The nature of the sub-Neptune K2-18b is debated between Hycean and mini-Neptune interpretations.
The upper atmospheres of temperate sub-Neptunes are strongly influenced by atmospheric dynamics due to their cool equilibrium temperature and thereby longer chemical timescales than the atmospheric dynamical timescales.
The organosulfur biosignature gases dimethylsulfide (DMS) and dimethlydisulfide (DMDS) have recently been claimed to be present in the atmosphere of sub-Neptune exoplanet K2-18b, leading to the suggestion of possible extraterrestrial […]
Context: JWST has enabled transmission spectroscopy at unprecedented precision, but stellar heterogeneities (spots and faculae) remain a dominant contamination source that can bias atmospheric retrievals if uncorrected.
K2-18b, a sub-Neptune exoplanet located in the habitable zone of its host star, has emerged as an important target for atmospheric characterization and assessments of potential habitability.
Sub-Neptune planets are often modeled with a dense rocky or metal-rich interior beneath a thick hydrogen/helium (H/He) atmosphere; though their bulk densities could also be explained by a water-rich interior […]
Recent transit observations of K2-18b and TOI-270d revealed strong molecular absorption signatures, lending credence to the idea that temperate sub-Neptunes (Teq=250-400K) have upper atmospheres mostly free of aerosols.
![Mass and radius for a number of potentially habitable ocean worlds. The bullet points show identified ocean worlds: listed from bottom to top: HD 11505b, WASP 35, TOI 157, TOI 1452b, KELT 10b, HD 80883b, HD 221585b, HIP 67537b, K2-18b, Kepler 1980b, HD 50499b, Kepler 1766b, HD 50499c. The green curve gives the mass-radius relation for planets with a water content of > ∼ 30 % (by mass) from [40]. The arrows (and black crosses [right-most one is white]) give the simulation atmosphere models. -- astro-ph.EP](https://i0.wp.com/astrobiology.com/wp-content/uploads/2025/10/A-Systematic-North-South-Asymmetry1.png?resize=1200%2C725&ssl=1)
Planetary obliquity (axial tilt) plays an important role in regulating the climate evolution and habitability of water-covered planets.
K2-18b, a temperate sub-Neptune, has garnered significant attention due to claims of possible biosignatures in its atmosphere. Low-confidence detections of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS) have sparked considerable […]
An exoplanet orbiting a dwarf star 124 light-years from Earth made headlines around the world in April 2025. Researchers at the University of Cambridge reported that planet K2-18b could be […]
