The thermal emission of the young and massive planet CoRoT-2b at 4.5 and 8 μm

We report measurements of the thermal emission of the young and massive planetCoRoT-2b at 4.5 and 8 μm with the Spitzer Infrared Array Camera (IRAC). Our measured occultation depths are 0.510 ± 0.042% at 4.5 and 0.41 ± 0.11 % at 8 μm. In addition to the CoRoT optical measurements, these planet/star flux ratios indicate a poor heat distribution on the night side of the planetand agree better with an atmosphere free of temperature inversion layer. Still, such an inversion is not definitely ruledout by the observations and a larger wavelength coverage is required to remove the current ambiguity. Our global analysisof CoRoT, Spitzer, and ground-based data confirms the high mass and large size of the planetwith slightly revised values (M p = 3.47 ± 0.22 M J , R p = 1.466 ± 0.044 R J ). We find a small but significant offset in the timing of the occultation when compared to a purely circular orbitalsolution, leading to e cos ω = -0.00291 ± 0.00063 where e is the orbital eccentricityand ω is the argument of periastron. Constraining the age of the system to at most a few hundred Myrand assuming that the non-zero orbital eccentricitydoes not come from a third undetected body, we modeled the coupled orbital-tidal evolution of the system with various tidal Q values, core sizes, and initial orbital parameters. For Q' s = 10 5 -10 6 , our modeling is able to explain the large radius of CoRoT-2b if Q' p ≤ 10 5.5 through a transient tidal circularizationand corresponding planet tidal heatingevent. Under this model, the planetwill reach its Roche limitwithin 20 Myrat most.