Scientific rationale for Saturn׳s in situ exploration

Mousis, O.; Fletcher, Leigh N.; Lebreton, Jean‐Pierre; Würz, Peter; Cavalié, T.; Coustenis, A.; Courtin, R.; Gautier, D.; Helled, Ravit; Irwin, Patrick; Morse, A. D.; Nettelmann, Nadine; Marty, Bernard; Rousselot, P.; Venot, Olivia; Atkinson, D. H.; Waite, J. H.; Reh, Kim; Simon-Miller, A. A.; Atreya, S. K.; André, Nicolas; Blanc, Michel; Daglis, Ioannis A.; Fischer, G.; Geppertt, W. D; Guillot, T.; Hedman, M. M.; Hueso, R.; Lellouch, E.; Lunine, Jonathan I.; Murray, C. D.; O’Donoghue, James; Rengel, Miriam; Sánchez‐Lavega, A.; Schmider, F. X.; Spiga, Aymeric; Spilker, Thomas R.; Petit, J. M.; Tiscareno, Matthew S.; Ali-Dib, Mohamad; Altwegg, Kathrin; Bolton, S. J.; Bouquet, Alexis; Briois, C.; Fouchet, Thierry; Guerlet, Sandrine; Kostiuk, T.; Lebleu, Denis; Moreno, R.; Orton, G. S.; Poncy, J.

doi:10.1016/j.pss.2014.09.014

Cited by 52 publications

(50 citation statements)

References 163 publications

(189 reference statements)

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“…If a new process is indeed at work, this would have important implications for our understanding of planetary formation and evolution, in our solar system and other planetary systems. Answering these fundamental questions warrants further investigation into the deuterium and helium abundances of both giant planets, and strengthens the case for a Galileo-like probe to Saturn to perform in situ measurements (Mousis et al 2014).…”

Section: Discussionmentioning

confidence: 77%

D/H Ratios on Saturn and Jupiter from Cassini CIRS

Pierel¹,

Nixon²,

Lellouch³

et al. 2017

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We present new measurements of the deuterium abundance on Jupiter and Saturn, showing evidence that Saturn's atmosphere contains less deuterium than Jupiter's. We analyzed far-infrared spectra from the Cassini Composite Infrared Spectrometer to measure the abundance of HD on both giant planets. Our estimate of the Jovian D/H = (2.95 ± 0.55) × 10 −5 is in agreement with previous measurements by ISO/SWS: (2.25 ± 0.35) × 10 −5 , and the Galileo probe: (2.6 ± 0.7) × 10 −5 . In contrast, our estimate of the Saturn value of (2.10 ± 0.13) × 10 −5 is somewhat lower than on Jupiter (by a factor of 0.71 0.15), contrary to model predictions of a higher ratio: Saturn/ Jupiter = 1.05-1.20. The Saturn D/H value is consistent with estimates for hydrogen in the protosolar nebula (2.1 ± 0.5) × 10 −5 , but its apparent divergence from the Jovian value suggests that our understanding of planetary formation and evolution is incomplete, which is in agreement with previous work.

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Section: Discussionmentioning

confidence: 77%

D/H Ratios on Saturn and Jupiter from Cassini CIRS

Pierel¹,

Nixon²,

Lellouch³

et al. 2017

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“…This code has been used to study exoplanets (Venot et al 2012(Venot et al , 2013(Venot et al , 2015Agúndez et al 2014) but also the deep atmosphere of giant planets of the Solar System (Cavalié et al 2014;Mousis et al 2014). We use the numerical solver DLSODES 1 .…”

Section: D Neutral Chemical Modelmentioning

confidence: 99%

Influence of Stellar Flares on the Chemical Composition of Exoplanets and Spectra

