NIRISS/SOSS Archives

Diagram of the dominant chemical reaction pathways in our photochemical network.

Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Press Release, Water/Hycean Worlds & Oceanography

A Hycean Interpretation of K2-18b Supported by Photochemical Atmospheric Compositional

by Keith CowingMay 20, 2026May 20, 2026

The nature of the sub-Neptune K2-18b is debated between Hycean and mini-Neptune interpretations.

Transmission spectrum of TOI-1130b with the best-fit free chemistry, equilibrium chemistry and grid model overplotted (left) and comparison between retrieved abundances from the three model fits for TOI-1130b (right). The points shown on the right panel are the best fit mass fractions from the free retrieval. The H2O and CO2 posterior distributions shows a lower limit, where as the other molecules show gaussian distributions. Therefore H2O and CO2 data points are shown with upper arrows. The solid lines show chemical abundance profiles from equilibrium chemistry and the dashed lines show the chemical profiles from the self-consistent forward model grid. -- astro-ph.EP

Astrochemistry, Astrogeology, Biochemistry & Organic Chemistry, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Icy Worlds, Imaging & Spectroscopy, Status Report

JWST Unveils A High Mean Molecular Weight Atmosphere For Mini-Neptune TOI-1130b: Evidence For Formation Beyond The Water Ice Line

by Keith CowingMay 6, 2026May 6, 2026

We present the combined JWST/NIRSpec G395H and NIRISS SOSS transmission spectrum of a warm mini-Neptune, TOI-1130b (3.66 R⊕, 19.8 M⊕, Teq∼825 K). It is part of a rare and unique […]

Comparison of the combined exoTEDRF + Eureka! transmission spectrum to Aurora retrievals (top) and various PLATON forward models (bottom). The best-fit retrieval model is shown in the top panel with the darkness of the shading indicating the 1- and 2-σ limits, and is re-plotted in the bottom panel for comparison against the other forward models. The middle panel shows the absorption cross-sections for key molecules, which demonstrates how the spectrum is a poor fit both for CH4 and CO2. The plotted forward models include different metallicity and C/O scenarios, as well as a water-rich composition, and the inclusion of disequilibrium SO2. Forward models incorporating equilibrium chemistry are shown with dashed lines. The ‘10× Solar + SO2’ model has 108 times the equilibrium SO2 abundance as its counterpart. Offsets have been applied to the forward models at 2.8 µm to account for the best-fit offset between the NIRISS/SOSS and NIRSpec/G395M data. -- astro-ph.EP

Astronomy & Telescopes, Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Icy Worlds, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

TOI-421 b: A Hot Sub-Neptune with a Haze-Free, Low Mean Molecular Weight Atmosphere

by Keith CowingJanuary 10, 2025January 10, 2025

Common features of sub-Neptunes atmospheres observed to date include signatures of aerosols at moderate equilibrium temperatures (~500-800 K), and a prevalence of high mean molecular weight atmospheres, perhaps indicating novel […]

The spectral decomposition of the Reference case retrieval of WASP-166b with the absorption contributions of the key atmospheric constituents shown. Spectra are plotted with resolution R = 100 for clarity. The combined forward model, shown as a heavy black line, is the median Reference retrieval result (see Table 5). The colored lines correspond to the individual opacity/absorption contributions (including Rayleigh scattering and collision absorption) of the various constituent molecules and clouds at specific wavelengths. (H2S is plotted but is not distinguishable from the bulk species line.) The transmission spectrum is dominated by contributions from H2O (15.2σ), and CO2 (14.7σ). The more subtle effects of NH3 (2.3σ) may be apparent at ∼ 2.3 µm, and possibly at ∼ 3.9 µm. The effects of the cloud deck (flat purple line at transit depth of ∼ 0.274 x10−2 ) are apparent in clipping the troughs of the water features from 0.85 to 1.7 µm -- astro-ph.EP

Astronomy & Telescopes, Exoplanets, -moons, -comets, Gas Giants, Imaging & Spectroscopy, Status Report

Detection of H2O and CO2 in the Atmosphere of the Hot Super-Neptune WASP-166b with JWST

by Keith CowingJanuary 3, 2025January 3, 2025

We characterize the atmosphere of the hot super-Neptune WASP-166b (P=5.44 d, Rp=6.9±0.3 R⊕, Mp=32.1±1.6 M⊕, Teq=1270±30 K) orbiting an F9V star using JWST transmission spectroscopy observations obtained with NIRISS SOSS […]

Comparison of nested POSEIDON Model B retrievals with and without H− and AlO, zooming on the 0.2 to 1.05 µm region. We display median retrieved spectra (solid lines) and 1σ confidence regions (shaded regions). Model B with both H− and AlO (blue) is the best fit model, but only due to imparting fine structure to fit the STIS slope. Future observations of the 0.2-0.8 µm region will provide more reliable inferences of metal species. -- astro-ph.EP

Astrochemistry, Astronomy & Telescopes, Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Gas Giants, Imaging & Spectroscopy, Status Report

JWST-TST DREAMS: A Precise Water Abundance for Hot Jupiter WASP-17b from the NIRISS SOSS Transmission Spectrum

by Keith CowingDecember 11, 2024December 11, 2024

Water has proven to be ubiquitously detected in near-infrared (NIR) transmission spectroscopy observations of hot Jupiter atmospheres, including WASP-17b.

