Estimating Soft X-Ray Emission from Uranus's Magnetosheath
By Dan Naylor (Lancaster University)
Soft X-rays can be generated within planetary magnetosheaths due to charge exchange between neutrals and highly charged solar wind ions such as O^7+. Imaging of the soft X-rays is an emerging technology that aims to provide global and dynamic views of the magnetosheath and cusps, and their response to solar wind driving. The ESA-CAS SMILE mission will soon be launched with a soft X-ray imager (SXI) instrument onboard to investigate the terrestrial magnetosheath. We explore the viability of similar investigations at Uranus.
Uranus has one of the most unusual and complex environments in the solar system. A large obliquity combined with a highly tilted, offset magnetic axis result in an asymmetric and constantly varying magnetosphere where the plasma and neutral source rates from the moons are unconstrained. We impose a simple bullet shaped magnetopause and moon tori informed by Voyager 2 observations to predict soft X-ray emission from the Uranian magnetosheath. We estimate volumetric emission rates of soft X-rays are on the order of 10^-10 photon cm^-3 s^-1, being higher at equinox due to the orientation of the magnetosheath relative to the moon tori. Simple estimates of intensity and flux find that a SMILE-like instrument could detect ~100 photons in a quarter of a planetary rotation at a distance of 212 R_U, as shown in the figure. A hypothetical future imager, with improved FOV and effective area, would detect ~20,000 photons per planetary rotation at 100 R_U. These are promising initial results that suggest imaging of the magnetosheath is possible within key system timescales. Future studies will include magnetospheric cusps and a full range of solar wind ions, which are anticipated to increase emission rates.

Modelled intensity maps for a SMILE‐like SXI at 212 R_U from different viewing geometries at (top row) equinox, where the neutrals are edge-on to the Sun, and (bottom row) solstice, where the neutrals are ring on to the Sun: (a/d) front‐on, (b/e) top‐down and (c/f) side‐on. The different panels show that the amount of flux detected is dependent on viewing position, and an orbital mission should consider the implications of different possible imaging positions.
See publication for details:
Naylor, D., Ray, L. C., Dunn, W. R., Jasinski, J. M., & Paty, C. (2025). Estimating soft X-ray emission from Uranus's magnetosheath. Journal of Geophysical Research: Space Physics, 130, e2025JA034171. https://doi.org/10.1029/2025JA034171