sub-Neptune Archives

Predicted relative transit depth change from the equilibrium chemistry CO2-only model retrieved for CRIRES+ data (green). The model predictions are plotted in high-resolution in the wavelength region overlapping with the CRIRES+ measurements indicated by the grey shaded areas and in low-resolution for the rest of the wavelength range. Space-based measurements from HST (blue) and JWST (orange) are also shown. The 1σ and 1.5σ uncertainties of the model are indicated as darker and lighter green shaded areas, respectively. We also mark the lower 1.1σ uncertainty boundary with a dotted green line as a potential match to the amplitude of the CO2 bump in the JWST measurements at 4200 nm. The HST-WFC3 and JWST NIRSpec G359H measurements were taken from the online data provided by Schlawin et al. (2024) containing the HST data adapted from Kreidberg et al. (2014).-- astro-ph.EP

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

Cloudy With A Chance Of Metals: Indications Of CO2 In The Atmosphere Of GJ 1214 b From High-resolution K-band Spectroscopy

by Keith CowingApril 19, 2026April 19, 2026

Sub-Neptune exoplanets frequently exhibit muted transmission spectra, with GJ 1214 b being the most prominent example. Following years of intense observing campaigns yielding featureless planetary spectra, recent observations with JWST […]

2D color map as a function of Teq and [M/H]

Astrochemistry, Astrogeology, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Sub-Neptunes As Soot Factories: Deep Atmosphere Hydrocarbon Formation and Quenching as the Origin of Sub-Neptune Aerosol Trends

by Keith CowingApril 16, 2026June 10, 2026

Recent population-level studies of sub-Neptune atmospheres have identified a parabolic trend in transmission spectrum amplitude for planets with Teq ~ 500-800 K. While the trend has been commonly attributed to […]

Effect of water dissolution on planetary radius (adapted from Luo et al (2024)). All interiors share identical bulk composition but differ in model assumptions. Classical models separated volatiles and refractories, and ignored melts (A). Alternative models that include melts but neglected volatile dissolution overestimate planetary radii (B). The water dissolution in the mantle (C) or mantle and core (D) reduces them. Scenario (D) is considered most realistic for hot super-Earths with magma oceans. -- astro-ph.EP

Exoplanets, -moons, -comets, Ice Giant, Status Report, Stellar Cartography

Origin And Characterization Of Super-Earths And Sub-Neptunes

by Keith CowingApril 15, 2026April 15, 2026

Super-Earths and sub-Neptunes represent the most common class of exoplanets discovered to date in our galaxy, yet they have no direct analogues in the Solar System. Since 2014, researchers within […]

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.

Example full-resolution Ariel transmission spectrum of the hot-Saturn WASP-39 b simulated at Tier 2 precision (black error bars). The underlying atmosphere model assumes chemical equilibrium with a solar C/O ratio (0.54), 10× solar metallicity, and no clouds. The opacity contributions of individual species to the total spectrum are shown with different colours and represent the major chemical species with significant opacity in the Ariel wavelength range. The wavebands of Ariel’s instruments are labelled underneath the spectrum. -- astro-ph.EP

Ariel Mission, Astronomy & Telescopes, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Habitable Zones, Imaging & Spectroscopy, Status Report

On The Information Content of Ariel Transmission Spectra: Reassessing The Tier System

by Keith CowingApril 10, 2026April 10, 2026

The European Space Agency’s Ariel mission will conduct a survey of the atmospheric properties of exoplanets around bright stars.

Period-radius plot for planets in single-star (gray points) and binary-star (colored points) systems considered in this work. Colors correspond to log10(ρ), i.e. the projected physical binary separation in au. We restricted the sample to planets with 1 < P < 100 d and 0.5 < Rp < 4R⊕. The planets in binary-star systems have a similar distribution in period-radius space as the planets in single-star systems, although the relative occurrence rate of sub-Neptunes (2 < Rp < 4R⊕) is suppressed in small-separation binary-star systems (K. Sullivan et al. 2024). -- astro-ph.EP

Exoplanets, -moons, -comets, Status Report, Stellar Cartography

Planetary Architectures of Kepler Compact Multis with Binary Star Companions

by Keith CowingApril 6, 2026April 6, 2026

Planets in binary-star systems exhibit demographic differences compared to planets in single-star systems.

