The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters

Abstract

Closing in on Extraterrestrial Earths With close to 500 extrasolar planets discovered to date, researchers are starting to estimate the occurrence of low-mass planets to help our understanding of how planets form and evolve. Based on observations of 166 nearby stars with the Keck Telescope, Howard et al. (p. 653 ) report the occurrence of short-period planets around Sun-like stars as a function of planet mass. Planet formation models predicted that planet occurrence would increase with decreasing mass, such that satellites with masses similar to that of Neptune, and less, would be more common than gas-giant planets like Jupiter. Contrary to predictions, there is no dearth of planets with masses 5 to 30 times that of Earth, implying that the models may need revision. Nevertheless, observations suggest that 23% of Sun-like stars may be orbited by a close-in, terrestrial mass planet.