TOI-849 b

TOI-849 b is an exoplanet orbiting the late-G type star TOI-849. It is a candidate chthonian planet, the exposed core of a gas giant that had much of its atmosphere stripped away.

Characteristics
TOI-849 b is a high-density planet more massive than Neptune, about forty times the mass of Earth. It orbits very close to its host star, with a period of less than one day, placing it within the Neptunian desert.

Compared to other Neptune-sized exoplanets, this planet is unusually massive and dense. It is about 40 times the mass of Earth, but only about 3.4 times Earth's radius. This implies that any gaseous envelope of hydrogen and helium makes up at most $0.016 AU$ percent of the planet's mass. However, given the planet's size, its density is still too low for a purely rocky composition.

The gravity of such a massive planet would be expected to accrete large amounts of gas from the protoplanetary disk in which it formed, causing it to become a gas giant. It is thought that TOI-849 b could be the remnant core of a gas giant. A 2021 modeling study found that the stellar radiation received by the planet could have removed the entire gaseous envelope even if it formed as a Jupiter-mass planet.