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

The origin of a recently discovered close-in Neptune-mass planet around GJ436poses a challenge to the current theories of planet formation. Based on thesequential accretion hypothesis and the standard theory of gap formation andorbital migration, we show that around M dwarf stars, close-in Neptune-massice-giant planets may be relatively common, while close-in Jupiter-massgas-giant planets are relatively rare. The mass distribution of close-inplanets generally has two peaks at about Neptune mass and Jupiter mass. Thelower-mass peak takes the maximum frequency for M dwarfs. Around more massivesolar-type stars (G dwarfs), the higher-mass peak is much more pronounced.These are because planets tend to undergo type II migration after fullyaccreting gas around G dwarfs while they tend to migrate faster than gasaccretion around M stars. Close-in Neptune-mass planets may also exist around Gdwarfs, though they tend to be mostly composed of silicates and iron cores andtheir frequency is expected to be much smaller than that of Neptune-massplanets around M dwarfs and that of gas giants around G dwarfs. We also showthat the conditions for planets' migration due to their tidal interaction withthe disk and the stellar-mass dependence in the disk-mass distribution can becalibrated by the mass distribution of short-period planets around host starswith various masses.Comment: accepted for publication in Astrophys.