Super Flares May Make It Hard For Life To Thrive on Earth's Nearest Exoplanet
The nearest exoplanet to Earth may get hit hard by damaging ultraviolet radiation, making it tough for life to survive there. That planet, the roughly Earth-mass Proxima B, circles the small, dim star, Proxima Centauri, which lies just 4.2 light-years from Earth. Proxima B orbits in its host's star, "habitable zone," the just-right range of distances where liquid water could theoretically exist on a world's surface. There's a lot more to habitability than just being in the habitable zone. A team of researchers who analyze observations by the Evryscope; an array of small telescopes at the Cerro Tololo Inter-American Observatory in the Chilean Andes, report that Proxima Centauri, fired off a powerful "super flare" whose light made it to Earth's neighborhood in March of 2016. The outburst was 10 times more energetic than any previously observed Proxima Centauri flare, and it briefly boosted the star's brightness by a factor of 68. In the flare's immediate aftermath, observers under dark skies would have been able to see the star with the naked eye, which is pretty much unheard of for "red dwarfs" such as Proxima Centauri. The Evryscope also spotted 23 less-powerful Proxima Centauri flares over the past two years, according to the study. Based on these observations, the researchers calculated that the red dwarf probably blasts out super flares at least five times per year. Such activity likely has a profound effect on Proxima B and its atmosphere. The team's computer-modeling work suggested that Proxima Centauri's repeated flaring would reduce concentrations of UV-blocking ozone in an Earth-like atmosphere by 90 percent in just five years, and would strip the stuff out of the air completely in a few hundred-thousand years. The UV light generated by the March 2016 super flare "therefore reached the surface with about 100 times the intensity required to kill simple UV-hardy microorganisms, suggesting that life would struggle to survive in the areas of Proxima B exposed to these flares. The new results further bolster a growing sense among astronomers and astrobiologists that radiation could pose a major hurdle to the establishment and evolution of life on Proxima B and other planets circling red dwarfs (which are also known as M dwarfs). Previous studies, for example, have suggested that flares might completely strip away the atmospheres of such worlds over time, leaving their surfaces bare and exposed. Such dangers aren't as high for possibly habitable worlds around sun-like stars, which tend not to be so active. Because sun-like stars are hotter than red dwarfs, their habitable zones are farther away, meaning potentially life-supporting worlds don't get hammered as hard by stellar eruptions. We still should not write off red-dwarf systems as possible abodes of life, said Ward Howard, the lead author of the new study. He cited the lack of detailed knowledge about such planetary systems, as well as the toughness and tenacity of "extremophile" organisms here on Earth, which have surprised researchers time and time again.
Researchers should be careful not to go beyond what we can actually compute, study, measure, and observe right now.