HARPS-N@TNG plays an important role in the discovery of a "sub-Earth" orbiting Barnard's star, the nearest isolated star to the Sun

An international team of astronomers has recently announced the discovery of a new exoplanet around the Barnard's star, the nearest isolated star to the Sun. On this newly discovered exoplanet, which is at least half the mass of Venus, a year lasts just a little over three Earth days. The team's observations also suggest the existence of three other exoplanet candidates, in different orbits around the star.

Located just six light-years away, Barnard's Star is the second closest star system to us, after the three-star cluster of Alpha Centauri, and the closest single star. Because of its proximity, it is a primary target in the search for Earth-like exoplanets. Despite a promising detection in 2018 (see Ribas et al. 2018, Nature, 563, 365), no planets have been confirmed orbiting Barnard's Star so far.

The discovery of this new exoplanet, announced in a paper published in the journal Astronomy & Astrophysics, is the result of observations carried out over the past five years with several facilities: VLT/ESPRESSO (ESO's Paranal Observatory, Chile), TNG/HARPS-N (Roque de Los Muchachos Observatory, La Palma), 3.6m Tel./HARPS (ESO's La Silla Observatory, Chile) and 3.5m Tel./CARMENES (Calar Alto Observatory, Spain).

In particular, the data taken with HARPS-N played an important role in 2020 during the Covid pandemic, when the TNG staff made an exceptional observational effort to guarantee the continuity of the survey of the Barnard's star during the closure of the Paranal site and other Observatories.

“Although it took a long time, we were always confident that we could find something,” says Jonay González Hernández, leading author of the paper. The international team was looking for signals from possible exoplanets within the habitable or temperate zone of Barnard’s Star, the range in which water can be liquid on the planet’s surface. Red dwarfs like Barnard’s Star are often considered by astronomers, as 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 the star in 3.15 Earth days and has a surface temperature of about 125 °C. "Barnard b is one of the known exoplanets with the smallest mass, and one of the few with a mass less than that of the Earth. But this planet is too near to its host star, nearer than the habitable zone", explains González Hernández. "Although the star is some 2,500 degrees cooler than our Sun, on the surface of the planet the temperature is too high for water to remain liquid."

Also note that the results reported in the paper do not support the existence of the exoplanet announced in 2018.

In addition to the confirmed planet, the international team also found signs of three other exoplanet candidates orbiting the same star. Further observations with ESPRESSO and other facilities will be needed for confirmation.

Further information in the paper J. González Hernández, et al. 2024, A&A, 690, A79 (see link).

Fig. 1. Artist’s impression showing Barnard b, a sub-Earth-mass planet that was discovered orbiting Barnard’s star. Credits: ESO/M. Kornmesser.