Molecular Abundances in Comets

Crovisier, J.

doi:10.1017/s0074180900046611

Cited by 6 publications

(4 citation statements)

References 67 publications

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“…The corresponding CO 2 /H 2 O ratio inferred for the exogenic oxygen source is 7% by volume or 16% by mass. This fraction is slightly larger than the estimated CO 2 /H 2 O ratio in cometary nuclei, 7-15% by mass according to Crovisier (1993) or 10-12% by mass according to Greenberg (1998). However, the organic material in cometary grains is likely to release CO when heated (Greenberg 1998), and much of the carbon-oxygen bonded species introduced from the ablation of IDPs could derive from an organic component rather than directly from the icy component.…”

Section: Sensitivity To the Molecular Form Of The Incoming Oxygenmentioning

confidence: 63%

“…In our nominal model, these molecules are introduced in the 10 −6 to 10 −4 mbar region, with relative fluxes (molecules cm −2 s −1 ) of H 2 O : CO : CO 2 : CH 3 OH equal to 100 : 50 : 5 : 5 and a deposition rate that is uniform within the ablation region. Note that the CO/H 2 O ratio here is higher than that implied by the composition of cometary ices (e.g., Crovisier 1993, Greenberg 1998); this issue is discussed more fully in Section 5.2. We also examine the sensitivity of our results to changes in the ablation altitude, relative fluxes, and molecular form of the oxygen-bearing material.…”

Section: Photochemical Model Descriptionmentioning

confidence: 89%

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Photochemistry of Saturn's Atmosphere II. Effects of an Influx of External Oxygen

Moses

Lellouch

Bézard

et al. 2000

Icarus

149

223

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Section: Sensitivity To the Molecular Form Of The Incoming Oxygenmentioning

confidence: 63%

Section: Photochemical Model Descriptionmentioning

confidence: 89%

Photochemistry of Saturn's Atmosphere II. Effects of an Influx of External Oxygen

Moses

Lellouch

Bézard

et al. 2000

Icarus

149

223

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“…M14a,b and T14 have run several models with different compositions, taking into account the formation of several refractory species (a list of these species is provided in Table 1 of T14) and eight main volatile molecules: H 2 O, CO, CO 2 , CH 3 OH, CH 4 , NH 3 , N 2 , and H 2 S -see Table 2. These species are the most abundant volatile molecules observed in the interstellar medium (ISM; Gibb et al 2000aGibb et al ,b, 2004van Dishoeck 2004;Whittet et al 2007;Boogert et al 2011;Mumma & Charnley 2011, and references in M14), and in solar cometary comas (Bockelée-Morvan et al 2004;Crovisier 2006;Mumma & Charnley 2011). Previous studies (T14, M14a,b) also explored the possible formation of clathrates and refractory organic compounds and studied the effect of irradiation.…”

Section: Solid Phasementioning

confidence: 99%

Gas composition of the main volatile elements in protoplanetary discs and its implication for planet formation

Thiabaud

Marboeuf

Alibert

et al. 2015

A&A

116

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Context. Direct observations of gaseous exoplanets reveal that their gas envelope has a higher C/O ratio than that of the host star (e.g., . This has been explained by considering that the gas phase of the disc could be inhomogeneous, exceeding the stellar C/O ratio in regions where these planets formed; but few studies have considered the drift of the gas and planet migration. Aims. We aim to derive the gas composition in planets through planet formation to evaluate if the formation of giant planets with an enriched C/O ratio is possible. The study focusses on the effects of different processes on the C/O ratio, such as the disc evolution, the drift of gas, and planet migration. Methods. We used our previous models for computing the chemical composition, together with a planet formation model, to which we added the composition and drift of the gas phase of the disc, which is composed of the main volatile species H 2 O, CO, CO 2 , NH 3 , N 2 , CH 3 OH, CH 4 , and H 2 S, H 2 and He. The study focusses on the region where ice lines are present and influence the C/O ratio of the planets. Results. Modelling shows that the condensation of volatile species as a function of radial distance allows for C/O enrichment in specific parts of the protoplanetary disc of up to four times the solar value. This leads to the formation of planets that can be enriched in C/O in their envelope up to three times the solar value. Planet migration, gas phase evolution and disc irradiation enables the evolution of the initial C/O ratio that decreases in the outer part of the disc and increases in the inner part of the disc. The total C/O ratio of the planets is governed by the contribution of ices accreted, suggesting that high C/O ratios measured in planetary atmospheres are indicative of a lack of exchange of material between the core of a planet and its envelope or an observational bias. It also suggests that the observed C/O ratio is not representative of the total C/O ratio of the planet.

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“…We now have a global idea of the composition of cometary volatiles using spectroscopy ranging from radio to UV wavelengths (Crovisier 1994). This knowledge, however, is biased towards comets observed around 1 AU, where their activity is governed by water sublimation.…”

Section: Introductionmentioning

confidence: 99%

Observational constraints on the composition and nature of comet D/Shoemaker-Levy 9

Crovisier¹

1996

International Astronomical Union Colloquium

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What did the break-up of comet Shoemaker-Levy 9 (SL9) and its subsequent impact on Jupiter teach us about the nature and constitution of this comet? The break-up of the comet apparently triggered activity of the fragments. Although a dust coma was continuously present around the fragments that orbited Jupiter, spectroscopic observations did not reveal any sign of gas. The impact itself was so energetic that most molecules of the impactor were dissociated and that any chemical memory was lost. Ultraviolet and visible spectroscopy of the impact sites revealed emission lines from several atoms, giving potential information on elemental abundances. However, the fact that both neutral and ionized atoms are emitting, and that both fundamental and inter-system lines are present, suggest that the medium is out-of-equilibrium and that emitting mechanisms other than simple resonance fluorescence are at work. Ultraviolet, infrared, and radio spectroscopy revealed lines of several molecular species, in emission and/or absorption, that are not normally present in Jupiter's upper atmosphere. In the visible, dark spots due to aerosols developed at the impact sites. It is not clear at the present time which part of this material is coming from preserved impactor material, from the recombination of the dissociated impactor material, from reactions between the impactor's and Jupiter's material, or from material coming from the lower layers of Jupiter's atmosphere. Realistic modelling of the impacts and of the following chemical reactions will be necessary to address all these issues. In this chapter, we will review the observational clues to the composition and structure of SL9 in the context of our knowledge of the composition and structure of comets and asteroids.

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Molecular Abundances in Comets

Cited by 6 publications

References 67 publications

Photochemistry of Saturn's Atmosphere II. Effects of an Influx of External Oxygen

Photochemistry of Saturn's Atmosphere II. Effects of an Influx of External Oxygen

Gas composition of the main volatile elements in protoplanetary discs and its implication for planet formation

Observational constraints on the composition and nature of comet D/Shoemaker-Levy 9

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