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Scientific rationale for Saturn׳s in situ exploration

O. Mousis 1 L.N. Fletcher 2 J.P Lebreton 3, 4 P. Wurz 5 T. Cavalié 6 A. Coustenis 7 R. Courtin 7 D. Gautier 7 R. Helled 8 P.G.J. Irwin 2 A.D. Morse 9 N. Nettelmann 10 B. Marty 11 P. Rousselot 1 O. Venot 12 D.H. Atkinson 13, 14 J.H. Waite 15 K.R. Reh 13 A.A. Simon 16 S. Atreya 17 N. André 18 M. Blanc 18 I.A. Daglis 19 G. Fischer 20 W.D. Geppert 21, 22 T. Guillot 23 M.M. Hedman 14 R. Hueso 24 E. Lellouch 7 J.I. Lunine 25 C.D. Murray 26 J. O׳donoghue 27 M. Rengel 6 A. Sánchez-Lavega 24 F.-X. Schmider 23 A. Spiga 28 T. Spilker J.-M. Petit 1 M.S. Tiscareno 29 M. Ali-Dib 1 Kathrin Altwegg 5 S.J. Bolton 15 A. Bouquet 1, 15 Christelle Briois 3 T. Fouchet 7 S. Guerlet 28 T. Kostiuk 16 D. Lebleu 30 R. Moreno 7 G.S. Orton 13 J. Poncy 30
Abstract : Remote sensing observations meet some limitations when used to study the bulk atmospheric composition of the giant planets of our solar system. A remarkable example of the superiority of in situ probe measurements is illustrated by the exploration of Jupiter, where key measurements such as the determination of the noble gases׳ abundances and the precise measurement of the helium mixing ratio have only been made available through in situ measurements by the Galileo probe. This paper describes the main scientific goals to be addressed by the future in situ exploration of Saturn placing the Galileo probe exploration of Jupiter in a broader context and before the future probe exploration of the more remote ice giants. In situ exploration of Saturn׳s atmosphere addresses two broad themes that are discussed throughout this paper: first, the formation history of our solar system and second, the processes at play in planetary atmospheres. In this context, we detail the reasons why measurements of Saturn׳s bulk elemental and isotopic composition would place important constraints on the volatile reservoirs in the protosolar nebula. We also show that the in situ measurement of CO (or any other disequilibrium species that is depleted by reaction with water) in Saturn׳s upper troposphere may help constraining its bulk O/H ratio. We compare predictions of Jupiter and Saturn׳s bulk compositions from different formation scenarios, and highlight the key measurements required to distinguish competing theories to shed light on giant planet formation as a common process in planetary systems with potential applications to most extrasolar systems. In situ measurements of Saturn׳s stratospheric and tropospheric dynamics, chemistry and cloud-forming processes will provide access to phenomena unreachable to remote sensing studies. Different mission architectures are envisaged, which would benefit from strong international collaborations, all based on an entry probe that would descend through Saturn׳s stratosphere and troposphere under parachute down to a minimum of 10 bar of atmospheric pressure. We finally discuss the science payload required on a Saturn probe to match the measurement requirements.
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O. Mousis, L.N. Fletcher, J.P Lebreton, P. Wurz, T. Cavalié, et al.. Scientific rationale for Saturn׳s in situ exploration. Planetary and Space Science, Elsevier, 2014, 104 (Part A), pp.29-47. ⟨10.1016/j.pss.2014.09.014⟩. ⟨hal-01276366⟩



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