Secondary eclipse observations of several of the hottest hot Jupiters show featureless , blackbody-like spectra or molecular emission features , which are consistent with thermal inversions being present in those atmospheres .
Theory predicts a transition between warmer atmospheres with thermal inversions and cooler atmospheres without inversions , but the exact transition point is unknown .
In order to further investigate this issue , we observed two secondary eclipses of the hot Jupiter HAT-P-7b with the Hubble Space Telescope ( HST ) WFC3 instrument and combined these data with previous Spitzer and Kepler secondary eclipse observations .
The HST and Spitzer data can be well fit by a blackbody with T = 2692 \pm 14 K , and the Kepler data point constrains the geometric albedo to A _ { g } = 0.077 \pm 0.006 .
We modeled these data with a 3D GCM and 1D self-consistent forward models .
The 1D models indicate that the atmosphere has a thermal inversion , weak heat redistribution , and water dissociation that limits the range of pressures probed .
This result suggests that WFC3 observations of HAT-P-7b and possibly some other ultra-hot Jupiters appear blackbody-like because they probe a region near the tropopause where the atmospheric temperature changes slowly with pressure .
Additionally , the 1D models constrain the atmospheric metallicity ( [ \text { M / H } ] = -0.87 ^ { +0.38 } _ { -0.34 } ) and the carbon-to-oxygen ratio ( C/O < 1 at 99 % confidence ) .
The solar composition 3D GCM matches the Spitzer data but generally underpredicts the flux in the WFC3 bandpass and can not reproduce its featureless shape .
This discrepancy could be explained by high atmospheric drag or nightside clouds , and may be better understood through further observation with the James Webb Space Telescope ( JWST ) .