Ice Giants

Ice Giants

The final GIANTCLIMES work package extends our understanding of planetary atmospheres out to the distant and under-explored Ice Giants, Uranus and Neptune. This theme will use existing ground- and space-based observations of the ice giants to prepare for observations with the James Webb Space Telescope (JWST), where guaranteed time observations of both worlds (programme IDs 1248 and 1249) have been awarded and prepared by Fletcher. Fletcher is supported by ERC-funded PhD student Naomi Rowe-Gurney; and two PDRAs – Michael Roman (for observations) and Jan Vatant d’Ollone (for numerical simulation). Progress to date includes:

  • Ground-based characterisation: PDRA Roman has lead the effort to characterise the atmospheres of Uranus and Neptune using existing Very Large Telescope (VLT) observations in the mid-infrared. This led to a serendipitous discovery of the Uranian rings in thermal emission (Molter et al., 2019,, and has allowed us to characterise Uranus’ stratospheric circulation pattern for the first time (Roman et al., submitted to AJ). Roman is currently applying similar techniques to new observations of Neptune (a preliminary paper on Neptune has been submitted by our collaborator, James Sinclair, exploring stratospheric conditions in 2008). In 2019 we observed Neptune from the Gemini telescope (full spectroscopy using the TEXES instrument), and we have proposals accepted by the Spanish GranteCan observatory and the VLT for future observations of both targets.

  • Space-based characterisation: PhD student Rowe-Gurney is mining an archive of Spitzer Space Telescope observations of Uranus and Neptune, taken between 2004 and 2007. She has developed the techniques to model the disc-averaged spectra, and has a paper in preparation exploring the longitudinal variability of Uranus’ stratosphere, due for submission in 2020. In addition, Fletcher used Spitzer and Cassini observations to discover hydrogen dimer features in the spectra of all four giants, most noticeably the ice giants (

  • Numerical Modelling: Working with Dr. Julianne Moses (Collaborator), we produced a seasonal photochemical model of both ice giants in the absence of dynamics, which was used to predict the appearance of both worlds using JWST ( Following this effort, we have formed a new collaboration with A. Spiga and S. Guerlet at the Laboratoire de Météorologie Dynamique (LMD) in Paris, through the hire of PDRA d’Ollone, to develop a numerical simulation of Ice Giant circulation, based upon the existing DYNAMICO model. This will be the first simulation of its type, and work on a preliminary publication characterising Ice Giant radiative balance is currently underway.

  • Winds and Clouds: Working with international collaborators, the ERC team have also explored shorter wavelength observations: Joshua Tollefson (Collaborator) used our temperature inversions to explore thermal windshear in Neptune’s atmosphere (; and Prof. Patrick Irwin (Collaborator) presented the first detections of hydrogen sulphide above the clouds of Uranus ( and Neptune ( using observations from Gemini.

  • Future Missions: The ERC team plays an active role in advocacy for future missions to Uranus and Neptune. Fletcher is the lead organiser of an Ice Giants Meeting at the Royal Society in London (January 2020), and led the submission of white papers to ensure that Ice Giant missions are part of ESA’s Voyage2050 programme. Fletcher is also contributing to mission studies and white papers associated with the next US decadal survey in planetary science.

Leigh Fletcher
Professor of Planetary Science