THE outlier in the stellar system closest to our own, the star Proxima Centauri, may not have formed with its two siblings. If so, nor would its planet, Proxima b, which is good news for the chances of life on it.
Proxima Centauri鈥檚 orbit is currently bound to Alpha Centauri A and B, but it is unclear if it will remain stable, say and at the University of Hertfordshire in the UK. They modelled 100 Proxima clones in orbits around their binary partners.
Over a simulated 10 billion years, Proxima Centauri became unbound from the pair due to an unstable orbit 26 per cent of the time. If it had been born in the system, it is unlikely the orbit would be unstable aeons later (). So, Proxima may have been captured by the stellar pair.
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Previous studies have found that Proxima contains much less metal than its binary companions, another hint that it might have come from afar. Feng says a more recent appearance might be good for the habitability of Proxima b. At certain points in its orbit, Proxima Centauri could get so close to the other stars, they could destabilise its planet鈥檚 orbit and push it out of the zone with temperatures right for life.
But if Proxima Centauri has only been there a short while, there would have been fewer chances for its planet to be knocked out of this zone.
Proxima b would have had longer in a stable orbit around a single star before feeling the influence of Alpha Centauri A and B. 鈥淟ife needs time to develop and emerge. This scenario gives it more time,鈥� says Feng.
But a capture would actually make Proxima b鈥檚 orbit less stable than if it had formed as part of the larger system, says at the Harvard-Smithsonian Center for Astrophysics in Massachusetts. 鈥淚f the three stars have been orbiting each other for a few billion years, one would think they鈥檇 be a nice happy family,鈥� he says.
This article appeared in print under the headline 鈥淧roxima may be an interloper from far away鈥