A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c

[en] Three Earth-sized exoplanets were recently discovered close to the habitable zone of the nearby ultracool dwarf star TRAPPIST-1 (ref. 3). The nature of these planets has yet to be determined, as their masses remain unmeasured and no observational constraint is available for the planetary population surrounding ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting example. Theoretical predictions span the entire atmospheric range, from depleted to extended hydrogen-dominated atmospheres. Here we report observations of the combined transmission spectrum of the two inner planets during their simultaneous transits on 4 May 2016. The lack of features in the combined spectrum rules out cloud-free hydrogen-dominated atmospheres for each planet at ≥10σ levels; TRAPPIST-1 b and c are therefore unlikely to have an extended gas envelope as they occupy a region of parameter space in which high-altitude cloud/haze formation is not expected to be significant for hydrogen-dominated atmospheres. Many denser atmospheres remain consistent with the featureless transmission spectrum—from a cloud-free water-vapour atmosphere to a Venus-like one.

Disciplines :

Space science, astronomy & astrophysics

Author, co-author :

de Wit, Julien

Wakeford, Hannah R.

Gillon, Michaël ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)

Lewis, Nikole K.

Valenti, Jeff A.

Demory, Brice-Olivier

Burgasser, Adam J.

Delrez, Laetitia ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)

Jehin, Emmanuel ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)

Lederer, Susan M.

Triaud, Amaury H. M. J.

Van Grootel, Valérie ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique stellaire théorique et astérosismologie

Language :

English

Title :

A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c

Publication date :

September 2016

Journal title :

Nature

ISSN :

0028-0836

eISSN :

1476-4687

Publisher :

Nature Publishing Group, Basingstoke, United Kingdom

Volume :

537

Pages :

Peer reviewed :

Peer Reviewed verified by ORBi

Additional URL :

http://adsabs.harvard.edu/abs/2016arXiv160601103D

Available on ORBi :

since 29 June 2016

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