Barnard's Star is the closest single star to the Sun, about six light-years away, and for most of a century it was the most famous place where planets were claimed and then taken back. Astronomers announced planets around it several times over the past century, from measurements of both the star's position and its motion, and each claim later failed under closer study. A candidate super-Earth reported in 2018 on a 233-day orbit did not hold up either.
Barnard b was the first claim to last. A team led by Jonay González Hernández at the Instituto de Astrofísica de Canarias announced it in 2024, using 156 measurements taken over four years with ESPRESSO, a spectrograph on the European Southern Observatory's Very Large Telescope. They used the radial velocity method: a planet's gravity pulls its star slightly toward and away from us, shifting the star's light by a measurable amount. Their data also showed no sign of the 233-day planet.
The planet has at least about a third of Earth's mass and goes around its star every 3.15 days, about 20 times closer than Mercury is to the Sun. That is closer to the star than its habitable zone, the range of distances where surface water could stay liquid, so it is far too hot for that. The discovery team estimated an equilibrium temperature, the temperature set by starlight alone, of about 400 kelvin, above the boiling point of water.
The ESPRESSO data hinted at three more small planets. In 2025 a team led by Ritvik Basant at the University of Chicago checked them independently with MAROON-X, a spectrograph on the Gemini North telescope in Hawaii. Their 112 measurements confirmed Barnard b and two of the candidates on their own, and together with ESPRESSO confirmed the fourth. All four are smaller than Earth and orbit within about a week. Because none of them passes in front of the star, only their minimum masses are known. The same data rule out any planet heavier than about 0.57 Earth masses in the star's habitable zone.