An article published in “The Astrophysical Journal Letters” reports confirmation of the existence of four exoplanets that are smaller than Earth orbiting Barnard’s Star. A team of researchers combined detections obtained with the MAROON-X instrument mounted on the Gemini North telescope in Hawaii with others obtained independently with the ESPRESSO instrument installed on ESO’s VLT in Chile. The result is the confirmation of the exoplanet Barnard b, whose existence was announced in October 2024, and three other sub-Earths, small planets that are almost certainly rocky.
Almost six light-years away from Earth, Barnard’s Star is the closest single star to the Sun, as the Alpha Centauri pair and their companion Proxima form a triple system. Despite this relative proximity, its system is at such an angle that from Earth, we cannot see exoplanets within it transiting in front of Barnard’s Star. This made their search difficult, and only the dataset collected over long periods by highly sensitive instruments started providing some reasonable certainty using the radial velocity method.
MAROON-X is an instrument designed specifically to find small exoplanets that orbit red dwarfs, stars with a mass significantly lower than the Sun’s that constitute the most common class in the universe. 112 detections obtained over the course of three years of Barnard’s star provided solid evidence for the presence of three exoplanets, confirming the one already discovered and two candidates that were proposed but still needed confirmation.
Another team announced the existence of the exoplanet Barnard b in October 2024 in an article published in the journal “Astronomy & Astrophysics” thanks to evidence obtained with the ESPRESSO instrument. This new study based on the MAROON-X detections has independently confirmed that exoplanet.
Evidence for the presence of another exoplanet orbiting Barnard’s Star has come from the combined detections of the MAROON-X and ESPRESSO instruments. This confirms the existence of another exoplanet candidate previously proposed and now referred to by researchers as Barnard e. With a mass of around 20% of the Earth’s, it’s the smallest exoplanet discovered with the radial velocity method.
All the planets confirmed by this study are sub-Earths since estimates of their masses range from 20% to 33% of the Earth’s. The amount of data collected over the years by two very sensitive instruments also allowed to provide good estimates of their orbits, very close to Barnard’s Star. The year of these planets is between 2.3 and 6.7 Earth days approximately. This proximity to their star was expected given that it’s a red dwarf and this class of stars has very compact planetary systems.
The data collected on Barnard’s Star system also rule out the possibility of planets in its habitable zone, where a planet with an atmosphere comparable to Earth’s can host liquid water on its surface. There’s much discussion about the possibility that a planet orbiting a red dwarf could be habitable for life forms similar to those on Earth because these stars are small but very active. They emit powerful flares that shower a planet with highly energetic particles and can even erode a planetary atmosphere.
The search for exoplanets orbiting red dwarfs will continue, and the results obtained by studying Barnard’s Star offer new hope. Sensitive instruments such as ESPRESSO and MAROON-X showed that it’s possible to find even planets much smaller than the Earth in a planetary system where it was particularly difficult to distinguish the various tracks. This is a progress that can continue with new instruments that will come into service in the coming years.
