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Astronomers have revealed the most detailed analysis yet of the four planets orbiting Barnard’s Star, one of the closest stars to Earth. The study, published inMonthly Notices of the Royal Astronomical Society, indicates that these small rocky worlds have unusual compositions, likely lost their atmospheres long ago, and are unlikely to provide conditions suitable for life.
Discovered in 2025, the four planets around Barnard’s Star are smaller than Earth and Venus but larger than Mars, placing them in a category of planets not represented in the solar system. Their proximity to their star and their chemical makeup make them a rare case for studying the formation and evolution of small rocky planets.
Researchers from the University of Cambridge investigated the relationship between the star’s composition and the possible composition of its planets. Their work provides new details about the materials that may exist inside these distant worlds.
The analysis showed that the unusual chemistry of Barnard’s Star provides important clues about its planets. Researchers found that the nearby red dwarf contains unusually high levels of magnesium, indicating that the worlds around it may share the same chemical signature.
A Mineral Composition Unlike Earth’s Rocky Worlds
The high magnesium content of the system appears to have influenced the minerals that formed inside the planets. Scientists found that the four worlds may contain large amounts of periclase, a mineral that differs from the materials commonly associated with Earth’s interior.
On Earth, magnesium is mainly found in minerals called olivines, which are important for storing water deep below the surface. The research team found that the planets around Barnard’s Star are more likely to contain periclase, which does not store water as effectively.
“Barnard’s Star has an enormous amount of the element magnesium compared to other stars, so its planets are likely to be rich in magnesium too,” said Xander Byrne, lead author of the study from the Institute of Astronomy at the University of Cambridge.
This chemical difference gives astronomers a new example of how planets with similar rocky structures can still develop very different internal compositions. The findings also show how the elements present in a star can influence the characteristics of the planets formed around it.
Too Close to Keep an Atmosphere
The planets’ extreme proximity to the nearby stellar neighbor has strongly shaped their evolution. Even the outermost planet in the system orbits about ten times closer to its star than Mercurydoes around the sun.
The researchers found that the planets were unlikely to have maintained their atmospheres over the full history of the system. Their calculations suggest that any atmospheres could have survived for no more than around 2 billion years, while the star system itself is about 10 billion years old.
The study reports that the combination of intense stellar influence and the planets’ low gravity made atmospheric loss likely.
“These planets were always going to be hostile because they’re really close to their star,” Byrne explained. “When you’re that close to your star and have such little gravity, your atmosphere just gets blown off.”
The absence of significant atmospheres means the planets would have very different environments from Earth, with little possibility of maintaining conditions similar to those found on our planet.
Orbital Resonance Keeps Planetary Systems Stable
The close arrangement of the four planets could have created another challenge: long-term stability. In tightly packed planetary systems, gravitational interactions between neighboring planets can sometimes disrupt their paths and lead to collisions, ejections, or falls into the host star.
The Cambridge team found that the system may remain stable because of orbital resonance, a phenomenon in which planets follow repeating orbital patterns. The orbital periods of the three inner planets are arranged in a 9:12:16 ratio.
The researchers noted that this type of gravitational pattern also helps stabilize the orbits of Jupiter’s moons. In the Barnard’s Star system, the same type of orbital relationship may be preventing major disturbances between the planets.
“Larger planets are much easier to detect than small ones, so we know about very few sub-Earth planets like the ones in this system,” stated Byrne. “But the sensitivity of these new missions will help reduce this bias, allowing us to discover more and more planets that are small and rocky, like Earth.”
The team said future missions such as theEuropean Space Agency’s PLATO missioncould help identify more planets similar in size to those around the star.
