JWST Archives

Images in the JWST/MIRI F560W, F1000W and F1500W filters (central wavelength ≈ 5.6, 10 and 15 𝜇m) of candidates D (first row) and E (second row). White stars mark the Gaia positions of the M dwarfs, which in both cases are seen to be located ≈ 1 arcsec from the centres of background galaxies. -- [astro-ph.GA]

Project Hephaistos — IV. James Webb Space Telescope Observations of Two Dyson Sphere Candidates

by Keith CowingJuly 14, 2026July 14, 2026

[astro-ph.GA] We report on JWST/MIRI imaging and spectroscopy of two M-dwarf stars previously singled out by project Hephaistos as potential Dyson-sphere candidates (their candidates D and E) due to the […]

Cartoon illustrating the effect of the runaway greenhouse transition on atmospheric composition for two rocky planets with identical He, H2O and CO2 inventories. With a thin He atmosphere, planets below the runaway greenhouse limit (right) will have He-rich upper atmospheres and may support surface liquid water. For planets inside the inner edge of the habitable zone (left), H2O from liquid water oceans and CO2 from carbonates are transported into the atmosphere, dramatically decreasing the scale height and making the transit spectrum of the planet flatter. -- [astro-ph.EP]

Exoplanets, -moons, -comets

Climates Of Temperate Rocky Planets With He-dominated Atmospheres

by Keith CowingJuly 12, 2026July 12, 2026

[astro-ph.EP] We present radiative-convective modeling of rocky exoplanets with He-dominated atmospheres and low envelope mass fractions. Helium has a steeper adiabatic temperature profile than N2 and H2 as it has […]

Best-fitting spectrum and atmospheric properties of WD 1856 b. a. Spectral decomposition illustrating the model components required to explain WD 1856 b’s JWST transmission spectrum (FIREFLy reduction; orange circles with 1 σ error bars). The best-fitting model (black curve) contains absorption from multiple CH4 features (purple shading), H2 + He continuum absorption (dark grey shading), and tentative evidence of C2H6 near 3.4 µm (brown shading) and PH3 near 4.3 µm (orange shading). Aerosol continuum opacity (silver shading) blocks thermal emission from the deep atmosphere in windows between CH4 bands, obscuring the ‘negative spikes’ that would otherwise be observed near 0.7 µm, 2.9 µm, and longwards of 4.0 µm for a clear atmosphere. The best-fitting model without nightside thermal emission (blue dashed curve) cannot explain the significantly lower transit depths longwards of 3.5 µm. b. Retrieved atmospheric properties, planetary mass, and aerosol properties from WD 1856 b’s JWST transmission spectrum for the FIREFLy (orange histograms) and Juniper (green histograms) data reductions. The median (solid line) and 1 σ credible intervals for each parameter (dashed lines) are overlaid. c. Residuals between the data and best-fitting model. -- [astro-ph.EP]

Atmospheres, Climate, Weather

Aerosols And Hydrocarbons In The Atmosphere Of A White Dwarf Planet

by Keith CowingJuly 12, 2026July 12, 2026

[astro-ph.EP] Most stars, including our Sun, will one day evolve into red giants and, subsequently, white dwarfs. Several planet candidates have recently been identified orbiting white dwarfs, demonstrating that planets […]

Geometry of the LTT 3780 planetary system at the time of our radio technosignature observations. The left panel shows the sky-plane (X–Y) view as seen from Earth, while the right panel shows the top-down (X–Z) view of the system. The orbits of planets b (blue) and c (green) are shown relative to the host star (yellow). Our observations from the ATA, mentioned in Table 1 on 5th November 2025, were timed to coincide with a planet–planet occultation (PPO), when planet b passes behind planet c along the line of sight, providing a unique configuration to search for radio technosignatures during mutual planetary alignment.-- [astro-ph.IM]

SETI & Technosignatures

A Search For Narrowband Technosignatures From LTT 3780 With The Allen Telescope Array And The Karl G. Jansky Very Large Array

by Keith CowingJuly 9, 2026July 9, 2026

[astro-ph.IM] The LTT3780 system hosts two known exoplanets-LTT3780b, a rocky super-Earth, and LTT3780c, a temperate sub-Neptune-orbiting a nearby M dwarf on opposite sides of the radius valley. LTT3780c has been […]

Artist’s concept of a bare rocky planet orbiting a red dwarf star. Artwork: NASA, ESA, CSA, Dani Player (STScI) larger image

Exoplanets, -moons, -comets

First Completed Rocky Worlds Program Observations Open New Era in Exoplanet Studies

by Keith CowingJuly 9, 2026July 9, 2026

[STScI] Scientists leading the astronomy community’s most ambitious effort to study rocky planets outside of our solar system have reached a major milestone.

