Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star

Bourrier, Vincent; Lovis, Christophe; Beust, Hervé; Ehrenreich, David; Henry, Gregory W.; Astudillo-Defru, Nicola; Allart, Romain; Bonfils, Xavier; Ségransan, Damien; Delfosse, Xavier; Cegla, Heather M.; Wyttenbach, Aurélien; Lavie, Baptiste; Pepe, Francesco; Heng, Kevin (2018). Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star. Nature, 553(7689), pp. 477-480. Macmillan Journals Ltd. 10.1038/nature24677

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The angle between the spin of a star and its planets' orbital planes 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 characterization of a planet three-dimensional trajectory 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. Eccentric, misaligned exoplanets orbiting close to cool stars might thus hint at the presence of unseen perturbers and illustrate the diversity of orbital architectures seen in exoplanetary systems.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
08 Faculty of Science > Physics Institute
10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Heng, Kevin

Subjects:

500 Science
500 Science > 520 Astronomy
500 Science > 530 Physics

ISSN:

0028-0836

Publisher:

Macmillan Journals Ltd.

Language:

English

Submitter:

Janine Jungo

Date Deposited:

18 Apr 2018 14:11

Last Modified:

01 Aug 2018 02:30

Publisher DOI:

10.1038/nature24677

BORIS DOI:

10.7892/boris.112375

URI:

https://boris.unibe.ch/id/eprint/112375

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