ATMOSPHERE-INTERIOR EXCHANGE ON HOT, ROCKY EXOPLANETS

1Edwin S. Kite, 2Bruce Fegley Jr., 3Laura Schaefer, 4Eric Gaidos
The Astrophysical Journal 828, 80 Link to Article [http://dx.doi.org/10.3847/0004-637X/828/2/80]
1University of Chicago, Chicago, IL 60637, USA
2Planetary Chemistry Laboratory, McDonnell Center for the Space Sciences & Department of Earth & Planetary Sciences, Washington University, St Louis MO 63130, USA
3Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
4University of Hawaii at Manoa, Honolulu, HI 96822, USA

We provide estimates of atmospheric pressure and surface composition on short-period, rocky exoplanets with dayside magma pools and silicate-vapor atmospheres. Atmospheric pressure tends toward vapor-pressure equilibrium with surface magma, and magma-surface composition is set by the competing effects of fractional vaporization and surface-interior exchange. We use basic models to show how surface-interior exchange is controlled by the planet’s temperature, mass, and initial composition. We assume that mantle rock undergoes bulk melting to form the magma pool, and that winds flow radially away from the substellar point. With these assumptions, we find that: (1) atmosphere-interior exchange is fast when the planet’s bulk-silicate FeO concentration is low, and slow when the planet’s bulk-silicate FeO concentration is high; (2) magma pools are compositionally well mixed for substellar temperatures lesssim2400 K, but compositionally variegated and rapidly variable for substellar temperatures gsim2400 K; (3) currents within the magma pool tend to cool the top of the solid mantle (“tectonic refrigeration”); (4) contrary to earlier work, many magma planets have time-variable surface compositions.

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