We present Spitzer Space Telescope time series photometry of the exoplanet system HD 189733 spanning two times of secondary eclipse , when the planet passes out of view behind the parent star .
We estimate the relative eclipse depth in 5 distinct bands and find the planet-to-star flux ratio to be 0.256 \pm 0.014 % ( 3.6 µm ) , 0.214 \pm 0.020 % ( 4.5 µm ) , 0.310 \pm 0.034 % ( 5.8 µm ) , 0.391 \pm 0.022 % ( 8.0 µm ) , and 0.598 \pm 0.038 % ( 24 µm ) .
For consistency , we re-analyze a previously published time series to deduce a contrast ratio in an additional band , 0.519 \pm 0.020 % ( 16 µm ) .
Our data are strongly inconsistent with a Planck spectrum , and we clearly detect emission near 4 µm as predicted by published theoretical models in which this feature arises from a corresponding opacity window .
Unlike recent results for the exoplanet HD 209458b , we find that the emergent spectrum from HD 189733b is best matched by models that do not include an atmospheric temperature inversion .
Taken together , these two studies provide initial observational support for the idea that hot Jupiter atmospheres diverge into two classes , in which a thermal inversion layer is present for the more strongly irradiated objects .