ABSTRACT

Over 130 planets are known to orbit stars other than the Sun. Until recently, all of these extrasolar planets were detected indirectly, and no photons emitted by the planets had been observed. In late 2004, two independent groups used the Spitzer Space Telescope to observe thermal infrared emission originating from two transiting extrasolar giant planets, HD209458b and TrES-1. The Spitzer measurements of these "hot Jupiters" confirm that these planets are strongly heated by stellar irradiation, but differences from simple irradiated models are already beginning to emerge. Follow-up observations by Spitzer will clarify these differences and will reveal the atmospheric structure, composition, and other characteristics of extrasolar giant planets.