Super-Earth found orbiting Barnard’s Star just six light years away

An artist’s impression of a newly discovered super-Earth exoplanet orbiting Barnard’s Star. Image: ESO/M. Kornmesser

Studying two decades of data charting the precise position of Barnard’s Star, astronomers have found the tell-tale gravitational wobbles produced by interactions with an unseen planet, a rocky super-Earth with a mass of at least 2.3 times that of Earth that orbits the star every 233 days or so.

Designated Barnard’s Star b, it is the second closest known exoplanet to Earth’s solar system at a distance of just six light years.

“After a very careful analysis, we are 99% confident that the planet is there,” said the team’s lead scientist, Ignasi Ribas of the Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain. “However, we’ll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet.”

Barnard’s Star is a red dwarf, a low-mass, relatively cool star possibly twice as old as the Sun. It is the closest single star to Earth’s solar system and the fastest in terms of its apparent motion across the sky.

Despite its relatively close orbit, just four tenths the distance between Earth and Sun, Barnard’s Star b receives just 2 percent the energy Earth takes in from its star. As such, the surface temperature is likely in the neighbourhood of -170 degrees Celsius, inhospitable to life as it’s known on Earth.

Previous searches for planets around Barnard’s Star were unsuccessful, but data from high-precision instruments in use by telescopes around the world enabled Ribas’ team to “find” the newly discovered exoplanet.

A cold, dimly-lighted world is imagined in this artist’s impression of Barnard’s Star b, showing an alien landscape bathed in the reddish light of the red dwarf. Image: ESO/M. Kornmesser

Using the High Accuracy Radial velocity Planet Searcher – HARPS – instrument at the European Southern Observatory’s La Silla 6-meter telescope, along with the UVES high-resolution spectrograph on ESO’s Very Large Telescope, astronomers were able to measure the extremely slight back-and-forth movement of Barnard’s Star due to the unseen planet’s gravity. HARPS can detect changes in a star’s velocity as small as 3.5 kilometres per hour.

“HARPS played a vital part in this project,” said Guillem Anglada Escudé of Queen Mary University of London, co-lead scientist of the team. “We combined archival data from other teams with new, overlapping, measurements of Barnard’s star from different facilities. The combination of instruments was key to allowing us to cross-check our result.”

Ribas said the discovery was based on “one of the largest and most extensive datasets ever used for precise radial velocity studies. The combination of all data led to a total of 771 measurements — a huge amount of information.”

In 2016, astronomers found a planet orbiting Proxima Centauri, the closest star to the Sun. With the addition of Barnard’s Star b, four planetary systems have now been found within 10 light years – just around the corner.