Planets Big and Small

Fri., Oct. 2, 2020 3:30 p.m. - Fri., Oct. 2, 2020 4:30 p.m.

Location: Zoom

Abstract: From gas-poor Earths to gas-rich Jupiters, planets come in a variety of sizes. I will describe the physics behind the diversity of exoplanets --- how the core and gas assembly processes give rise to the observed distribution of radii and orbital periods. Observationally, there is a pronounced gap in the radius distribution, demaracating the boundary between rocky Earths and super-Earths from gas-enveloped sub-Neptunes. We show that gas accretion alone can reproduce this feature as gas thermodynamics precludes planets lighter than 1--2 Earth masses to ever accruing enough gas to appear as sub-Neptunes. Basic astrophysical considerations of gas dynamical friction, gravitational scattering, collisional mergers, and gas accretion by cooling inform us that planets smaller than Neptune likely emerged in situ, in the late stages of disk evolution. Larger planets on the other hand must have nucleated from massive cores that assemble in the early stages of disk evolution. Yet, disk-planet tidal interaction in such gas-heavy disk forces planets to rapidly shuttle to the inner edges of the disks. We show that such large-scale inward migration is unable to explain the distribution of the observed orbital periods and masses, suggesting even gas giants likely assembled close to where we observe them.

Speaker: Dr. Eve J. Lee, McGill