Astrobiology Colloquium research rotation presentation Samantha Gilbert-Janizek.

Predicting Outgassing Rates for L 98-59 b with an Interior Model
AB Rotation with Prof. Laura Schaefer (Stanford University)
JWST is providing our first glimpses of rocky exoplanet atmospheres and ushering in an era of exoplanet characterization. Inner planets orbiting M-dwarf stars with higher equilibrium temperatures are particularly advantageous for observation in thermal emission, which has already been used to rule out thick CO2 atmospheres on TRAPPIST-1 c. To support the interpretation of JWST observations, we require interior models, which self-consistently calculate the planet’s thermal evolution, to evaluate the stability of potential atmospheric states. While numerous planetary interior models assume that exoplanets evolve with Earth-like plate tectonics, it is thought that stagnant-lid planets, like present-day Mars and Venus in our Solar System, occur more commonly. We use a revised thermal evolution model to predict outgassing rates for CO2, CO, H2, and H2O for the M-dwarf planet L 98-59 b, a current JWST Cycle 2 target. We modify the thermal evolution model to enforce a stagnant lid carbon cycle regime in which eruption from the melt layer replaces outgassing at mid ocean ridges, and inter-plate subduction is neglected. Though further model debugging is required, we preliminarily show that, even when varying the mantle redox state and the initial water inventory, eruption cannot outgas volatiles efficiently enough to maintain water on the planet’s surface. Similarly, we predict relatively low CO2 outgassing rates compared to the Earth. If the planet retains its atmospheric CO2, it may sustain planetary surface temperatures of 800-900 K, which are significantly hotter than the planet’s predicted equilibrium temperature (Teq = 558).