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Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star.
Nature 2018; 553(7689):477-480Nat

Abstract

The angle between the spin of a star and the orbital planes of its planets traces the history of the planetary system. Exoplanets orbiting close to cool stars are expected to be on circular, aligned orbits because of strong tidal interactions with the stellar convective envelope. Spin-orbit alignment can be measured when the planet transits its star, but such ground-based spectroscopic measurements are challenging for cool, slowly rotating stars. Here we report the three-dimensional characterization of the trajectory of an exoplanet around an M dwarf star, derived by mapping the spectrum of the stellar photosphere along the chord transited by the planet. We find that the eccentric orbit of the Neptune-mass exoplanet GJ 436b is nearly perpendicular to the stellar equator. Both eccentricity and misalignment, surprising around a cool star, can result from dynamical interactions (via Kozai migration) with a yet-undetected outer companion. This inward migration of GJ 436b could have triggered the atmospheric escape that now sustains its giant exosphere.

Authors+Show Affiliations

Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.Center of Excellence in Information Systems, Tennessee State University, Nashville, Tennessee 37209, USA.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012 Bern, Switzerland.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.Observatoire de l'Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

29258300

Citation

Bourrier, Vincent, et al. "Orbital Misalignment of the Neptune-mass Exoplanet GJ 436b With the Spin of Its Cool Star." Nature, vol. 553, no. 7689, 2018, pp. 477-480.
Bourrier V, Lovis C, Beust H, et al. Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star. Nature. 2018;553(7689):477-480.
Bourrier, V., Lovis, C., Beust, H., Ehrenreich, D., Henry, G. W., Astudillo-Defru, N., ... Pepe, F. (2018). Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star. Nature, 553(7689), pp. 477-480. doi:10.1038/nature24677.
Bourrier V, et al. Orbital Misalignment of the Neptune-mass Exoplanet GJ 436b With the Spin of Its Cool Star. Nature. 2018 01 25;553(7689):477-480. PubMed PMID: 29258300.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star. AU - Bourrier,Vincent, AU - Lovis,Christophe, AU - Beust,Hervé, AU - Ehrenreich,David, AU - Henry,Gregory W, AU - Astudillo-Defru,Nicola, AU - Allart,Romain, AU - Bonfils,Xavier, AU - Ségransan,Damien, AU - Delfosse,Xavier, AU - Cegla,Heather M, AU - Wyttenbach,Aurélien, AU - Heng,Kevin, AU - Lavie,Baptiste, AU - Pepe,Francesco, Y1 - 2017/12/18/ PY - 2017/08/11/received PY - 2017/10/20/accepted PY - 2017/12/21/pubmed PY - 2017/12/21/medline PY - 2017/12/21/entrez SP - 477 EP - 480 JF - Nature JO - Nature VL - 553 IS - 7689 N2 - The angle between the spin of a star and the orbital planes of its planets traces the history of the planetary system. Exoplanets orbiting close to cool stars are expected to be on circular, aligned orbits because of strong tidal interactions with the stellar convective envelope. Spin-orbit alignment can be measured when the planet transits its star, but such ground-based spectroscopic measurements are challenging for cool, slowly rotating stars. Here we report the three-dimensional characterization of the trajectory of an exoplanet around an M dwarf star, derived by mapping the spectrum of the stellar photosphere along the chord transited by the planet. We find that the eccentric orbit of the Neptune-mass exoplanet GJ 436b is nearly perpendicular to the stellar equator. Both eccentricity and misalignment, surprising around a cool star, can result from dynamical interactions (via Kozai migration) with a yet-undetected outer companion. This inward migration of GJ 436b could have triggered the atmospheric escape that now sustains its giant exosphere. SN - 1476-4687 UR - https://www.unboundmedicine.com/medline/citation/29258300/Orbital_misalignment_of_the_Neptune_mass_exoplanet_GJ_436b_with_the_spin_of_its_cool_star_ L2 - https://doi.org/10.1038/nature24677 DB - PRIME DP - Unbound Medicine ER -