Key Atmospheric Signatures for Identifying the Source Reservoirs of Volatiles in Uranus and Neptune
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Key Atmospheric Signatures for Identifying the Source Reservoirs of Volatiles in Uranus and Neptune O. Mousis1 · A. Aguichine1 · D.H. Atkinson2 · S.K. Atreya3 · T. Cavalié4,5 · J.I. Lunine6 · K.E. Mandt7 · T. Ronnet8
Received: 15 November 2019 / Accepted: 24 April 2020 © Springer Nature B.V. 2020
Abstract We investigate the enrichment patterns of several delivery scenarios of the volatiles to the atmospheres of ice giants, having in mind that the only well constrained determination made remotely, namely the carbon abundance measurement, suggests that their envelopes possess highly supersolar metallicities, i.e., close to two orders of magnitude above that of the protosolar nebula. In the framework of the core accretion model, only the delivery of volatiles in solid forms (amorphous ice, clathrates, pure condensates) to these planets can account for the apparent supersolar metallicity of their envelopes. In contrast, because of the inward drift of icy particles through various snowlines, all mechanisms invoking the delivery of volatiles in vapor forms predict subsolar abundances in the envelopes of Uranus and Neptune. Alternatively, even if the disk instability mechanism remains questionable in our solar system, it might be consistent with the supersolar metallicities observed in Uranus and Neptune, assuming the two planets suffered subsequent erosion of their H-He In Situ Exploration of the Ice Giants: Science and Technology Edited by Olivier J. Mousis and David H. Atkinson
B O. Mousis
[email protected]
1
Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
2
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA, 91109, USA
3
Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109-2143, USA
4
Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
5
LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 92195 Meudon, France
6
Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
7
Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA
8
Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, 221 00 Lund, Sweden
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envelopes. The enrichment patterns derived for each delivery scenario considered should be useful to interpret future in situ measurements by atmospheric entry probes. Keywords Uranus · Neptune · Atmospheric probes · Formation models · In situ measurements
1 Introduction The ice giant planets Uranus and Neptune represent a largely unexplored class of planetary objects that bridges the gap between the larger gas giants and the smaller terrestrial worlds. Uranus and Neptune’s great heliocentric distances have made exploration challenging, being limited to flybys by the Voyager 2 mission in 1986 and 1989, respective
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