The Curious Westward Hotspot Offset of CoRoT-2b

Hot Jupiters’ rotation rates are expected to rapidly synchronize due to tidal interaction with their host stars. Blasted with stellar irradiation, they typically exhibit large temperature gradients between the dayside and nightside hemispheres which drives a broad equatorial eastward flowing jet, displacing the hottest region east of the substellar point. This eastward shift has been predicted by dynamical models, and all Spitzer phase observations to date are consistent with this offset. We present the first counter-example: the detection of a westward hotspot offset in the 4.5 micron phase curve of CoRoT-2b. With an inflated radius and a remarkably featureless spectrum, this target is not a typical hot Jupiter. Now, a westward offset can be added to the list of unusual characteristics and this may not be coincidental. Hydrodynamic simulations alone cannot explain this westward offset without considering non-synchronous rotation, the presence of a deep-seated magnetic field, or inhomogeneous aerosol coverage on the dayside. In my talk, I will present possible explanations for this westward offset and how each of these scenarios challenges our understanding of hot Jupiters, their interaction with their host star, and their large-scale atmospheric circulation. While a single full-orbit phase curve alone cannot distinguish between these scenarios, I will discuss how additional optical and infrared observations can break the degeneracy.

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