Oct. 13, 2004 — An image released this week shows a 2,980-mile-wide gap in Saturn's rings caused by the gravitational tug of its small moon, Mimas.

Mimas is puny compared to its sister moons in orbit around Saturn. But the satellite has shown the Cassini science team an impressive demonstration of its power.

The size of the gap is mathematically matched to the 247-mile-diameter moon, complete with a precise fringing on the ring that corresponds to Mimas' shape, said Carolyn Porco, head of the Cassini imaging team at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

The image was taken in visible light with the spacecraft's narrow angle camera on Aug. 25, 2004. Mimas was about 5.5 million miles away at the time.

The Cassini spacecraft is three months into a planned four-year study of the Saturn system. It is the first probe to enter into orbit around Saturn and follows two Voyager flyby missions in 1980 and 1981.

Voyager data showed that Mimas, one of Saturn's inner moons, is marked with a giant crater that encompasses one-third of the moon's surface.

"It looks like the Death Star," said Porco.

Scientists suspect the crater, named Herschel after the astronomer William Herschel who discovered the moon in 1789, dates back to the time of the moon's creation. The crater is six miles deep and sports a central mountain rising four miles from the crater floor, almost as high as Mount Everest on Earth. The impact that caused the crater probably came close to destroying the moon entirely.

One of the goals of the Cassini mission is to study the moons and the planet's elaborate rings, which are comprised of rocks and ice particles ranging in size from a house to small pebbles and clouds of dust. Scientists believe the rings may be one or two moons that were smashed to bits by impacts.

"If you took all the mass of the rings and put it back together again, you'd come up with the equivalent of about one moon," said Porco.

The structure of the rings is stable, Porco added, but everything is in motion.

The Cassini team is about to get its first close up look at one of the Saturn moons. Titan, Saturn's largest moon and the only one in the solar system that has its own atmosphere, will be the focus of a flyby on Oct. 26.

"We'll probably get to about 1,200 kilometers (746 miles)," said Porco. "We want to get as close as possible to get the highest detail data we can."

Cassini flew past Titan on July 2 at a distance of 340,000 kilometers (211,000 miles) shortly after its arrival at Saturn.

Over the next four years, Cassini is expected to fly past Titan 45 times. In January, a piggyback satellite built by the European Space Agency is expected to descend through Titan's thick atmosphere to the moon's surface.