petitRADTRANS documentation

Welcome to the petitRADTRANS (pRT) documentation. pRT is a Python package for calculating transmission and emission spectra of exoplanets, at low (\(\lambda/\Delta\lambda=1000\)) and high (\(\lambda/\Delta\lambda=10^6\)) resolution, for clear and cloudy atmospheres.


In addition to transmission spectra, pRT now includes scattering also for emission spectra, if specifically turned on (note that scattering increases the runtime), see Scattering for Emission Spectra.

petitRADTRANS is available under the MIT License, and documented in Mollière et al. (2019), for the general code, and Mollière et al. (2020), Alei et al. (in prep.), for the scattering implementation. Please cite these papers if you make use of petitRADTRANS in your work.

This documentation webpage currently contains an installation guide, a tutorial, a first code documentation, and an implemented retrieval example for mock JWST emission and transmission spectra. Also, we give a tutorial on how to include opacities that may be missing from our database.


December 2020: stellar and planetary surface scattering added
pRT now includes the scattering of the incoming stellar flux for irradiated planets. Also a scattering surface for terrestrial planets has been added, see Scattering for Emission Spectra. The surface albedo and emissivity are both freely tunable parameters (as a function of wavelength). Surface scattering is treated to be isotropic (that is, assuming that the surface is Lambertian).
September 2020: self-scattering for emission spectra and chemical equilibrium interpolation now available
pRT now includes scattering also for emission spectra, if specifically turned on (note that scattering increases the runtime), see Scattering for Emission Spectra. Currently the self-scattering by the planetary atmosphere is included, which is appropriate for, for example, brown dwarf and directly imaged atmospheres. In addition, you can now download our chemical equilibrium interpolation package, which is documented in Interpolating chemical equilibrium abundances
September 2020: petitRADTRANS opacities available on the Exomol website
Opacity tables created specifically in the petitRADTRANS format are now available on the Exomol website, also see Chubb et al. (2020) for the accompanying paper. The opacities can be installed in petitRADTRANS in an easy plug-and-play fashion. Please see Section Adding opacities for more information.
September 2020: More high-temperature atom and ion opacities available
We have added more atom and ion opacities, bringing the total list to Al, AlII, AlIII, AlIV, AlV, AlVI, B, BII, BIII, Be, BeII, C, CII, CIII, CIV, Ca, CaII, Cr, Fe, FeII, K, KII, KIII, KIV, KV, KVI, Li, Mg, MgII, MgIII, MgIV, MgV, MgVI, N, NII, NIII, NIV, NV, Na, NaII, NaIII, NaIV, NaV, NaVI, Si, SiII, Ti, TiII, V, VII, Y
May 2019: high-temperature atom and ion opacities now available
We have added the opacities of Fe, Fe+, Mg, Mg+, Li, Ca, Ca+, Si, Si+, O, O+, Al, Al+, Ti, Ti+, V and V+, up to temperatures of 4000 K. As usual, if the atmospheric temperatures increase above 4000 K, petitRADTRANS will use the absorbers respective opacities at 4000 K. Please make sure to install the latest petitRADTRANS version to make use of the high-temperature points of the new opacity tables!


  • Paul Mollière
  • Eleonora Alei
  • Evert Nasedkin