Study Examines Impact of Star Variability on Exoplanet Habitability

A new study accepted for publication in The Astronomical Journal sheds light on the relationship between star variability and the habitability of exoplanets. Researchers investigated how fluctuations in a star’s brightness affect the atmospheres of exoplanets, specifically focusing on those orbiting stars significantly different from our Sun. This research aims to enhance astronomers’ understanding of which types of stars could host habitable planets.

The study analyzed data from nine exoplanets orbiting nine separate stars, all located within their respective habitable zones. Each of these stars exhibits notable variability. The exoplanets included in the study are TOI-1227 b, located 328 light-years away; HD 142415 b at 116 light-years; HD 147513 b at 42 light-years; and several others, with the most distant being HD 238914 b at 1,694 light-years.

The research team aimed to determine how their star’s variability influenced the exoplanets’ equilibrium temperatures and their ability to retain water. The equilibrium temperature is defined as the temperature a planetary body would stabilize at if no heat transfer occurred. Surprisingly, the findings indicated that the nine stars had minimal impact on their exoplanets’ equilibrium temperatures. Furthermore, the study concluded that exoplanets situated within the inner edge of their star’s habitable zone could maintain water, independent of stellar variability.

Understanding Stellar Types and Their Lifetimes

The stars examined in this study varied in size from 0.17 to 1.25 solar masses, encompassing M-, K-, G-, and F-type stars. M-type stars, the smallest among them, are of particular interest as they represent the majority of stars in the universe and have incredibly long lifespans, estimated to last up to trillions of years. In contrast, our Sun, classified as a G-type star, has a lifespan estimated between 10 to 12 billion years.

M-type stars exhibit extreme variability, characterized by sunspots, flares, rotational changes, and fluctuations in their magnetic fields. This variability raises questions about the habitability of their exoplanets since intense stellar flares can strip away atmospheres and ozone layers, potentially jeopardizing any prospect for life.

Among the notable M-type stars are Proxima Centauri and TRAPPIST-1, located approximately 4.24 and 39.5 light-years from Earth, respectively. Both stars have shown significant activity, including ultraviolet bursts and high radiation output. As a result, Proxima Centauri has been deemed harsh for life, especially concerning its known rocky exoplanet. In contrast, TRAPPIST-1, which hosts seven rocky exoplanets, offers the potential for habitability despite the variability associated with its star.

The findings from this study provide critical insights into the conditions that might allow for life on exoplanets orbiting variable stars. As astronomers continue to explore the cosmos, the focus on M-type stars is expected to grow, especially given their prevalence and longevity.

As research in this field advances, the understanding of how stellar activity influences exoplanetary atmospheres will evolve, paving the way for more informed searches for potentially habitable worlds.