Reversing Type I Migration in Gap Shadows

Abstract

AbstractType I migration refers to the radial drift of a sub-Jupiter mass planet resulting from tidal interactions with a protoplanetary disk. It results in the rapid inward migration of small planets and planet cores through the disk. Type I migration is so rapid compared to disk dissipation time scales that explaining distant planets, such as the HR 8799 planets and Jupiter itself, is problematic because their growing cores should have been lost. Here, we present a scenario for solving the Type I migration problem. As a planet grows in mass, its Type I migration rate should increase, assuming that disk properties are not significantly altered by the forming planet. But a growing planet clears some, but not all, material from its orbital path, creating a partial gap in the disk. The trough of a partially cleared gap such as this is shadowed from stellar illumination while the far side of the gap is illuminated. Since stellar irradiation is the primary heat source of passively accreting protoplanetary disks, gap self-shadowing can significantly change the local temperature profile. This change to the local temperature gradient can significantly slow, or even reverse Type I migration.