Giant planet discovered around super-tiny star 'should not exist'

ASTRONOMERS HAVE DISCOVERED THAT TINY STAR HAS FORMED A 'MASSIVE PLANET' – BUT NO ONE KNOWS HOW 19:07, 04 Jun 2025 Astronomers have discovered a giant planet orbiting a tiny star,

but claim they "don't really understand" how this cosmic mystery happened. The planet, called TOI-6894b, was found orbiting a red dwarf star that is just 20 per cent the mass

of our Sun. Until now, experts believed that stars this small lacked the material needed to form such large planets. The discovery has baffled astronomers – and challenges long-held theories

of planet formation. The existence of TOI-6894b could rewrite what we know about the birth of planets in our galaxy. "I was very excited by this discovery," said Dr Edward Bryant,

Warwick Astrophysics Prize Fellow and first author. Article continues below He added: "We did not expect planets like TOI-6894b to be able to form around stars this low-mass. This

discovery will be a cornerstone for understanding the extremes of giant planet formation." TOI-6894b is a gas giant roughly the size of Saturn but with about half its mass – meaning it

is large, but light. It orbits a star that is the smallest ever found to host a planet of this size. For comparison, the next smallest star known to host such a giant planet is 60 per cent

larger than Star TOI-6894. "Most stars in our galaxy are actually small stars exactly like this, with low masses and previously thought to not be able to host gas giant planets,"

said Dr Daniel Bayliss, Associate Professor at The University of Warwick. "So, the fact that this star hosts a giant planet has big implications for the total number of giant planets we

estimate exist in our galaxy." The intriguing system was first identified in data from NASA’s Transiting Exoplanet Survey Satellite (TESS). Dr Bryant said: "I originally searched

through TESS observations of more than 91,000 low-mass red-dwarf stars looking for giant planets. "Then, using observations taken with one of the world’s largest telescopes, ESO’s VLT,

I discovered TOI-6894b, a giant planet transiting the lowest mass star known to date to host such a planet." The discovery challenges what scientists thought they knew about how planets

form. The most widely accepted idea, called the core accretion theory, says that giant planets are born when dust and rocks around a young star slowly stick together and form a solid core,

pulling in huge amounts of gas and growing into gas giants like Jupiter or Saturn. However, small stars like TOI-6894b's host star usually don't have enough material to do this,

which is why scientists didn't expect a planet like this to exist. Dr Vincent Van Eylen, from UCL’s Mullard Space Science Laboratory, said: "It’s an intriguing discovery. We don’t

really understand how a star with so little mass can form such a massive planet! "This is one of the goals of the search for more exoplanets. By finding planetary systems different from

our solar system, we can test our models and better understand how our own solar system formed." The atmosphere of TOI-6894b is already scheduled to be observed by NASA's James

Webb Space Telescope (JWST) within the next year. Article continues below These observations should allow astronomers to explain the formation of this unexpected planet. The study was

published in the journal _Nature Astronomy_.