Back in the summer of 2016, planetary scientists were rocked by the announcement of the indirect discovery of an exoplanet. These are relatively common revelations these days, but this new and likely rocky world, Proxima b, happened to be orbiting Proxima Centauri, the closest star to our own Sun, just over 4 measly light-years away.
Another Earth away from home? Potentially, although several studies released since then have doubted how habitable it may be. The latest blow comes courtesy of a new paper in The Astrophysical Journal Letters, whose authors describe the detection of a powerful stellar flare that likely blasted Proxima b with a solid dose of high-energy radiation.
Picked up by the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope last March, the outburst was carefully analyzed by a team of astrophysicists led by the Carnegie Institute for Science.
It appears that, on one rather angst-ridden day, this red dwarf star unleashed a flare so energetic it increased its brightness by 1,000 times for around 10 seconds, just after a smaller flare.
In somewhat crude terms, solar flares take place when an accumulation of magnetic energy on or near the surface of the star is let loose. Releasing plenty of high-energy radiation, they’re often spotted as incredibly bright outbursts – and they can take place on a wide range of stars, including our own.
The Sun’s fireworks couldn’t possibly compete with Proxima Centauri’s rage, though: This stellar flare was 10 times more luminous than our Sun’s largest flares, at least when observed through X-ray wavelengths.
This, of course, has implications for the habitability of Proxima b.
The compositions of Proxima b’s geology and atmosphere remains somewhat unclear. We rely on exoplanets' ability to move in front of their host star, something known as a transit, in order to obtain all-important details about them.
Thanks to the silhouette such transits create, scientists can more precisely work out the planet’s mass and therefore its constitution; at the same time, starlight penetrating through its atmosphere can reveal, through its individual wavelengths, what its skies may be comprised of.
Proxima b has yet to make one, and it may never do so. That means that much of the potential habitability of this newly discovered world relies on the idea that it has an atmosphere that’s able to trap enough heat to keep water liquid at the surface. This, of course, assumes there is enough water there in the first place, and that alien life requires it.
In any case, previous studies have pointed out that its proximity to its (relatively cool) red dwarf may mean that, over time, its atmosphere would have been stripped away by fairly conventional stellar radiation, making it uninhabitable.
This massive flare suggests that even if Proxima b did have a rigid atmosphere, and even if it could withstand regular levels of stellar radiation over time, it wouldn’t matter. Flares this powerful would quickly boil off any standing water and annihilate the atmosphere.
“While this result doesn’t entirely rule out the possibility of life on Proxima b – it is only one event after all – it does raise some serious questions,” lead author Dr Meredith MacGregor, a postdoctoral researcher at Carnegie, told IFLScience.
However, as the star was only intermittently observed by ALMA, it’s likely that this gigantic flare was in fact just one of several taking place throughout the year.
Life on Proxima b? We’re not sure we’d bet on it just yet.