Planetary atmosphere observation analysis

Abstract:

Future missions to measure the mid-infrared spectra of extrasolar planets will obtain spectra spatially integrated over the visible hemisphere of the planet. Interpretation of these spectra will be difficult because they will depend on several imponderable factors; the axial inclination of the planet to the line of sight, the illumination of the planet by its parent star, and the planets' season and climatic state. The spectra will also contain variable components due to changing clouds, planetary rotation and the presence of large satellites. In order to interpret better such spectra, and to constrain the design of missions to measure them, a study is underway of a dedicated mission to take spectra of the spatially-unresolved Earth and to quantify the dependence of the spectrum on these variables.

Abstract:

Models of Jupiter's formation and structure predict that its atmosphere is enriched in oxygen, relative to the Sun, and that consequently water clouds should be present globally near the 5-bar pressure level. Past attempts to confirm these predictions have led to contradictory results; in particular, the Galileo probe revealed a very dry atmosphere at the entry site, with no significant clouds at depths exceeding the 2-bar level. Although the entry site was known to be relatively cloud-free, the contrast between the observed local dryness and the expected global wetness was surprising. Here we analyse near-infrared (around 5 μm) observations of Jupiter, a spectral region that can reveal the water vapour abundance and vertical cloud structure in the troposphere. We find that humid and extremely dry regions exist in close proximity, and that some humid regions are spatially correlated with bright convective clouds extending from the deep water clouds to the visible atmosphere.