation of the Moon, seas, oceans and atmosphere and to creation of conditions for life origin. The analysis of kimberlitic pipes distribution, as markers of comet fragments motion under a crust, shows that the comet has broken up under crust with formation of many gas bubbles. An analysis of the Martian topography revealed that the comet hit Mars not under a glancing angle. As a result, the products of TNE remained under the Marian crust. The track of the comet movement under the Venus crust was also established. It is shown that the planet surface near comet track is spotted by numerous cracks.

We present an improved model for interplanetary dust grain fluxes in the outer Solar System constrained by in situ dust density observations. A dynamical dust grain tracing code is used to establish relative dust grain densities and three-dimensional velocity distributions in the outer Solar System for four main sources of dust grains: Jupiter-family comets, Halley-type comets, Oort-Cloud comets, and Edgeworth-Kuiper Belt objects. Model densities are constrained by in situ dust measurements by the New Horizons Student Dust Counter, the Pioneer 10 meteoroid detector, and the Galileo Dust Detection System (DDS). The model predicts that Jupiter-family comet grains dominate the interplanetary dust grain mass flux inside approximately 10 AU, Oort-Cloud cometary grains may dominate between 10 and 25 AU, and Edgeworth-Kuiper Belt grains are dominant outside 25 AU. The model also predicts that while the total interplanetary mass flux at Jupiter roughly matches that inferred by the analysis of the Galileo DDS measurements, mass fluxes to Saturn, Uranus, and Neptune are at least one order-of-magnitude lower than that predicted by extrapolations of dust grain flux models from 1 AU. Finally, we compare the model predictions of interplanetary dust oxygen influx to the giant planet atmospheres with various observational and photochemical constraints and generally find good agreement, with the exception of Jupiter, which suggests the possibility of additional chemical pathways for exogenous oxygen in Jupiter’s atmosphere.