Astronomers Detect Sub-Earth-Mass Exoplanet around Barnard’s Star

An exoplanet at least half the mass of Venus orbits Barnard’s star, the closest single star to the Sun, once every 3.15 days.

Barnard’s star is a 10-billion-year-old red dwarf star located in the constellation of Ophiuchus.

At nearly 6 light-years away, it is the next closest star to the Sun after the Alpha Centauri triple stellar system.

Otherwise known as Gliese 699 or GJ 699, the star is much smaller than the Sun and is classified as an M3.5 dwarf.

Despite a promising detection of a ‘super-Earth’ with a mass of 3.2 times that of Earth back in 2018, no planet orbiting the star had been confirmed until now.

The discovery of the new exoplanet is the result of observations made over five years with the ESPRESSO instrument on ESO’s Very Large Telescope (VLT) at Paranal Observatory in Chile.

“Even if it took a long time, we were always confident that we could find something,” said Dr. Jonay González Hernández, an astronomer at the Instituto de Astrofísica de Canarias.

Named Barnard b, the newfound planet is around 20 times closer to Barnard’s star than Mercury is to the Sun.

It orbits its parent star in 3.15 Earth days and has a surface temperature around 125 degrees Celsius (257 degrees Fahrenheit).

“Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of Earth,” Dr. González Hernández said.

“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.”

In addition to the confirmed planet, the astronomers also found hints of three more exoplanet candidates orbiting the same star.

These candidates, however, will require additional observations to be confirmed.

“We now need to continue observing this star to confirm the other candidate signals,” said Dr. Alejandro Suárez Mascareño, also from the Instituto de Astrofísica de Canarias and co-author of the study.

“But the discovery of this planet, along with other previous discoveries such as Proxima b and Proxima d, shows that our cosmic backyard is full of low-mass planets.”

The discovery of Barnard b is announced in a paper in the journal Astronomy & Astrophysics.

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J.I. González Hernández et al. 2024. A sub-Earth-mass planet orbiting Barnard’s star. A&A 690, A79; doi: 10.1051/0004-6361/202451311