The discovery of an Earth-like planet orbiting Proxima Centauri back in August 2016 was an exciting moment for astronomers and space exploration enthusiasts alike. Not only was the planet nearly the same size as Earth (1.3x larger), it also existed within the narrow habitable range of its host star. Unfortunately, a recently detected massive X-ray flare suggests Proxima Centauri b is almost certainly devoid of any life.
Proxima Centauri is a red dwarf star, compared with Alpha Centauri A (classified as G2V, the same as our own sun) and Alpha Centauri B (classified as K1V, a cooler, smaller star). This system, visible below as a single star, is referred to as α Centauri AB.
Red dwarfs are some of the oldest and most stable stars; Proxima Centauri is expected to remain a main sequence star for the next 4 trillion years. The three stars form a trinary star system, with Proxima Centauri far removed from its distant cousins.
Image by Wikipedia. Alpha Centauri AB is on the left, Beta Centauri on the right, and Proxima Centauri is at the center of the red circle.
Unlike Alpha Centauri A or B, Proxima Centauri is known to be a flare star, a type of star that can undergo a tremendous shift in luminosity driven by magnetic activity. When this happens, the X-ray output of Proxima Centauri can match that of the sun. That matters for Proxima Centauri b (the aforementioned planet), because it orbits its host star at just 0.05 AU and has a year just 11.2 days long. There’s been some question of whether life could exist on Proxima Centauri b because of these characteristics, and a recent flare up casts doubt on its ability to sustain life.
A new astronomical survey of data collected on Proxima Centauri from January 21 through April 25 showed that the star flared on March 24 for a full minute, reaching a brightness 1000x higher than is typical. This is one of the first studies to image Proxima Centauri using submillimeter wavelengths, and its findings suggest Proxima Centauri b’s host star is extremely volatile. Bombarding the planet with such huge amounts of energy could strip water from the atmosphere or oceans and sterilize the ground.
This is a known problem with red dwarf stars that’s led some to question whether they’re suitable environments for life to develop. Because the habitable zone of such stars is so small, planets have to orbit extremely close to their host stars, which increases the chance of tidal locking, where just one side of the planet faces the star and the other side is perpetually shadowed. The variability of many red dwarfs is a further blow to potential habitability, especially if the star has been this volatile throughout its life. This is generally thought to the be the case, given how long red dwarfs remain in main sequence, though we obviously haven’t been taking measurements for long enough to be absolutely certain. Regardless, the chance of life in our proverbial backyard seems to have dropped with these findings.