Toward a Deterministic Model of Planetary Formation. III. Mass Distribution of Short‐Period Planets around Stars of Various Masses

Abstract

The origin of a recently discovered close-in Neptune-mass planet around GJ436\nposes a challenge to the current theories of planet formation. Based on the\nsequential accretion hypothesis and the standard theory of gap formation and\norbital migration, we show that around M dwarf stars, close-in Neptune-mass\nice-giant planets may be relatively common, while close-in Jupiter-mass\ngas-giant planets are relatively rare. The mass distribution of close-in\nplanets generally has two peaks at about Neptune mass and Jupiter mass. The\nlower-mass peak takes the maximum frequency for M dwarfs. Around more massive\nsolar-type stars (G dwarfs), the higher-mass peak is much more pronounced.\nThese are because planets tend to undergo type II migration after fully\naccreting gas around G dwarfs while they tend to migrate faster than gas\naccretion around M stars. Close-in Neptune-mass planets may also exist around G\ndwarfs, though they tend to be mostly composed of silicates and iron cores and\ntheir frequency is expected to be much smaller than that of Neptune-mass\nplanets around M dwarfs and that of gas giants around G dwarfs. We also show\nthat the conditions for planets' migration due to their tidal interaction with\nthe disk and the stellar-mass dependence in the disk-mass distribution can be\ncalibrated by the mass distribution of short-period planets around host stars\nwith various masses.\n