The Photochemistry of Low-Mass Exoplanets Across the Mini-Neptune / Super-Earth Regime

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The powerful new capabilities soon to be provided by the James Webb Space Telescope (JWST) and by ground based "Extremely Large Telescopes" will enable many new astronomical observations. One of the most exciting of these will be obtaining spectra of the atmospheres of individual exoplanets. This team will provide a theoretical framework within which to understand these sorts of measurements. They will develop models for the photochemistry and chemical kinetics of exoplanetary atmospheres. This will include the formation and development of hazes and other atmospheric constituents. The team will conduct a robust K-12 outreach program. Graduate and undergraduate student volunteers will speak at schools local to the University. This program will also support the work of a graduate student.This research will advance chemical kinetics and photochemistry modeling of low-mass exoplanets to fill in critical gaps in our predictive and interpretive phase space. The team will develop the opensource numerical chemical kinetics code PHOTOCHEM to be applicable to a wider array of exoplanet environments, including hydrogen-rich sub-Neptunes and the metal-rich secondary atmospheres of super-Earths, pushing well beyond the modeling parameter space enabled by solar system studies. They will investigate several key open scientific questions and will provide a modeling framework for exoplanet observers performing spectroscopic studies of transiting planet atmospheres. The specific studies that the team will undertake include: (1) calculating photochemical haze formation rates for a broad parameter space of low-mass exoplanet atmospheres to make testable predictions for which sub-classes of planets should be most affected by photochemical aerosols; (2) determining the necessary level of precision and wavelength coverage for UV observations of exoplanet host stars to be used as input to photochemical modeling studies; (3) directly modeling the outcomes of laboratory haze experiments to provide a foundational basis for comparing between the theory and measurement of haze formation; (4) producing observables (transmission and emission spectra) for each of the modeled planets, to motivate and interpret atmospheric characterization studies with JWST and ground-based telescopes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.