Exposed: The first exoplanet to bare its core only takes 18 hours to complete a year and sizzles at 1,500 degrees Celsius

Artist's impression of a Neptune-sized planet in the Neptunian desertUniversity of Warwick/Mark Garlick

  • The first-ever exoplanet with an exposed core was discovered by scientists at the University of Warwick.
  • It’s so close to its star that it only takes 18 hours to complete a year with a surface temperature of 1,500 degrees Celsius.
  • Scientists assume that it either never formed an atmosphere, to begin with, or was stripped of its gases sometime during its life cycle.
730 light-years away an exoplanet⁠— a planet that lies outside the Earth’s solar system ⁠— is the first to be discovered with its core exposed. It only takes 18 hours to complete its orbit and has a surface temperature that’s sizzling at 1,500 degrees Celsius.

Dubbed TOI 849 b, the planet is around the same size as Neptune — an anomaly for the region where it was discovered. It orbits a star similar to our sun in an area that scientists call the ‘Neptune Desert’, a term used to describe a region of stars where it’s very rare to find planets that are bigger than Neptune.

However, unlike Neptune, it’s much hotter due to its proximity to its star.
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“The planet is strangely close to its star, considering its mass. In other words, we don’t see planets with this mass at these short orbital periods,” said David Armstrong, the lead author of the study published in Nature. It is the first time that an intact exposed core of a gas giant has been discovered around a star.

  • 40 times heavier than Earth
  • 3.4 times bigger than Earth
  • Made up of iron, rock and water
  • Very little hydrogen and helium
"Such a small amount of hydrogen and helium is really astonishing for such a massive planet. We would expect a planet this massive to have accreted large quantities of hydrogen and helium when it formed," said Christoph Mordasini, co-author of the paper.

Exposed without an atmosphere
Researchers from the University of Warwick assume the gas giant was once a lot like Jupiter but was stripped of its gaseous atmosphere. This could be due to multiple reasons like being ripped apart for orbiting too close to its star or colliding with another planet.
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Another explanation is that it's a ‘failed’ gas giant, which was never able to form an atmosphere, to begin with.

"The fact that we don’t see those gases lets us know TOI 849 b is an exposed planetary core," remarked Armstrong.

TOI 849 b was found in a survey of stars by NASA’s Transiting Exoplanet Survey Satellite (TESS), using the transit method. This is when the satellite measures the brightness of a star. A dip in brightness indicates that a planet has passed in front of them.
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