As much as ultraviolet light could render some planets too dry for life around TRAPPIST-1 and other M dwarfs, another new study found a dearth of it may also make these red stars uninhabitable for life as we know it. Using computer models and the known properties of red dwarfs, researchers found that such stars might not emit enough of the long-wavelength, medium-energy ultraviolet light that likely helped trigger chemical processes key to the rise of biology on Earth and might be the key to finding life elsewhere in the universe.
Ranjan suggests that red dwarf stars – by far the most common sort of starsalthough smaller and less massive than our sun, and thought by some to be the best star systems in which to search for life – might not emit enough UV light to jump-start the biological processes most familiar to our planet. "For example, certain levels of UV might be necessary for the formation of ribonucleic acid, a molecule necessary for all forms of known life. It would be like having a pile of wood and kindling and wanting to light a fire," he added, "but not having a match. Our research shows that the right amount of UV light might be one of the matches that gets life as we know it to ignite."
Recently discovered red-dwarf planetary systems with potential habitable zones where liquid water can exist – include red dwarfs such as Proxima Centauri, TRAPPIST-1, and LHS 1140.
These scientists used computer models and the known properties of red dwarfs to estimate that the surface of rocky planets in the potentially habitable zones around red dwarfs would experience 100 to 1,00
It remains uncertain whether the best hosts for habitable planets are ultracool M dwarfs such as the recently discovered TRAPPIST-1 or much warmer stars such as the sun, says Jeffrey Linsky, an astrophysicist at the University of Colorado at Boulder. “The argument has gone back and forth like a pendulum several times and will likely continue to do so as we learn more about physical processes in planet atmospheres and the emission of host stars at all wavelengths,” Linsky says. “It would not surprise me if the best host stars are intermediate in temperature.”
Image credit: NASA. Astronomers were surprised to discover a 25-million-year-old protoplanetary disk around a pair of red dwarf stars 350 light-years away in the Stephenson 34 system. Gravitational stirring by the binary star system (shown in this artist's conception) may have prevented planet formation. David A. Aguilar (CfA)