LPL Colloquium: Dr. Gilda Ballester

Tuesday, Feb 25, 2014
3:45 pm
Location: Kuiper Space Sciences
Room: 312

Dr. Gilda Ballester
Associate Staff Scientist
U of A Lunar and Planetary Laboratory

Surprisingly great variety in the lower atmospheres of hot Jupiters as observed with HST
Hot Jupiters remain the most accessible of exoplanets for transit (and eclipse) studies, but their characterization is still in the early stages. We are using HST for an optical and near-IR spectral transit survey of eight hot Jupiters spanning the 1000-3000 K regime. Our recent results emphasize the great variety in the atmospheres of these planets.

Transit absorption signatures show the radius at which the atmosphere becomes optically thick to absorbing and scattering species. The optical (~0.3-1.0 micron) spectra are sensitive to scattering by molecular hydrogen and by aerosols, as well as to the strong Na I and K I D-lines that are expected to be prominent on these planets. The near-IR spectra sample the 1.4-micron water band also expected to be prominent for a solar-abundance (C/O<1) hot Jupiter.

Some results were initially unexpected, such as the detection on condensates on the hottest planet Wasp-12b, but they are beginning to be understood based on the temperature regime that spans the condensation of different species, on the day-to-night temperature contrast which is pronounced in the hottest targets, and on the strong ~1 day 3D dynamics on these tidally-locked planets. Nevertheless, large differences are also observed in the clarity of the atmospheres of planets with fairly similar effective temperatures. Another key result is that the aerosols can mute or totally obscure the 1.4-micron water band absorption in some planets, and thus interfere with the interpretation of C/O ratios based solely on IR transit data.

An unexpectedly large diversity is also seen in the alkalis. In some planets, a strong, high-altitude Na I absorption is detected that requires super-solar abundances, while no corresponding K I absorption is observed. Processes such as photo-ionization could be explored to enhance the Na/K neutral abundance ratios at these altitudes. In sharp contrast, however, the opposite Na I and K I absorption ratio is also observed. The planet with the strongest K I absorption has an effective temperature that is too high for the predicted path of Na condensation as Na2S, so unexpected element-to-element metallicity variations and chemical/condensation schemes must the explored in future models.