Today we’re visiting Proxima Centauri, one of three stars in the Alpha Centauri system, the star system right next door to our own. And it turns out Proxima has at least one planet. Not only that: Proxima’s planet is orbiting within the habitable zone. That planet may have liquid water on its surface, and perhaps even life!
Proxima’s planet, known officially as Proxima b, orbits about 0.05 AU away from its star. That puts Proxima b closer to its star than Mercury is to our Sun. But that’s okay. Proxima Centauri is much smaller, dimmer, and colder than our own Sun, so everything balances out.
But I have bad news. The temperature might be right for life, but the radiation environment is all wrong. Proxima Centauri is a very angry little star. It’s much angrier than our Sun. Solar flares, solar wind, and solar radiation are a whole lot worse than anything Earth would normally have to worry about.
In March of 2016, Earth-based astronomers observed a “superflare” on Proxima Centauri. As you can see in the highly technical diagram below, that superflare would have done serious damage to Proxima b’s ozone layer (assuming Proxima b had an ozone layer in the first place).
According to this 2018 paper on ozone loss, if superflares like that are normal for Proxima Centauri, we should expect Proxima b to lose 90% of its ozone layer in just five years (again, assuming Proxima b had an ozone layer in the first place). Without an ozone layer, incoming ultraviolet radiation would thoroughly sterilize Proxima b’s surface (much like it does on Mars).
And it gets worse. Earth’s magnetic field deflects a lot of harmful solar and cosmic radiation away. But according to this 2016 paper on space weather, Proxima b’s magnetic field (assuming Proxima b has a magnetic field) is taking a real beating. The magnetic field would be badly weakened and compressed. As a result, Proxima b’s atmosphere would start eroding away, due to the solar wind, and if those UV rays haven’t already killed everything on the surface, all that solar and cosmic radiation would have a chance to finish the job.
Even the most extreme of extremophiles here on Earth would have a tough time surviving on Proxima b. But the situation is not hopeless. That 2016 paper on space weather and that 2018 paper on ozone loss both acknowledge that there are still plausible scenarios where life could evolve and thrive on Proxima b. But in order to do it, the Proxima b-ians must have done one of two things:
- Life on Proxima b must be very specifically adapted to that radiation environment, or…
- Life on Proxima b must have found a good hiding place, perhaps deep underwater or underground, where the radiation can’t reach it.
Next time on Planet Pailly, it’s a bird! It’s a plane! It’s… oh no, it’s a killer asteroid!!!