Estimating the atmospheric mass loss of V1298 Tau's four young planets & the role of the host star in planet population studies

Kepler observations revealed two striking features in the distribution of exoplanet radii: a dearth of short period sub-Neptune-sized planets, and a relatively clean gap around 2 Earth radii. Atmospheric escape of planetary H/He envelopes driven by the high-energy X-ray and UV irradiation from the host star can explain the presence of the desert at short periods as well as the radius valley. The very young (~ 25 Myr) V1298 Tau system with its four Neptune- to Jupiter-sized planets is an excellent system to test planet formation and evolution models.

To investigate the fate of the four planets, we obtained X-ray measurements of V1298 Tau with Chandra. We then calculated the future photoevaporative mass loss rates using PLATYPOS, an open-source tool to model the (energy-limited) atmospheric escape of planetary systems over several Giga years. We allowed for the host star to spin down at three different ages, which translates into a low, intermediate, and high activity stellar evolutionary track. Our findings show that in certain planetary mass and orbital distance regimes, the stellar high-energy evolution determines if a planet is stripped completely or can retain some fraction of its initial gaseous envelope.