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The hot Jupiter HD 189733b is probably the best studied of the knownextrasolar planets, with published transit and eclipse spectra covering thenear UV to mid-IR range. Recent work on the transmission spectrum has shownclear evidence for the presence of clouds in its atmosphere, whichsignificantly increases the model atmosphere parameter space that must beexplored in order to fully characterise this planet. In this work, we apply theNEMESIS atmospheric retrieval code to the recently published HST/STISreflection spectrum, and also to the dayside thermal emission spectrum in thelight of new Spitzer/IRAC measurements, as well as our own re-analysis of theHST/NICMOS data. We first use the STIS data to place some constraints on thenature of the cloud on HD189733b, and explore solution degeneracy betweendifferent cloud properties and the abundance of Na in the atmosphere; asalready noted in previous work, absorption due to Na plays a significant rolein determining the shape of the reflection spectrum. We then perform a newretrieval of the temperature profile and abundances of H2O, CO2, CO and CH4from the dayside thermal emission spectrum. Finally, we investigate the effectof including cloud in the model on this retrieval process. We find that thecurrent quality of data does not warrant the extra complexity introduced byincluding cloud in the model; however, future data are likely to be ofsufficient resolution and signal-to-noise that a more complete model, includingscattering particles, will be required.

Clouds on the hot Jupiter HD189733b: constraints from the reflection spectrum