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

Exoplanets, -moons, -comets

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.

Carbon ion chemistry network. The red arrows indicate endoergic reactions, which proceed rapidly at high T or in regions with significant FUV-pumped H∗ 2 . We also show possible reactions (dashed) involving Polyaromatic Hydrocarbon (PAH) and Hydrogenated Amorphous Carbon (HAC) grains, which may be relevant in certain conditions. The figure is adapted from Goicoechea et al. (2025a). -- astro-ph.GA

Astrochemistry

Searching For The Elusive CH2+ With The James Webb Space Telescope. Another Carbocation To Constrain Astrochemical Networks

by Keith CowingJuly 7, 2026July 7, 2026

[astro-ph.GA] Carbocations are key species in interstellar chemistry, providing entry points for building larger hydrocarbons. CH+, and more recently, CH3+, have been detected. Other carbocations await detection to provide a […]

Exoplanets, -moons, -comets

Photochemical Production of CS2 in Temperate-to-Warm Gas Giant Exoplanet Atmospheres

by Keith CowingJuly 7, 2026July 7, 2026

[astro-ph.EP] Sulfur chemistry has emerged as an important probe of exoplanet atmospheres in the JWST era, although observational constraints have thus far been largely limited to SO2 and H2S in […]

Integrated MIRI-MRS spectrum of HK Tau A (top) and B (bottom) in grey, with the black line representing the continuum baseline. In the top panel, the insets zoom into wavelength regions where molecular emission from 12CO, H2O, 12CO2 , and H2 is visible. In the bottom panel, the shaded bands in the indicate the main ices absorption regions. H2 rotational lines are marked with blue ticks, and gas emission features are labelled where present. -- astro-ph.EP

Astrochemistry

MINDS: Complementary Inclinations In The Binary Ssystem HK Tau Reveal Gas- And Ice-phase Chemistry

by Keith CowingJuly 7, 2026July 7, 2026

[astro-ph.EP] HK Tau is a roughly equal mass pre-main sequence binary system consisting of a low-inclination primary (57 deg) and an edge-on (83 deg) secondary. We present JWST/MIRI observations targeting […]

The transmission spectrum of TOI-1231 b. The observed JWST spectrum and retrieved model fits are shown for the fiducial retrieval using the JexoPipe data, considering the six prominent CNO molecules, with a single offset and no stellar heterogeneity, as discussed in Section 3. For visual clarity, the data shown here have been binned to R∼50. A retrieved offset of 79.38 ppm has been added to the NIRSpec data. The dark blue line indicates the median retrieved spectrum, with the shaded regions indicating the 1σ and 2σ uncertainties. The yellow points show the median retrieved spectrum binned at the same resolution as the plotted data. -- astro-ph.EP

Exoplanets, -moons, -comets

Transmission Spectrum of the Benchmark Temperate Exo-Neptune TOI-1231 b

by Keith CowingJuly 7, 2026July 7, 2026

[astro-ph.EP] The JWST is revolutionizing our understanding of the temperate sub-Neptune population through atmospheric spectroscopy.

JWST

Project Hephaistos — IV. James Webb Space Telescope Observations of Two Dyson Sphere Candidates

Climates Of Temperate Rocky Planets With He-dominated Atmospheres

Aerosols And Hydrocarbons In The Atmosphere Of A White Dwarf Planet

A Search For Narrowband Technosignatures From LTT 3780 With The Allen Telescope Array And The Karl G. Jansky Very Large Array

First Completed Rocky Worlds Program Observations Open New Era in Exoplanet Studies

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

Searching For The Elusive CH2+ With The James Webb Space Telescope. Another Carbocation To Constrain Astrochemical Networks

Photochemical Production of CS2 in Temperate-to-Warm Gas Giant Exoplanet Atmospheres

MINDS: Complementary Inclinations In The Binary Ssystem HK Tau Reveal Gas- And Ice-phase Chemistry

Transmission Spectrum of the Benchmark Temperate Exo-Neptune TOI-1231 b

A Mars Impact Crater Surrounded By Chunks Of Water Ice

Gaia DR3 Limits on Stellar Engine Technosignatures in Nearby Stars

Catalytic Formation of H2 On Carbonaceous Dust Grains – Implications For Interstellar Observations

A High-Resolution Spectroscopic Survey of Directly Imaged Companion Hosts: III. Characterization of the Cold Imaged Planet Hosts AF Lep A and ε Indi A

The Viability of Life in Helium-Dominated Exoplanet Atmospheres