Speaker: Prof. Edwin(Ted) Bergin, University of Michigan
Abstract: 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 explore the disposition of elemental carbon via new model of planet formation in the inner parts of the disk. This model relates the initial mantle composition of the planet to its formation zone around its star, factoring in the relative contributions of refractories (metals and silicates) and volatile components (solid state organics, water vapor/ice, and hydrogen-dominated nebular gas). We predict that a population of super-Earth’s and mini-Neptune’s will form in particular locations in their protoplanetary disks such that they receive significant inventories of organics, but very low amounts of water. As a result of geochemical equilibrium, the mantle of such a planet would 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 these systems. Although this type of planet has no solar system counterpart, it should be common in the galaxy.