2,2,2,4,4,5,6,7- 1Universidad Adolfo Ibáñez, Facultad de Ingeniería y Ciencias, Santiago, Chile (mr359@le.ac.uk)
- 2School of Physics and Astronomy, University of Leicester, Leicester, UK
- 3Association of Universities for Research in Astronomy, Washington, DC, USA
- 4Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, UK
- 5Department of Astronomy, University of California, Berkeley, UK
- 6Department of Maths, Physics, and Electrical Engineering, Northumbria University, Newcastle upon Tyne, UK
- 7Astrochemistry Laboratory Code 691, NASA Goddard Space Flight24 Center, Greenbelt, MD, USA
JWST-NIRSpec observations are providing our first detailed view of the Ice Giants in the 5-micron spectral window [1]. Observations of Jupiter and Saturn (see Figure) at 5 microns have historically revealed important insights into their tropospheric composition, along with striking images of clouds silhouetted against the glowing thermal emission from deeper atmospheric layers [2]. Comparable observations of the colder Ice Giants, however, have long remained beyond observational reach—until now.
In this talk, we present JWST-NIRSpec 5-micron observations of the Ice Giants and discuss their implications. We examine what these observations reveal about the tropospheric temperatures, clouds, and composition of Uranus and Neptune, as well as what they may imply for current radiative transfer models at these wavelengths.
In particular, we find that the JWST data may suggest sub-adiabatic temperature gradients near the cloud layers, resulting in colder temperatures in the deeper atmosphere. However, these conclusions depend sensitively on the scattering properties of Ice Giant clouds and on accurate modelling of the gaseous opacity, both of which, we argue, remain uncertain under these conditions.
Figure: Saturn at 5 microns (left, in red) from Cassini, with hazes shown in green (Image credits: NASA/JPL-Caltech/University of Arizona), compared to Uranus at 5 microns from JWST-NIRSpec [1].
[1] Roman, M.T., et al., The Infrared Spectrum of Uranus Revealed with JWST (submitted)
[2] Wong, M.H., Bjoraker, G.L., Goullaud, C., Stephens, A.W., Luszcz-Cook, S.H.,1047
Atreya, S.K., Pater, I., Brown, S.T.: Deep clouds on jupiter. Remote Sensing1048
15(3), 702 (2023)
How to cite: Roman, M., Fletcher, L., King, O., Toogood, S., Hammel, H., Irwin, P., Penn, J., de Pater, I., Melin, H., and Miliam, S.: Cold Temperatures, Dark Clouds, or Missing Absorption: What Does the 5-Micron Window Tell Us about the Ice Giants?, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1050, https://doi.org/10.5194/epsc2026-1050, 2026.
