PASADENA, Calif. - Hours after settling into orbit around Saturn, the international Cassini spacecraft on Thursday sent back unprecedented glimpses of the planet's rings from above, revealing patterned waves that looked like ripples in a pond.

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Cassini's first images were taken looking down on the rings as the spacecraft flew through a successful maneuver more than 900 million miles from Earth. The probe's trajectory took it through a gap between two of the rings.

"Absolutely mind-blowing," imaging team leader Carolyn Porco said as the images started streaming in.

The imagery capped what Cassini program manager Robert Mitchell called a "nail-biter" of a night.

Mission scientists and engineers at NASA’s Jet Propulsion Laboratory watched tensely late Wednesday as signals indicated that the Cassini spacecraft — launched nearly seven years ago — had safely passed through the ring plane and then performed a crucial engine firing. It squeezed through a gap in Saturn’s shimmering rings, fired its brakes and settled into a near-perfect orbit around the giant planet. If the engine burn had failed, the craft could have simply flown past Saturn.

“I can tell you it feels awfully good to be in orbit around the lord of the rings,” said Charles Elachi, JPL's director and a member of Cassini's radar team.

“The spacecraft couldn’t have performed any better,” said Julie Webster, the spacecraft team chief. At its closest, the probe came within 12,500 miles of Saturn's cloud tops. Cassini will never come as close to the planet again in its four-year mission.

NASA TV An image of Saturn's rings, taken by the Cassini spacecraft and sent back Thursday, shows the Keeler Gap, close to the edge of Saturn's A ring. The ripples are density waves caused by the gravitational influence of Saturn's moons, scientists say.

After flying through the plane of the rings, Cassini turned its cameras to take pictures from above, and when the images were downloaded, smiles once again spread across the faces of the mission team.

"This is really a new era in the study of outer-planet systems," Porco said.

The black-and-white images of Saturn's A ring, the outermost of the two brightest rings, showed patterns of ripples that Porco said were "density waves," caused by the gravitational influences of the planet's moons. Although the rings look like solid, flat doughnuts from Earth, they actually behave more like rivers of dust and ice, with particles ranging in size from specks to mountains.

"These density waves are like books, just waiting to be read," she said.

Porco estimated that some of the waves might measure as little as a quarter of a mile (half a kilometer) across. Earlier NASA probes had taken pictures of the rings as they flew by, but with nowhere near the resolution seen in the Cassini images. Some of the pictures had a resolution of 164 feet (50 meters) per pixel, Porco said.

Two decades of work
Wednesday's orbit insertion maneuver came after two decades of work by scientists in 18 nations.

“This wasn’t NASA going into orbit around Saturn. This was the Earth going into orbit around Saturn,” said Ed Weiler, NASA’s associate administrator.

The $3.3 billion mission, funded by U.S. and European space agencies, was designed to give scientists at least a four-year tour of Saturn and some of its 31 known moons. Cassini is scheduled to make 76 orbits and repeated fly-bys of the moons.

Scientists hope the mission will provide important clues about how the planets formed. Saturn, the sixth planet from the sun and the second-largest, intrigues scientists because it is like a model of the early solar system, when the sun was surrounded by a disk of gas and dust.

Roundabout route
Cassini has traveled 2.2 billion miles since it was launched in 1997, getting gravitational assists from Earth and Venus as it caromed around the solar system.

MISSION TO SATURN • Fast facts about Saturn and Cassini: — Saturn: Planet second in size to Jupiter with diameter of 74,898 miles (119,837 kilometers). Mean distance from sun is 890 million miles (1.42 billion kilometers). Has seven rings, 31 known moons. — Cassini orbiter: Launched Oct. 15, 1997. Spacecraft is 22 feet (6.7 meters) long, 13.1 feet (4 meters) wide. Weighs 12,593 pounds (5,724 kilograms) with fuel and Huygens probe. Will make 76 orbits in four years. — Huygens probe: Wok-shaped spacecraft is 8.9 feet (2.7 meters) in diameter and 705 pounds (320 kilograms). Will be released from Cassini on Dec. 24 and enter Titan’s atmosphere on Jan. 14. — Mission cost: $3.3 billion, shared by NASA, European Space Agency, Italian Space Agency.

The spacecraft took the roundabout route because the 22-foot-long, 13-foot-wide craft was too massive to be launched on a direct trajectory to Saturn.

Cassini also carried with it a probe — named Huygens — to be sent into the atmosphere of Saturn’s big moon Titan in January. The moon, blanketed by a thick atmosphere of nitrogen and methane, is believed to have organic compounds resembling those on Earth billions of years before life appeared.

Cassini and its probe are named for 17th-century astronomers Jean Dominique Cassini and Christiaan Huygens.

Previous expeditions to Saturn were brief. There were fly-bys by Pioneer 11 and the Voyager missions from 1979 to 1981.