An emerging population of irradiated, low-mass exoplanets falls close to rocky bulk densities but are underdense relative to Earth-like composition. In this talk, I will first discuss my previous work, where Prof. Diana Valencia and I proposed puffy Venuses, magma ocean worlds with thick carbon-rich atmospheres, as a potential explanation. To this end, we constructed a coupled magma-ocean atmosphere model that accounted for carbon and hydrogen partitioning between the atmosphere and molten mantle, as well as the C-H-O thermochemistry in a dual-gray radiative-convective atmosphere. We demonstrated that moderate, chondritic C abundance can generate observable underdensity in puffy Venuses, and highlighted exoplanet candidates for this interpretation. I will then discuss recent theoretical and observational works in relation to puffy Venuses. Finally, I will present my ongoing work with Prof. Laura Schaefer on C precipitation in rocky planets. C precipitation, in both the atmosphere and the interior, can facilitate the long-term survival of an outgassed atmosphere by enhancing their C storage capacity. This is because C precipitation can both limit the atmosphere’s mass and form a mantle C reservoir independent from dissolved atmospheric species. We adapt the puffy Venus atmosphere model to probe the irradiation and redox conditions that lead to C precipitation-limited atmospheres, and their observational consequences. We also discuss the phases and distribution of atomic C in the primordial magma oceans of C-rich super-Earths by calculating their buoyancy in molten MgSiO3 across wide P-T ranges. 

Speaker-suggested reading: Piette, A. A. A., Gao, P., Brugman, K., Shahar, A., Lichtenberg, T., Miozzi, F., and Driscoll, P., 2023, Rocky planet or water world? Observability of low-density lava world atmospheres: The Astrophysical Journal, v. 954, p. 29, doi:10.3847/1538-4357/acdef2.

Dr. Bo Peng is a postdoctoral fellow investigating magma ocean worlds both beyond and within our Solar System, in the Earth & Planetary Sciences department under the mentorship of Prof. Laura Schaefer. He recently completed his PhD in Astronomy & Astrophysics at the University of Toronto, where he worked on volatile delivery during planet formation, chondritic parent body evolution, giant impact-induced magma oceans and lava world exoplanets. Bo completed his bachelor’s degree in physics and astronomy at the University of Rochester. In his free time, Bo enjoys cooking and recently started birdwatching.