NEMESIS

NEMESIS (Non-linear Optimal Estimator for MultivariatE Spectral AnalySIS) is a general purpose radiative transfer and retrieval tool designed for analysing visible/infrared observations of any planetary atmosphere and was originated at the University of Oxford in 2003. Its chief developer is Patrick Irwin at Oxford University, but many others have contributed to it, including: Leigh Fletcher, Nick Teanby, Conor Nixon, Jo Barstow, Simon Calcutt, and many more.

Key points of NEMESIS:

• Originally developed for solar system studies (Cassini/CIRS observations of Jupiter, Saturn and Titan), but extended for primary transit, secondary eclipse and direct imaging of exoplanets/brown dwarfs.
• Designed from start to be generally applicable to any planetary atmosphere and originally designed for use with a correlated-k forward model.
• Now extended to model line-by-line spectra also.
• Handles thermal emission and scattering (multiple and single-scattering).
• Main code written in FORTRAN.
• Core retrieval code based on Optimal Estimation, but Nested Sampling implementation now available, using python wrapper around FORTRAN core.

NEMESIS is now managed via GitHub and is open-source and free to use. The code repository can be found here.