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arXiv · 1012.1603

High C/O Ratio and Weak Thermal Inversion in the Very Hot Atmosphere of Exoplanet WASP-12b

Nikku Madhusudhan·Joseph Harrington·Kevin B. Stevenson·Sarah Nymeyer·Christopher J. Campo·Peter J. Wheatley·Drake Deming·Jasmina Blecic·Ryan A. Hardy·Nate B. Lust·David R. Anderson·Andrew Collier-Cameron·Christopher B. T. Britt·William C. Bowman·Leslie Hebb·Coel Hellier·Pierre F. L. Maxted·Don Pollacco·Richard G. West
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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 a silicate-dominated composition as found on Earth, and the atmospheres can also differ from those in the Solar System. The solar C/O is 0.54. Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b that reveals C/O >= 1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapor and enhanced in methane by over two orders of magnitude each 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 a 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.

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Nikku Madhusudhan, Joseph Harrington, Kevin B. Stevenson, Sarah Nymeyer, Christopher J. Campo, Peter J. Wheatley, Drake Deming, Jasmina Blecic, Ryan A. Hardy, Nate B. Lust, David R. Anderson, Andrew Collier-Cameron, Christopher B. T. Britt, William C. Bowman, Leslie Hebb, Coel Hellier, Pierre F. L. Maxted, Don Pollacco, Richard G. West. 2010-12-07. High C/O Ratio and Weak Thermal Inversion in the Very Hot Atmosphere of Exoplanet WASP-12b. https://doi.org/10.1038/nature09602

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