ice giant Archives - Astrobiology

Models for Neptune and Uranus derived in this study expressed as density versus radius. Contour colors show density. Key elements of the models are labelled. The bright narrow band at the base of the envelope in each case is the boundary region stable against convection, ∼ 120 km and ∼ 180 km wide in the cases of Neptune and Uranus, respectively. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Ice Giant, Lava / magma ocean / Volcanic Worlds, Neptune, Status Report, Uranus, Water/Hycean Worlds & Oceanography

Ice Giants Revisited: Uranus And Neptune As Magma Ocean Worlds

by Keith CowingJune 18, 2026June 18, 2026

Uranus and Neptune are commonly interpreted as volatile-rich “ice giants”, an assumption that underpins most interior models.

Recovery of an injected signal for the cloud-free case of V1298 Tau b on a vrest − KP grid for each synthetic night simulated using Ratri for the case of (top row) the optimistic detrending scenario and (bottom row) the non-reprocessing scenario where the SVD+MLR based detrending is followed by cross-correlation with a template model with no reprocessing performed on it. The injected signal is successfully detected in all three nights for the optimistic detrending scenario. For the non-reprocessing scenario, the injected signal is successfully detected only in Night 3 but with weaker constraints on KP compared to the optimistic detrending case. For the other two nights, the signal is either completely removed by the detrending scenario resulting in a non-detection (Night 1) or a detection at a much higher value of KP compared to the injected value (Night2). For more discussion about confidence intervals and what constitutes a detection, please see Section 2.4.3. -- astro-ph.EP

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

Probing The Atmospheres Of Young Long-Period Sub-Neptune Progenitors With ELT/ANDES

by Keith CowingMarch 1, 2026March 1, 2026

High-resolution cross-correlation spectroscopy (HRCCS) has emerged as a powerful technique for detecting and characterizing exoplanet atmospheres from the ground.

Artist’s impression of four orbiting exoplanets. Intense radiation from the host star may be heating their puffy atmospheres, causing atmospheric escape into space. (Credit: Astrobiology Center)

Astronomy & Telescopes, Exoplanets, -moons, -comets, Ice Giant, Icy Worlds, Imaging & Spectroscopy, Press Release, Stellar Cartography, Water/Hycean Worlds & Oceanography

Astronomers Find Missing Link To Our Galaxy’s Most Common Planets

by Keith CowingJanuary 8, 2026January 8, 2026

One of the biggest recent surprises in astronomy is the discovery that most stars like the Sun harbor a planet between the size of Earth and Neptune within the orbit […]

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.

Uranus Flagship Workshop -- astro-ph.IM

Ariel, Ice Giant, Icy Worlds, Miranda, Missions & Hardware, Oberon, Press Release, Titania, Umbriel, Uranus

The Uranus Flagship: Investigating New Paradigms for Outer Solar System Exploration Workshop Summary Report

by Keith CowingSeptember 2, 2025September 2, 2025

This white paper is a summary of the Uranus Flagship Workshop that took place 21 to 23 May 2024 at NASA’s Goddard Space Flight Center. Co-led by Goddard and Johns […]

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.

Envelope H2O mass fraction as a function of semi-major axis. The same dataset as in Figure 1 is shown. The left panel shows planets that predominantly formed inside the water ice line; the right panel shows those that formed outside. Classification is based on the accreted H2O mass fraction, with a threshold set at 5% of the total planetary mass. The colorbar indicates the molar bulk C/O ratio. Planets formed inside the ice line are systematically depleted in carbon due to the lack of volatile ice accretion and exhibit higher envelope H2O mass fractions. In contrast, planets formed beyond the ice line retain lower H2O content despite higher bulk volatile abundances. Each pie chart shows the mean mass fraction of hydrogen in H2 (gas), H (metal), H2 (silicate), H2O (gas), and H2O (silicate), normalized to the total mean hydrogen inventory for each population. Only components contributing more than 5% are labeled. Planets that formed beyond the ice line store most hydrogen as H2 (gas) and H (metal), while those that formed inside the ice line retain a larger share of hydrogen in H (metal) H2 (silicate) and H2O (gas + silicate). -- astro-ph.EP

Astrochemistry, Astrogeology, Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Ice Giant, Icy Worlds, Status Report, Water/Hycean Worlds & Oceanography

Sub-Neptunes Are Drier Than They Seem: Rethinking the Origins of Water-Rich Worlds

by Keith CowingJuly 3, 2025July 3, 2025

Recent claims of biosignature gases in sub-Neptune atmospheres have renewed interest in water-rich sub-Neptunes with surface oceans, often referred to as Hycean planets.

Planetary growth timescales in an irradiated disc

Exoplanets, -moons, -comets, Gas Giants, Ice Giant, Icy Worlds, Status Report

Super-Earth Formation In Systems With Cold Giants

by Keith CowingJune 29, 2025June 28, 2025

Around our Sun, terrestrial planets did not grow beyond Earth in mass, while super-Earths are found to orbit approximately every other solar-like star.

Mass-Radius plot of asteroids, moons, planets, brown dwarfs and low-mass stars. From nearly 5600 exoplanets listed in the PHL-HWC database, 1504 are categorized as terrestrial worlds (orange dots), 2609 as Neptunian worlds (green dots), 1355 as Jovian worlds (purple dots), and 115 as brown dwarfs (brown dots). -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Brown Dwarfs, Exoplanets, -moons, -comets, Gas Giants, Ice Giant, Nomenclature, Systematics, Natural History, Status Report

(Re)-Defining Planets — the Fundamental Plane of Planets

by Keith CowingJune 23, 2025June 23, 2025

6000+ exoplanets are now detected using various techniques, with estimates of billions of planets existing in our Galaxy alone.