The phase-dependent Infrared brightness of the extrasolar planet upsilon Andromedae b

Abstract

The star upsilon Andromeda is orbited by three known planets, the innermost of which has an orbital period of 4.617 days and a mass at least 0.69 that of Jupiter. This planet is close enough to its host star that the radiation it absorbs overwhelms its internal heat losses. Here we present the 24 micron light curve of this system, obtained with the Spitzer Space Telescope. It shows a clear variation in phase with the orbital motion of the innermost planet. This is the first demonstration that such planets possess distinct hot substellar (day) and cold antistellar (night) faces.