Abstract:
It is now well-established that mass loss processes play an important role in sculpting the population of Neptunes and sub-Neptunes. For higher-mass planets, while XUV-driven mass loss has been both theoretically predicted and observed, it has been less clear how strongly this impacts the population. I argue that XUV-driven mass loss substantially impacts the low-density planet population due to the inherent relation between their masses and radii. Hot Saturns become larger when mass is removed, and the mass loss rate increases as radius cubed. This feedback loop can in some cases strip the entire gaseous envelope off of a planet, and is strongest with planets that were already at a low bulk density – those below about 10 g/cc are generally torn apart within a Gyr or so. This matches a density “edge” observed in the hot Saturn population which is otherwise unexplained; however, the better-known sub-Jovian desert does not appear to result from this feedback loop. I will discuss some specific case studies of planets undergoing mass loss and our ongoing efforts to identify their mass-loss histories, especially in the context of stellar XUV and He triplet transit observations.
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