Astronomers find first exposed planetary core 730 light-years from Earth

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For the first time, scientists have found an exposed planetary core. The discovery — published Wednesday in the journal Nature — could offer astronomers new insights into the interiors of planets.

Earth’s core remains a source of many scientific mysteries, and planetary scientists know even less about the cores of Earth’s neighbors. To understand planetary formation and evolution, researchers need to know more about the inside of planets.

For obvious reason, planetary cores are difficult to study. Now, scientists have found a planetary core that is entirely exposed, they said.

Researchers estimate the core, located 730 light-years from Earth, once formed the interior of a gas giant. It’s possible the gas giant’s growth was stunted during its infancy, but researchers suspect it’s more likely the gas giant had its outer layers stripped away over billions of years.

The planetary core, named TOI-849 b, is too big to be a rocky planet, researchers say.

David Armstrong, lead researcher on the study, told UPI that researchers concluded the planetary core was the remains of a gas giant based on its size and an expectation it underwent “runaway gas accretion,” a process of accumulating gas and growing even bigger.

“For such massive planets, gases like hydrogen and helium fall onto the forming planet very quickly, until the planet becomes something like Jupiter,” said Armstrong, an astrophysicist at the University of Warwick. “It’s very difficult to make a planet as massive and dense as TOI-849 b without it becoming a gas giant.”

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But if TOI-849 b was once a gas giant, its gas layers are now nowhere to be found, researchers say.

Scientists suspect they were expelled during an unusually violent period of planetary evolution.

“This could be because it collided with another planet toward the end of its formation, or later ventured too close to its host star and was stripped of its atmosphere,” Armstrong said. “An alternative is that the planet got stuck while forming, building up a core but failing to collect the gas we would normally expect. That can happen if the core opens up a large gap in the disk of material it forms from, which is easier to do very close to the star.”

The planetary core enjoys an extremely intimate orbit, completing a lap around its sun once every 18 hours. Its surface is a scorching 1,800 degrees Kelvin.

The core is located in what’s called the “Neptunian desert,” as large planets are rarely found so close to their host stars.

“It suggests that the planet had a more unusual history, which supports a more aggressive past such as a planetary impact or tidal disruption by the host star,” Armstrong said.

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Astronomers first spotted the planetary core using data collected by NASA’s TESS mission.

“We see small dips in the brightness of the star as the planet blocks some of the light reaching Earth,” Armstrong said. “We followed up the discovery using the HARPS spectrograph at the European Southern Observatory, trying to measure the mass of the planet using the ‘doppler technique,’ where we measure the movement of the host star as the planet orbits.”

To better understand how such a big, dense core ended up without gas layers and so close to its host stars, scientists need to acquire more detailed observations, Armstrong said.

“We are trying to measure the alignment of the planet’s orbit with the spin of its host star, which will help us work out what its past evolution was,” Armstrong said. “In the longer term, we would like to measure the constituents of the planet’s atmosphere, but that will require next-generation telescopes to do.”

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