Proxima Centuri, as has been know for a few years now, has a roughly Earth-sized planet in it’s habitable zone. Yay! But… Proxima is a red dwarf. Worse, it’s a red dwarf with some serious flare activity. Since it is so small and dim, the habitable zone is *real* close to the star, which means that flares can do some serious damage to planeary atmospheres. How bad are Proximas flares? Well…
“In March 2016 the Evryscope detected the first-known Proxima superflare. The superflare had a bolometric energy of 10^33.5 erg, ~10× larger than any previously-detected flare from Proxima, and 30×larger than any optically measured Proxima flare. The event briefly increased Proxima’s visible-light emission by a factor of 38× averaged over the Evryscope’s 2-minute cadence, or ~68× at the cadence of the human eye. Although no M-dwarfs are usually visible to the naked-eye, Proxima briefly became a magnitude-6.8 star during this superflare, visible to dark-site naked-eye observers.”
When a flare is 68 times brighter than the rest of the star… that means you have some variability issues. An earth-like world around Proxima is *real* unlikely. Assume that one – let’s say Earth – was suddenly miracled into existence smack in the middle of the habitable zone. You’re going about your day when there is a sudden “BING” sound, and the quality of the sunlight suddenly changes. Not quite as bright, a bit redder (almost like a really powerful incandescent bulb), but just as warm. You look at the sky. It had been a nice bright blue; now its a darker, less happy blue, leaning a bit purplish and gray. You look at the sun and it hits you: “hey, that ain’t right.” It’s the wrong size… visually much bigger. You can almost look at it with just sunglasses. When you do, it looks blotchy.
But you’re not a terribly jittery person. Things looks slightly different, but everything seems to still be functioning, so who cares.
And then SURPRISE FLARE. The sunlight gets ~70 times brighter for a few minutes. Anything flammable flamms. The road melts. You go blind. A portion of the atmosphere says “screw this noise” and blows off into space; there is a slight but measurable permanent decrease in atmospheric pressure even after all the CO2 from the fires settles out.