Description:

For the past decade we have begun to explore the origin of planetary compositions which are set in the natal protoplanetary disk.   In this talk I will explore these links via two lenses that of  giant planets formed far from their star and in smaller Earth-sized planets in the inner regions of planetary systems.    For giant planets the primary link has been through the elemental C/O ratio.  This is theorized to vary with position in the planet-forming disk as the main carriers of C and O (H2O, CO, and CO2) have spatially separated gas-ice sublimation fronts.   I will outline the methodology via which the C/O ratio is traced within disk systems using data from the Atacama Large Millimeter Array (ALMA).   I will then summarize the state of knowledge through a comparison of ALMA measurements of the C/O ratio to those measured with high accuracy in distant exoplanets and discuss what this means for the origins of these planetary systems.   For the second part of my talk, I will present a new model for the composition of planets that form in the inner few au near their stellar hosts.   This model focuses on the supply of carbon to terrestrial worlds, both Earth-like and super-Earth’s, and sub-Neptune’s.   This is the result of a collaboration that melds astrophysics and geophysics to predict that a population of these planets will form in particular locations in their protoplanetary disks such that they receive significant inventories of organics, with low water content.   As a result of geochemical equilibrium, the mantle of such a planet could be rich in reduced carbon but have relatively low oxygen (water) content.   Outgassing would naturally yield the ingredients for haze production, which is widely observed in super-Earth’s and sub-Neptune’s. Although this type of planet has no solar system counterpart, it should be common in the galaxy, and for terrestrial worlds, it will hold uncertain effects on the potential for habitability.

Ted Bergen, Professor and Chair of Astronomy, University of Michigan

Host: Giles Novak