Planetary Science Seminar fall-2018

Akash Gupta: Using the 'core-powered mass-loss' mechanism to understand the radius distribution of small, short-period exoplanets
NASA's Kepler mission has been a significant step in improving our understanding of planetary formation and evolution. One of its key findings is that the planets of size 1 - 4 Earth radii are the most abundant planets discovered to date. Interestingly, further observations have revealed a paucity in the occurrence of small, short-period planets around 1.5 - 2.0 Earth radii, a radius ‘valley’. Planets that fall below this radius valley are consistent with Earth-like compositions while planets above the valley have large enough radii that their cores must be engulfed in H/He atmospheres. High-energy stellar radiation is generally considered responsible for explaining these observations. However, a recent study has proposed an alternative mechanism, the ‘core-powered mass-loss’. In this talk, I will discuss the ‘core-powered mass-loss’ mechanism and will present the results from our work consisting of thermal evolution and mass-loss of small, short-period exoplanets. I will show that our results are in excellent agreement with the observations, and that they constrain the composition, mass-distribution and initial atmospheric masses of the observed exoplanet population.
---------------------
Alexandra Schneider: Exoplanetary Oxygen Fugacities From Externally-Polluted White Dwarfs
White dwarf stars polluted by accretion of rocky material from their remnant planetary systems offer unique opportunities to study the chemistry and structure of extrasolar terrestrial planets. We use HIRES observations targeting white dwarfs exhibiting an abundance of major rock-forming elements to characterize the intrinsic oxidation states of the accreted bodies. Oxidation state and core-mass fractions are key aspects of rocky, potentially Earth-like, worlds.