A recent study accepted to The Astronomical Journal delves into how star variability—fluctuations in a star’s brightness—might influence the habitability of exoplanets. A team of scientists investigated the interaction between stellar activity and the atmospheres of nine exoplanets orbiting stars that exhibit significant variability. This research could enhance our understanding of which stars may host habitable planets, particularly those that differ from our own Sun.
The study focused on nine exoplanets, each orbiting a different star within the habitable zone. These included TOI-1227 b located 328 light-years away, HD 142415 b at 116 light-years, HD 147513 b at 42 light-years, and others, spanning distances from 35 to 1,694 light-years. The primary objective was to determine how the variability of these stars might affect their exoplanets’ equilibrium temperatures and the ability of planets situated near the inner edge of their habitable zones to retain water.
Equilibrium temperature refers to the temperature a celestial body would maintain if heat transfer did not occur. The researchers concluded that the stellar variability of the nine stars in their study had minimal influence on the equilibrium temperatures of the associated exoplanets. Notably, they found that planets located within the inner edge of their stars’ habitable zones could retain water, irrespective of the stars’ variability.
The stars in the study varied in size from 0.17 to 1.25 solar masses, encompassing M-, K-, G-, and F-type stars. M-type stars, which are the smallest, are particularly significant as they represent the largest population of stars in our galaxy and have lifespans estimated to extend to trillions of years, in contrast to our Sun’s estimated lifespan of 10 to 12 billion years. M-type stars are also characterized by extreme variability, including changes related to sunspots, flares, and magnetic field fluctuations.
These characteristics present challenges for the habitability of exoplanets orbiting M-type stars. High levels of stellar activity, such as flares, can strip away atmospheres and ozone layers, raising concerns about the potential for life. Well-known examples include Proxima Centauri and TRAPPIST-1, located approximately 4.24 and 39.5 light-years from Earth, respectively. Both stars exhibit significant activity, including ultraviolet bursts and high radiation levels. Consequently, Proxima Centauri is considered harsh for life on its known rocky exoplanet, while TRAPPIST-1, which hosts seven rocky exoplanets, has one that may be habitable despite its star’s variability.
As researchers continue to unravel the complexities of star variability and its implications for exoplanet habitability, the scientific community remains eager for insights that may emerge in the coming years. Understanding these dynamics is crucial as astronomers refine their search for potentially habitable worlds beyond our solar system. The ongoing exploration in this field emphasizes the importance of rigorous scientific inquiry and the excitement of discovery in the universe.
