Inviting nearby exoplanet revealed as radiation-baked hell

Seekers of new worlds for humans to colonise will have to look further afield than Proxima Centauri after the detection of huge solar flares showed its planets are probably uninhabitable.

Proxima Centauri became a candidate for exploration, colonisation and/or alien investigation in 2016, when its second planet - Proxima Centauri b - was spotted and hailed as “Earth-like” (not only by El Reg: even the august New Scientist was excited).

With the planet just four light-years from Earth, the 2016 discovery prompted the Breakthrough Starshot project to put the star system on its priority list for probe visits.

Later modelling suggested that even though the planet looked to be in a good spot to have liquid water on the surface, it may lack an atmosphere thanks to local levels of solar radiation.

That theory's now been proven - and how! - after boffins from Carnegie Institution for Science researchers detected a solar flare that's probably toasted the planet.

The MacGregor/Weinberger team made their discovery in an analysis of observations from ALMA, the Atacama Large Millimeter/submillimeter Array taken in March 2017. Since it takes four-plus years for light to get here from Proxima Centauri, any hypothetical life there joined the choir invisible in 2013.

The flare they found was 10 times more intense than Sol's nastiest flares and increased Proxima Centauri's brightness by “1,000 times over 10 seconds”, Carnegie said.

A smaller flare erupted a little earlier and the whole event was over in two minutes.

The high-energy radiation that blasted Proxima Centauri b last year probably wasn't the first time: MacGregor said smaller but regular X-ray flares are probably a regular occurrence. We just haven't been watching for that long.

“Over the billions of years since Proxima b formed, flares like this one could have evaporated any atmosphere or ocean and sterilised the surface, suggesting that habitability may involve more than just being the right distance from the host star to have liquid water”, she said.

The boffins also believe their observations put paid to suggestions late last year that Proxima Centauri hosts a huge dust ring. Weinberger said: "There is now no reason to think that there is a substantial amount of dust around Proxima Cen".

The team's paper published in The Astrophysical Journal Letters can be read at the arXiv pre-print site here. ®