July 01, 2004

Spacecraft Sends Back Images of Saturn

PASADENA, Calif. - Hours after settling into orbit around Saturn, the Cassini spacecraft sent back "mind-blowing" photographs Thursday of the planet's shimmering rings that resembled a fine-grain piece of wood or a grooved phonograph record.

Scientists could not contain their excitement as the raw black-and-white pictures of the rings and the inky gaps between them arrived at NASA's Jet Propulsion Laboratory from more than 900 million miles away.

The photographs showed concentric bands — some dark, some light-colored, some broad, some extremely narrow. Some had wavy edges, some had sharp ones. Some had rippled surfaces, like corrugated cardboard. Some appeared smooth.

"Wow, look at that scallop on the inner edge. That's a beauty," said imaging scientist Jeff Cuzzi as a picture from the sunlit side of the rings was displayed.

Cassini, a spacecraft the size of a bus, passed between two of the rings late Wednesday and settled into orbit around the giant planet to begin the most detailed study ever of Saturn and many of its 31 moons. Imaging team leader Carolyn Porco watched the photographs stream in before dawn.

"It was beyond description, really, it was mind-blowing," she said. "I'm surprised at how surprised I am at the beauty and the clarity of these images. They are shocking to me."

The $3.3 billion mission is funded by NASA and the European and Italian space agencies. Cassini is the first spacecraft to orbit the solar system's second-largest planet. Pioneer 11 and Voyagers 1 and 2 made only fly-bys between 1979 and 1981.

Cassini passed through the rings unscathed and was in perfect condition, program manager Robert Mitchell said.

The rings, which have fascinated astronomers for centuries, were the mission's first priority in the minutes after achieving orbit because Cassini will never again be as close to them during its planned 76 orbits over four years.

Cassini images have five times higher resolution than the best Voyager pictures, Cuzzi said. He called the stream from Cassini "a very rich harvest of data."

The first images to arrive were dark and indistinct because Cassini photographed them from the side not illuminated by the sun. But they quickly became crisper.

"Look at that sharp edge. That brings tears to my eyes," Porco exclaimed.

The major rings, ranging in width from 30 miles to 188,000 miles, are named for the first seven letters of the alphabet — but in the order of discovery, not distance from Saturn. From closest to farthest they are D, C, B, A, F, G and E.

Subject to various vorces, including "shepherding" by Saturn's many moons, the rings have structures that scientists described with terms like "spiral waves," "density waves," "bending waves" and even "notes on a chord."

The causes of most of the observed structures are not known, Porco said.

The sharp edges, for example.

"Ring scientists love sharp edges. They have to be held sharp by some mechanism," Porco said. "We don't know the mechanism so we're intrigued by them."

On the Net:

Jet Propulsion Laboratory: http://www.jpl.nasa.gov

First Saturn Pictures Show Sharp-Edged Rings

PASADENA, Calif. (Reuters) - The spacecraft Cassini sent its first images of Saturn's majestic rings back to Earth on Thursday, showing surprisingly sharp edges and ripples of energy within the mysterious formations.

Scientists also got a bonus from the early data: the sounds of Saturn, as the craft passed through the "bow shock," or leading edge of the planet's magnetic field, which ebbs and flows like the ocean. The noise had a deep quality, rising to a guttural crescendo at the point where Cassini met the field.

Though they had little time to analyze what they were seeing and hearing, scientists said the data could help them explain the birth of the entire solar system.

"If you want to understand how the solar system was formed, you go to Saturn," said Carolyn Porco, leader of the Cassini imaging science team.

Program manager Robert Mitchell said the craft was in perfect health after a seven-year journey and had entered orbit so precisely that team leaders were now debating whether they needed to make a corrective move planned for Saturday.

The early photos, taken from the unlit side of the rings, were black and white and full of electronic "noise," but were clear enough to show fine ring structures and edges that were unexpectedly sharp, given all the colliding particles.

"Ring scientists love sharp edges. They're very mysterious -- they have to be held sharp by some mechanism," Porco said.

A second set of images, taken from the sunlit side of the rings, arrived about two hours later and was far sharper, showing the rings and gaps in much greater detail. With illumination, the close-up view of the "A" set of rings made them look something like the surface of a vinyl record.

Scientists were thrilled with the quantity and clarity of the images -- the closest pictures of the rings that will be taken during the mission, in some cases five times sharper than those taken by the Voyager missions more than 20 years ago.

"Citizens of Earth, I would like to present the majestic rings of Saturn," Ed Weiler, the associate administrator of NASA, said during a global press conference.


The images showed "density waves," disruptions in the particles in the rings caused by the energy of moonlets passing outside them, that scientists said could best be compared to the pattern of bunching and thinning out seen in traffic jams.

In addition, they showed "bending waves," where the rings had been warped by the effects of the passing moons.

Scientists were also able to construct their first full image of the planet's magnetosphere, using a new instrument flying for the first time on Cassini. The Voyager probes had been able to capture the magnetic bubble that surrounds the planet only in part.

Mission scientists, many of whom have devoted more than a decade to the Cassini project, cheered and called the photos "beautiful" and "mind-blowing."

"It's so flawless it almost seems faked -- but it's not," Porco said in live commentary from the Jet Propulsion Laboratory here.

The truck-sized probe slipped through those rings and entered orbit around Saturn on Wednesday night, after traveling 2.2 billion miles since its October 1997 launch. Along the way, it used the gravity of Venus, Earth and Jupiter to slingshot it out to the sixth planet from the sun.

Cassini is set to spend at least four years studying the planet, its rings and some of its 31 known moons.

It carries on its back a smaller craft, Huygens, which is designed to break away in December and plummet onto the surface of Titan for a brief study of that moon's atmosphere.

That portion of the mission was designed largely by the European and Italian space agencies. The $3 billion mission has been hailed as a model of international cooperation, with scientists from 17 countries participating.

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