Scientists Explore How Variable Stars Affect Exoplanet Habitability

Astronomers are gaining new insights into how the variability of stars influences the habitability of exoplanets. A recent study accepted into The Astronomical Journal investigates the relationship between stellar activity—changes in a star’s brightness—and exoplanetary atmospheres. This research aims to enhance our understanding of how such variability affects the search for habitable exoplanets, particularly those orbiting stars distinctly different from our Sun.

The research team examined data related to nine exoplanets, each orbiting a separate star located within the habitable zone. These stars exhibit varying levels of stellar variability, which is crucial in determining the potential for life-supporting conditions. The exoplanets analyzed include TOI-1227 b (328 light-years), 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 primary aim of the study was to determine how the variability of these stars impacts the equilibrium temperature of their orbiting exoplanets and whether planets situated on the inner edge of their stars’ habitable zones could retain water. Equilibrium temperature refers to the ideal temperature of a planetary body without any heat exchange.

Findings indicated that the nine stars analyzed displayed minimal influence on the equilibrium temperature of their respective exoplanets. Moreover, the research confirmed that exoplanets within the inner edge of their stars’ habitable zones have the potential to retain water, irrespective of the stars’ variability.

The study encompassed stars with mass ranging from 0.17 to 1.25 solar masses, including M-, K-, G-, and F-type stars. M-type stars, which are the smallest, contrast with our Sun, categorized as a G-type star. Understanding this diversity is essential for identifying stars that might host habitable exoplanets. Notably, M-type stars are of particular interest due to their abundance and extended lifetimes, estimated to last up to trillions of years. In comparison, the Sun’s lifetime is projected to be between 10 and 12 billion years.

M-type stars are also characterized by significant variability, including sunspots, flares, and fluctuations in magnetic fields. This extreme activity raises questions about the habitability of their exoplanets, as stellar flares can strip atmospheres and ozone layers, potentially jeopardizing conditions suitable for life.

Two prominent examples of M-type stars are Proxima Centauri and TRAPPIST-1. Proxima Centauri, located approximately 4.24 light-years from Earth, is known for its intense activity, which has raised concerns about the habitability of its single rocky exoplanet. Similarly, TRAPPIST-1, about 39.5 light-years away, hosts seven rocky exoplanets, one of which may be habitable, despite the star’s significant variability.

As researchers continue to explore the dynamics between star variability and exoplanet habitability, new insights are expected to emerge in the coming years. This ongoing investigation reflects the broader quest to better understand the cosmos and the conditions that foster life beyond our planet.