Planet Probabilities

Abstract

Models of planet formation favor accretion into spheres in protoplanetary disks around young stars. The smaller, rocky planets (Earth-like) would form closer to their central star where the more refractory metals (elements heavier than helium) can accrete, and the larger, icy planets (Jupiter-like) would form farther from their central star where volatile-rich ices can accumulate. The Jupiter-like planets could then migrate inward, causing any Earth-like planets to be pushed into the star, increasing the star's concentration of metals (metallicity). About 40 “hot Jupiters” (Jupiter-like planets that have migrated to smaller orbits) have been detected, and at least 32 of these planets orbit stars that are richer in metals than typical solar-mass stars.