Proxima b is a likely a rocky planet in the habitable-zone of Proxima Centauri, the star nearest to our Sun. Proxima Centauri’s high stellar activity casts doubt on whether Proxima b can host life: bright and frequent flares may destroy the planet’s ozone layer, allowing lethal levels of UV flux to reach its surface.

The Evryscope, a telescope which observes the entire accessible sky every two minutes, has been searching Proxima for extreme flare events. In March 2016 we saw a superflare: Proxima briefly became nearly a factor of 100 brighter, reaching a brightness just visible to the naked eye from dark sites. (and easily visible with binoculars, if someone was looking in the right direction; more info below).

Above: The sequence of Evryscope images showing the flare. At its peak Proxima was ~35x brighter in the Evryscope images; over shorter timescales relevant for the human eye Proxima was (very conservatively) 70x brighter, just visible to the naked eye at dark sites.

 

Above: artist’s conception of a bright flare on Proxima.

Using the Evryscope’s measurement of how often Proxima flares, we modeled the impact of this extreme stellar activity on the planet Proxima b. Our results suggest that the repeated flaring reduces the ozone of an Earth-like atmosphere by 90% within five years, and it is likely that the ozone is completely destroyed within a geologically short time. The UV light produced by the Evryscope superflare therefore likely reached the surface with ∼100× the intensity required to kill simple UV-hardy microorganisms. Life not protected by the ocean or below the surface would have to undergo complex adaptation to survive in the areas of the planet exposed to these flares.

Can you see the flare? The superflare happened in March 2016, and reached a brightness that people with exceptional eyesight could see from a very dark site, for less than a minute — so it’s not visible now. It’s worth mentioning that some have misinterpreted our paper to suggest that we’re claiming this event would have been easily visible to most people at most sites — which it would not have been. We just use “naked-eye” as a compact way to say the event reached a brightness in visible-light that can be detected by the human eye without optical aids under ideal conditions, to give an idea of how bright it was compared to other astronomical events.

Our statistics suggest that Proxima produces a superflare around five times a year — and some of those flares would be even brighter than the one we saw, perhaps even to the level that they could be easily visible to most people. So there’s a (very) small chance that if you’re in the Southern Hemisphere and look up at Proxima Centauri, you could see a superflare going off!

The team: The Proxima Superflare was discovered by Ward Howard (wshoward at live.unc.edu), a graduate student at the University of North Carolina at Chapel Hill, Department of Physics and Astronomy. Ward’s advisor, and the Evryscope project leader, is Nicholas Law (nmlaw at physics.unc.edu), Assistant Professor at UNC Chapel Hill. The other members of the Evryscope team are Hank Corbett, Jeffrey Ratzloff, Erin Goeke, Aaron Pietraallo and Joshua Haislip at UNC Chapel Hill, and Octavi Fors and Daniel del Ser at the University of Barcelona.

To model the atmospheric effects of the superflare, we were joined by Matt Tilley at the Dept. of Earth & Space Sciences, University of Washington, who led the atmospheric modeling, Allison Youngblood at NASA Goddard who led the flare UV and proton emission analysis, Evgenya Shkolnik at Arizona State University, and Parke Loyd at Arizona State University.