Phase Variations, Transits and Eclipses of the Misfit CoRoT-2b

We propose to observe the nearby transiting hot Jupiter CoRoT-2b for a little over one planetary orbit on two occasions, yielding two secondary eclipses, a transit, and a full phase curve in each of the 3.6 and 4.5 micron channels. These data will help resolve the unique nature of this bloated planet: CoRoT-2b is the only hot Jupiter that is poorly fit by either inverted or non-inverted spectral models (Deming et al. 2011). Two hypotheses have been proposed to explain the peculiar mid-IR colors of CoRoT-2b, and thermal phase measurements with Spitzer's continuous, high-precision photometry will be able to distinguish between them: the planet has a non-inverted atmosphere but is losing mass to its host star, or the planet has a peculiar kind of temperature inversion due to mysterious atmospheric scatterers. CoRoT-2b is also among the most inflated hot Jupiters and, because of its relatively large mass, cannot be reconciled with interior evolution models, despite a small but non-zero eccentricity. A recent planetary collision may be necessary to explain the planet's youthful radius (Guillot & Havel 2011). Finally, the planet's extremely young host star, CoRoT-2, is the most chromospherically active of all transit hosts. This appears to be a common thread connecting all of its planet's peculiarities: the high UV flux of the star will drive mass loss, as well as photochemistry. Most importantly, the radius measurement of the planet at optical wavelengths may be contaminated by star spots. Mid-IR transit measurements from Spitzer will help resolve the mystery of CoRoT-2b's inflated radius.