Flared! How a planetary ‘neighbor’ may have been fried

The sun’s nearest planet-hosting neighbor has a temper. A new analysis shows this star — Proxima Centauri — released a gigantic flare in March 2017. And that’s bad news in terms of hopes for finding life on its planet, Proxima b.

Observations show that over one 10-second period, the star got 1,000 times brighter. Then it dimmed again. This event can best be explained by an enormous stellar flare, explains a team of scientists in the February 26 Astrophysical Journal Letters. A flare is an intense — indeed, explosive — burst of energy by a star.

Because Proxima b is so much closer to its star than Earth is to our sun, the flare would have blasted that exoplanet with 4,000 times more radiation than Earth typically gets from our sun’s flares.

Meredith MacGregor is an astronomer with the Carnegie Institution for Science in Washington, D.C. She also co-authored the new paper. “If there are flares like this at all frequently, then [Proxima b] is likely not in the best shape,” she says.

Just four light-years away, Proxima b has a mass about the same as Earth’s. It likely also has temperatures suitable for liquid water. And that’s why Proxima b was quickly identified as one of the most interesting candidates for hosting life outside our solar system. But its star is what’s known as an M dwarf. Such small dim stars are well known to be prone to flares that could rip away a planet’s atmosphere.

MacGregor was part of a team that reanalyzed data from a recent study. That research had been led by astronomer Guillem Anglada. He works in Spain at the Institute of Astrophysics of Andalusia in Granada. Anglada’s group used the Atacama Large Millimeter Array telescopes in Chile to observe Proxima Centauri. That team saw extra light being scattering in all directions. The group interpreted it as coming from a glittering dust ring. Anglada’s team reported this November 15 in Astrophysical Journal Letters.

But those researchers had averaged the light output over 10 hours of viewing. This would smear out any short-term explosive change in the star’s brightness — such as a bright flare.

MacGregor’s team took a second look at these data. And it found that all the excess light came from a two-minute period on March 24. A massive flare explains all the extra light, MacGregor now says.

Anglada says he and his colleagues are aware of the March 24 flare. As a result, they currently are revising their original claim. But, that astronomer argues, the flare can’t account for all the extra light. So he still thinks the dust-ring theory might hold up.