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Uranus from JWST

Presentation #401.01 in the session JWST Views of the Outer Planets and their Moons (Oral Presentation)

Published onOct 23, 2023
Uranus from JWST

We present the first results from JWST observations of Uranus, representing the most significant new IR observations of Uranus since Voyager 2.

Owing to its frigid atmospheric temperatures, Uranus’ infrared spectrum is extremely weak. Prior to JWST, much of this spectrum had never been spatially resolved before, while other regions were completely inaccessible. From the ground, spatially resolved observations of Uranus’ mid-infrared emission are limited to imaging observations targeting the brighter regions of the infrared spectrum (i.e. ~13 µm emission from stratospheric acetylene, and 17-25 µm from the H2 continuum). Images from the Very Large Telescope VISIR instrument at 13 µm show a stratospheric structure distinct to Uranus, with elevated radiance at high latitudes. The physical nature of this structure–-whether produced by chemical or thermal gradients–-is unclear given previously available data [1]. From space, the Spitzer Space Telescope observed Uranus’ mid-infrared spectrum between ~7 and 36 µm, but it lacked the spatial resolution necessary to resolve potential thermal and chemical structure across the disk [2].

Now, with its exceptional sensitivity and outstanding spatial and spectral resolution, JWST reveals Uranus’ stratospheric temperature and chemistry with exquisite new detail, placing new constraints on hydrocarbon abundances and temperature structure across the disk.

In this talk, we introduce these new data along with results of an initial radiative transfer analysis. The data reveal meridional temperature variation over an enormous range of pressures, ranging from <microbar to >1bar, including the first measurements of variation at the 1-2 bar haze/cloud level. Wavelengths sensitive to the atmospheric chemistry provide new constraints on the vertical and latitudinal variation of key hydrocarbons, including ethane, acetylene, and methane, along with other molecules, including several first detections.

With a projected lifetime of over a decade, JWST promises to continue providing exciting new insights into the atmospheric structure, composition, and variability of the ice giants for years to come.

[1] Roman, M.T, et al. “Uranus in northern...” AJ 159.2 (2020): 45.

[2] Rowe-Gurney, N., et al. “Longitudinal variations...” Icarus 365 (2021): 114506.

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