Venot

Rocchetto

Carl

et al. 2016

ApJ

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More than three thousand exoplanets have been detected so far, and more and more spectroscopic observations of exoplanets are performed. Future instruments (JWST, E-ELT, PLATO, Ariel, . . . ) are eagerly awaited as they will be able to provide spectroscopic data with a greater accuracy and sensitivity than what is currently available. This will allow more accurate conclusions to be drawn on the chemistry and dynamics of the exoplanet atmospheres, on condition that the observational data are processed carefully. An important aspect to consider is temporal stellar atmospheric disturbances that can influence the planetary composition, and hence spectra, and potentially can lead to incorrect assumptions about the steady-state atmospheric composition of the planet. In this paper, we focus on perturbations that come from the host star in the form of flare events that significantly increase the photon flux impingement on the exoplanets atmosphere. In some cases, and particularly for M stars, this sudden increase may last for several hours. We aim at answering the question to what extent a stellar flare is able to modify the chemical composition of the planetary atmosphere and, therefore influence the resulting spectra. We use a one-dimensional thermo-photochemical model to study the neutral atmospheric composition of two hypothetic planets located around the star AD Leo. We place the two planets at different distances from the star, which results in effective atmospheric temperatures of 412 K and 1303 K. AD Leo is an active star that has already been observed during a flare. We therefore use the spectroscopic data from this flare event to simulate the evolution of the chemical composition of the atmospheres of the two hypothetic planets. We compute synthetic spectra to evaluate the implications for observations. The increase of the incoming photon flux affects the chemical abundances of some important species (such as H and NH 3 ) down to altitudes associated with an atmospheric pressure of 1 bar, that can lead to variations in planetary spectra (up to 150 ppm) if performed during transit. We find that each exoplanet has a post-flare steady-state composition that is significantly different from the preflare steady-state. We predict that these variations could be detectable with both current and future spectroscopic instruments if sufficiently high signal-to-noise spectra are obtained.

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“…Main text: Thermochemical models of the protosolar nebula (PSN) suggest that molecular nitrogen N 2 was the principal nitrogen species during the disk's phase (1) and that the nitrogen present in the giant planets was accreted in this form (2).…”

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confidence: 99%

Molecular nitrogen in comet 67P/Churyumov-Gerasimenko indicates a low formation temperature

Rubin

Altwegg

Balsiger

et al. 2015

Science

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214

163

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One sentence summary: The first direct detection of dinitrogen in a cometary coma by Rosetta/ROSINA indicates a low formation temperature of comet 67P/Churyumov-Gerasimenko.3 Abstract: Molecular nitrogen (N 2 ) is thought to have been the most abundant form of nitrogen in the protosolar nebula. N 2 is also the main N-bearing molecule in the atmospheres of Pluto and Triton, and was probably the main nitrogen reservoir from which the giant planets formed. Yet in comets, often considered as the most primitive bodies in the solar system, N 2 has not been detected. Here we report the direct in situ measurement of N 2 in the Jupiter family comet 67P/Churyumov-Gerasimenko made by the ROSINA mass spectrometer aboard the Rosetta spacecraft. A N 2 /CO ratio of 5.70 ± 0.66"3 was measured, corresponding to depletion by a factor of ~25.4 ± 8.9 compared to the protosolar value. This depletion suggests that cometary grains formed at low temperature conditions below ~30 K, and that the amount of N 2 delivered by comets to the terrestrial planets was a small fraction of that contributed by the other N-bearing species.Main text: Thermochemical models of the protosolar nebula (PSN) suggest that molecular nitrogen N 2 was the principal nitrogen species during the disk's phase (1) and that the nitrogen present in the giant planets was accreted in this form (2).

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Scientific rationale for Saturn׳s in situ exploration

Cited by 52 publications

References 163 publications

D/H Ratios on Saturn and Jupiter from Cassini CIRS

D/H Ratios on Saturn and Jupiter from Cassini CIRS

Influence of Stellar Flares on the Chemical Composition of Exoplanets and Spectra

Molecular nitrogen in comet 67P/Churyumov-Gerasimenko indicates a low formation temperature

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