We present Spitzer Space Telescope infrared photometric time series of the transiting extrasolar planet system TrES-1 .
The data span a predicted time of secondary eclipse , corresponding to the passage of the planet behind the star .
In both bands of our observations , we detect a flux decrement with a timing , amplitude , and duration as predicted by published parameters of the system .
This signal represents the first direct detection of ( i.e .
the observation of photons emitted by ) a planet orbiting another star .
The observed eclipse depths ( in units of relative flux ) are 0.00066 \pm 0.00013 at 4.5 \mu m and 0.00225 \pm 0.00036 at 8.0 \mu m. These estimates provide the first observational constraints on models of the thermal emission of hot Jupiters .
Assuming that the planet emits as a blackbody , we estimate an effective temperature of T _ { p } = 1060 \pm 50 K. Under the additional assumptions that the planet is in thermal equilibrium with the radiation from the star and emits isotropically , we find a Bond albedo of A = 0.31 \pm 0.14 .
This would imply that the planet absorbs the majority of stellar radiation incident upon it , a conclusion of significant impact to atmospheric models of these objects .
We also compare our data to a previously-published model of the planetary thermal emission , which predicts prominent spectral features in our observational bands due to water and carbon monoxide .
This model adequately reproduces the observed planet-to-star flux ratio at 8.0 \mu m , however it significantly over-predicts the ratio at 4.5 \mu m. We also present an estimate of the timing of the secondary eclipse , which we use to place a strong constraint on the expression e \cos { \omega } , where e is the orbital eccentricity and \omega is the longitude of periastron .
The resulting upper limit on e is sufficiently small that we conclude that tidal dissipation is unlikely to provide a significant source of energy interior to the planet .