Astronomers have discovered a Saturn-sized planet orbiting a red dwarf so small, the finding threatens to rewrite everything we thought we knew about how planets form.
Key Points at a Glance
- TOI-6894b is the largest planet ever found orbiting the smallest known star of its kind
- The star is only 20% the mass of our Sun, making such a giant planet’s existence puzzling
- TOI-6894b is unusually cold and may have an atmosphere rich in methane and ammonia
- Current planet formation models can’t fully explain how this system came to be
In a jaw-dropping astronomical discovery, researchers from University College London and the University of Warwick have found a giant gas planet orbiting a star so small that it challenges long-standing models of planetary formation. Published in Nature Astronomy, the study introduces TOI-6894b, a planet with the radius of Saturn but only half its mass, orbiting a red dwarf with just 20% the Sun’s mass.
“We did not expect planets like TOI-6894b to be able to form around stars this low-mass,” said Dr Edward Bryant, who led the discovery. “This planet completely changes the game for our understanding of planetary system formation.”
Traditionally, giant planets are believed to form via the core accretion model: small rocky bodies collide and merge until they attract a thick atmosphere. This process requires a massive disc of gas and dust—something thought to be lacking around tiny stars like TOI-6894. The team explored alternate explanations, including steady accretion without runaway growth or gravitational disc instability, but even these fall short of fully explaining the planet’s origins.
Adding to the mystery, TOI-6894b is extremely cold for a gas giant. Unlike the hot Jupiters orbiting close to their stars with surface temperatures above 1000K, this planet orbits at a comfortable 420K. This cool environment makes it a rare candidate for studying atmospheric components like methane and ammonia—chemicals that are difficult to detect on hotter exoplanets.
“This planet likely presents a benchmark for studying methane-dominated atmospheres,” said Professor Amaury Triaud from the University of Birmingham. “We may even detect ammonia, which would be a first in exoplanetary science.”
TOI-6894b will be observed by the James Webb Space Telescope within the next year. By analyzing the planet’s atmosphere, scientists hope to determine whether it formed by gradual accretion or through a violent gravitational collapse.
With most stars in our galaxy being small red dwarfs like TOI-6894, this discovery may dramatically increase estimates for how many gas giants might be hiding in plain sight—hidden worlds that challenge everything we thought we knew about where planets can and can’t form.
Source: University College London
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