Astronomers have found that some of the nearest stars to Earth may be better places for life than we thought – although it’s bad news for another.
Presenting their findings recently at the 232nd meeting of the American Astronomical Society meeting in Denver, Colorado, researchers used NASA's Chandra X-ray Observatory to study the Alpha Centauri system, the closest star system to Earth at just 4.4 light-years.
This system contains three stars, two Sun-like stars called Alpha Centauri A and B, and a third red dwarf called Alpha Centauri C (or Proxima Centauri). The team found that any planets orbiting the former two were likely not being pummeled by large amounts of X-ray radiation from their stars.
We don’t yet know of any planets around these two stars, despite a previous false detection around Alpha Centauri B. But their proximity to Earth makes them tantalizing prospects for future study, so finding out if any planets could be habitable is key.
"Because it is relatively close, the Alpha Centauri system is seen by many as the best candidate to explore for signs of life," said Tom Ayres of the University of Colorado Boulder in a statement. "The question is, will we find planets in an environment conducive to life as we know it?"
The team carried out this research by studying the stars with Chandra every six months since 2005. The long-term measurements showed the cycle of X-ray activity around A and B, which was compared to the Sun’s 11-year sunspot cycle.
The team found that for Alpha Cen A, the amount of X-rays were actually better for life than the Sun, with planets receiving less radiation than our planets. Alpha Cen B was only slightly worse, a factor of five higher than the Sun’s planets. Ayres said this was “very good news” in terms of “the ability of possible life” on any planets around the stars.
Unfortunately, it’s not such good news for Proxima Centauri. The team found that as it’s an active red dwarf star that frequently sends out flares of X-rays, it’s probably hostile to life, something that has been considered before.
We know of one planet here, Proxima b, which orbits much closer than Mercury does from our Sun. Unfortunately, planets in the habitable zone around this star receive about 500 times more X-rays than Earth and 50,000 times more during a large flare from the star.
So if we’re looking for habitable worlds in this system, it looks like Alpha Centauri A and B might be the best bets. And understanding stars like this can even tell us a little bit more about our own star, too.