POSEIDON’s documentation

POSEIDON is a Python package designed to rapidly retrieve atmospheric properties from exoplanet spectra. POSEIDON includes modelling capabilities to generate 1D, 2D, or 3D exoplanet transmission spectra (TRIDENT) alongside emission and/or reflection spectra for substellar atmospheres. For fitting observed spectra (‘atmospheric retrieval’), POSEIDON uses a nested sampling retrieval framework, via the sampling algorithm PyMultiNest, to explore the range of allowed atmospheric properties.

POSEIDON’s official features currently include:

  • Transmission spectra modelling and retrievals for 1D, 2D, and 3D exoplanet atmospheres.

  • Emission and reflection spectra, including scattering, for modelling and retrievals.

  • Rapid atmospheric retrievals that can run on your laptop.

  • Model planets ranging from ultra-hot Jupiters to temperate terrestrials.

  • Parametric prescriptions for stellar contamination, multidimensional clouds, and more.

  • High-resolution line-by-line models (\(R \sim 10^6\)) for cross correlation analyses.

  • Modelling and retrievals for brown dwarfs and directly imaged exoplanets.

  • High-resolution cross correlation retrievals for ground-based exoplanet datasets.

  • NEW: surface thermal emission and reflection retrievals for rocky planets.

POSEIDON contains an extensive range of tutorials covering forward models and retrievals for a wide variety of different applications.

New in POSEIDON v1.4:

  • Inclusion of surfaces with wavelength-dependent albedos for thermal emission and reflection spectra.

  • An extensive database of lab-measured surface albedos with detailed documentation.

  • New tutorials illustrating rocky planet thermal emission and reflection spectra for JWST and HWO.

  • New tutorial illustrating stellar contamination in transmission.

For a comprehensive list of new features, see the POSEIDON Release Notes on GitHub.

To use the new surface reflection features, you will need to re-download the POSEIDON input data. Please see the installation instructions.

New in POSEIDON v1.3:

  • High-resolution cross correlation retrievals for transmission and emission spectra.

  • New tutorials illustrating applications of cross correlations and high-resolution retrievals to WASP-121b and WASP-77 Ab.

New in POSEIDON v1.2:

  • Mie scattering aerosols for exoplanet forward models and retrievals.

  • An extensive database of pre-computed aerosol optical properties covering the full range of substellar atmospheres.

  • New opacity database with state-of-the-art molecular line lists.

  • Emission and reflection spectra, including scattering, for modelling and retrievals.

  • Many new tutorials.

New in POSEIDON v1.1:

  • Chemical equilibrium models and retrievals, demonstrated in two new tutorials.

  • JWST proposal tutorial (PandExo + retrieving simulated JWST data).

  • Bayesian model comparison demonstration in first retrieval tutorial.

  • Improved stellar contamination retrieval capabilities (e.g. spots + faculae).

Contributor Hall of Fame:

  • Ryan MacDonald (Lead Developer) — Ryan.MacDonald@st-andrews.ac.uk

  • Elijah Mullens (Aerosols, emission with scattering, and reflection spectra)

  • Ruizhe Wang (High-resolution cross correlation retrievals and equilibrium chemistry)

  • Charlotte Fairman (Contributor)

  • John Kappelmeier (Contributor)

  • Aiden Zelakiewicz (HWO reflection tutorial)

Installation:

Guide:

Code Documentation:

License:

POSEIDON is available under the BSD 3-Clause License. If you use POSEIDON, please cite MacDonald & Madhusudhan (2017) and MacDonald (2023). Guidance on specific papers to cite for individual features included within POSEIDON is provided on the page “What to Cite”.