This artist’s impression shows Barnard b, a sub-Earth-mass planet that was discovered orbiting Barnard’s star. Its signal was detected with the ESPRESSO instrument on ESO’s Very Large Telescope (VLT), and astronomers were able to confirm it with data from other instruments. An earlier promising detection in 2018 around the same star could not be confirmed by these data. On this newly discovered exoplanet, which has at least half the mass of Venus but is too hot to support liquid water, a year lasts just over three Earth days. Credit: ESO/ M Kornmesser. CC BY.
Using the ESO VLT, astronomers have discovered an exoplanet orbiting Barnard’s star, the closest single star to our Sun.
On this newly discovered exoplanet, which has at least half the mass of Venus, a year lasts just over three Earth days.
The team’s observations also hint at the existence of three more exoplanet candidates, in various orbits around the star.
Located just six light-years away, Barnard’s star is the second-closest stellar system — after Alpha Centauri’s three-star group — and the closest individual star to us. Owing to its proximity, it is a primary target in the search for Earth-like exoplanets.
Despite a promising detection in 2018, no planet orbiting Barnard’s star had been confirmed until now.
The discovery of this new exoplanet is the result of observations made over the last five years with ESO’s Very Large Telescope, located at Paranal Observatory in Chile.
Lead author of the paper, Jonay González Hernández, a researcher at the Instituto de Astrofísica de Canarias in Spain, said: “Even if it took a long time, we were always confident that we could find something.”
Red dwarfs
The team were looking for signals from possible exoplanets within the habitable or temperate zone of Barnard’s star – the range where liquid water can exist on the planet’s surface.
Red dwarfs like Barnard’s star are often targeted by astronomers since low-mass rocky planets are easier to detect there than around larger Sun-like stars.
Barnard b, as the newly discovered exoplanet is called, is twenty times closer to Barnard’s star than Mercury is to the Sun.
It orbits its star in 3.15 Earth days and has a surface temperature around 125°C.
González Hernández explained: “Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of Earth.
“But the planet is too close to the host star, closer than the habitable zone. Even if the star is about 2,500 degrees cooler than our Sun, it is too hot there to maintain liquid water on the surface.”
ESPRESSO
For their observations, the team used ESPRESSO, a highly precise instrument designed to measure the wobble of a star caused by the gravitational pull of one or more orbiting planets.
The results obtained from these observations were confirmed by data from other instruments also specialised in exoplanet hunting: HARPS at ESO’s La Silla Observatory, HARPS-N and CARMENES. The new data do not, however, support the existence of the exoplanet reported in 2018.
In addition to the confirmed planet, the international team also found hints of three more exoplanet candidates orbiting the same star.
These candidates, however, will require additional observations with ESPRESSO to be confirmed.
Alejandro Suárez Mascareño, also a researcher at the Instituto de Astrofísica de Canarias and co-author of the study, said: “We now need to continue observing this star to confirm the other candidate signals, but the discovery of this planet, along with other previous discoveries such as Proxima b and d, shows that our cosmic backyard is full of low-mass planets.”
ESO’s Extremely Large Telescope (ELT), currently under construction, is set to transform the field of exoplanet research.
The ELT’s ANDES instrument will allow researchers to detect more of these small, rocky planets in the temperate zone around nearby stars, beyond the reach of current telescopes, and enable them to study the composition of their atmospheres.
The paper is published in Astronomy & Astrophysics.
