X-ray irradiation and evaporation of the four young planets around V1298 Tau

TL;DR

This study investigates the high-energy X-ray irradiation of the young star V1298 Tau and its four exoplanets, modeling their atmospheric evaporation and evolution to understand their current states and future development.

Contribution

It combines X-ray observations with stellar activity models and planetary mass loss estimates to assess atmospheric evaporation of young exoplanets around V1298 Tau.

Findings

V1298 Tau is highly X-ray luminous with $ ext{log} L_X=30.1$ erg/s.

Inner planets could lose significant gaseous envelopes due to evaporation.

Planetary densities critically influence their potential to reach the rocky core stage.

Abstract

Planets around young stars are thought to undergo atmospheric evaporation due to the high magnetic activity of the host stars. Here we report on X-ray observations of V1298 Tau, a young star with four transiting exoplanets. We use X-ray observations of the host star with Chandra and ROSAT to measure the current high-energy irradiation level of the planets, and employ a model for the stellar activity evolution together with exoplanetary mass loss to estimate the possible evolution of the planets. We find that V1298 Tau is X-ray bright with $\log L_X$ [erg/s] $=30.1$ and has a mean coronal temperature of $\approx 9$ MK. This places the star amongst the more X-ray luminous ones at this stellar age. We estimate the radiation-driven mass loss of the exoplanets, and find that it depends sensitively on the possible evolutionary spin-down tracks of the star as well as on the current planetary densities. Assuming the planets are of low density due to their youth, we find that the innermost two planets can lose significant parts of their gaseous envelopes, and could be evaporated down to their rocky cores depending on the stellar spin evolution. However, if the planets are heavier and follow the mass-radius relation of older planets, then even in the highest XUV irradiation scenario none of the planets is expected to cross the radius gap into the rocky regime until the system reaches an age of 5 Gyr.