The Sun's closest neighbors are locked in eternal day and night
In short: Just under six light-years away, Barnard’s Star hosts a planetary system that defies our own solar system's rules. These four worlds are smaller than Venus but larger than Mars, yet they possess geological signatures and orbital behaviors that make them utterly hostile to life.
Discovered in 2025, the Barnard’s Star system offers a rare glimpse into compact planetary dynamics. The four planets orbiting this star—the Sun's closest neighbor after Alpha Centauri—occupy a size niche not found in our own solar system: they are smaller than Earth and Venus but larger than Mars. Because of their proximity to the host star, these worlds are tidally locked. Much like how the Moon shows only one face to Earth, each of these planets has one hemisphere trapped in permanent daylight while the other remains in perpetual night.
The chemical composition of Barnard's Star reveals a significant magnesium surplus compared to other stars. On Earth, this magnesium typically forms olivines, minerals essential for storing water within a planet. However, the extreme magnesium levels in this system favor the creation of periclase—a mineral found only hundreds of kilometers below Earth's surface. Periclase is notably poor at storing water, suggesting these planets are geologically distinct from our own.
Survival on these worlds is impossible due to their proximity to the star. Even the outermost planet orbits ten times closer than Mercury does to the Sun. With such low gravity and intense stellar proximity, any atmosphere would be stripped away; researchers estimate these planets could have held onto an atmosphere for at most 2 billion years, a mere fraction of the system's 10-billion-year age. While compact systems are often unstable—risking collisions or ejections—this specific system may be preserved by orbital resonance.
The research was led by Xander Byrne from the University of Cambridge’s Institute of Astronomy and published in Monthly Notices of the Royal Astronomical Society.
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Sources
- Summary by Intellect · source: Earth’s Closest Planetary Neighbors Are Utterly Uninhabitable
- Also: Astronomers find nearby planets to be small, strange, and utterly uninhabitable | Institute of Astronomy
- Also: Astronomers find nearby planets to be small, strange, and utterly uninhabitable
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