Distributed Sources in Comets

Cottin, Hervé; Fray, N.

doi:10.1007/s11214-008-9399-z

Cited by 68 publications

(47 citation statements)

References 90 publications

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“…This confirms previous analysis with the PICCA instruments on comet Halley during the Giotto mission where a similar regular pattern of peaks was observed which was at that time tentatively assigned to POM-like structures (Huebner 1987). It should be kept in mind that currently polyoxymethylene is the best explanation for the distributed source of formaldehyde in cometary comae (Cottin & Fray 2008). The presence of POM in comets is also supported by experimental results (Schutte et al 1993).…”

Section: Astrophysical Significancesupporting

confidence: 88%

Radical-induced chemistry from VUV photolysis of interstellar ice analogues containing formaldehyde

Butscher

Duvernay

Danger

et al. 2016

A&A

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Surface processes and radical chemistry within interstellar ices are increasingly suspected to play an important role in the formation of complex organic molecules (COMs) observed in several astrophysical regions and cometary environments. We present new laboratory experiments on the low-temperature solid state formation of complex organic molecules -glycolaldehyde, ethylene glycol, and polyoxymethylene -through radical-induced reactivity from VUV photolysis of formaldehyde in water-free and water-dominated ices. Radical reactivity and endogenous formation of COMs were monitored in situ via infrared spectroscopy in the solid state and post photolysis with temperature programmed desorption (TPD) using a quadripole mass spectrometer. We show the ability of free radicals to be stored when formed at low temperature in water-dominated ices, and to react with other radicals or on double bonds of unsaturated molecules when the temperature increases. It experimentally confirms the role of thermal diffusion in radical reactivity. We propose a new pathway for formaldehyde polymerisation induced by HCO radicals that might explain some observations made by the Ptolemy instrument on board the Rosetta lander Philae. In addition, our results seem to indicate that H-atom additions on H 2 CO proceed preferentially through CH 2 OH intermediate radicals rather than the CH 3 O radical.

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Section: Astrophysical Significancesupporting

confidence: 88%

Radical-induced chemistry from VUV photolysis of interstellar ice analogues containing formaldehyde

Butscher

Duvernay

Danger

et al. 2016

A&A

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“…The other equally abundant molecules H 2 CO, CH 3 OH and NH 3 are not considered in this model for the following reasons. H 2 CO is not mostly produced in the nucleus of comets but is rather the result of a distributed source in the coma, which could be provided by the photo and thermal degradation of dust (Fray et al 2004;Fray et al 2006;Cottin & Fray 2008). Moreover, no data is available on its stability curves either in the form of clathrate or as a pure condensate (Fray & Schmitt 2009) and thus this molecule cannot be considered in the mixture of ices of our comet nucleus model.…”

Section: Dust Ejection and Mantle Formation At The Surface Of The Nucmentioning

confidence: 99%

A cometary nucleus model taking into account all phase changes of water ice: amorphous, crystalline, and clathrate

