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Nature. 2011 Jan 6;469(7328):64-7. doi: 10.1038/nature09602. Epub 2010 Dec 8.

A high C/O ratio and weak thermal inversion in the atmosphere of exoplanet WASP-12b.

Author information

1
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. nmadhu@mit.edu

Abstract

The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior, as opposed to the silicate-dominated composition found on Earth; the atmosphere can also differ from those in the Solar System. The solar C/O is 0.54 (ref. 3). Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b (ref. 6) that reveals C/O ≥ 1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T > 2,500 K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.

PMID:
21150901
DOI:
10.1038/nature09602

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