Uranus May Have Two Undiscovered Moons

NASA's Voyager 2 spacecraft flew by Uranus 30 years ago, but researchers are still making discoveries from the data it gathered then. A new study led by University of Idaho researchers suggests there could be two tiny, previously undiscovered moonlets orbiting near two of the planet’s rings.

Uranus is seen in this false-color view from NASA's Hubble Space Telescope from August 2003. The brightness of the planet's faint rings and dark moons has been enhanced for visibility. Image credits: NASA/Erich Karkoschka (Univ. Arizona)

The amount of ring material on the edge of the alpha ring -- one of the brightest of Uranus' multiple rings -- varied periodically. A similar, even more promising pattern occurred in the same part of the neighboring beta ring.

The researchers analyzed radio occultations -- made when Voyager 2 sent radio waves through the rings to be detected back on Earth -- and stellar occultations, made when the spacecraft measured the light of background stars shining through the rings, which helps reveal how much material they contain.

They found the pattern in Uranus' rings was similar to moon-related structures in Saturn's rings called moonlet wakes.

The researchers estimate the hypothesized moonlets in Uranus' rings would be 2 to 9 miles (4 to 14 kilometers) in diameter -- as small as some identified moons of Saturn, but smaller than any of Uranus' known moons. Uranian moons are especially hard to spot because their surfaces are covered in dark material.

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. Two of Uranus' 27 known moons, Ophelia and Cordelia, act as shepherds to Uranus' epsilon ring. (NASA)

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