The Voyager 2 spacecraft, now hurtling toward a 1989 rendezvous with Neptune, returned stunning new photographs as it swept past Uranus, showing surface features found nowhere else in the solar system, scientists said today.
Voyager also detected a 15th moon and a 10th ring on the fly-by, experts said, as they began reviewing reams of data and dozens of striking photos taken Friday, as the probe surveyed the seventh planet from the sun, and today as it looked back toward the planet backlit by the sun. The photos revealed vivid detail never seen from Earth, particularly of the moons.
The moons -- viewed from only a few thousand miles away -- showed cracks, bumps and bruises that suggest these distant bodies have undergone some of the same chaotic impacts and internal heat processes as most of the other moons in the solar system.
The new moon found today lies about 38,000 miles from the planet and is about 30 miles across, the average size of the 10 new moons found by Voyager. The new ring lies just inside the outermost of the nine previously known rings and is just as faint and as dark as a few of the older rings closer to the planet.
"We have now begun to see dust among the particles in the rings," Bradford A. Smith of the University of Arizona said. "Our first pictures of the rings from behind the planet were disappointing, but as we move further behind Uranus we are beginning to get very good pictures."
Two pictures of Miranda received late today showed spectacular features on the small moon, which appeared to be covered with craters on one hemisphere. Fault patterns appeared in the other hemisphere unlike any seen before in any of the moons in the solar system, most of them oval-shaped, one inside the other like a race track or a football stadium.
"Bizarre is an understatement to describe these patterns," Laurence Soderblom of the U.S. Geological Survey in Flagstaff, Ariz., said. "These pictures are amazing the way they show these fault patterns turning corners. They're remarkable, to say the least."
Another arrowhead-shaped feature on Miranda looked as if a giant claw had dug out a huge chunk of the moon's surface. The dark-colored feature was splotched with bright spots, suggesting that ice had seeped up through cracks in the surface.
The moon Ariel showed huge cracks, one of which appeared to be almost as large as the Grand Canyon. The large moons, Titania and Oberon, also were covered with cracks and craters, some of which contained huge pools of ice.
An icy mountain at least three miles high showed up on the limb of Oberon, presumably put there when a meteorite collided with the moon and sent millions of tons of ice rushing out from the interior to form the highest known peak on any of the Uranian moons.
"We're beginning to see valleys and mountains on most of the moons that are anywhere from two miles deep to three miles high," said Soderblom. "These moons are all similar objects but they all look different at the same time."
Soderblom said that the only moon that appears bland and featureless is Umbriel, the fourth largest of the five large moons. Photos show only one feature on the face of the moon, a doughnut-shaped patch at its north pole that could be a shallow impact crater.
"Umbriel is the real enigma in the moon system," Soderblom said. "Why is it so bland and so free of features when the others are not?"
A number of scientific discoveries have been made during the Voyager fly-by, but scientists still do not know the length of the Uranian day.
"We have not yet settled on a rotation rate for Uranus but we are zeroing in and expect to solve that mystery," said Voyager Project Scientist Edward C. Stone at the Jet Propulsion Laboratory where Voyager's mission is directed. "It will take us at least another day or so before we can settle on a rotation rate."
Voyager found a surprisingly strong magnetic field earlier, and revealed today that Uranus' magnetic poles are tilted 55 degrees away from its rotational poles. This magnetic tilt is larger than any other in the solar system. Usually, the magnetic and rotational poles are only a few degrees off, as are Earth's.
Voyager's infrared instrument measured temperatures across the planet that were no more than 64 degrees Fahrenheit above absolute zero, putting the temperatures in the deep freeze of the solar system at about minus 390 degrees Fahrenheit, a little colder than predicted