An artist’s impression of Proxima b orbiting the red dwarf star Proxima Centauri. Double star Alpha Centauri AB can also be seen between the planet and its host star. Image Credit: ESO/M. Kornmesser
Astronomers have found strong evidence of a rocky, Earth-like planet orbiting Proxima Centauri, the closest star outside of our Solar System.
The exoplanet, named Proxima b, orbits its red dwarf star every 11 days and is thought to be in the habitable zone, meaning it has a temperature suited for liquid water to exist on its surface.
However, its habitability cannot be confirmed as it could be subject to blasts of radiation from its host star.
Proxima b was confirmed by ESO’s Pale Red Dot campaign, in which a team of astronomers observed Proxima Centauri to look for tiny wobbles that might indicate the gravitational pull of an orbiting planet.
“The first hints of a possible planet were spotted back in 2013, but the detection was not convincing," says team leader Guillem Anglada-Escudé.
"Since then we have worked hard to get further observations off the ground with help from ESO and others.
The recent Pale Red Dot campaign has been about two years in the planning.”
Observations revealed the planet is about 1.3 times the mass of Earth and orbits its star at a distance of about 7 million kilometres, or 5% of the distance between Earth and the Sun.
Despite this proximity, the ability for liquid water to pool on the surface of the exoplanet exists because Proxima Centauri is much cooler than our own Sun.
However, Proxima b could be subject to ultraviolet and X-ray flares from the star that would render it uninhabitable for humans.
"That's the worry in terms of habitability," says Scott Gaudi, an astronomy professor at Ohio State University, Columbus.
"This thing is being bombarded by a fair amount of high-energy radiation.
It's not obvious if it's going to have a magnetic field strong enough to prevent its whole atmosphere from getting blown away.
But those are really hard calculations, and I certainly wouldn't put my money either way on that."
It was also revealed that the exoplanet orbits the star with one side constantly facing it, in the same way as the Moon orbits Earth.
"This is really a game-changer in our field," says Olivier Guyon of NASA's Jet Propulsion Laboratory.
"The closest star to us has a possible rocky planet in the habitable zone.
That's a huge deal. It also boosts the already existing, mounting body of evidence that such planets are near, and that several of them are probably sitting quite close to us.
This is extremely exciting."