DLS - Hilke Schilchting (UCLA)
Metamorphosis: Turning (sub-)Neptunes into (super-)Earths
The discovery of thousands of new planetary candidates over the last decade has revolutionized the field of planet formation. One of Kepler's key findings is that the most abundant planets in our galaxy, observed to date, are larger than Earth but smaller than Neptune. Intriguingly, further observations have revealed a ‘radius valley' in the distribution of such small exoplanets. I will review the origin and formation of this small, close-in exoplanet population, demonstrating that the two planet populations located above and below the radius valley likely started out as one and that the smaller and closer planets lost their primordial hydrogen dominated atmospheres (super-Earths), while the larger and further away planets retained a significant fraction of their primordial envelope (sub-Neptunes). Comparing theory and observations, I will show that we can already infer important properties about the underlying planet population. I will show that typical core densities are similar to earth and, using data from polluted white dwarfs, that these rocky exoplanets are likely geochemically similar to earth as well. I will conclude with demonstrating that even some super-Earths can retain small residual hydrogen envelopes (10s to 100s of bars) and show that this has interesting implications for their redox state, outgassing and further observations.
Zoom link: https://mit.zoom.us/j/96754760318
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