A team of international astronomers has discovered a new solar system with a "super-earth" planet that could be habitable. Picture: AFP/DESIREE MARTIN
A team of international astronomers has discovered a new solar system with a "super-earth" planet that could be habitable. Picture: AFP/DESIREE MARTIN

Madrid — An international team of astronomers has discovered a new solar system with a planet that could be habitable, a Spanish astrophysicist who led the research said on Thursday.

Three new planets were discovered orbiting GJ 357, a red dwarf — a small and cooling star — 31 light years away, relatively close in space terms, said Rafael Luque of Spain’s Institute of Astrophysics in the Canary Islands.

The discovery was also reported by Nasa, whose TESS planet-hunting satellite made it possible.

The planet, known as GJ 257d — the furthest away from the star — is particularly intriguing as researchers estimate it could be habitable. The other two are deemed too hot.

Signs of habitability in any planet include a rocky terrain, a size similar to Earth and a distance from their sun — the temperate “Goldilocks” zone, neither too close nor too far — that allows the right temperature for liquid water, a key requirement for life.

Given its distance from its star, similar to that of Mars to our Sun, researchers estimate the planet has temperatures of -53ºC, Luque told AFP. “That seems a little cold at first,” he said, but “if this planet had an atmosphere [unlike Mars], it could retain the heat it receives from its star, and water could be liquid”.

Researchers also estimate GJ 257d could be roughly the same size as Earth, or up to twice the size.

It is not the first potentially habitable planet to have been discovered close to us. In 2016, the discovery of Proxima b at a mere four light years from the Solar System made waves.

But there is a hitch. 

Proxima b and GJ 257d were discovered via so-called radial velocity, which involves looking for signs of a wobble in a star from the gravitational tug of an orbiting planet. But Luque says the method is not precise enough to ascertain whether it is actually habitable.

As things stand, to measure its size, density and composition, the planet has to pass directly between its star and an observer, the so-called “transit” method, he says. This has not been possible for Proxima b and other closer, potentially habitable planets, Luque says.

In the coming months, Luque and his team will be working to try and catch GJ 257d in “transit” to confirm it as a habitable planet. “The probability that a planet passes in front of a star from our line of vision on Earth is pretty small.” 

AFP