Astronomers locate lost pair of Uranus moons

Uranus

In this story: Moons' diameters only 25 miles Hubble, ripples aid in search RELATED STORIES, SITES

From staff reports

March 8, 2000
Web posted at: 4:37 p.m. EST (2137 GMT)

TUCSON, Arizona -- Fourteen years after disappearing from astronomical observations, two moons of Uranus have been rediscovered.

Voyager II first observed Ophelia and Cordelia more than a decade ago, but they quickly faded from view after the spacecraft left the Uranus system -- until this month, when scientists sifting through Hubble images spotted the tiny satellites.

The new sighting strengthens Uranus' claim as the moon king of the solar system. The seventh planet from the sun has 20 known natural satellites, more than any other planet.

Scientists looking at Voyager 2 images discovered the moons in 1986. Voyager 2 observed the satellites for two weeks and then left Uranus for the Neptune system.

But scientists soon lost sight of the moon pair, having insufficient data to predict their orbits and inadequate instruments to observe them.

They remained lost until this year. Astronomers from three academic institutions announced last week that they found the moons.

For years, telescopes on Earth were unable to spot the tiny, distant satellites. Each moon has a diameter of about 25 miles (40 km) and is more than 1.7 billion miles (2.7 billion km) away.

But Hubble images have become significantly more detailed in recent years. And a few weeks ago Erich Karkoschka, a researcher at the University of Arizona, spotted Ophelia while conducting a computer-enhanced search of 1997 Hubble data.

Meanwhile, astronomers at Wellesley College and Cornell University had found promising signs of the two moons by checking ripple patterns, likely caused by the moons' gravity, on the edge of Uranus' brightest ring.

"Ever since these narrow rings were found around Uranus, (we) realized that something must be holding them together," Philip Nicholson, a Cornell astronomy professor who participated in the search, said in a statement.

Karkoschka checked for Cordelia based on the work of the Wellesley and Cornell astronomers. He found it right where they predicted it would be.

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