How small can a planet be and still maintain an atmosphere? While the upper size boundary of where a terrestrial planet becomes a gaseous planet has been studied in detail, there are few studies that examine the lower planet mass and radius limit of habitability. At what point is a planet too small to maintain an atmosphere? To explore this question, we developed the Smaller Than Earth Habitability Model (STEHM), a model that couples the thermal evolution of the planet interior with atmospheric escape driven by stellar flux of a Sun-like star. Starting with an Earth-sized planet that orbits in the habitable zone of a sun-like star, we step down in size to 0.5 Earth radii to determine at what point the planet can no longer maintain an atmosphere. We test variations of the initial conditions of carbon abundance, heat producing elements (HPE), mantle temperature, planet density and position in the habitable zone. Join us to discover the results of our study, and what parameters were the most influential in determining atmospheric retention.

Dr. Michelle Hill is a postdoctoral researcher and Stanford Science Fellow investigating exoplanet habitability in the Earth and Planetary Sciences Department under the mentorship of Laura Schaefer. She recently completed her PhD in Earth and Planetary Sciences at the University of California, Riverside, where her work centered on exoplanet habitability, planet detection using transit, radial-velocity and astrometry methods, mass measurements and orbital refinement, planet population studies, and exomoons. Originally from Australia, Michelle completed her bachelor’s degree in astrophysics at the University of Southern Queensland.