Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects

Exoplanetary science is on the verge of an unprecedented revolution. The thousands of exoplanets discovered over the past decade have most recently been supplemented by discoveries of potentially habitable planets around nearby low-mass stars. Currently, the field is rapidly progressing toward detailed spectroscopic observations to characterize the atmospheres of these planets. Various surveys from space and the ground are expected to detect numerous more exoplanets orbiting nearby stars that make the planets conducive for atmospheric characterization. The current state of this frontier of exoplanetary atmospheres may be summarized as follows. We have entered the era of comparative exoplanetology thanks to high-fidelity atmospheric observations now available for tens of exoplanets. Recent studies reveal a rich diversity of chemical compositions and atmospheric processes hitherto unseen in the Solar System. Elemental abundances of exoplanetary atmospheres place important constraints on exoplanetary formation and migration histories. Upcoming observational facilities promise to revolutionize exoplanetary spectroscopy down to rocky exoplanets. The detection of a biosignature in an exoplanetary atmosphere is conceivable over the next decade. In the present review, we discuss the modern and future landscape of this frontier area of exoplanetary atmospheres. We start with a brief review of the area, emphasising the key insights gained from different observationalmethods and theoretical studies. This is followed by an in-depth discussion of the state of the art, challenges, and future prospects in three forefront branches of the area.