Nikku Madhusudhan (Princeton)

Chemical Characterization of Exoplanetary Atmospheres

Chemical abundances derived from planetary spectra provide critical clues on the chemical and dynamical processes in planetary atmospheres and interiors, on their formation environments, and, for super-Earths, on their habitability conditions. Recent advances in observations and theoretical modeling are leading to unprecedented constraints on elemental abundances in exoplanetary atmospheres. The first statistical constraint on the carbon-to-oxygen (C/O) ratio in an exoplanetary atmosphere was reported recently and was found to be greater than unity, opening the possibility of exotic carbon-rich planets (CRPs). In this talk, I will present emerging observational constraints on atmospheric elemental and molecular abundances for an ensemble of exoplanets, and associated theoretical avenues. Key constraints are emerging for the C/H, O/H, and C/O ratios, and for molecular mixing ratios of H2O, CO, CH4, and CO2. The C/O ratios provide particularly strong constraints on the atmospheric chemistry and temperature structures of the planets, planet formation conditions, and the chemistry and apportionment of ices, rocks, and volatiles in their interiors. I will also present a new two-dimensional classification scheme for characterizing exoplanetary atmospheres, and will discuss major observational and theoretical initiatives in this direction.