MATs (Monday Afternoon Talks)

3:00pm – 3:30pm, Rachel Bowens-Rubin

The observer that cried Wolf 359: hunting for exoplanets in the fifth-closest system using direct imaging and radial velocity
Wolf 359 is a low-mass star in the fifth-closest neighboring system. Because of its relative youth and proximity, Wolf 359 offers a unique opportunity to study substellar companions around M stars using infrared high-contrast imaging and radial velocity monitoring.  I will present the results of our Wolf 359 joint radial velocity/direct imaging survey and the current status of the Wolf 359 b cold Neptune-like planet candidate. I will conclude by sharing the prospects for directly detecting an ice-giant exoplanet with JWST in the Wolf 359 system and other nearby, young low-mass star systems.

3:30pm – 4:00pm, William Misener

A window into sub-Neptune interiors: coupled chemistry and structure of hydrogen-silane-water atmospheres
Sub-Neptunes are among the most common classes of exoplanet discovered to date, but there is considerable uncertainty surrounding their interiors. One model consistent with observations is that these planets consist of silicate cores surrounded by hydrogen envelopes. At the conditions of the magma-atmosphere interface of sub-Neptune planets, substantial silicate vapor is expected to be in chemical equilibrium in the atmosphere. These species could greatly alter the atmospheric structure and evolution of these exoplanets, but previous models have neglected this compositional coupling. I present a coupled chemical equilibrium and atmospheric structure model, including silicate gas and its interactions with the background hydrogen. We find that silane, SiH4, and water, H2O, are the main products of atmosphere-interior interactions in sub-Neptune planets. These vapor products act as condensable species, decreasing in abundance with altitude. The resultant mean molecular weight gradient inhibits convection at temperatures above ∼2500 K, inducing a non-convective layer near the magma surface. This layer decreases the planet’s radius compared to a planet with the same base temperature and a convective, pure H/He atmosphere. Therefore, we expect silicate vapor to have major effects on the inferred envelope mass fraction of sub-Neptune planets, and on their thermal and mass evolution. The presence of silicon species in the atmosphere may also be observable, allowing a window into the interiors of these planets.