Planet heating prevents inward migration of planetary cores

摘要

Planetary systems are born in the disks of gas, dust and rocky fragments that surround newly formed stars. Solid content assembles into ever-larger rocky fragments that eventually become planetary embryos. These then continue their growth by accreting leftover material in the disk. Concurrently, tidal effects in the disk cause a radial drift in the embryo orbits, a process known as migration Fast inward migration is predicted by theory for embryos smaller than three to five Earth masses. With only inward migration, these embryos can only rarely become giant planets located at Earth's distance from the Sun and beyond, in contrast with observations. Here we report that asymmetries in the temperature rise associated with accreting infalling material produce a force (which gives rise to an effect that we call 'heating torque') that counteracts inward migration. This provides a channel for the formation of giant planets and also explains the strong planet-metallicity correlation found between the incidence of giant planets and the heavy-element abundance of the host stars.%行星形成理论预测，小于大约五个地球质量的"胚胎行星"将会向主恒星迅速迁移，在这种情况下，这些"胚胎行星"只有在罕见情形下才会变成巨型行星，轨道与地球和太阳的距离相当或更远。观测显示，巨型行星在这样的距离的确存在，在太阳系外行星系统中以及在我们自己的行星系统中都有。在这项研究中，Benitez-Llambay等人介绍了一个机制，它能为巨型行星的形成提供了一个渠道。他们发现，与吸积的降落物质（infalling material)相关的温度上升所存在的不对称性会产生一种力（被称为"heating torque"),这种力会对行星向内迁移（inward migration)产生反作用。