A new study accepted for publication in The Astronomical Journal explores how star variability, or changes in a star’s brightness over time, influences the potential habitability of exoplanets. Researchers examined the interactions between stellar activity and the atmospheres of exoplanets orbiting stars with varying levels of brightness. This investigation aims to provide insights into the conditions necessary for finding habitable exoplanets, particularly around stars distinct from our Sun.
The research team focused on data from nine exoplanets, each orbiting a different star within their respective habitable zones. The stars selected for the study demonstrate elevated levels of stellar variability. The exoplanets included are TOI-1227 b, located 328 light-years away, HD 142415 b at 116 light-years, HD 147513 b at 42 light-years, HD 221287 b at 182 light-years, BD-08 2823 c at 135 light-years, KELT-6 c at 785 light-years, HD 238914 b at 1,694 light-years, HD 147379 b at 35 light-years, and HD 63765 b at 106 light-years.
The study’s primary objective was to determine how the variability of a star affects the equilibrium temperature of its orbiting exoplanets. The equilibrium temperature refers to the temperature a planetary body would maintain in the absence of heat transfer. Researchers concluded that the nine stars exhibited minimal influence on the equilibrium temperatures of their corresponding exoplanets. Remarkably, the findings indicated that exoplanets situated within the inner edge of their star’s habitable zone could retain water, irrespective of the star’s variability.
The analysis included a diverse range of stars, varying in size from 0.17 to 1.25 solar masses, encompassing M-, K-, G-, and F-type stars. M-type stars, the smallest category, are notable for their long lifespans, estimated to reach up to trillions of years. In comparison, our Sun, classified as a G-type star, has a projected lifetime of 10-12 billion years. The longevity and abundance of M-type stars make them prime candidates for searching for habitable exoplanets.
However, M-type stars are also known for their significant variability, characterized by sunspots, flares, rotational changes, and fluctuations in magnetic fields. These factors raise concerns regarding the habitability of their exoplanets, as stellar flares can potentially strip away atmospheres and ozone layers, severely limiting the prospects for life.
Two prominent examples of M-type stars with exoplanets whose habitability is under scrutiny are Proxima Centauri and TRAPPIST-1. Located approximately 4.24 and 39.5 light-years from Earth, respectively, both stars exhibit high levels of activity, including ultraviolet bursts and elevated radiation. Proxima Centauri has been classified as a challenging environment for life due to its active stellar nature, affecting the lone rocky exoplanet in its orbit. Conversely, TRAPPIST-1 hosts seven rocky exoplanets, one of which may be habitable despite the star’s variability.
The insights gained from this research could pave the way for future exploration into the relationship between star variability and exoplanet habitability. As astronomers continue to refine their methods of detecting and analyzing exoplanets, the quest for understanding the conditions necessary for life beyond Earth remains a dynamic field of study. The findings from this investigation emphasize the importance of considering stellar characteristics in the search for habitable worlds.
As scientists continue to unravel the complexities of planetary systems, the implications of this study may influence the strategies employed in future astronomical observations. The pursuit of knowledge about exoplanets and their potential for supporting life is an ongoing journey, inviting curiosity and exploration in the years to come.
