Illustration of atmosphere–mantle–core coupling across rocky embryos to gas-rich planets. Mantle convection acts as a planetary-scale “conveyor belt,” facilitating chemical communication between the atmosphere and the core. The efficiency of this volatile cycling—potentially probed by the He 1083 nm feature, especially when combined with H Lyman-α—depends on the partition coefficients derived in this study. It governs the redistribution of H and He, the timescale of primordial atmosphere retention, aspects of redox balance in secondary atmospheres, and model predictions for the abundances of atmospheric CHNOPS species, ultimately shaping the H-to-He ratio in the atmospheres of Earth- to Neptune-like planets. -- physics.ao-ph

Astrochemistry, Astrogeology, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Ice Giant, Icy Worlds, Neptune, Status Report, Water/Hycean Worlds & Oceanography

The Fate of Hydrogen and Helium: From Planetary Embryos to Earth- and Neptune-like Worlds

by Keith CowingNovember 3, 2025November 3, 2025

Hydrogen, helium, silicates, and iron are key building blocks of rocky and gas-rich planets, yet their chemical interactions remain poorly constrained.

The four giant planets as seen by Hubble WFC3/UVIS at different near-UV wavelengths, and processed by Judy Schmidt (note - these images are not shown to scale). The Jupiter and Saturn images are constructed from F343N (red), F275W (green), and F225 (blue), whereas a lack of observations for Uranus and Neptune required us to shift to redder wavelengths: F547M (red), F467M (green), and F336W (blue) for the Ice Giants. Jupiter and Ganymede were observed 2017-02-02 at 12:16UT, Saturn was observed at 2018-06-07 at 00:06UT, Uranus on 2015-08-30 at 10:08UT, and Neptune on 2015-09-02 at 07:58UT. Strong UV absorption is visible at the poles of Jupiter and Saturn due to the nature of highaltitude aerosols and the potential link to auroral chemistry. Red vortices, such as Jupiter’s Great Red Spot and Oval BA (lower left), appear dark due to the blue-absorbing chromophore responsible for their red colours. Uranus’ bright north polar cap of aerosols, and its narrow rings, are just visible in this image. Neptune’s banding, and some bright high clouds (appearing in pink) can be seen in both northern and southern hemispheres. In addition, Saturn’s rings appear reddish due to UV absorption. Credit: NASA/ESA/CSA/Hubble/Judy Schmidt.

Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Gas Giants, Ice Giant, Imaging & Spectroscopy, Jupiter, Neptune, Saturn, Status Report, Uranus

Exploring Giant Planet Atmospheres with Habitable Worlds Observatory

by Keith CowingOctober 22, 2025October 22, 2025

Visible and ultraviolet imaging and spectroscopy of Solar System giant planets can set the paradigm for the atmospheric, ionospheric, and magnetospheric processes shaping the diversity of giant exoplanets, brown dwarfs, […]

Radius evolution for a metal-enriched planet (Z=0.1) as computed with our approach (square points) versus the planetsynth models of M¨uller & Helled (2021) (solid curves; note that they employ a different EOS than us). Red and blue curves correspond to 300 and 32 M⊕ planets (with 10 M⊕ cores), respectively, at an equilibrium temperature 288 K. The giant planet’s cooling curve is in excellent agreement between the two approaches. Lower mass planets however exhibit ∼15% radius discrepancies, possibly due to EOS differences. -- astro-ph.EP

Astrogeology, Exoplanets, -moons, -comets, Ice Giant, Neptune, Status Report

Coupled Planetary Interior and Tidal Evolution

by Keith CowingOctober 10, 2025

We present a new planetary structure/thermal evolution model, designed for use in problems that couple orbital dynamics with planetary structure.

Reprocessed images of Uranus [L]] and Neptune [R] NASA/JPL-Caltech (Uranus and Neptune); “Modelling the Seasonal Cycle of Uranus’s Colour and Magnitude, and Comparison with Neptune,” by Patrick G. J. Irwin et al., in Monthly Notices of the Royal Astronomical Society, Vol. 527, No. 4; February 2024 (reprocessed images)

Astrogeology, Exoplanets, -moons, -comets, Ice Giant, Icy Worlds, Neptune, Status Report, Uranus

Icy or Rocky? Convective Or Stable? New Interior Models Of Uranus and Neptune

by Keith CowingOctober 3, 2025October 3, 2025

We present a new framework for constructing agnostic and yet physical models for planetary interiors and apply it to Uranus and Neptune.

Two representative interior models for Uranus and Neptune with four layers: 1) hydrogen and helium, 2) H2O and hydrogen, 3) carbon-nitrogen-hydrogen mixture and 4) the rocky core composed of iron and rock. m specifies the fractional layer masses. The temperatures for B and C type models are printed without and with parenthesis. The dashed lines in the second layer mark the conditions for the transition from liquid to superionic in pure H2O. -- astro-ph.EP

Exoplanets, -moons, -comets, Ice Giant, Icy Worlds, Neptune, Status Report, Uranus

Ab Initio Entropy Calculations of Water Predict the Interiors of Uranus and Neptune to be 15-30% Colder than Previous Models

by Keith CowingAugust 29, 2025August 29, 2025

Ab initio free energy calculations are employed to derive the entropy of liquid and superionic water over a wide range of conditions in the interiors of Uranus and Neptune. The […]

Potential interior structures of Uranus, Neptune, K2-18 b and TOI-270 d if they have undergone hydrogen-water demixing. We note that alternatives models are also possible (see Secs. 3 and 4). For Uranus and Neptune, the sketches correspond to the cases with Toffset = 1100 K, in which both planets are fully demixed. However, we can’t exclude scenarios in which demixing is still ongoing or does not occur at all. The sketch for K2-18 b shows a mini-Neptune scenario with ongoing demixing, while the one for TOI-270 d corresponds to a case of full demixing. -- astro-ph.EP

Ariel Mission, Astrochemistry, Astrogeology, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Ice Giant, Icy Worlds, Neptune, Status Report, Uranus

The Possibility of Hydrogen-Water Demixing in Uranus, Neptune, K2-18b and TOI-270d

by Keith CowingJuly 13, 2025July 13, 2025

The internal structures of Uranus and Neptune remain unknown. In addition, sub-Neptunes are now thought to be the most common type of exoplanets.

