Scientists have detected a super-Earth planet around a nearby red dwarf star, an important discovery as we continue to look for other habitable worlds.
The planet, GJ 625 b, is in orbit around an M dwarf star called GJ 625 about 21.2 light-years from us. It is thought to be at least 2.8 times the mass of Earth, and orbits its host in 14.6 Earth days. The findings, available on arXiv and led by the Canary Islands Institute of Astrophysics, will be published in the journal Astronomy and Astrophysics.
GJ 625 b is located on the inner edge of the habitable zone of the star, where temperatures are just right for liquid water to exist. It orbits at a distance of about 0.08 AU (astronomical unit, 1 AU is the distance from Earth to the Sun).
“GJ 625 b is a small super-Earth in the habitable zone of a nearby M-dwarf,” lead author Alejandro Suarez Mascareño, from the Canary Islands Institute of Astrophysics, told IFLScience. “Even after the last round of discoveries of small exoplanets around M-dwarfs, the number of rocky planets known around this kind of star is relatively small.”
This particular star is an M2 type of M dwarf, about a third the size and mass of our Sun. GJ 625 b is the lightest planet found around such a star.
Finding planets around M dwarfs is important, because it provides a “shortcut” to finding potentially habitable worlds. Planets around Sun-like stars are much more difficult to study, as they are in much wider orbits and their stars are much brighter.
Recently, worlds including Proxima b and LHS 1140 b have garnered a lot of interest, as they represent opportunities to study rocky exoplanets in more detail. But bigger (and rarer) planets like GJ 625 b present a better chance for study, being less drowned out by their host star in our observations.
“Being so close to us, if the planet transits [passes in front of its star relative to us], it is also a very promising target to study its atmosphere," said Mascareño. He also noted the world was "probably rocky", but the radius of the planet was needed to know for sure.
“If the planet is rocky, then it would possibly be habitable depending on its atmospheric composition,” added Mascareño. “It receives more energy from its star than Earth receives from the Sun, but with the right kind of atmosphere it could harbor liquid water on its surface.”
This particular world was found using the radial velocity method, which involves seeing the wobble in the star as the planet orbits. The team used the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph at the Roque de los Muchachos Observatory on La Palma, Canary Islands, in Spain to make the discovery.
"The detection looks very robust and solid," said Guillem Anglada-Escude from Queen Mary University of London, who was not directly involved in the study.
The team estimate that the planet has a surface temperature of 75°C (170°F), but this will depend on what sort of atmosphere it has – if any. There may be other planets in orbit around the star, too.
Just how habitable planets around M dwarfs might be is still up for debate. These stars are prone to more flaring events than those like our Sun, which could blow away atmospheres. At the moment, we just don’t know – but worlds like GJ 625 b may help us get an answer.