Astronomers have taken their most detailed look yet at the planetary system orbiting Barnard’s Star, one of the Sun’s closest stellar neighbors, and the results suggest these nearby worlds are unlike anything in our own solar system.
Although they are relatively close to Earth in cosmic terms, the newly studied planets appear to be dry, airless, and far too hostile to support life.
Barnard’s Star lies just under six light-years away, making it the closest single star to the Sun after the Alpha Centauri system.
In 2025, astronomers confirmed that four small rocky planets orbit the star. Each is smaller than Earth and Venus but larger than Mars, placing them in a size category that does not exist anywhere in our own solar system.
In the new study, published in Monthly Notices of the Royal Astronomical Society, researchers from the University of Cambridge examined the star’s chemical composition to better understand what its planets are made of.
They discovered that Barnard’s Star contains unusually high levels of magnesium. According to lead author Xander Byrne from Cambridge’s Institute of Astronomy, that extra magnesium likely shaped the planets as they formed billions of years ago.
On Earth, much of the magnesium becomes minerals called olivines, which play an important role in storing water deep inside the planet.
But on the Barnard’s Star planets, scientists believe the magnesium instead formed large amounts of a different mineral called periclase. Unlike olivine, periclase does a poor job of holding water, making these planets much drier than Earth.
The planets also appear unlikely to have long-lasting atmospheres. They orbit extremely close to their star, with even the outermost planet circling about ten times closer than Mercury is to the Sun. At such close distances, intense radiation and stellar winds can gradually strip away a planet’s atmosphere.
Combined with the planets’ relatively weak gravity, the researchers estimate that any atmosphere they once had could have survived for no more than about two billion years. Since Barnard’s Star is roughly 10 billion years old, those atmospheres would have disappeared billions of years ago.
Another unusual feature is that all four planets are probably tidally locked. This means they always keep the same side facing their star, much like the Moon always shows the same face to Earth. One side of each planet would experience endless daylight and scorching heat, while the opposite side would remain in permanent darkness.
Despite being packed tightly together, the planetary system appears surprisingly stable. Normally, planets orbiting so close to one another would strongly tug on each other, increasing the risk of collisions or ejections from the system.
However, the researchers found that the planets’ orbits are linked by a pattern known as orbital resonance. The inner three planets complete their orbits in a repeating 9:12:16 rhythm, a gravitational arrangement similar to one that helps keep some of Jupiter’s moons in stable orbits.
Scientists expect future space missions, including the European Space Agency’s Plato mission, to discover many more small rocky planets like these.
While the Barnard’s Star planets are almost certainly uninhabitable, the study shows that a star’s chemical makeup can reveal valuable clues about the nature of its planets. That knowledge could help researchers identify more promising worlds elsewhere in the galaxy where life might be possible.
