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Astronomers find the first known exposed core of a gas giant

Jon Fingas
Associate Editor
Neptune-sized planet in the Neptunian Desert

Gas giants like Jupiter and Saturn are known to have cores at their centers, but seeing those is difficult — unless nature cooperates, that is. University of Warwick astronomers have discovered (via ScienceNews) what they say is the first known exposed gas giant core. TOI-849b is a planet about 730 light-years away that’s close to Neptune’s size (nearly four times Earth’s) but with an Earth-like density that suggests it should have accumulated layers of hydrogen and helium. It didn’t, however — this indicates that something stripped the gas away, assuming it formed properly in the first place.

The team found the planet by using data from NASA’s Transiting Exoplanet Survey Satellite and refining it using telescopes from the Chile-based Next-Generation Transit Survey and La Silla Observatory. This included gauging the mass of the planet by studying the slight changes in light spectrum from the celestial body’s wobble.

It’s not certain just what led to the ‘naked’ jovian world, but there are two theories. TOI-849b is so close to its star that it completes an orbit in 18 hours, raising the possibility that tidal disruptions or a planetary collision stripped it of gas. Evaporation due to starlight is a possibility, but wouldn’t account for all the lost gas. This could also be a failed gas giant where a gap in the formative dust disc, or a late formation, robbed the planet of gas.

More observations will be necessary to determine just what materials are part of the core. Even so, this is notable simply for showing that these kinds of planets can exist. Like other recent findings, it’s illustrating how complex the cosmos can be.