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A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b

Knutson, Heather A. and Benneke, Björn and Deming, Drake and Homeier, Derek (2014) A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b. Nature, 505 (7481). pp. 66-68. ISSN 0028-0836.

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GJ 436b is a warm—approximately 800 kelvin—exoplanet that periodically eclipses its low-mass (half the mass of the Sun) host star, and is one of the few Neptune-mass planets that is amenable to detailed characterization. Previous observations have indicated that its atmosphere has a ratio of methane to carbon monoxide that is 10^5 times smaller than predicted by models for hydrogen-dominated atmospheres at these temperatures. A recent study proposed that this unusual chemistry could be explained if the planet’s atmosphere is significantly enhanced in elements heavier than hydrogen and helium. Here we report observations of GJ 436b’s atmosphere obtained during transit. The data indicate that the planet’s transmission spectrum is featureless, ruling out cloud-free, hydrogen-dominated atmosphere models with an extremely high significance of 48σ. The measured spectrum is consistent with either a layer of high cloud located at a pressure level of approximately one millibar or with a relatively hydrogen-poor (three per cent hydrogen and helium mass fraction) atmospheric composition.

Item Type:Article
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URLURL TypeDescription Paper ReadCube access
Knutson, Heather A.0000-0002-0822-3095
Benneke, Björn0000-0001-5578-1498
Deming, Drake0000-0001-5727-4094
Additional Information:© 2014 Macmillan Publishers Limited. Received 24 July; accepted 18 November 2013. We thank P. McCullough for his assistance in the planning and executing of these observations. We are also grateful to J. Moses, M. Line and N. Nettelmann for conversations on the nature of high-metallicity atmospheres as well as discussions of specific interior and atmosphere models for GJ436b. D.H. has received support from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013 grant agreement number 247060). Author Contributions: H.A.K. carried out the data analysis for this project with input from D.D. B.B. provided the planetary atmosphere models and accompanying fits, and D.H. supplied the PHOENIX atmosphere models used to calculate the stellar limb-darkening coefficients.
Funding AgencyGrant Number
European Research Council (ERC)247060
Subject Keywords:Exoplanets
Issue or Number:7481
Record Number:CaltechAUTHORS:20140123-095106704
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43486
Deposited By: Jason Perez
Deposited On:23 Jan 2014 19:18
Last Modified:11 Oct 2019 23:36

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