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- Southworth, John, et al.
(author)
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Detection of the Atmosphere of the 1.6 M-circle plus Exoplanet GJ 1132 b
- 2017
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In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 153:4
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Journal article (peer-reviewed)abstract
- 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-circle plus transiting exoplanet, GJ 1132 b, with an equilibrium temperature of similar to 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-circle plus for the planet, averaged over all the passbands, and a radius of 0.255 +/- 0.023 R-circle dot for the star, both of which are significantly greater than previously found. The planet radius can be decomposed into a surface radius at similar to 1.375 R-circle plus overlaid by atmospheric features that increase the observed radius 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 a hitherto-unconsidered opacity. A surface radius of 1.375 +/- 0.16 R-circle plus allows for a wide range of interior compositions ranging from a nearly Earth-like rocky interior, with similar to 70% silicate and similar to 30% Fe, to a substantially H2O-rich water world.
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