POSEIDON Archives - Astrobiology

Analog Studies, Astronomy & Telescopes, Atmospheres, Climate, Weather, Exoplanets, -moons, -comets, Imaging & Spectroscopy, Press Release

Identifying Surface Degeneracies in Single-Visit Reflected Light Observations of Modern Earth using the Habitable Worlds Observatory

by Keith CowingMarch 31, 2026March 31, 2026

Characterizing the surface and atmosphere of Earth-like planets in reflected light is a key goal for upcoming direct imaging surveys.

Upper panel: the reduced IGRINS observation of WASP-77Ab. The flux at each phase is calibrated to the same level. The emission signal of WASP-77Ab is buried under the background and noise. Lower panel: Residual after removing the first 4 principal components. The residual should be a good representation of the signal. -- astro-ph.EP

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

Open Source High-Resolution Exoplanet Atmosphere Retrievals with POSEIDON

by Keith CowingMay 19, 2025May 19, 2025

High-resolution spectroscopy (R > 25,000) has opened new opportunities to characterize exoplanet atmospheres from the ground.

Contributions of molecules in the JWST MIRI range for the transmission spectrum of K2-18 b, assuming 1% CO2 and CH4, and 10−5 by volume for each of DMS, diethyl sulfide, methacrylonitrile, trans-2-pentene, 2-butene and propyne. -- astro-ph.EP

Astrochemistry, Astronomy & Telescopes, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report

A Systematic Search for Trace Molecules in Exoplanet K2-18 b

by Keith CowingMay 16, 2025May 16, 2025

The first transmission spectrum of the habitable-zone sub-Neptune K2-18 b with JWST has opened a new avenue for atmospheric characterisation of temperate low-mass exoplanets.

Differential transmission spectra of various superhabitable (SH) planet scenarios, as well as Kepler-62e and modern Earth around the Sun, calculated using the forward model code POSEIDON. Spectral features are displayed in parts per million (ppm) relative to each planet's baseline transit depth, enhancing the visibility of individual molecular signatures. Key absorption features of major atmospheric constituents, including O2 , O3 , CH4 , H2O, N2O, CO2 , CH3Cl, and CO, are indicated (see Table 3). Line descriptions are consistent with those in Figure 3. Solid gray lines represent SH planets receiving an incident stellar flux of 0.8 solar constants (S0 = 1366 W/m2 ), positioned between the inner edge and center of their respective host star’s habitable zone (HZ), while dashed lines represent SH planets at 0.6 S0 , aligned with the center of the HZ. -- astro-ph.EP

Astronomy & Telescopes, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report, Water/Hycean Worlds & Oceanography

Superhabitable Planets Around Mid-Type K Dwarf Stars Enhance Simulated JWST Observability and Surface Habitability

by Keith CowingJanuary 8, 2025January 8, 2025

In our search for life beyond the Solar System, certain planetary bodies may be more conducive to life than Earth. However, the observability of these `superhabitable’ planets in the habitable […]

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.

Schematic architecture of the POSEIDON atmospheric retrieval code. Users can call POSEIDON in two main ways: (i) to generate a model exoplanet spectrum for a specified planet atmosphere (green arrows); or (ii) to fit an observed exoplanet spectrum by statistical sampling of a model’s atmospheric properties (purple arrows). The diagram highlights code inputs (circles), algorithm steps (rectangles), and code outputs (bottom green or purple boxes). -- astro-ph.IM

Astrochemistry, Astronomy & Telescopes, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Exoplanets, -moons, -comets, Habitable Zones, Imaging & Spectroscopy, Status Report

POSEIDON: A Multidimensional Atmospheric Retrieval Code for Exoplanet Spectra

by Keith CowingOctober 29, 2024October 29, 2024

Spectroscopic observations of exoplanet atmospheres can reveal the chemical composition, temperature, cloud properties, and (potentially) the habitability of these distant worlds. The inference of such properties is generally enabled by […]