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Hubble Observations Reveal Unexpected Darkening of Uranus’s Moons

Ultraviolet measurements attribute unexpected dark, red hues on the leading hemispheres of Uranus’s outer moons to dust from irregular satellites, upending expectations of magnetospheric effects

Image
This Webb image shows Uranus and six of its 27 known moons (most of which are too small and faint to be seen in this short exposure). Image credit: NASA / ESA / CSA / STScI / J. DePasquale, STScI.

Overview

  • The leading hemispheres of Titania and Oberon appear darker and redder than their trailing sides, contradicting predictions of radiation darkening by charged particles.
  • Ariel and Umbriel show no significant brightness difference between their leading and trailing hemispheres, indicating minimal magnetospheric interaction.
  • Researchers attribute the color asymmetry to dust from Uranus’s irregular satellites coating the forward-facing surfaces of the outer moons.
  • Hubble’s ultraviolet imaging and spectroscopy enabled the discovery by revealing surface variations that ground-based telescopes cannot detect.
  • The findings challenge existing models of Uranus’s magnetosphere, bolster the case for a dedicated orbiter mission and highlight the difficulties of securing funding under current budget constraints.