  Precision infrared photometry from Spitzer has enabled the first direct
studies of light from extrasolar planets, via observations at secondary eclipse
in transiting systems. Current Spitzer results include the first longitudinal
temperature map of an extrasolar planet, and the first spectra of their
atmospheres. Spitzer has also measured a temperature and precise radius for the
first transiting Neptune-sized exoplanet, and is beginning to make precise
transit timing measurements to infer the existence of unseen low mass planets.
The lack of stellar limb darkening in the infrared facilitates precise radius
and transit timing measurements of transiting planets. Warm Spitzer will be
capable of a precise radius measurement for Earth-sized planets transiting
nearby M-dwarfs, thereby constraining their bulk composition. It will continue
to measure thermal emission at secondary eclipse for transiting hot Jupiters,
and be able to distinguish between planets having broad band emission versus
absorption spectra. It will also be able to measure the orbital phase variation
of thermal emission for close-in planets, even non-transiting planets, and
these measurements will be of special interest for planets in eccentric orbits.
Warm Spitzer will be a significant complement to Kepler, particularly as
regards transit timing in the Kepler field. In addition to studying close-in
planets, Warm Spitzer will have significant application in sensitive imaging
searches for young planets at relatively large angular separations from their
parent stars.
