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The small exoplanets of our Sun’s second-nearest neighbor, Barnard’s Star, are inhospitable wastelands, British astronomers say.
Located six light-years from Earth, Barnard’s Star is separated from our closest neighbor, Alpha Centauri, by about 66° in our sky. Now, University of Cambridge researchers have revealed their findings on this exosolar system in a recent paper published in the Monthly Notices of the Royal Astronomical Society.
After careful analysis, the astronomers announced that the exoplanets are unlike any in our solar system, presenting a brutal and barren environment.
Scientists only discovered these four small planets orbiting Barnard’s Star in 2025. Unlike anything in our solar system, these orbital bodies fit into a size range larger than Mars, but smaller than Earth or Venus.
Like a peeled onion, these smaller planets are rich in a mineral only found deep below the Earth’s surface. Chemical analysis revealed large amounts of the mineral periclase on the surface of these planets, something typically only found hundreds of kilometers deep on our planet.
“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 lead author Xander Byrne from Cambridge’s Institute of Astronomy. “On Earth, that magnesium goes into making minerals called olivines, which are really important for storing water within the planet.”
Unfortunately for those looking for extraterrestrial life, magnesium serves a different purpose on these exoplanets. Instead of water-storing olivine, it produces the abundant periclase, which is a poor store of water.
Even worse, these inhospitable exoplanets likely no longer have an atmosphere. According to the University of Cambridge team, these ten-billion-year-old planets probably only managed to hold an atmosphere for two billion years at most.
“These planets were always going to be hostile, because they’re really close to their star,” said Byrne. “Even the outermost planet orbits ten times closer than Mercury orbits the Sun. When you’re that close to your star, and have such little gravity, your atmosphere just gets blown off.”
In addition to the lack of atmosphere, the planets’ proximity to Barnard’s Star leaves them tidally locked, like our Moon, with one side always facing toward the star.
However, there is one positive element to these small planets. Typically, such close-orbiting systems are highly unstable, with the planets shooting out from the system, falling into their host star, or catastrophically colliding. Yet in this case, the system is as ordered as a piece of music.
The three inner planets of the exosolar system have years in a 9:12:16 ratio, producing two of what is known as a “perfect fourth” in music. This musical harmony is known as an orbital resonance, with the same type of effect stabilizing Jupiter’s moons in their orbits around that planet.
While our ability to view Barnard’s Star from Earth may be limited, the European Space Agency’s upcoming Plato mission may allow astronomers to discover ever smaller worlds orbiting in the nearby exosolar system.
“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,” said Byrne. “But the sensitivity of these new missions will help to reduce this bias, allowing us to discover more and more planets that are small and rocky, like Earth.”
The true significance of the research may lie in the value of a null result. While these planets are bleakly hostile to life, observing this exosolar system’s composition can aid future astronomers in narrowing down the search for extraterrestrial life.
The paper, “The Barnard’s Star Planetary System: Stability, Composition, and Evolution of Four Sub-Earth Exoplanets,” appeared in Monthly Notices of the Royal Astronomical Society on June 24, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.
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Researchers from the private nuclear fusion energy company Commonwealth Fusion Systems have published a series of papers that they claim confirm that their flagship ARC reactor will produce more usable energy than it consumes if built as designed.
Although the company projects it will deliver the first commercial fusion plants by the early 2030s, other researchers say there are remaining challenges to overcome, and won’t declare the ARC reactor successful until an operational version is constructed to validate the research team’s theoretical predictions.
Scientists have long dreamed of capturing the nuclear fusion reaction that fuels our Sun and using it to generate clean, renewable power. Private fusion firms like CFS have received nearly $10 billion in funding over the last decade alone.
The first laboratory “net-energy” controlled fusion reaction, which fusion scientists call “ignition,” didn’t occur until 2022, when physicists at the US National Ignition Facility in Livermore, California, successfully produced more energy than was used to generate the reaction. Although brief, that moment has fueled speculation that practical fusion energy generation may be right around the corner.
Now, the Commonwealth team, which includes 58 researchers from the company and partner institutes, has published scientific papers outlining the physics of their ARC reactor, including new models that they say account for the “expected behavior” of the superhot plasma at the heart of the design.
Brandon Sorbom, the company’s chief science officer, said that the published works “confirm that when we build the ARC fusion power plant, it will work”.
After nearly a decade of research, CFS, founded in 2018, is currently preparing its prototype for a 2027 demonstration it calls ‘SPARC.’ The company said they expect that trial run, which will demonstrate their technology’s ability to generate more energy than it needs to heat the plasma, will help them fine-tune ARC’s final design.
According to the Commonwealth-led team, ARC will generate more energy than is required to operate the entire facility, including plasma heating, resulting in a true net-positive power-generation facility. This includes producing approximately 400 megawatts of net electricity, which the team noted is enough to power 280,000 average US homes. For comparison, recent census data indicates that Boston, Massachusetts, near the company’s headquarters in Cambridge, has around 271,000 U.S. homes.
Like SPARC, the ARC reactor uses high-temperature superconducting magnets to compress the plasma, which remains suspended by the magnetic fields, preventing it from damaging the chamber walls and terminating any potential fusion reaction. Under this extreme pressure, the nuclei of heavy hydrogen trapped inside the chamber fuse to form helium, the same reaction that takes place inside the Sun.
This fusion reaction results in the release of energy, primarily high-speed neutrons. At its hottest, the donut-shaped ring of plasma reaches seven times the temperature of the Sun.
Tony Roulstone, a nuclear engineer at the University of Cambridge, UK, conceded that the CFS team and its collaborating authors are “some of the best in the fusion business” and noted the company’s ARC reactor concept is the result of “good work over many years.” However, Roulstone also warned of the pressure on researchers in privately funded companies to “claim things before the evidence is fully in place.”
David Hammer, a nuclear engineer at Cornell University in Ithaca, New York, said it is a good sign that the team is publishing at a high volume, but also warned that published papers will not guarantee that the built device will work as intended.
Their modeling “has to be proven correct by a fusion reactor that works as designed”, he adds. If the firm can get SPARC operating successfully next year, “it will be an important step forward”, he says.
Hamner also noted that several of the design’s subsystems require further development before it can be declared complete. This includes addressing how plasma will behave in the real world when it becomes unstable versus its modeled behavior, proving out the process for extracting usable energy from the generated heat, and demonstrating that the reactor is robust enough to operate for long periods.
The scientists also noted the challenges in sourcing tritium, the isotopic fuel the reactor requires to operate. Although CFS has outlined its tritium generation process, Hamner noted that the series of published papers neither details the process nor demonstrates its viability.
“There are candidate blanket materials and blanket designs, but there are many engineering person-years needed” to bring a functional ARC-style plant to fruition, he explained.
“We certainly have to build more on top of that foundation laid out in these papers,” a company spokesperson said, adding that they will “be able to produce tritium for operations and for future power plants.”
The following articles were published by the CFS-led team: “Overview of the physics basis for the ARC fusion power plant“; “ARC disruption physics and strategy“; “Performance and Transport in the ARC Tokamak“; “Power and particle exhaust for the ARC fusion power plant“; “ARC Physics Basis-Magnetohydrodynamics.”
Editor’s Note: This article was updated to correct a previous version that described neutrinos, rather than fast-neutrons, in the context of the reporting, and to clarify that the first achievement of a “net-energy” controlled fusion reaction (ignition) occurred in 2022.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.
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