We report on the measurement of the 7.5-14.7 micron spectrum for the transiting extrasolar giant planet HD 189733b using the Infrared Spectrograph on the Spitzer Space Telescope .
Though the observations comprise only 12 hours of telescope time , the continuum is well measured and has a flux ranging from 0.6 mJy to 1.8 mJy over the wavelength range , or 0.49 \pm 0.02 \% of the flux of the parent star .
The variation in the measured fractional flux is very nearly flat over the entire wavelength range and shows no indication of significant absorption by water or methane , in contrast with the predictions of most atmospheric models .
Models with strong day/night differences appear to be disfavored by the data , suggesting that heat redistribution to the night side of the planet is highly efficient .