MIRI F1500W light curves of GJ 3473 b at secondary eclipse. The raw and binned data are shown in light grey and purple, respectively. The pink curves correspond to the median model predictions from the joint fit, while the brown data points depict the binned model. The model shown here corresponds to the G. Tovar Mendoza et al. (2022) flare model case, as described in Appendix C, used to model the flare-like feature during the second visit. The dotted vertical lines show the nominally masked region in the second visit. Compared to Figure 2, this figure displays the data without correcting for systematics. -- astro-ph.EP

Astronomy & Telescopes, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Status Report

Hot Rocks Survey V: Secondary Eclipse Photometry of GJ 3473 b with JWST/MIRI

by Keith CowingApril 3, 2026April 3, 2026

JWST is transforming our ability to characterise small exoplanets, from sub-Neptunes to rocky worlds. A key open question is whether highly irradiated rocky planets can retain atmospheres or are stripped […]

Transit spectrum of K2-18 b based on the detection with Kepler (Montet et al. 2015) and characterisation with HST/WFC (Benneke et al. 2017), Spitzer (Benneke et al. 2019), JWST/NIRISS &/NIRSpec (Madhusudhan et al. 2023; Schmidt et al. 2025) and JWST/MIRI (Madhusudhan et al. 2025; Liu et al. 2025). Different panels compare different pipelines for the NIRISS and NIRSpec analyses. -- astro-ph.EP

Astrochemistry, Astronomy & Telescopes, Atmospheres, Climate, Weather, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Icy Worlds, Imaging & Spectroscopy, Status Report

The Atmosphere Of K2-18 b: The Role Of Hazes, Clouds And Photoelectrons

by Keith CowingMarch 30, 2026March 30, 2026

The atmospheric characterisation of temperate exoplanets is becoming accessible with JWST, providing a critical connection between Solar System planets and the more commonly observed hot-Jupiters.

Radius-density diagram of confirmed exoplanets from the NASA Exoplanet Archive with radii below 5 R⊕ and mass and radius measurements significant at better than 4σ. The best-fit Gaussian mixture model, described in Section 6, is shown by the purple contours and has been rescaled for visibility. The model approximately recovers the loci of super-Earths (tan), sub-Neptunes (green), and Neptune-like planets (blue). A fourth component contains planets that do not belong to those main groups, including the mega-Earths (red), such as GJ 523b, and other high-density outliers (black). The observational mega-Earth class is indicated by the red arrows (Rp ≥ 2.1 R⊕, ρp ≥ 5.5 g cm−3). -- astro-ph.EP

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

GJ 523b Is A Massive, 170 Myr-old Mega-Earth, Likely On A Polar Orbit

by Keith CowingMarch 29, 2026March 29, 2026

We use WIYN/NEID radial velocity measurements to confirm the planetary nature and measure the mass of the TESS transiting exoplanet candidate around the mid-K dwarf GJ 523 (V=9.23, K=6.525).

The volume mixing ratios of key gases in the Hycean and sub-Neptune atmospheres, averaged across 0.1 – 10−5 bar to represent the expected abundances of photochemical products probed by transmission spectroscopy. CH4 and CO2 are prescribed manually at the lower boundary in the Hycean model, and the DMS distribution is also imposed for our consistency tests, as described in Sections 3.2.1 and 3.2.2. -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Ice Giant, Imaging & Spectroscopy, Status Report

Three Outstanding Physical Questions For K2-18 b And Other Temperate sub-Neptunes

by Keith CowingMarch 24, 2026June 11, 2026

Recent transmission spectra of the temperate sub-Neptune K2-18 b obtained with JWST have attracted significant attention. Debates have quickly arisen over the interpretation of the spectral data, particularly the recent […]

sub-Neptune

Cloudy With A Chance Of Metals: Indications Of CO2 In The Atmosphere Of GJ 1214 b From High-resolution K-band Spectroscopy

Sub-Neptunes As Soot Factories: Deep Atmosphere Hydrocarbon Formation and Quenching as the Origin of Sub-Neptune Aerosol Trends

Origin And Characterization Of Super-Earths And Sub-Neptunes

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

On The Information Content of Ariel Transmission Spectra: Reassessing The Tier System

Planetary Architectures of Kepler Compact Multis with Binary Star Companions

Hot Rocks Survey V: Secondary Eclipse Photometry of GJ 3473 b with JWST/MIRI

The Atmosphere Of K2-18 b: The Role Of Hazes, Clouds And Photoelectrons

GJ 523b Is A Massive, 170 Myr-old Mega-Earth, Likely On A Polar Orbit

Three Outstanding Physical Questions For K2-18 b And Other Temperate sub-Neptunes

Tricorder Tech: New Handheld Device Maps Chemical Composition Using Infrared Light

No Statistically Significant Evidence For A Correlation Between Stellar And planetary Composition

Water Planet Recon: How Accurately Can We Measure Earth Ocean’s Deepest Point?

Webb Reveals A Stunning Panorama Of Star Formation

Deep Learning of SHERLOC Raman Spectra For Facilitating Mars Astromaterial Identification