Top panels: Results from the white light curve fit of the supreme-SPOON reduction for Visits 1 (left) and 2 (right), and fitted systematics models. The order 1 systematics-corrected light-curves are shown (teal points), binned for visual purposes, along with the best-fit transit model (black) and the systematics model including the GP component (red, with the GP scaled for visualization purposes). The vertical blue shaded regions indicate the three candidate flares with the highest signal-to-noise spectra and following typical flare evolution profiles (see Section C). Bottom panels: Spectroscopic light-curve fits to the two NIRISS/SOSS transits of GJ 9827 d from the supreme-SPOON reduction. The left panel corresponds to the first visit and the right panel to the second visit. We show the detrended broadband light-curve for order 2, and seven spectroscopic light-curves from order 1, from top to bottom. The best-fit astrophysical model is shown for each light-curve (black) and light-curves are offset relative to each other for clarity. -- astro-ph.EP

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

JWST/NIRISS Reveals The Water-rich Steam World Atmosphere of GJ 9827 d

by Keith CowingOctober 7, 2024October 7, 2024

With sizable volatile envelopes but smaller radii than the solar system ice giants, sub-Neptunes have been revealed as one of the most common types of planet in the galaxy.

Broadband and spectroscopic light-curve fits of the NIRISS/SOSS (left) and NIRSpec/G395H (right) transits of TOI-270 d. For both instruments, examples of 10 normalized and systematics-corrected light curves are shown (colored points) along with their best-fitting transit models (black lines) and labelled with the central wavelength of the spectroscopic channel. Broadband light-curve fits (white) are also shown at the top for Order 1 in the NIRISS/SOSS case, and for NRS1 in the NIRSpec/G395H case. For clarity, the spectroscopic light curves are plotted with a relative flux offset. For NIRSpec/G395H, light curves with wavelengths below 3.8 µm are from the NRS1 detector and the remaining from NRS2. For visual purposes, the light curves are also binned in time in groups of 10 (NIRISS/SOSS) and 20 (NIRSpec/G395H) data points, resulting in 3.6 minute bins. A full transit of planet b occurs at the start of the NIRSpec/G395H exposure, with both transits overlapping shortly as planet d starts transiting. All light curves are well-behaved, with no signs of spot-crossing events or Hα flares. -- astro-ph.EP

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

JWST Reveals CH4, CO2, and H2O in a Metal-rich Miscible Atmosphere on a Two-Earth-Radius Exoplanet

by Keith CowingMarch 7, 2024March 7, 2024

Even though sub-Neptunes likely represent the most common outcome of planet formation, their natures remain poorly understood.

Atmospheric and stellar retrieval results for HAT-P-18 b. Top: Retrieved model transmission spectra from our JWST/NIRISS spectra (black errors). For each of the three retrieval codes (Poseidon; purple, SCARLET; orange, and Aurora; blue), the median retrieved spectrum (solid lines) and 1 𝜎 confidence intervals (shaded contours) are shown. The most important model features required to explain HAT-P-18 b’s NIRISS transmission spectrum are annotated. All three codes adopt the one heterogeneity model for this comparison. Bottom: Posterior probability distributions corresponding to the retrieval model in the top panel. The top row shows retrieved atmospheric properties with constrained values, the middle row shows non-detected chemical species with abundance upper limits, and the bottom row shows the retrieved unocculted starspot properties. Each histogram is annotated with the retrieved median and ± 1 𝜎 confidence intervals from the Poseidon retrieval for reference (see Table 4 for the results from all three codes). -- astro-ph.SR

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

Near-Infrared Transmission Spectroscopy of HAT-P-18b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST

by Keith CowingOctober 24, 2023October 24, 2023

The JWST Early Release Observations (ERO) included a NIRISS/SOSS (0.6-2.8μm) transit of the ∼850K Saturn-mass exoplanet HAT-P-18b. Initial analysis of these data reported detections of water, escaping helium, and haze.

The full 0.6–2.8 µm NIRISS/SOSS spectrum of WASP-96 b from Radica et al. (submitted). The pixel level spectrum is shown in grey, as well as when binned to a resolution of R=500, 250, and 125 in purple, blue, and red respectively. -- astro-ph.EP

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

Awesome SOSS: Atmospheric Characterisation of WASP-96 b using the JWST Early Release Observations

by Keith CowingMay 31, 2023May 29, 2023

The newly operational JWST offers the potential to study the atmospheres of distant worlds with precision that has not been achieved before.

NIRISS/SOSS

A Hycean Interpretation of K2-18b Supported by Photochemical Atmospheric Compositional

JWST Unveils A High Mean Molecular Weight Atmosphere For Mini-Neptune TOI-1130b: Evidence For Formation Beyond The Water Ice Line

TOI-421 b: A Hot Sub-Neptune with a Haze-Free, Low Mean Molecular Weight Atmosphere

Detection of H2O and CO2 in the Atmosphere of the Hot Super-Neptune WASP-166b with JWST

JWST-TST DREAMS: A Precise Water Abundance for Hot Jupiter WASP-17b from the NIRISS SOSS Transmission Spectrum

JWST/NIRISS Reveals The Water-rich Steam World Atmosphere of GJ 9827 d

JWST Reveals CH4, CO2, and H2O in a Metal-rich Miscible Atmosphere on a Two-Earth-Radius Exoplanet

Near-Infrared Transmission Spectroscopy of HAT-P-18b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST

Awesome SOSS: Atmospheric Characterisation of WASP-96 b using the JWST Early Release Observations

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

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

Miraflores Butte On Mars

Ocean World Exploration: 2026 American Samoa ROV + Mapping Exploration

Development Of An Adaptive Optics Testbed At MPIA For The ELT/Planetary Camera And Spectrograph (PCS)