New insights on the atmospheric structure and dynamics of strongly irradiated exoplanets

A new population of exoplanets is emerging: the very hot gas giants, whose dayside atmospheres share many properties in common with stellar photospheres. In this presentation, we show that important molecular species dissociate in these atmospheres, and that opacities from H- cannot be ignored when estimating the planets’ energy budgets and atmospheric dynamics. Ultimately, because of its properties, this new family of planets forms a unique laboratory to study atmospheres in extreme regimes, and can shed light on their cooler counterparts.

In this context, we present spectroscopic phase-curve observations of some of the hottest gas giants obtained with HST/WFC3 by our group, and demonstrate that the atmospheric properties of such planet's can be retrieved with high level of precision. We show that these extreme systems exhibit large temperature gradients between their day and nightside atmospheres. These gradients lead to two very different physical regimes in the same atmosphere, controlled by the recirculation and irradiation of the incoming stellar light. 

We first show that the daysides atmospheres of these planets should be significantly ionized, in particular the alkali metals provide the bulk of the free electrons. We then show that this ionization has an important effect on the atmospheric circulation, through effects such as drag, and thus can provide a test for the theory of Ohmic dissipation. These planets therefore hint to the possible existence of magnetic fields, and provide clues to answering the long standing question of hot Jupiter inflation. 

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