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STScI Webcast

STScI Astrobiology Lecture Series

Exoplanetary Atmospheres

Presented by: Kevin Heng (University of Bern, Center for Space and Habitability, Exoplanets and Exoclimes Group)
Category: Science Colloquia   Duration: 1 hour   Broadcast date: October 28, 2016
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The study of exoplanetary atmospheres is one of the frontiers of exoplanet science. It enables us to remotely sense the surface (or photospheric) environment of an exoplanet and ask questions related to chemistry and formation history. In the first part of the talk, I will give a brisk review of the tools of the trade: the assumptions and concepts that go into constructing a model atmosphere. I will focus on the caveats and challenges associated with opacities, billion-line radiative transfer and chemistry. In the second part of the talk, I will apply these concepts towards the study of the four directly imaged exoplanets in the HR 8799 system. I will review why the radii and surface gravities of these exoplanets are model-dependent and somewhat controversial. I will dissect our implementation of a nested sampling atmospheric retrieval tool and explain why our retrieved elemental abundances and carbon-to-oxygen ratios are, at zeroth order, inconsistent with exoplanet formation via gravitational instability. Finally, I will share some (speculative) thoughts for the future, including on the habitable zone, geochemical cycles, biosignature gases (and false positives) and astrochemistry.