On June 30, 2004, one of the most sophisticated spacecraft ever built screamed toward Saturn at 54,483 mph. Then, for 96 minutes, it burned half its weight in fuel, braking just enough to settle into orbit. In the two years since, Cassini has floated over the planet's delicately banded atmosphere, glided by its ancient, cratered moons, and passed right through its iconic rings--returning images that surpassed even the mission scientists' wildest expectations.

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"It's been a joyride," says Carolyn Porco, who worked on the Voyager mission to Saturn 25 years ago and now leads the imaging team for Cassini. "Our cameras can see deeper, pick up fainter light and go to higher resolution, and that opens up brand-new areas of discovery." Her team plans each image that will be taken months in advance, but actually seeing them, she says, is like having Lasik surgery. "Suddenly you're looking at something that was familiar to you with completely new eyes."

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Cassini's mission will last at least two more years, its pair of cameras probing a corner of the solar system that, day by day, becomes a little less alien. "Being in orbit around a place as dynamic as Saturn gives us a lot of opportunity to investigate the processes that shape it," Porco says. "What we really want to do is understand how planets work, how they change and evolve. Because, after all, we live on one."


Carolyn Porco, a research scientist at the Space Science Institute in Boulder, Colo., leads the team in charge of operating Cassini's wide- and narrow-angle cameras. Eleven other instruments on the spacecraft's upper equipment module measure everything from magnetic fields to dust particles. When it was launched in 1997, Cassini weighed 6 metric tons. Even a Titan 4 missile and solid rocket boosters couldn't provide enough power to get the school-bus-size craft all the way to Saturn, 890 million miles away. Cassini used gravity assist from Venus (twice), Earth and Jupiter to build momentum for the seven-year journey.

ENCELADUS This bright, icy moon has always been peculiar, but now "it is defying explanation," Porco says. The blue fractures in this false-color mosaic contain coarse-grained ice and spew organic materials. They are also surprisingly warm (minus 279 F) compared to surrounding areas. Porco adds: "It's lopsided in its distribution of heat. It's geologically active at the south pole. And we think that it has liquid water close to the surface." The provocative conclusion, she says, is that Enceladus may have subterranean environments capable of supporting life.

S/2005 S1 Cassini has discovered four moons (so far), bringing Saturn's total to 47. The most recent find--so new it is still only provisionally named--creates the Keeler Gap in the planet's A ring. "We could never have seen a moon that small with the Voyager cameras," Porco says. The 4-mile-wide object was resolved with Cassini's narrow-angle camera last May. The tiny satellite throws nearby ring particles into an eccentric orbit, causing the gap's scalloped appearance. Studying interactions in the ring provides scientists with insight into planet formation.

TITAN Saturn's F ring is only about 30 ft. thick, and so in this image appears to be two thin, bright lines in front of Titan. Spectral filters on Cassini's cameras were able to cut through the moon's methane haze for the first time. "We're getting a really good dose of what the surface of Titan looks like," Porco says, "and it's very complex." In fact, it may resemble Earth's surface more than anything else in the solar system. Scientists believe Titan's atmospheric methane condenses and rains down on the surface, forming what appear to be highlands and braided, streamlike channels.

IAPETUS First discovered in the 17th century by the spacecraft's namesake, Italian astronomer Giovanni Cassini, Iapetus has two distinct faces--one bright and one dark. A flyby on New Year's Eve of 2004 revealed that the dark side is heavily cratered and therefore quite old. This finding wiped out a whole class of explanations attributing the terrain's surface to volcanic activity. Even more remarkable is the topographic ridge that traces Iapetus's equator. "In some places it reaches 12 miles high. That's big," Porco says. "No one had ever seen anything like it before."

This mosaic of 126 images from Cassini is the most detailed, natural-color view of Saturn ever made.

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