Voyager Finds a Sixth Moon Orbiting Uranus

A sixth moon orbiting Uranus has been discovered by the Voyager 2 space probe, scientists at Caltech’s Jet Propulsion Laboratory announced Tuesday.

The new moon, temporarily designated 1985 U1, “is both closer to the surface of Uranus and smaller than any of the five previously known moons,” according to Ellis Miner, deputy Voyager project scientist.

Based on its brightness, Miner said, the new moon appears to be less than 45 miles in diameter. Its orbit is about 37,500 miles from the top of the planet’s atmosphere, and it completes one revolution in 18 hours, 17 minutes, 9 seconds.

Larger Moons

The other five moons range in diameter from 300 to 1,500 miles, and their orbits range from 80,000 to 364,000 miles above the top of the atmosphere.

The new moon was first observed in a series of pictures taken in December by Voyager’s telephoto television camera when the probe was about 19 million miles from Uranus. JPL will not release any of the pictures, spokeswoman Mary Beth Murrill said, because the moon “is just a blip” on the photographic images.

The Voyager team expects to find “evidence of several new moons” circling Uranus, Miner said, because of the extreme narrowness of the planet’s rings. Those rings extend out to only about 15,000 miles from the top of the planet’s atmosphere--much less distance than the rings of Saturn, for example.

Unseen Moonlets

Astronomers speculate that the rings are constrained into the narrow orbit by several previously unseen small moons or moonlets.

Miner said that the team is now beginning a systematic search for other moons around Uranus, and added that “it is fairly safe to say that none will be larger” than 1985 U1.

Voyager 2 will pass within 50,000 miles of Uranus’ cloud tops on Jan. 24 and scientists hope to get much better pictures of all the moons.