Core of a gas planet seen for the first time

Planetary coreImage copyright
Uni Warwick / Mark Garlick

Image caption

Artwork: The planetary core orbits very close to its parent star

Astronomers have found a previously unseen type of object circling a distant star.

It could be the core of a gas world like Jupiter, offering an unprecedented glimpse inside one of these giant planets.

Giant planets like Jupiter and Saturn have a solid planetary core beneath a thick envelope of hydrogen and helium gas.

But no-one has previously been able to see what these solid cores are like.

Now, a team of astronomers has discovered what they think are the rocky innards of a giant planet that’s missing its thick atmosphere. Their findings have been published in the journal Nature.

Lead author David Armstrong, from Warwick University, and colleagues had been running a programme to detect exposed planetary cores in data from the Tess space telescope.

“This was one of the candidates we picked out as something to try to observe,” he told BBC News.

“We followed it up with an instrument called the Harps spectrograph in Chile, which we used to measure the masses of these candidates. This one came out as being exceptionally massive – much more than we expected really. That’s when we started to look into what could have caused that.”

When the researchers first looked at the object, they thought it might be a binary star.

“We kept taking data and it turned out to still be a planet – just an exceptionally massive one for its size,” Dr Armstrong explained.

It’s radius is about three and a half times larger than Earth’s but the planet is around 39 times more massive.

The object, called TOI 849 b, was found circling a star much like the Sun that’s located 730 light-years away.

The core orbits so close to its parent star that a year is a mere 18 hours and its surface temperature is around 1,527C.

Researchers aren’t sure whether the core lost its atmosphere in a collision or just never developed one.

But more observations are planned, which could help test ideas about how giant gas planets develop.

“One way or another, TOI 849 b either used to be a gas giant or is a ‘failed’ gas giant,” said Dr Armstrong.

“It’s a first, telling us that planets like this exist and can be found. 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.

“There are still big open questions about the nature of Jupiter’s core, for example, so strange and unusual exoplanets like this give us a window into planet formation that we have no other way to explore.”

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