Understanding the Ultraviolet Habitable Zone Around Stars

Recent research has examined the time evolution of the ultraviolet habitable zone (UHZ) surrounding stars that host circumstellar habitable zone (CHZ) exoplanets. The study, titled "The time evolution of the ultraviolet habitable zone," was conducted by R. Spinelli and colleagues and is available on arXiv (arXiv:2409.01401). The researchers focused on the annular region around a star where an exoplanet could experience a suitable ultraviolet environment conducive to the presence and emergence of life.

To estimate the evolution of the UHZ, the authors analyzed observations from the Swift-UV/Optical telescope and utilized near-UV luminosity evolutionary tracks derived from GALEX observations of young moving groups. They found that an intersection between the CHZ and UHZ could exist or have existed around all stars in their sample at different epochs, except for the coldest M-dwarfs (temperature < 2800 K, such as Trappist-1).

For hotter M-dwarfs, the study suggests that the formation of RNA precursors through cyanosulfidic chemistry, triggered by near-UV radiation, could occur during the first 1-2 billion years. The research indicates that the radial extension and duration of the CHZ-UHZ intersection increase with the stellar effective temperature and the exoplanet's atmospheric transmissivity at near-UV wavelengths.

Among the stars studied, Proxima Centauri was highlighted as a significant target in the search for life beyond our solar system, as it has experienced a long-lasting and more extensive CHZ-UHZ intersection compared to similar M-dwarfs. This finding could have implications for understanding the conditions necessary for life on exoplanets and the potential for discovering habitable worlds in the universe.