Chthonian planet

A hypothetical planet formed when a hot gas giant loses its atmosphere, leaving a dense rocky or metallic core exposed.

Atmospheric escape: The loss of gas from a planet’s atmosphere into space. It is the process that could strip a close-in gas giant down to its core.
CoRoT-7b: A dense, short-period exoplanet orbiting the star CoRoT-7. It was proposed as a possible remnant of a much larger, atmosphere-stripped planet.
Super-Earth: An exoplanet larger or more massive than Earth but smaller than the Solar System’s ice giants. A rocky super-Earth can resemble a stripped core without having originated as a gas giant.
Planetary mass-radius relation: The relationship between a planet’s mass and radius, shaped by its composition and internal structure. Mass and radius constrain whether a candidate could be a dense exposed core.
Photoevaporation: Atmospheric loss driven by high-energy radiation that heats and accelerates gas into space. Stellar radiation can erode the atmosphere of a hot gas giant over time.
Kepler-10b: A dense rocky exoplanet with an orbital period of less than one Earth day. Its compact, irradiated state has made it a proposed chthonian candidate.
Mini-Neptune: A small exoplanet with a substantial volatile-rich atmosphere surrounding a rocky or icy interior. Unlike a chthonian planet, it retains a thick envelope.
Exoplanet atmosphere: The layer of gas surrounding a planet outside the Solar System. Detecting even a thin atmosphere can challenge the claim that a candidate is fully stripped.
Roche-lobe overflow: Mass transfer that occurs when an object expands beyond the region gravitationally bound to it in a binary system. A close orbit can let a planet’s expanding atmosphere spill toward its star.
HD 209458 b: A transiting hot Jupiter whose atmosphere has been observed escaping into space. Its atmospheric escape demonstrates a process that could precede core exposure.

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Iron planetCompared with: Both ideas involve material loss, but chthonian planets originate from gas giants rather than rocky bodies.