Comets provide unique information about the physical and chemical properties of the environment in which the Solar system was formed. Understanding how cometary dust and ice evolve under the effect of sunlight is essential for constraining nuclear structure and triggering mechanism of comet activity. In this paper, we first study rotational disruption of dust grains lifted by outgassing from comet nuclei by radiative torques (RATs). We find that composite grains could be rapidly disrupted into small fragments by the Radiative Torque Disruption (RATD) mechanism. We then study rotational desorption of ice grains by RATs and find that icy grains could be desorbed from large heliocentric distances, beyond the sublimation radius of water at $R_{\rm sub}(\H_{2}Ø)\sim 3\AU$. We also calculate the production rate of water vapor versus the heliocentric distance of comets due to rotational desorption. Our results could explain the variation of dust properties and the presence of small grains frequently observed from cometary comae. Finally, we suggest that the activity of distant comets could be triggered by rotational disruption of grains and desorption of water ice grains at large heliocentric distances.
Remote and in-situ observations of cometary gases have revealed the presence of a wealth of complex organic molecules, including carbon chains, alcohols, imines and the amino acid glycine. Such chemical complexity in cometary material implies that impacts by comets could have supplied reagents for prebiotic chemistry to young planetary surfaces. However, the assumption that some of the molecules observed in cometary comae at millimetre wavelengths originate from ices stored inside the nucleus has not yet been proven. In fact, the comae of moderately-active comets reach sufficient densities wit…
In this chapter, we provide a review of radiative processes in cometary atmospheres spanning a broad range of wavelengths, from radio to X-rays. We focus on spectral modeling, observational opportunities, and anticipated challenges in the interpretation of new observations, based on our current understanding of the atomic and molecular processes occurring in the atmospheres of small, icy bodies. Close to the surface, comets possess a thermalized atmosphere that traces the irregular shape of the nucleus. Gravity is too low to retain the gas, which flows out to form a large, collisionless exosph…
A Multi-Wavelength Study of Comet C/2022 E3 (ZTF): Complementary ALMA and JWST Investigations of Water and Methanol in Cometary Comae
University of Virginia（弗吉尼亚大学）；NASA Goddard Space Flight Center（NASA戈达德太空飞行中心）；Catholic University of America（美利坚天主教大学）；American University（美国大学）；National Radio Astronomy Observatory（国家射电天文台）；Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université（巴黎天文台、巴黎文理研究大学、法国国家科学研究中心、索邦大学、巴黎西岱大学、CY塞尔吉-蓬图瓦兹大学）；Institut de Radioastronomie Millimetrique（毫米波射电天文学研究所）
本研究利用JWST和ALMA对彗星C/2022 E3 (ZTF)的多波段观测，分析了水和甲醇的分布及旋转温度变化，揭示了彗核 coma 中的化学特征与热力学过程。
The composition of cometary ices provides key information on the thermal and chemical properties of the outer parts of the protoplanetary disk where they formed 4.6 Gy ago. This chapter reviews our knowledge of composition of cometary comae based on remote spectroscopy and in-situ investigations techniques. Cometary comae can be dominated by water vapour, CO or CO2. The abundances of several dozen of molecules, with a growing number of complex organics, have been measured in comets. Many species that are not directly sublimating from the nucleus ices have also been observed and traced out into…
Mapping the release of volatiles in the inner comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) using the Atacama Large Millimeter/Submillimeter Array
Context. Cometary dust particles are subjected to various forces after being lifted off the nucleus. These forces define the dynamics of dust, trajectories, alignment, and fragmentation, which, in turn, have a significant effect on the particle distribution in the coma. Aims. We develop a numerical thermophysical model that is applicable to icy cometary dust to study the forces attributed to the sublimation of ice. Methods. We extended the recently introduced synoptic model for ice-free dust particles to ice-containing dust. We introduced an additional source term to the energy balance equatio…
JWST Reveals Refractory-Rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks
Southwest Research Institute（西南研究院）；University of Maryland, College Park（马里兰大学帕克分校）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Catholic University of America（美利坚天主教大学）；Auburn University（奥本大学）；Universität Bern（伯尔尼大学）
To date, at least three comets -- 2I/Borisov, C/2016 R2 (PanSTARRS), and C/2009 P1 (Garradd) -- have been observed to have unusually high CO concentrations compared to water. We attempt to explain these observations by modeling the effect of drifting solid (ice and dust) material on the ice compositions in protoplanetary disks. We find that, independent of the exact disk model parameters, we always obtain a region of enhanced ice-phase CO/H2O that spreads out in radius over time. The inner edge of this feature coincides with the CO snowline. Almost every model achieves at least CO/H2O of unity…
Over 200 molecules have been detected in multiple extraterrestrial environments, including glycolaldehyde (C2(H2O)2, GLA), a two-carbon sugar precursor that has been detected in regions of the interstellar medium. Its recent in situ detection on the nucleus of comet 67P/Churyumov-Gerasimenko and via remote observations in the comae of others, provides tantalizing evidence that it is common on most (if not all) comets. Impact experiments conducted at the Experimental Impact Laboratory at NASA's Johnson Space Center have shown that samples of GLA and GLA mixed with montmorillonite clays can surv…
Comets are small bodies thought to contain the most pristine material in the solar system. However, since their formation 4.5 Gy ago, they have been altered by different processes. While not exposed to much electromagnetic radiation, they experience intense particle radiation. Galactic cosmic rays and solar energetic particles have a broad spectrum of energies and interact with the cometary surface and subsurface; they are the main source of space weathering for a comet in the Kuiper Belt or in the Oort cloud; and also affect the ice prior to the comet agglomeration. While low energy particles…
The proposed CUBES spectrograph for ESO's Very Large Telescope will be an exceptionally powerful instrument for the study of comets. The gas coma of a comet contains a large number of emission features in the near-UV range covered by CUBES (305-400 nm), which are diagnostic of the composition of the ices in its nucleus and the chemistry in the coma. Production rates and relative ratios between different species reveal how much ice is present and inform models of the conditions in the early solar system. In particular, CUBES will lead to advances in detection of water from very faint comets, re…
Recent observations show activity in long-period comet C/2017 K2 at heliocentric distances beyond the orbit of Uranus. With this as motivation, we constructed a simple model that takes a detailed account of gas transport modes and simulates the time-dependent sublimation of super-volatile ice from beneath a porous mantle on an incoming cometary nucleus. The model reveals a localized increase in carbon monoxide (CO) sublimation close to heliocentric distance rH = 150 AU (local blackbody temperature around 23 K), followed by a plateau and then a slow increase in activity towards smaller distance…
The CoPhyLab (Cometary Physics Laboratory) project is designed to study the physics of comets through a series of earth-based experiments. For these experiments, a dust analogue was created with physical properties comparable to those of the non-volatile dust found on comets. This "CoPhyLab dust" is planned to be mixed with water and CO$_2$ ice and placed under cometary conditions in vacuum chambers to study the physical processes taking place on the nuclei of comets. In order to develop this dust analogue, we mixed two components representative for the non-volatile materials present in cometa…
Cometary activity may be driven by ices with very low sublimation temperatures, such as carbon monoxide ice, which can sublimate at distances well beyond 20 au. This point is emphasized by the discovery of Oort cloud comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein), and its observed activity out to $\sim$26 au. Through observations of this comet's optical brightness and behavior, we can potentially discern the drivers of activity in the outer solar system. We present a study of the activity of comet Bernardinelli-Bernstein with broad-band optical photometry taken at 19-20 au from the Sun (202…
Cometary surface dust layers built out of millimetre-scale aggregates: dependence of modelled cometary gas production on the layer transport properties
