TOI-270 d Archives

The mid-infrared transmission spectrum of TOI-270 d obtained with the JWST MIRI LRS instrument and the JExoRES pipeline. The data points with error bars (in dark red) show the observed spectrum. The horizontal error bars correspond to the spectral bin width. The dark blue curve denotes the median retrieved spectral fit to this MIRI dataset using the canonical retrieval discussed in Section 3.2, while the two lighter shaded regions denote the 1σ and 2σ intervals. The yellow points denote the binned median model. -- astro-ph.EP

The Mid-Infrared Transmission Spectrum of the Temperate Sub-Neptune TOI-270 d

by Keith CowingJuly 8, 2026July 7, 2026

[astro-ph.EP] Observations of temperate sub-Neptunes with JWST have ushered in a new era for atmospheric characterization of small exoplanets.

Each panel shows the T(P) profiles for the clear atmosphere (red line) and cloudy atmosphere (blue line) computed for a sub-Neptune belonging to our sample of 8 sub-Neptunes. The phases of the interfaces for TOI-270 d and TOI-1231 b are shown in Figure 5, while those for the rest of the sub-Neptunes in our sample are shown here. Similar to Figure 5, the thicker lines depict the convective regions of the atmosphere. The locus of blue and red crosses show the P and T locations of the atmosphere-mantle interface computed by coupling our atmosphere model with the interior structure model for the cloudy and clear models, respectively. The P − T location and the T(P) profiles are overlaid on the phase–diagram for silicates, depicting its solid and molten phases as blue and red shaded regions. -- astro-ph.EP

Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Ice Giant, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

Impact of Clouds on the Atmosphere-Mantle Interface of Sub-Neptunes

by Keith CowingMay 29, 2026May 29, 2026

Sub-Neptunes are among the most common type of close-in planets found in our galaxy, yet their bulk composition remains largely uncertain; H-rich envelopes overlaying rocky cores, volatile-rich planets, and carbon-rich […]

Schematics of the MELTYQ coupled magma-atmosphere retrieval. The model is valid for sub-Neptune hosting a thick H2-rich atmosphere with enough surface temperature to melt rocks. The model splits the planet in three regions: a rocky core, a deep atmosphere, and an upper atmosphere. The chemistry is coupled allowing to retrieve the composition of the rocky magma via it’s influence on the observable atmosphere. -- astro-ph.EP

Astrogeology, Astronomy & Telescopes, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Lava / magma ocean / Volcanic Worlds, Status Report

Coupling Magma-ocean And Atmospheres In Spectral Retrievals Of Sub-Neptunes

by Keith CowingMay 14, 2026May 14, 2026

Recent high-precision atmospheric observations with JWST is enabling detailed characterization of sub-Neptune atmospheres and motivating efforts to understand and constrain their interiors.

Interior structure schematic for the interior composition of sub-Neptune models presented in this work. Color is an approximate indicator of temperature (specific values depend on the model). The envelope (∼5% by mass) is a mixture of hydrogen, helium, and heavy elements (Z) represented by either water (Section 3.1) or silicates (Sections 3.2, 3.3). The mantle composition is MgSiO3, and the core composition is Fe16Si. We maintain a 2:1 mass ratio between the core and the mantle. For this work, the EMB represents a steep compositional gradient and thus controls mantle cooling by transferring heat to the envelope via conduction. Since conductive flux alone is insufficient to transport the entire interior heat to the envelope, a steep temperature gradient forms at the EMB, as seen in all models in this work. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Status Report

Sub-Neptune Memories I: Implications of Inefficient Mantle Cooling and Silicate Rain

by Keith CowingJanuary 12, 2026January 12, 2026

We explore the evolution of sub-Neptune (radii between ∼1.5 and 4 R⊕) exoplanet interior structures using our upgraded planetary evolution code, APPLE, which self-consistently couples the thermal and compositional evolution […]

Illustration of the workflow for the construction of coupled interior-atmosphere models with ATHENAIA.

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

A Window For Water-hydrogen Demixing On Warm Metal-rich Sub-Neptunes

by Keith CowingDecember 3, 2025December 3, 2025

Sub-Neptunes represent the largest exoplanet demographic, yet their bulk compositions remain poorly understood.

Examples of interior scenarios consistent with the bulk properties of TOI-270 d, spanning different atmospheric temperature structures and water mass fractions. The thickness of the layers are not to scale. -- astro-ph.EP

Astrogeology, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Status Report, Water/Hycean Worlds & Oceanography

The Surface and Interior Conditions of Temperate Sub-Neptune TOI-270 d

by Keith CowingNovember 27, 2025November 27, 2025

Sub-Neptune planets, with no analogue in our solar system, provide a wealth of information about exoplanet diversity, formation & evolution, and habitability.

