Wavy rings point to two undiscovered moons at Uranus


A couple of moonlets would bring the gas giant's moon tally to 29.


The Hubble Space Telescope took this false-colour image of Uranus in 2003. The planet's faint rings and moons have been enhanced.
NASA / Erich Karkoschka (Univ. Arizona)

Patterns in Uranus’ icy rings hint at the presence of two tiny, previously undiscovered moons orbiting the gas giant.

Rob Chancia and Matthew Hedman from the University of Idaho, US, examined 30-year-old data collected by the Voyager 2 probe and found the amount of icy material on the edge of two of Uranus' brightest rings varied periodically.

This pattern at Uranus was similar to moon-related structures in Saturn’s rings, called moonlet wakes.

In a paper to be published in the Astrophysical Journal (and available on Arxiv), the pair estimates the moonlets in Uranus' rings would be four to 14 kilometres in diameter – as small as some identified moons of Saturn, but smaller than any of Uranus' 27 known moons.

Hedman said their findings could help explain some characteristics of Uranus' rings, which are strangely narrow compared to Saturn's.

The moonlets, if they exist, may be acting as "shepherd" moons, helping to keep the rings from spreading out.

Confirming whether or not the moonlets actually exist using telescope or spacecraft images will be left to other researchers, Chancia and Hedman said. They will continue examining patterns and structures in Uranus' rings, helping uncover more of the planet's many secrets.

  1. https://arxiv.org/pdf/1610.02376v1.pdf
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