The D/H ratio in water from comet P/Halley

Eberhardt, P.; Dolder, U.; Schulte, W.; Krankowsky, D.; Lämmerzahl, P.; Hoffman, J. H.; Hodges, R. R.; Berthelier, J. J.; Illiano, J. M.

doi:10.1007/978-3-642-82971-0_79

Cited by 132 publications

(196 citation statements)

References 20 publications

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“…In Comet Hale-Bopp DCN/HCN is about 150 times the protosolar value (Meier et al, 1998a). HDO/H 2 O as measured in Halley, Hale-Bopp and Hyakutake is about 20 times the protosolar value (BockeleÂ e- Morvan et al, 1998;Meier et al, 1998b;Balsiger et al, 1995;Eberhardt et al, 1995). Thus, unless other comets (for example, from the Kuiper Belt rather than the Oort Cloud) show much smaller D/H enrichments, condensed matter from the outer solar nebula would seem to be a poor direct source for Titan's volatiles.…”

Section: Methanementioning

confidence: 92%

On the volatile inventory of Titan from isotopic abundances in nitrogen and methane

Lunine

Yung

Lorenz

1999

Planetary and Space Science

102

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We analyze recently published nitrogen and hydrogen isotopic data to constrain the initial volatile abundances on Saturn's giant moon Titan. The nitrogen data are interpreted in terms of a model of non-thermal escape processes that lead to enhancement in the heavier isotope. We show that these data do not, in fact, strongly constrain the abundance of nitrogen present in Titan's early atmosphere, and that a wide range of initial atmospheric masses (all larger than the present value) can yield the measured enhancement. The enrichment in deuterated methane is now much better determined than it was when Pinto et al. (1986. Nature 319, 388±390) ®rst proposed a photochemical mechanism to preferentially retain the deuterium. We develop a simple linear theory to provide a more reliable estimate of the relative dissociation rates of normal and deuterated methane. We utilize the improved data and models to compute initial methane reservoirs consistent with the observed enhancement. The result of this analysis agrees with an independent estimate for the initial methane abundance based solely on the present-day rate of photolysis and an assumption of steady state. This consistency in reservoir size is necessary but not su cient to infer that methane photolysis has proceeded steadily over the age of the solar system to produce large quantities of less volatile organics. Our analysis indicates an epoch of early atmospheric escape of nitrogen, followed by a later addition of methane by outgassing from the interior. The results also suggest that Titan's volatile inventory came in part or largely from a circum-Saturnian disk of material more reducing than the surrounding solar nebula. Many of the ambiguities inherent in the present analysis can be resolved through Cassini±Huygens data and a program of laboratory studies on isotopic and molecular exchange processes. The value of, and interest in, the Cassini±Huygens data can be greatly enhanced if such a program were undertaken prior to the prime phase of the mission. #

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Section: Methanementioning

confidence: 92%

On the volatile inventory of Titan from isotopic abundances in nitrogen and methane

Lunine

Yung

Lorenz

1999

Planetary and Space Science

102

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“…At all distances, CH 3 + dominates at m/q = 15. These results are of importance in trying to derive isotope ratios from ion mass spectra (see, for example, Eberhardt et al, 1986b).…”

Section: The Radial Distribution Of Ion Concentrationsmentioning

confidence: 99%

Evidence for methane and ammonia in the coma of comet P/Halley

Allen

Delitsky

Huntress

et al. 1988

Exploration of Halley’s Comet

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Summary. Methane and ammonia abundances in the coma of Halley are derived from Giotto IMS data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto HIS ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio m/q = 19/18 as a function of distance from the nucleus is not reproduced by a model for a pure water coma. It is necessary to include the presence of NH 3 , and uniquely NH 3 , in coma gases in order to explain the data. A ratio of production rates Q(NH3)/Q(H20) = 0.01-Q.02 results in model values approximating the Giotto data. Methane is identified as the most probable source of the distinct peak at m/q = 15. The observations are fit best with Q(CH4 )/Q(H2 0) = 0.02. The chemical composition of the comet nucleus implied by these production rate ratios is unlike that of the outer planets. On the other hand, there are also significant differences from observations of gas phase interstellar material.

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“…c Average value derived from ultraviolet (UV) spectra (Pasachoff and Vidal-Madjar (1989)). d Mass spectrometry in situ by Eberhardt et al (1987). e Data for P/Halley.…”

Section: Introductionmentioning

confidence: 99%

“…m Estimated possible lower limit from visual spectra (Wyckoff et al (1989)). n From Eberhardt et al (1987). 0 The data for dust particles obtained by in situ mass spectrometry.…”

Section: Introductionmentioning

confidence: 99%

Isotopic Ratios in Comets

Vanysek

1991

International Astronomical Union Colloquium

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ABSTRACT. The isotopic abundances depend on the universal evolution of elements and on the individual history of particular objects. Since it is believed that unprocessed material of the solar nebula is preserved in comets, the data concerning the abundance of stable isotopes in these primitive bodies are of some importance in the cosmological context. The present status of this problem is reviewed. The reliability of results for nuclear species with cosmological and cosmogonical implications, such as D/H, C 12/13, N 14/15, O 16/18, and Mg 24/25/26, is discussed. Significant variation is found for the isotopic abundance of carbon, depending upon which carbon reservoir is sampled. Deuterium is probably enhanced relative to the interstellar ratio. For other isotopes, the ratios are close to those of the terrestrial data. The tendency of the D/H ratio to be at higher values indicates a low temperature in the environment of the comet's formation, and, together with similar effects in the outer planets, suggests that there were two different primordial reservoirs of deuterium in the solar system. The 12 C/ 13 C ratio inferred from in situ mass spectrometry of the dust, as well as from the ground-based optical spectra of the Swan band, tends to be approximately equal to the average terrestrial ratio (89) or larger. Recent results obtained from the CN band provide a significantly lower value (about 65), which corresponds to the carbon isotopic ratio in the diffuse interstellar clouds. The enhancement of deuterium and the possible differences of the carbon isotopic ratio in different species and refractory material are indicative of chemical fractionation processes in the protosolar nebula.

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The D/H ratio in water from comet P/Halley

Cited by 132 publications

References 20 publications

On the volatile inventory of Titan from isotopic abundances in nitrogen and methane

On the volatile inventory of Titan from isotopic abundances in nitrogen and methane

Evidence for methane and ammonia in the coma of comet P/Halley

Isotopic Ratios in Comets

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