WIRED Staff
Science

Slideshow: Cassini Slips Into Saturn Orbit

The $3.3 billion space probe completes a risky maneuver through Saturn's rings, becoming the first spacecraft ever to orbit the planet. Let the discoveries begin. Amit Asaravala reports from Pasadena, California.
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The sharp lines at the edges of the ringlets in many of these images from Cassini are forcing scientists to reevaluate their theories about where Saturn's rings begin and end. Previously, scientists had thought the edges of the ringlets tapered off over a distance of approximately 1 kilometer. But the relatively fine resolution of the camera now has them believing that the transition occurs over a range of just two football fields or less.NASA/JPL

See related story: Cassini Slips Into Saturn Orbit

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JPL technicians put the finishing touches on the Cassini spacecraft at the Kennedy Space Center in Florida, three months before its October 1997 launch.

NASA/JPL
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Cassini took this image of the underside of Saturn's rings from approximately 88,800 miles away. Images taken from this side of the ring plane are much brighter than those taken from above the plane because the rings are lit by the sun. The first gap in the rings, from left to right, is known as the Cassini Division. The second, thin gap at the right edge of image is the Encke gap.

NASA/JPL
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The gradually diminishing size of these ring-like strands, from left to right, illustrates a phenomenon known to astrophysicists as a "density wave." The effect occurs when the gravitational pull from a nearby moon causes the particles in a ring to align in a rippled pattern. The strands are all part of the same ring, wound in a tight spiral around Saturn. The density wave phenomenon also effects the formation of spiral solar systems, albeit on a much larger scale, according to Linda Spilker, deputy project scientist for Cassini.

NASA/JPL
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Scientists believe the gnarled edges of the ring alongside the Encke gap in Saturn's rings are caused by the moon Pan, which orbits Saturn from within the gap. Such moons are called shepherd moons because their gravitational forces hold the particles that make up Saturn's rings in place.

NASA/JPL
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The Cassini space probe successfully slipped through a gap in the rings surrounding Saturn -- not once, but twice -- on Wednesday night, kicking off a four-year mission to study the second largest planet in our solar system.

NASA/JPL/Space Science Institute