[en] Astrophysics - Earth and Planetary Astrophysics
[en] The transiting exoplanet WASP-18b was discovered in 2008 by the Wide Angle Search for Planets (WASP) project. The Spitzer Exoplanet Target of Opportunity Program observed secondary eclipses of WASP-18b using Spitzer's Infrared Array Camera (IRAC) in the 3.6-micron and 5.8-micron bands on 2008 December 20, and in the 4.5-micron and 8.0-micron bands on 2008 December 24. We report eclipse depths of 0.31+-0.02, 0.38+-0.03, 0.41+-0.02, 0.43+-0.03 %, and brightness temperatures of 2920 +- 90, 3150 +- 130, 3040 +- 130 and 2960 +- 130 K, respectively. WASP-18b is one of the hottest planets yet discovered - as hot as an M-class star. The planet's pressure-temperature profile features a thermal inversion. The observations also require WASP-18b to have near-zero albedo and almost no redistribution of energy from the day-side to the night side of the planet.