Astronomers discover a bizarre, naked planet in the 'Neptune desert'

TOI-849b is extremely hot and incredibly close to its parent star, and it might be the exposed core of a failed gas giant.

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Jackson Ryan was CNET's science editor, and a multiple award-winning one at that. Earlier, he'd been a scientist, but he realized he wasn't very happy sitting at a lab bench all day. Science writing, he realized, was the best job in the world -- it let him tell stories about space, the planet, climate change and the people working at the frontiers of human knowledge. He also owns a lot of ugly Christmas sweaters.
Jackson Ryan
2 min read

TOI-849b is so close to its star one "year" takes 18 hours. Bless.

University of Warwick/Mark Garlick

If there's one thing we can all agree on about 2020, it's this: it would be perfect if it only lasted 18 hours. On TOI-849b, an exoplanet around 730 light-years from Earth, that dream "year" is a reality. The planet is so close to its star that it takes just 18 hours to make a full orbit. 

But as you might imagine, being so close to its sun, TOI-849b is particularly hot. Like 2,700 degrees Fahrenheit hot.

And it's incredibly weird: The team of astronomers that uncovered it thinks it's kind of naked. It's size suggests it should be a gas giant planet -- think Jupiter -- but it isn't. Instead, what's left orbiting the star is the rocky core of the planet.

The study, published in the journal Nature on Wednesday, details the discovery of TOI-849b, which orbits the sun-like star TOI-849. It was discovered by researchers using NASA's TESS telescope, a space-based observatory that looks for periodic dimming of a star -- a potential sign it's accompanied by a planet. The European Southern Observatory's La Silla Observatory helped characterize the unusual world.

TOI-849b is around 40 times as massive as the Earth and 3.5 times as wide. It exists in the "hot-Neptune desert" region around its star -- a place where astronomers don't typically find this type of planet because they get shredded by the neighboring massive furnace.

But then there's TOI-849b just hanging out, in the scorching heat. According to modelling used by the team, the density of the planet suggests it should have been able to accrete lots of hydrogen and helium gas, but it appears to have gathered only a fraction of what's expected.

"Such a small amount of hydrogen and helium is really astonishing for such a massive planet," Christoph Mordasini, a physicist at the University of Bern and co-author on the study, said in a press release. "We would expect a planet this massive to have accreted large quantities of hydrogen and helium when it formed."

The researchers believe they've detected an "exposed planetary core," and if their theory holds, it would be the first time such a discovery has been made. But how did it happen?

Mordasini notes TOI-849b could have lost its gas during its formation, with the star nearby stripping it down to the core because of its huge gravitational pull. A collision with another planet may have also contributed. 

It may have also forgotten to dress itself. If the planet began forming in a region of space where there was no dust, gas or debris to gobble up, it may have never been able to accrete the material usually expected of a planet of this size.

"Our discovery proves that planets like this exist and we can track them down," said David Armstrong, an astrophysicist at the University of Warwick. "We have the opportunity to look at the core of a planet in a way that we can't do in our own solar system."

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