  WASP-8b has 2.18 times Jupiter's mass and is on an eccentric ($e=0.31$)
8.16-day orbit. With a time-averaged equilibrium temperature of 948 K, it is
one of the least-irradiated hot Jupiters observed with the Spitzer Space
Telescope. We have analyzed six photometric light curves of WASP-8b during
secondary eclipse observed in the 3.6, 4.5, and 8.0 {\microns} Infrared Array
Camera bands. The eclipse depths are $0.113\pm 0.018$%, $0.069\pm 0.007$%, and
$0.093\pm 0.023$%, respectively, giving respective brightness temperatures of
1552, 1131, and 938 K. We characterized the atmospheric thermal profile and
composition of the planet using a line-by-line radiative transfer code and a
Markov-chain Monte Carlo sampler. The data indicated no thermal inversion,
independently of any assumption about chemical composition. We noted an
anomalously high 3.6-{\microns} brightness temperature (1552 K); by modeling
the eccentricity-caused thermal variation, we found that this temperature is
plausible for radiative time scales less than $\sim 10^{2}$ hours. However, as
no model spectra fit all three data points well, the temperature discrepancy
remains as an open question.
