Planetary Habitability Under the Light of a Rapidly Changing Star

TL;DR

This study assesses how stellar variability affects planetary habitability, focusing on equilibrium temperature and water retention, and finds that moderate variability has minimal impact on planets in the habitable zone.

Contribution

It provides new insights into the effects of stellar variability on planetary climates, especially for stars with moderate activity levels, using observational data from TESS.

Findings

Stellar variability has negligible effect on equilibrium temperature for the studied stars.

Water loss rates are similar for Earth-like planets around variable and quiet stars.

Extreme stellar variability could pose greater challenges for habitability assessments.

Abstract

Planetary atmospheric energy budgets primarily depend on stellar incident flux. However, stellar variability can have major consequences for the evolution of planetary climates. In this work, we evaluate how stellar variability influences the equilibrium temperature and water retention of planets within the Habitable Zone (HZ). We present a sample of 9 stars that are known to host at least one planet within the HZ and that were identified to have a variability amplitude exceeding 100 ppm based on photometry from the Transiting Exoplanet Survey Satellite (TESS). We investigate the effect that the variability of these stars have on the insolation flux of their HZ planets and the resulting changes in the induced planetary equilibrium temperature. Our results show that for the stars in our sample, the stellar variability has an insignificant effect on the equilibrium temperature of HZ planets. However, we also emphasize that these stars are not representative of more extreme variable stars, since exoplanets are more difficult to detect and characterize in the presence of extreme variability. We also investigate the equilibrium temperature and long-term evolution of a hypothetical Earth-like planet placed at the inner edge of the HZ around a highly variable star. We found that the water loss rates are comparable between both variable and quiet host stars for Earth-like planets in the inner HZ. Overall, these results broaden our knowledge on the impact of stellar variability on planetary habitability.