NEMESIS is a general-purpose radiative transfer and retrieval code, written in FORTRAN, designed to be applicable
to any planetary atmosphere (solar system and exoplanets) and can handle a wide range of
observation geometries.
The NEMESIS code actually has three components, the NEMESIS FORTRAN retrieval tool itself,
the more general FORTRAN radiative transfer code, RADTRAN, from which it was developed, and the ArchNEMESIS
Python code, derived from NEMESIS.
The Nemesis project is a collaborative effort and is continually being developed and extended. It is
managed with Github and the repository for the FORTRAN code can be found here.
Scientists interested in running either NEMESIS, RADTRAN or ArchNEMESIS to analyse their
data are very welcome to contact us.
NEMESIS
NEMESIS (Non-linear optimal Estimator for MultivariatE spectral
analySIS) is the general purpose correlated-k/LBL retrieval code developed from the
RADTRAN project. The original version, developed in 2003 and used for analysing Cassini/CIRS observations of
Jupiter, Saturn and Titan, was based on the correlated-k approximation. However, NEMESIS now also now works in
line-by-line (LBL) mode, and there is also new mode that uses pre-calculate line-by-line look-up tables.
NEMESIS has been designed to be generally applicable to any planet and with
any observing mode and so is suitable for both solar-system studies and also exoplanetary studies.
The reference NEMESIS paper is "The NEMESIS planetary atmosphere radiative transfer and retrieval tool",
J. Quant. Spectrosc. and Rad. Trans., 109, 1136-1150, 2008. (DOI: 10.1016/j.jqsrt.2007.11.006):
the accepted manuscript of this paper is here. For
more details please see our Manuals page.
RADTRAN
RADTRAN is a general purpose FORTRAN planetary radiative transfer model for computing
the transmission of atmospheric paths and/or the radiances emitted by
planetary atmospheres. The code is general purpose and not hard-wired to any
specific planet. RADTRAN evolved from Genlbl, which was a general purpose
planetary line-by-line model, developed by Dr Simon Calcutt. RADTRAN extended
the functionality of this program to also allow the computation of planetary
spectra using both band model approximations and also the correlated-k
approximation. The code has also been extended to incorporate both multiple
scattering and single scattering calculations. For
more details please see our Manuals page.
ArchNEMESIS
The functionality of NEMESIS has now been reproduced in a Python package as
ArchNEMESIS. It can be
installed via PyPI.
Team NEMESIS
Originated in Oxford in 2003, NEMESIS has since grown and become used by many groups around the world.
Many individuals have contributed to the development of NEMESIS, including:
Patrick Irwin
Patrick Irwin is a Professor of Planetary Physics at the University of Oxford and is the lead developer of
NEMESIS, developing the original version in 2003. He works in the fields of both solar system and exoplanetary atmospheres
and specialises in modelling the scattering effects of clouds.
He has over 20 years experience in remote sensing of planetary atmospheres from satellite observations and
more recently ground-based observations. He is the principal author or co-author of over 300 papers published
in the open scientific literature.
Leigh Fletcher
Leigh Fletcher is an Associate Professor in Planetary Science at the University of Leicester and is a lead
contributer to NEMESIS in the field of solar system science. More bio. to be added.
Nick Teanby
Nick Teanby is a Reader in Planetary Science at the University of Bristol and is a lead
contributer to NEMESIS in the field of solar system science from the sub-mm to mid-IR. In particular the atmospheres of Titan and the ice giants, but also the gas giants and Mars.
Juan Alday
Juan Alday is a Postdoctoral Fellow at Instituto de Astrofísica de Andalucía (IAA-CSIC) and is the lead
developer of ArchNEMESIS. His research concentrates on the atmospheres of Mars and Venus.
Joe Penn
Joe Penn is a Doctoral student at the University of Oxfor and is a senior
developer of ArchNEMESIS. His research concentrates on the atmospheres of Uranus and Neptune.
Other biographies and links to be added here.
References
Irwin, P.G.J., N.A. Teanby, R. de Kok, L.N. Fletcher, C.J.A. Howett,
C.C.C. Tsang, C.F. Wilson, S.B. Calcutt, C.A. Nixon, P.D. Parrish (2008),
The NEMESIS planetary atmosphere radiative transfer and retrieval tool,
J. Quant. Spectrosc. and Rad. Trans., 109, 1136-1150, 2008.
doi:10.1016/j.jqsrt.2007.11.006.
The accepted open-access manuscript is here.
Irwin, P. G. J., S. B. Calcutt and F. W. Taylor (1997), Radiative transfer models
for Galileo NIMS studies of the atmosphere of Jupiter. Adv. Space. Res. 19,
doi:10.1016/S0273-1177(97)00266-4.
Alday, J., Penn, J., Irwin, P., Mason, J., Yang, J. and Dobinson, J. (2025),
archNEMESIS: An Open-Source Python Package for Analysis of Planetary Atmospheric Spectra,
Journal of Open Research Software, 13(1), p. 10. doi:10.5334/jors.554.
Why is it called NEMESIS?
Nemesis is traditionally known as the Goddess of Vengeance and Retribution.
Some authors connect the name with “to feel just resentment” or “righteous anger”.
However, the word Nemesis originally meant the distributor of fortune, whether
good or bad, in due proportion to each man according to his deserts.
As Nemesis/Fortuna, a conflation of the Greek deity of fate with the Roman Fortuna,
she was perceived not as bringer of retribution, but as having the power of changing
fortune. Hence, she was an ideal deity to make patron goddess of gladiators. It is
thought that gladiators made offerings to this “goddess of fortune” before fighting
in the Roman arenas. It is the “goddess of fortune” view of Nemesis, which inspired
the naming of this retrieval code in her honour. It is hoped that Nemesis will bring
good fortune and will considerably improve the retrieval of atmospheric properties
from remotely-sensed infrared planetary spectra.
