LHS 1140b is a super-Earth – meaning it is larger and more massive than our own planet – orbiting a faint red dwarf star in the constellation Cetus.
While the planet orbits the star ten times closer than Earth orbits the Sun, it receives about half as much sunlight because the star is so faint.
This puts it in the habitable zone, and makes it a prime target for further study.
For a planet to host life as we know it, it must be able to retain liquid water on its surface and have an atmosphere. This is true for life that evolved on the planet, or life delivered there via panspermia.
Red dwarf stars are known to emit radiation that can damage the planets that orbit them, but in the case of this planet, its large size means that a magma ocean may have existed on its surface for millions of years.
This lava could have fed steam into the atmosphere long after the star’s radioactivity had calmed, replenishing the planet with water.
“This is the most exciting exoplanet I’ve seen in the past decade,” says Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics, who led the study.
“We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”
“The present conditions of the red dwarf are particularly favourable — LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars,” says team member Nicola Astudillo-Defru from Geneva Observatory, Switzerland.
The planet is thought to be at least five billion years old and have a diameter 1.4 times larger than Earth, almost 18,000km.
Its mass is about seven times greater than Earth’s, meaning it is more dense and could be rocky with a dense iron core.
The fact that it orbits in front of its star from Earth’s perspective makes it a good target for study, as scientists can analyse light from the star that has passed through the exoplanet’s atmosphere and learn more about what conditions may be like on the surface.
“The LHS 1140 system might prove to be an even more important target for the future characterisation of planets in the habitable zone than Proxima b or TRAPPIST-1,” say team members Xavier Delfosse and Xavier Bonfils of the CNRS and IPAG in Grenoble, France.
“This has been a remarkable year for exoplanet discoveries!”