Pyrat Bay:

Python Radiative Transfer in a Bayesian framework

Build Status Documentation Status Latest Version conda License


Patricio Cubillos and contributors (see Contributors)




Space Research Institute (IWF)

Web Site:


Feb 19, 2023


Pyrat Bay is an efficient, user-friendly Python tool to compute radiative-transfer spectra, and fit exoplanet atmospheric properties. This package offers:

  • Transmission or emission spectra of exoplanet transit or eclipses, respectively.

  • Forward-model or retrieval calculations.

The radiative-transfer include opacity sources from:

  • Line-by-line molecular absorption

  • Collision-induced absorption

  • Rayleigh scattering absorption

  • Na and K alkali resonant lines

  • Gray and Mie (soon) aerosol opacities

Bayesian (MCMC) posterior sampling of atmospheric parameters:

  • Molecular abundances

  • Temperature profile

  • Pressure-radius

  • Rayleigh and cloud properties



Be Kind

If you found Pyrat Bay useful for your research, please cite this article:

Cubillos & Blecic (2021): The Pyrat Bay Framework for Exoplanet Atmospheric Modeling: A Population Study of Hubble/WFC3 Transmission Spectra, MNRAS, 505, 2675.

Please prefer to channel your feedback or inquiries through the Github issue tracker:, or alternatively through this email: patricio.cubillos[at]

Pyrat Bay is open-source software under the GNU GPL v2 license (see License) and is compatible with Python>=3.6.