Planetary Physics from Population Statistics

Daniel Thorngren

UC Santa Cruz

The large and expanding sample of known exoplanets presents a valuable avenue for understanding their physics across a wide range of parameter space. For my PhD work, I have applied structure evolution modeling and Bayesian statistics to understand the properties of giant planets as a population. First, I studied the cooler giant planets (T_eq <1000 K), and showed that their bulk composition is correlated with their total mass, consistent with the core-accretion model of planet formation. Then, by assuming that hot Jupiters (on average) share this compositional trend, I was able to quantify the amount of heating needed to explain their anomalously large radii. I am currently investigating whether hot Jupiters reinflate as their parent stars brighten on the main sequence; this possibility is directly to the physics underlying hot Jupiter inflation. These population analyses only scratch the surface of what will be possible as TESS expands the sample with potentially thousands of new discoveries. The core of my postdoctoral work will be to apply this technique to new physical questions. Hot Saturns are the next logical regime to look at. Their mass-flux-radius relations do not follow any clean pattern like that seen in hot Jupiters, and they are surprisingly rare compared to only moderately more massive objects. Modeling the structures of this population could shed light on how this came to be. Another promising regime is the higher mass Jupiters -- the hypothesized transition between core-accretion and gravitational instability could be evident in the resulting planetary composition. On a separate track, I'm interested in whether observed giant exoplanets have cores; while this is not an easy problem, I suggest two avenues of attack. First, we can compare a planet's atmospheric metallicity to its bulk metallicity -- if the atmosphere is relatively depleted, it suggests that some metal may be hidden in a core or by composition gradients. Second, there may be cases where strong energy flow out of the core (from radioactive decays and tidal dissipation) can effectively mix the planet. I will check this with interior modelling using a careful treatment of energy flow and stability against convection. Each of these projects can help to better connect observations to underlying theory, elucidating the nature, formation, and subsequent evolution of these objects.

Date: Thursday, 31 January 2019
Time: 11:30
Where: Université de Montréal
  Pavillon Roger-Gaudry, Local D-460
Contact: Björn Benneke