Barnard c is the heaviest of the four small planets around Barnard's Star, the closest single star to the Sun at about six light-years. Its minimum mass is about a third of Earth's, 0.335 Earth masses, yet it moves its star by less than half a metre per second. It was found together with its siblings: its signal first appeared in 2024 alongside Barnard b, and it was confirmed in 2025 along with planets d and e.
Those signals came from the radial velocity method, which finds a planet from the slight back-and-forth motion its gravity gives its star. A team led by Jonay González Hernández saw this one in four years of ESPRESSO measurements from the European Southern Observatory's Very Large Telescope while confirming Barnard b, and listed it as a candidate. A year later, University of Chicago astronomers led by Ritvik Basant checked the star with a different instrument, MAROON-X on the Gemini North telescope. MAROON-X alone was enough to confirm Barnard c, an important check for a star with a long history of planet claims that later fell apart.
Barnard c orbits every 4.12 days, between Barnard b and Barnard e, at about 0.027 astronomical units from its star, under a tenth of Mercury's distance from the Sun. The 2025 paper estimates an equilibrium temperature, the temperature set by starlight alone assuming the planet reflects none of it, of about 400 kelvin, above the boiling point of water. That places it closer in than the habitable zone, the range of distances where liquid water could last on a surface. It does not pass in front of its star, so its size and true mass are unknown; only the lower limit on its mass has been measured.