Astronomers – Tiny Star Hosting a Giant Planet That Shouldn’t Exist

When you think of a massive gas giant, you probably imagine it orbiting a large, bright star—something like Jupiter circling our Sun. But astronomers have just found something that flips that script: a bloated planet bigger than Saturn orbiting a star that’s just one-fifth the Sun’s mass.

The planet, named TOI-6894b, was known using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), and it’s got scientists scratching their heads—and rewriting the rules of planet formation.

Surprise

TOI-6894b orbits a tiny red dwarf star named TOI-6894. The star is cool, dim, and only about 20% the mass of our Sun. Yet somehow, it’s hosting a huge gas planet—something we’ve never seen around such a small star before.

The planet itself is even stranger. While it’s physically larger than Saturn, it’s only about half its mass. That makes it incredibly low-density—almost puffed-up, like a cosmic marshmallow.

Edward Bryant, the astronomer from University College London (UCL) who led the study, wasn’t expecting anything like it. “I searched through TESS data on over 91,000 low-mass stars and this one stood out. It’s the lowest-mass star ever discovered to host such a big planet.”

Mystery

The current understanding of planet formation doesn’t really allow for something like TOI-6894b to exist around such a small star.

Here’s why: small stars typically have small disks of gas and dust surrounding them during formation. These disks aren’t supposed to have enough material to build a giant planet before the gas disappears. Yet, here we are.

“This planet shouldn’t be there,” said Vincent Van Eylen, another UCL exoplanet expert. “It goes against the standard core-accretion theory that most of our planet formation models rely on.”

Theory

So how did it get there?

Astronomers have come up with two possibilities—though neither is a perfect fit.

1. Intermediate Core-Accretion: A slightly modified version of the classic model where a core forms fast enough to pull in gas before the disk vanishes.
2. Disk Instability: The disk collapses under its own gravity and forms a planet quickly in one go—more like how stars form.

Still, the data doesn’t clearly support either explanation yet. TOI-6894b remains a planetary puzzle.

Chemistry

The planet’s atmosphere is also exciting. Because it orbits at a decent distance, it’s cooler than many other gas giants we’ve studied—about 420 Kelvin (or roughly 300°F). That makes it one of the rare exoplanets cold enough to possibly show methane chemistry in its atmosphere.

It could even reveal traces of ammonia, something scientists haven’t yet detected in an exoplanet atmosphere. If so, TOI-6894b could be the first of its kind—a benchmark planet for studying carbon, nitrogen, and oxygen outside our solar system.

JWST

The James Webb Space Telescope (JWST) is already lined up to take a closer look. It will use its powerful spectrometers to analyze the planet’s atmospheric gases and cloud layers.

These upcoming observations may finally help answer the question of how such a big world formed around such a tiny star.

Implications

TOI-6894b’s discovery doesn’t just change what we thought we knew—it also opens new doors.

Daniel Bayliss from the University of Warwick explains, “Most stars in the galaxy are small, low-mass stars like this one. If even a fraction of them host gas giants like TOI-6894b, then the total number of giant planets in the Milky Way may be much higher than we thought.”

Future

This finding is just the beginning. With more surveys of red dwarfs underway, astronomers may uncover even more gas giants in unlikely places.

“This system provides a new challenge for models of planet formation,” says co-author Andrés Jordán. “And it’s a very promising target for follow-up with JWST and other space-based telescopes.”

In the end, TOI-6894b is a cosmic curveball—a giant reminder that nature doesn’t always follow our rules.

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