Detection of the Atmosphere of the 1.6 Earth Mass Exoplanet GJ 1132b

Detecting the atmospheres of low-mass low-temperature exoplanets is a high-priority goal on the path to ultimately detect biosignatures in the atmospheres of habitable exoplanets.

High-precision HST observations of several super-Earths with equilibrium temperatures below 1000 K have to date all resulted in featureless transmission spectra, which have been suggested to be due to high-altitude clouds. We report the detection of an atmospheric feature in the atmosphere of a 1.6 Mearth transiting exoplanet, GJ 1132b, with an equilibrium temperature of ~600 K and orbiting a nearby M dwarf. We present observations of nine transits of the planet obtained simultaneously in the griz and JHK passbands. We find an average radius of 1.44 +/- 0.21 Rearth for the planet, averaged over all the passbands, which can be decomposed into a "surface radius" at ~1.35 Rearth, and higher contributions in the z and K bands.

The z-band radius is 4 sigma higher than the continuum, suggesting a strong detection of an atmosphere. We deploy a suite of tests to verify the reliability of the transmission spectrum, which are greatly helped by the existence of repeat observations. The large z-band transit depth indicates strong opacity from H2O and/or CH4 or an hitherto unconsidered opacity. A surface radius of 1.35 +/- 0.21 Rearth allows for a wide range of interior compositions ranging from a nearly Earth-like rocky interior, with ~70% silicate and ~30% Fe, to a substantially H2O-rich water world.

New observations with HST and existing ground-based facilities would be able to confirm the present detection and further constrain the atmospheric composition of the planet.

John Southworth, Luigi Mancini, Nikku Madhusudhan, Paul Molliere, Simona Ciceri, Thomas Henning
(Submitted on 7 Dec 2016)

Comments: 13 pages, 10 colour figures, 5 tables. Submitted on 2016/12/05
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1612.02425 [astro-ph.EP] (or arXiv:1612.02425v1 [astro-ph.EP] for this version)
Submission history
From: John Southworth
[v1] Wed, 7 Dec 2016 21:00:00 GMT (220kb)
https://arxiv.org/abs/1612.02425

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