Planets and X-rays: a radiation diet

TL;DR

This study investigates how X-ray radiation from stellar coronae can erode exoplanet atmospheres over time, showing that massive planets survive better under lower radiation exposure and highlighting the need for improved models.

Contribution

It provides observational evidence linking stellar X-ray emission to planetary atmospheric erosion and assesses the survival likelihood of planets based on their mass and density.

Findings

Massive planets may only survive low coronal radiation exposure.

HD 209458 b could have lost over 1 Jupiter mass.

Higher density planets resist radiation effects better.

Abstract

According to theory, high energy emission from the coronae of cool stars can severely erode the atmosphere of orbiting planets. To test the long term effects of the erosion we study a large sample of planet-hosting stars observed in X-rays. The results reveal that massive planets (Mp sin i > 1.5 Mj) may survive only if exposed to low accumulated coronal radiation. The planet HD 209458 b might have lost more than 1 Mj already, and other cases, like tau Boo b, could be losing mass at a rate of 3.4 Earth masses per Gyr. The strongest erosive effects would take place during the first stages of the stellar life, when the faster rotation generates more energetic coronal radiation. The planets with higher density seem to resist better the radiation effects, as foreseen by models. Current models need to be improved to explain the observed distribution of planetary masses with the coronal radiation received.