Researchers Explore Exoplanet Habitability Around Variable Stars

A new study accepted for publication in The Astronomical Journal examines the relationship between star variability and the habitability of exoplanets. The research focuses on how fluctuations in a star’s brightness over time affect the atmospheres of planets orbiting around them. The findings could significantly enhance astronomers’ understanding of which types of stars might host habitable exoplanets, especially those that differ from our own Sun.

The research team analyzed data from nine exoplanets, which orbit stars exhibiting heightened levels of variability. These planets include TOI-1227 b (328 light-years away), HD 142415 b (116 light-years), HD 147513 b (42 light-years), HD 221287 b (182 light-years), BD-08 2823 c (135 light-years), KELT-6 c (785 light-years), HD 238914 b (1,694 light-years), HD 147379 b (35 light-years), and HD 63765 b (106 light-years). The study aimed to determine how the variability of these stars influences the equilibrium temperature of their respective exoplanets and whether those planets could retain water.

Researchers found that the nine stars included in the study had minimal impact on the equilibrium temperature of the exoplanets. Notably, planets situated within the inner edge of their star’s habitable zone demonstrated the ability to retain water, irrespective of the star’s variability. The stars analyzed varied in size from 0.17 to 1.25 solar masses, encompassing M-, K-, G-, and F-type stars. M-type stars, the smallest category, have gained attention due to their abundance and longevity, often lasting up to trillions of years, compared to our Sun’s estimated lifespan of 10 to 12 billion years.

These M-type stars are characterized by significant variability, including sunspots, flares, and changes in rotational speed, raising questions about the habitability of their exoplanets. Such stellar activity can strip atmospheres and ozone layers, which may severely hinder the potential for life.

Two notable M-type stars, Proxima Centauri and TRAPPIST-1, are approximately 4.24 and 39.5 light-years from Earth, respectively. Both stars exhibit high levels of activity, marked by ultraviolet (UV) bursts and considerable radiation output. Consequently, Proxima Centauri presents a harsh environment for life on its known rocky exoplanet, while TRAPPIST-1, which has seven rocky exoplanets, includes one that may be habitable despite its star’s variability.

As astronomers continue to investigate the complexities of star variability and its implications for exoplanet habitability, the findings of this study pave the way for future research. Understanding the conditions under which exoplanets can maintain water and support life remains a critical focus in the field of astronomy. The ongoing exploration of these celestial bodies will likely yield new insights, contributing to our broader understanding of the universe and the potential for life beyond Earth.