Marboeuf

Schmitt

Petit

et al. 2012

A&A

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Context. Current theories, models of cometary nuclei and of ice formation in the protoplanetary disk, and laboratory studies suggest that cometary materials could be formed of pure crystalline water ice, amorphous water ice, clathrate hydrate, or a mixture of these structures of water ice. However, current models of cometary nuclei consider only two forms of ice during the thermodynamic evolution of comets: amorphous and crystalline water ices. Aims. In this work, we have developed a model of cometary nucleus that takes into account all water ice structures and phase changes in order to predict the outgassing profile of volatile molecules that could be measured by the Rosetta mission and can be used to constrain the structural type of ice existing in the interior of the Comet 67P/Churyumov-Gerasimenko, the target comet of the Rosetta mission, and, hopefully, its initial composition. Methods. We added the physic of formation/dissociation of clathrate hydrates in addition to others physical processes that are taken into account in models without clathrate hydrates. All thermal changes, as well as the release and trapping of gas with water phase changes are taken into account. Results. This model describes heat transmission, latent heat exchanges, all water ices structures and transitions (amorphous-to-pure crystalline, amorphous-to-clathrate hydrates and pure crystalline-to-clathrate hydrates and vise versa), sublimation/recondensation of volatile molecules in the nucleus, gas diffusion, gas released and trapped by crystallization and clathrate formation/dissociation processes, as well as gas and dust release and mantle formation at the surface. Applying this model to the comet 67P/ChuryumovGerasimenko, results show different outgassing profiles of volatiles molecules from the nucleus depending on the water ice structure, the distribution of volatile molecules between the "trapped" and "condensed" states in the nucleus and the thermal inertia of its porous matrix. Conclusions. Given these results, we pretend that this model is able to constrain the water ice structure and chemical composition in comets from outgassing profiles of volatile molecules, and especially those of the target comet of the Rosetta mission.

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“…It has to be noted that the dust grains from comet Halley were analysed a few hours after their release when they were already heated to a high temperature by illumination from sunlight for some hours, such that the more volatile condensed phases evaporated. That some of the less-refractory carbonaceous material is desorbed before measurement by the space probes is suggested by the results for the distribution of gas species in the coma of comet Halley, which seems to require that the coma has an extended source of carbon (Eberhardt et al 1987;Cottin & Fray 2008).…”

Section: Analysis Of Cometary Materialsmentioning

confidence: 99%

Spatial distribution of carbon dust in the early solar nebula and the carbon content of planetesimals

Gail

Trieloff

2017

A&A

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Context. A high fraction of carbon bound in solid carbonaceous material is observed to exist in bodies formed in the cold outskirts of the solar nebula, while bodies in the region of terrestrial planets contain only very small mass fractions of carbon. Most of the solid carbon component is lost and converted into CO during the spiral-in of matter as the Sun accretes matter from the solar nebula. Aims. We study the fate of the carbonaceous material that entered the proto-solar disc by comparing the initial carbon abundance in primitive solar system material and the abundance of residual carbon in planetesimals and planets in the asteroid belt and the terrestrial planet region. Methods. We constructed a model for the composition of the pristine carbonaceous material from observational data on the composition of the dust component in comets and of interplanetary dust particles and from published data on pyrolysis experiments. This material entered the inner parts of the solar nebula during the course of the build-up of the proto-sun by accreting matter from the proto-stellar disc. Based on a one-zone evolution model of the solar nebula, we studied the pyrolysis of the refractory and volatile organic component and the concomitant release of hydrocarbons of high molecular weight under quiescent conditions of disc evolution, while matter migrates into the central parts of the solar nebula. We also studied the decomposition and oxidation of the carbonaceous material during violent flash heating events, which are thought to be responsible for the formation of chondrules. To do this, we calculated pyrolysis and oxidation of the carbonaceous material in temperature spikes that were modeled according to cosmochemical models for the temperature history of chondrules. Results. We find that the complex hydrocarbon components of the carbonaceous material are removed from the disc matter in the temperature range between 250 and 400 K, but the amorphous carbon component survives to temperatures of 1200 K. Without efficient carbon destruction during flash-heating associated with chondrule formation, the carbon abundance of terrestrial planets, except for Mercury, would be of several percent and not as low as it is found in cosmochemical studies. Chondrule formation seems to be a crucial process for the carbon-poor composition of the material of terrestrial planets.

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Distributed Sources in Comets

Cited by 68 publications

References 90 publications

Radical-induced chemistry from VUV photolysis of interstellar ice analogues containing formaldehyde

Radical-induced chemistry from VUV photolysis of interstellar ice analogues containing formaldehyde

A cometary nucleus model taking into account all phase changes of water ice: amorphous, crystalline, and clathrate

Spatial distribution of carbon dust in the early solar nebula and the carbon content of planetesimals

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