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In Orbit, Cassini Sends Close-Ups of Saturn's Rings

Posted on: Friday, 2 July 2004, 06:00 CDT

Hours after entering into orbit around Saturn, the Cassini spacecraft began sending back close-up images of the giant planet's rings back to Earth, a billion and a half kilometers away, as awed scientists watched Thursday morning here at NASA's Jet Propulsion Laboratory.

As the black and white images began coming in, 80 minutes after they were transmitted from the American-European craft, they grew crisper, showing the close-ups of the rings that appeared like the edges of corrugated cardboard. Some of the rings' particles, which are mainly grains of water, ice and rock, showed straw-like patterns that the scientists said they do not understand.

Carolyn Porco, the mission's chief photo interpreter, said at a news conference here Thursday that she was "surprised by the beauty and clarity of these images." On first seeing them, she said, she "thought they were simulations of the rings and not rings themselves."

Some of the photo images, taken as the spacecraft passed through a large gap in the rings, exposed the scalloped edges of icy material, which scientists ascribe to gravitational effects of tiny moonlets that orbit within the rings and apparently help shape them.

"I can't describe how exciting this is for us," Porco said. "It's just mind blowing."

Cassini, launched seven years ago, is beginning a four-year mission of the ringed planet and its 31 known moons.

On Wednesday night, Cassini became the first exploring vehicle to orbit Saturn, the faraway planet of serene beauty embellished by an exquisite array of encircling rings. At the news conference on Thursday, Robert Mitchell, the program manager, said that tracking data showed that the initial orbit would take 116 days.

He also said that engineering data transmitted back to Pasadena showed that the craft survived its entry into Saturn's rings with no damage.

When confirmation was received here that the Cassini had entered its orbit, members of the Cassini-Huygens mission broke into cheers and high-fives.

Cassini squeezed through a gap in Saturn's shimmering rings, fired its brakes and settled into a near-perfect orbit around the giant planet.

"It feels awfully good to be in orbit around the lord of the rings," said Charles Elachi, the team leader for the radar instrument onboard Cassini said, according to NASA officials. "This is the result of 22 years of effort, of commitment, of ingenuity, and that's what exploration is all about."

A planned highlight of the $3.3 billion American-European mission is the first thorough investigation of Saturn's mysterious planet- size moon, Titan. Earlier, the spacecraft had approached Saturn from underneath the plane of the rings, gathering speed from the giant planet's gravity. When it threaded its way through a gap in the broad system, it was traveling more than 80,000 kilometers, or 50,000 miles, an hour, almost twice its velocity at the beginning of the day. The spacecraft has seemed to have had a charmed life since its launching in 1997. Its quirks and malfunctions have been few. Before the orbital maneuver, Julie Webster, chief of the spacecraft operations team, said that Cassini was "in an excellent state of health." Propulsion engineers had expressed confidence in the rocket engines, noting that they performed flawlessly in 17 previous trajectory maneuvers.

As for the risks of a passage through the Saturnian rings, flight controllers were reassured by telescopic observations that found no sign of hazards in the gap between the F and G rings, which Cassini had to traverse. They also pointed out that previous Pioneer and Voyager spacecraft, on flyby missions, had passed safely through gaps in the ice, dust and rock of the rings. As a precaution, though, the spacecraft turned its large dish-shaped antenna into the direction of flight, so that it acted as a shield against small objects that could have caused serious damage.

The first mission to orbit Saturn, planned since the early 1980s, is a partnership of the National Aeronautics and Space Administration, the European Space Agency and the Italian Space Agency. The 2,125 kilogram, or 4,700-pound, Cassini was developed by NASA, and the attached 320-kilogram Huygens craft for probing Titan, by the Europeans. Cassini's main antenna was provided by the Italians. With its 18 scientific instruments and cameras, the combined craft is considered the most complex ever to explore the planets, and it is the first to visit Saturn since Voyager 2's flyby in 1981. On Friday the spacecraft is expected to be in range for its first close photography of Titan, a moon bigger than the planets Mercury or Pluto. In Cassini's planned 76 orbits around the Saturn system, 44 are to be plotted to provide close encounters with Titan.

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