JWST transmission spectrum of TOI-270 d. Orange errorbars correspond to NIRISS observations, presented in this work, while dark red errorbars correspond to NIRSpec G395H observations presented by HM24. The NIRISS observations were binned down to R=25 for order 1 and R=12 for Order 2 for visual clarity. The blue curve denotes the median retrieved spectral fit obtained with our canonical retrieval, described in Section 3. Darker and lighter turquoise shaded regions denote the spectral 1- and 2-σ contours corresponding to the spectral fit. Yellow dots denote the median spectrum binned to the resolution of the datapoints. The NIRISS data are vertically offset by +28 ppm, which is the median offset retrieved for our canonical model. -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Exploration Gear & Tech, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

The Atmospheric Composition Of TOI-270 d

by Keith CowingNovember 22, 2025November 22, 2025

The first explorations of temperate sub-Neptune exoplanets have been the hallmark of early JWST observations.

Schematic of the modeling framework used in this study. Chemical equilibrium between the core, mantle and atmosphere is calculated using the model from H. E. Schlichting & E. D. Young (2022). Upper atmospheric temperature profiles are calculated using HELIOS (M. Malik et al. 2017). Fastchem cond (J. W. Stock et al. 2022) is used to find equilibrium chemical abundances throughout the upper atmosphere, accounting for rainout condensation. After iterating between HELIOS and Fastchem cond until convergence is reached, we account for photochemical processes and vertical mixing using Photochem (N. F. Wogan et al. 2023, 2025). -- astro-ph.EP

Lava / magma ocean / Volcanic Worlds, Status Report

Magma Ocean Interactions Can Explain JWST Observations Of The sub-Neptune TOI-270 d

by Keith CowingOctober 21, 2025October 21, 2025

Sub-Neptunes with substantial atmospheres may possess magma oceans in contact with the overlying gas, with chemical interactions between the atmosphere and magma playing an important role in shaping atmospheric composition.

Possible interior compositions of 55 Cnc e. Compositions consistent within the 1σ, 2σ, and 3σ M-R uncertainties are shown in orange, dark teal, and light teal, respectively. The red dashed and solid lines show xcarbon = 12 wt% and 24 wt%, respectively, the upper bounds of xcarbon assuming no volatile loss (E. A. Bergin et al. 2023). The blue curve shows interior solution from N. Madhusudhan et al. (2012), to the right of which are allowed values (1σ uncertainty). Ternary diagrams are shown for two radius assumptions: (a) visible radius, 2.04 ± 0.15 R⊕, and (b) gray radius, 2.20 ± 0.12 R⊕, following N. Madhusudhan et al. (2012). Our interior models with updated carbon and SiC EOSs are consistent with earlier studies. -- astro-ph.EP

Astrochemistry, Astrogeology, Biogeochemical Cycles & Geobiology, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Press Release

Carbon-rich Sub-Neptune Interiors Are Compatible With JWST Observations

by Keith CowingAugust 22, 2025

Many possible interior compositions exist for sub-Neptunes: ice-poor, ice-rich, and water-dominated interiors can all match the measured masses and radii.

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.

TOI-270 d

The Mid-Infrared Transmission Spectrum of the Temperate Sub-Neptune TOI-270 d

Impact of Clouds on the Atmosphere-Mantle Interface of Sub-Neptunes

Coupling Magma-ocean And Atmospheres In Spectral Retrievals Of Sub-Neptunes

Sub-Neptune Memories I: Implications of Inefficient Mantle Cooling and Silicate Rain

A Window For Water-hydrogen Demixing On Warm Metal-rich Sub-Neptunes

The Surface and Interior Conditions of Temperate Sub-Neptune TOI-270 d

The Atmospheric Composition Of TOI-270 d

Magma Ocean Interactions Can Explain JWST Observations Of The sub-Neptune TOI-270 d

Carbon-rich Sub-Neptune Interiors Are Compatible With JWST Observations

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

Roman Space Telescope: Enabling Images Of Distant Worlds

NASA Solar System Exploration Research Virtual Institute (SSERVI) Cooperative Agreement Notice (NNH26ZDA016C) Final Text And Due Dates

Interstellar Aromatic Infrared Bands: IR Absorption Spectroscopy Of The Lowest Triplet State Of Naphthalene

The Highly Unusual Behavior And Chemical Composition Of Interstellar Comet 2I/Borisov

Volatile Depletion In Rocky Planets As A Chemical Fingerprint Of Hybrid Accretion