The Primary Atmospheres of Planets: The Formation, The Impact on Planet Formation and How to Characterize Them
Planets are generally believed to form in protoplanetary disks within a few million years (Myr) to several hundred Myr. But planetary embryos or protoplanets likely exist before disk gas dissipates (in three to ten Myr), capturing H2 -rich primary atmospheres from the nebula. Exploring these primordial atmospheres of planets provides a pathway to understanding the origins and the diversity of planets in the solar system and beyond. In this dissertation, I studied the primary atmospheres by modeling their formation, their impacts on planet formation, and determining methods to characterize them on exoplanets.
First, I numerically investigated the ﬂow structures and dynamics of the primary atmospheres accreted on Earth-sized planets with eccentric orbits. Such planets can generate atmosphere-stripping bow shocks, as their relative velocities to the gas are generally supersonic. The atmospheres are three to four orders of magnitude less massive than those of planets with circular orbits. Hydrodynamic simulations also revealed large-scale recycling gas ﬂow in the post-shock regions. This study provides important insights into the impacts of migration and scattering on primary atmospheres.
Second, I looked into how the presence of the primary atmosphere aﬀects the trajectories of chondrule precursors passing through a planetary bow shock. To determine what magnetic ﬁelds chondrules were exposed to as they cooled below their Curie points, I computed the gas properties and magnetic diﬀusion rates in the bow shock region of a planet with and without the primary atmosphere. I concluded that, if melted in planetary bow shocks, most chondrules were cooled in the far downstream and they probably recorded the background nebular ﬁeld.
Last, I studied the characterization of cloudy primary atmospheres on exoplanets using a Bayesian retrieval approach. I focused on obtaining bulk cloud properties and the impact of clouds on constraining various atmospheric properties through transmission spectroscopy using the James Webb Space Telescope (JWST). Most key atmospheric and cloud inferences can be well constrained in the wavelength range (0.6 – 11 µ m) but there are diﬀerent optimal wavelengths for constraining atmosphere or cloud parameters. Other results including degeneracies among cloud parameters can also serve as a guideline for future observers.