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


Jul 16, 2021


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.