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Detection of the Atmosphere of the 1.6 M ? Exoplanet GJ 1132 b

Southworth, John; Mancini, Luigi; Madhusudhan, Nikku; Mollière, Paul; Ciceri, Simona; Henning, Thomas

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Luigi Mancini

Nikku Madhusudhan

Paul Mollière

Simona Ciceri

Thomas Henning


Detecting the atmospheres of low-mass, low-temperature exoplanets is a high-priority goal on the path to ultimately detecting 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 ${M}_{\oplus }$ transiting exoplanet, GJ 1132 b, 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 1.43 ± 0.16 ${R}_{\oplus }$ for the planet, averaged over all the passbands, and a radius of 0.255 ± 0.023 ${R}_{\odot }$ for the star, both of which are significantly greater than previously found. The planet radius can be decomposed into a "surface radius" at ~1.375 ${R}_{\oplus }$ overlaid by atmospheric features that increase the observed radius in the z and K bands. The z-band radius is 4s 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 a hitherto-unconsidered opacity. A surface radius of 1.375 ± 0.16 ${R}_{\oplus }$ 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.


Southworth, J., Mancini, L., Madhusudhan, N., Mollière, P., Ciceri, S., & Henning, T. (2017). Detection of the Atmosphere of the 1.6 M ? Exoplanet GJ 1132 b. Astronomical Journal, 153(4), Article 191.

Journal Article Type Article
Acceptance Date Feb 27, 2017
Online Publication Date Mar 31, 2017
Publication Date Mar 31, 2017
Journal The Astronomical Journal
Print ISSN 0004-6256
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 153
Issue 4
Article Number 191
Keywords planetary systems; stars: fundamental parameters; stars: individual (GJ 1132)
Publisher URL;


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