Including PS Division Outstanding ECS Award Lecture
To extract, or 'retrieve' atmospheric properties from the observed radiance spectra from a planetary atmosphere requires software that can generate the expected radiances from a guessed atmospheric model, compare the radiances with those measured, determine how the model should be updated to reduce any discrepancy between the modelled and observed radiances, and then iterate these steps until these differences are minimised. One such retrieval model is NEMESIS (Nonlinear optimal Estimator for MultivariatE Spectral analySIS), which was initially developed by myself and my colleagues in the 1990s, and which has since been continually updated and enhanced. NEMESIS has now been used in more than 300 papers retrieving atmospheric properties from observed thermal and solar-reflected radiance spectra from all the planetary atmospheres in our solar system and also some beyond. NEMESIS uses the Optimal Estimation framework for atmospheric retrievals and is written in FORTRAN. Recently, more Bayesian frameworks have become computationally possible and favoured, especially for exoplanetary retrievals where prior constraints are almost entirely absent. Hence, NEMESIS has recently been updated to Python (ArchNEMESIS), and combined with PyMultiNest to allow nested sampling retrievals that can better explore the degeneracy between different atmospheric properties. I will review how NEMESIS retrievals have improved our understanding of planetary atmospheres over the last 30 years and how the development of ArchNEMESIS has breathed new life into the NEMESIS/ArchNEMESIS project.
How to cite: Irwin, P.: A voyage of discovery: Exploring the atmospheres of solar system planets and exoplanets with NEMESIS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2813, https://doi.org/10.5194/egusphere-egu26-2813, 2026.
There is astonishing diversity in outer solar system satellites. While many of these bodies are of great interest due to their astrobiological potential, they are fascinating celestial bodies in their own right. They feature a vast array of interacting geophysical, geochemcial, and celestial mechanical processes for which straightforward Earth-analogues do not always exist. The thermal evolution of these moons—a primary concern for notions of habitability—is often strongly influenced by tides, the periodic, heat-generating deformation of their ice, water, and rock layers. While significant advancements in tidal modelling have been made in the last 25 years, we still do not understand some of the details behind the basic mechanisms for how tidal deformation in solid and liquid saps energy from the rotational–orbital state of the deformed body. In this lecture, I will review my recent contributions in this field, including discovering the mechanism through which neighbouring moons can accelerate tidal deformation in ocean worlds, and new steps towards a self-consistent geodynamical model of Io’s thermal evolution, before summarising the major gaps that must be resolved if we are to most successfully exploit data returned by Europa Clipper and JUICE.
How to cite: Hay, H.: Neighbouring moons, partial melt, and oceans: Tides of rocky and icy outer solar system satellites , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7478, https://doi.org/10.5194/egusphere-egu26-7478, 2026.
Speakers
- Patrick Irwin, University of Oxford, United Kingdom
- Hamish Hay, University of St Andrews, United Kingdom