Neptunelike

Neptunelike is a descriptor used in planetary science and exoplanet studies to describe planets whose properties resemble the ice giants Neptune and Uranus, rather than a gas giant like Jupiter. In the exoplanet context, Neptunelike planets typically have masses about 10 to 20 Earth masses and radii of roughly 2 to 4 Earth radii, yielding densities that indicate a substantial volatile-rich envelope surrounding a likely rocky or icy core.

These worlds are expected to possess thick atmospheres dominated by hydrogen and helium with higher metallicity, and interiors enriched with volatiles such as water, methane, and ammonia. Neptunelike planets may orbit close to their host stars, producing warm or hot Neptunes, or exist farther away as cool Neptunes, reflecting a range of formation and migration histories.

Formation and evolution: they are believed to form beyond the frost line, accreting ices and gas; migration can bring them inward; irradiation and atmospheric escape can sculpt their envelopes, resulting in a diversity of densities and atmospheric compositions.

Observational status: detected primarily through the transit and radial-velocity methods; their mass and radius yield mean density and hints about composition. Atmospheric characterization is pursued by transmission spectroscopy, though clouds and hazes can obscure spectral features.

Classification: neptunelike is often included in the broader category of sub-Neptunes or mini-Neptunes, distinct from rocky super-Earths and from true gas giants. Examples of exoplanets with Neptune-like properties include GJ 436b, HAT-P-11b, and GJ 3470 b.