A SUBLIME 3D Model for Non-LTE Emission from Cometary and Icy Moon Atmospheres

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In its early history, the Sun was embedded in a debris disk of dust and gas that extended beyond the orbit of Pluto. Comets formed in the outer regions of this disk, where they remain unchanged until a gravitational encounter with another object sends them in towards the Sun in a highly eccentric orbit. Cometary nuclei thus provide a crucial window back in time to the earliest stages of planet formation. This team will investigate the physical processes and chemical makeup of comets and planetary icy moons. They will use new computational tools to interpret high-resolution radio/submillimeter images of a significant sample of comets to gain new insights into the chemistry of cometary nuclei, and they will study the atmospheres of the icy moons of Jupiter and Saturn. Atmospheric plumes from these icy moons can reveal the compositions of hidden, sub- surface oceans, which might provide potential habitats for life. The PI will mentor undergraduate students from minority-serving university institutions through a summer research internship program. The grant will produce a new spectral line modeling suite (SUBLIME), based on the open source Line Modeling Engine, adapted for low-density atmospheres/exospheres of comets and icy moons. This code will accurately solve the molecular excitation and radiation transfer in three dimensions. The model will combine a 3D Monte Carlo radiative transfer and excitation code with a parameterized optimal estimation (retrieval) engine. New collisional rates for CO-CO, HCN-H2O and CH3-OH-H2O systems will be generated via quantum chemical calculations, including the construction of detailed potential energy surfaces and subsequent solving of the molecular dynamics. The model will be applied to ALMA observations of cometary and icy moon atmospheres to gain understanding of their physical processes and chemical abundances.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.