mini-Neptune Archives - Astrobiology

An artist’s concept of what the faraway planet TOI-270 d may look like. A new study suggests these types of planets may be hiding more water than they let on.Illustration courtesy NASA

Exoplanets, -moons, -comets

Distant Exoplanets May Be Hiding Water Beyond Webb Telescope’s Reach, Study Finds

by Keith CowingJuly 15, 2026July 15, 2026

[University of Chicago] The planets that appear most common in the universe could have a lot of water—but it could be hiding where telescopes can’t detect it, according to a […]

Radii and eccentricities of the comparison NEA sample. (A to C) Same as Fig. 1 but for the comparison sample of individual eccentricity measurements reported in the NEA database (27). All data points are individual measurements and have not been binned. Error bars indicate the 1 𝜎 uncertainties from previous studies as reported in the NEA database. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Status Report, Stellar Cartography

Super-Earths And Mini-Neptunes Follow Different Orbital Period-eccentricity Relations

by Keith CowingJune 19, 2026June 19, 2026

Many exoplanets have been observed with radius sizes between that of Earth and that of Neptune and are thus classified into two groups: super-earths (SEs) and mini-neptunes (MNs).

Diagram of the dominant chemical reaction pathways in our photochemical network.

Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Press Release, Water/Hycean Worlds & Oceanography

A Hycean Interpretation of K2-18b Supported by Photochemical Atmospheric Compositional

by Keith CowingMay 20, 2026May 20, 2026

The nature of the sub-Neptune K2-18b is debated between Hycean and mini-Neptune interpretations.

Transmission spectrum of TOI-1130b with the best-fit free chemistry, equilibrium chemistry and grid model overplotted (left) and comparison between retrieved abundances from the three model fits for TOI-1130b (right). The points shown on the right panel are the best fit mass fractions from the free retrieval. The H2O and CO2 posterior distributions shows a lower limit, where as the other molecules show gaussian distributions. Therefore H2O and CO2 data points are shown with upper arrows. The solid lines show chemical abundance profiles from equilibrium chemistry and the dashed lines show the chemical profiles from the self-consistent forward model grid. -- astro-ph.EP

Astrochemistry, Astrogeology, Biochemistry & Organic Chemistry, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Icy Worlds, Imaging & Spectroscopy, Status Report

JWST Unveils A High Mean Molecular Weight Atmosphere For Mini-Neptune TOI-1130b: Evidence For Formation Beyond The Water Ice Line

by Keith CowingMay 6, 2026May 6, 2026

We present the combined JWST/NIRSpec G395H and NIRISS SOSS transmission spectrum of a warm mini-Neptune, TOI-1130b (3.66 R⊕, 19.8 M⊕, Teq∼825 K). It is part of a rare and unique […]

The planetary odd couple of a mini-Neptune and hot Jupiter probably formed out beyond its star’s “frostline,” in the colder region of the system’s early protoplanetary disk. Credit Jose-Luis Olivares, MIT

Astrogeology, Astronomy & Telescopes, Exoplanets, -moons, -comets, Press Release

Astronomers Pin Down The Origins Of A Planetary Odd Couple

by Keith CowingMay 6, 2026May 6, 2026

Across the Milky Way galaxy, a planetary odd couple is circling a star some 190 light years from Earth. A normally “lonely” hot Jupiter is sharing space with a mini-Neptune, […]

Wind structures for the synchronous and 10:1 SOR simulations, reproduced from fig. 5 of Part I and included here for reference. Columns from left to right show the horizontal distribution of zonal wind, meridional wind, and vertical wind at 0.001 bar. Streamlines indicate the direction of the horizontal flow. Results are shown in the heliocentric frame to more clearly illustrate the wind patterns. Black star-shaped markers indicate the location of the substellar point. The first and second rows show results from the synchronous and 10:1 SOR simulations as examples, with the wind patterns in other simulations being similar. -- astro-ph.EP

Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Three-dimensional Transport-induced Chemistry On Temperate Sub-Neptune K2-18b, Part II: The Combined Effects Of Atmospheric Dynamics And Chemical Reactions

by Keith CowingApril 12, 2026April 12, 2026

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.

Astronomy & Telescopes, Exoplanets, -moons, -comets, Ice Giant, Icy Worlds, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

Elevated Eccentricities In The Radius Valley Hint At Water-Rich Mini-Neptunes

by Keith CowingMarch 2, 2026March 2, 2026

While recent planet-formation models broadly reproduce the observed population of super-Earths and mini-Neptunes, as well as the bimodal radius distribution (the “radius valley”), it remains unclear whether all these planets […]