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PUFFY HELIUM PLANETS COULD EXPLAIN AN EXOPLANET SIZE MYSTERY
The fate of Neptune-like worlds that migrate close to their stars is to be whittled away by stellar radiation
Reported by Tariq Malik
H elium could make up almost half the mass of the atmospheres of giant exoplanets that have migrated close to their stars, explaining why there’s a mysterious size gap among these worlds. Over 5,200 exoplanets have been confirmed, and many are larger worlds that orbit close to their stars, in some cases with orbital periods lasting just a few days. However, transit observations by NASA’s Kepler Space Telescope and now TESS, the Transiting Exoplanet Survey Satellite, have found a puzzling dearth of planets with radii between 1.4 and 2.4 times that of Earth. Astronomers call this the ‘radius valley’. Though it seems to be telling us something fundamental about the nature, formation and evolution of planets, scientists have yet to ascertain what that something is.