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Title: Superabundance of Exoplanet Sub-Neptunes Explained by Fugacity Crisis
Authors: Edwin S. Kite, et al.
First Author’s Institution: University of Chicago
Status: Published in ApJL
In the few decades since the discovery of the first exoplanet in 1992, we’ve realized that our own solar system is just plain weird. We have no hot-Jupiter gas-giant planets whizzing around our star in a matter of days, nor do we have any sub-Neptune planets, the most common type of planet in the galaxy. Critically, our lack of sub-Neptunes severely hinders our understanding of the transition between Earth-like and Neptune-like planets.
The Kepler Space Telescope operated 2009—2018 and discovered over 2,600 exoplanets, nearly 1,000 of which were classified as sub-Neptunes. But Neptune-like planets are considerably rarer, despite being only slightly bigger. This “radius cliff” (Fig. 1) separates sub-Neptunes (radii < 3 R⨁, where R⨁ is Earth’s radius) from Neptunes (radii > 3 R⨁). What could cause ...