Astrogeology, Atmospheres, Climate, Weather, Ice Giant, Icy Worlds, Imaging & Spectroscopy, Neptune, Status Report, Uranus

Different Inhomogeneous Evolutionary Histories for Uranus and Neptune

by Keith CowingJune 19, 2025

We present updated non-adiabatic and inhomogeneous evolution models for Uranus and Neptune, employing an interior composition of methane, ammonia, water, and rocks.

Binary collision-induced H2–He absorption coefficient, α, normalized by the hydrogen and helium gas densities, as function of frequency in the fundamental band, at 296 K. The parato-ortho distribution, is representative of equilibrium H2, just as in Fig. 2. Our model (“this work”), is compared with the model of Abel et al.17 for T = 300K, and with the laboratory measurements of Vitali et al. 18 and Brodbeck et al.19 , both of which were made near 296 K. We note that neither our model nor that of Abel et al. considered the discrete, intercollisional interference dips present in the laboratory spectra. -- astro-ph.EP

Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Gas Giants, Ice Giant, Jupiter, Neptune, Saturn, Status Report, Uranus

Improved H2-He and H2-H2 Collision-Induced Absorption Models and Application to Outer-Planet Atmospheres

by Keith CowingJune 15, 2025June 13, 2025

Using state-of-the-art ab initio interaction-induced dipole and potential-energy surfaces for hydrogen-helium (H2-He) pairs, we compute the rototranslational collision-induced absorption coefficient at 40-400 K for frequencies covering 0-4000 cm-1.

Sketches of the two end-members of possible bulk compositions of Uranus and Neptune: a water-dominated interior (left) and a rock-dominated interior (right). The dark brown at the planetary center represents the core, which is expected to be composed of iron and rocks. The atmosphere is represented with gray. Note that the transition between different layers may be fuzzy and that currently it is still unknown whether the planetary interiors are differentiated with distinct compositional layers. Keck Institute for Space Studies / Chuck Carter

Astrochemistry, Atmospheres, Climate, Weather, Exploration Gear & Tech, Gas Giants, Icy Worlds, Neptune, Status Report, Uranus

Ice Giants

by Keith CowingApril 29, 2025April 29, 2025

Uranus and Neptune, the so-called “ice giants”, represent a fascinating class of planets. They are the outermost planets in the solar system with intermediate masses/sizes, complex non-polar magnetic fields, strong […]

An SwRI-led study modeled the chemistry of TOI-270 d, a nearby exoplanet between Earth and Neptune in size, finding evidence that it is a giant rocky world (super-Earth) surrounded by a deep, hot atmosphere. - SwRI

Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Habitable Zones, Neptune, Press Release, Water/Hycean Worlds & Oceanography

Deciphering The Mysterious Atmosphere Of ‘Rosetta Stone’ Exoplanet TOI-270 d

by Keith CowingApril 15, 2025April 15, 2025

A Southwest Research Institute-led study modeled the chemistry of TOI-270 d, an exoplanet between Earth and Neptune in size, finding evidence that it could be a giant rocky planet shrouded […]

Neptune

The Fate of Hydrogen and Helium: From Planetary Embryos to Earth- and Neptune-like Worlds

Exploring Giant Planet Atmospheres with Habitable Worlds Observatory

Coupled Planetary Interior and Tidal Evolution

Icy or Rocky? Convective Or Stable? New Interior Models Of Uranus and Neptune

Ab Initio Entropy Calculations of Water Predict the Interiors of Uranus and Neptune to be 15-30% Colder than Previous Models

The Possibility of Hydrogen-Water Demixing in Uranus, Neptune, K2-18b and TOI-270d

Different Inhomogeneous Evolutionary Histories for Uranus and Neptune

Improved H2-He and H2-H2 Collision-Induced Absorption Models and Application to Outer-Planet Atmospheres

Ice Giants

Deciphering The Mysterious Atmosphere Of ‘Rosetta Stone’ Exoplanet TOI-270 d

NASA Establishes Mars Forward Operational Risk and Contamination Evaluation (M-FORCE) Tiger Team to Shape Mars Planetary Protection Protocols

Opportunity to Contribute to NASA DARES Community White Paper on Phototrophic Biosignatures

The Search For Life Elsewhere: Avoiding Hype and Fostering Public Understanding

Panchromatic Spectra of Nearby Low-mass and Sun-like Stars with Directly Imageable Habitable Zones

Alfred: A Flexible, User-Friendly Python Package for Exoplanet Confirmation

Interdisciplinary Origin of Life Meeting for Early Career Researchers (IOoL2026)

Europlanet Early-Career (EPEC) Committee Meeting

The Science of Star Trek: Strange New Worlds

Women of Astrobiology: Intelligence on and off Earth with Dr. Lori Marino

Astrobiology Graduate Conference (AbGradCon) 2026