A remnant planetary core in the hot-Neptune desert

Area of Science:

• Planetary Science
• Exoplanet Research
• Astrophysics

Background:

• Giant planet interiors and cores are poorly understood, with significant observational uncertainties.
• Exoplanets undergoing rare evolutionary processes, like those in the hot-Neptune desert, aid in studying planetary interiors.
• Planets like HD149026b, LTT9779b, and NGTS-4b highlight atmospheric loss and massive cores.

Purpose of the Study:

• To investigate the nature of the exoplanet TOI-849b, characterized by its small radius and large mass.
• To determine the composition and evolutionary history of TOI-849b using interior-structure models.
• To understand the mechanisms responsible for potential mass loss in giant planets.

Main Methods:

• Observation of the exoplanet TOI-849b.
• Analysis of TOI-849b's mass, radius, and density.
• Application of interior-structure models to constrain the gaseous envelope mass.

Main Results:

• TOI-849b has a radius smaller than Neptune but a mass of 7.7 Earth masses and a density similar to Earth's.
• Interior-structure models indicate a hydrogen and helium envelope comprising no more than 15% of the total planetary mass.
• The planet's characteristics suggest it was once a gas giant that lost substantial mass.

Conclusions:

• TOI-849b is likely the remnant core of a giant planet.
• Mass loss could have occurred through thermal self-disruption, giant planet collisions, or by avoiding substantial gas accretion.
• Photoevaporation can remove smaller hydrogen/helium envelopes over billions of years, implying TOI-849b's remaining atmosphere may be volatile-enriched.