Cassini to explore Saturn

Cassini will rendezvous with Saturn on July 1, after travelling 1 billion miles, and will begin a mission that may last for many years.

Two months from now, headlines about spacecraft exploring other worlds will shift from the exploits of NASA's two Mars explorers to a pair of probes now careening towards glorious Saturn, reports UPI.

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If all goes well, the Cassini spacecraft will rendezvous with the giant planet on July 1, after travelling nearly one billion miles, and will begin a mission that could last for many years.

Launched on Oct 15, 1997, Cassini is set to train its sensitive instruments on Saturn's atmosphere, its extraordinarily complex ring system and its array of 31 known moons.

Six months later, in early January 2005, the European Space Agency's Huygens probe, which has piggy-backed aboard Cassini, will detach from the orbiter, plunge into the thick atmosphere of Saturn's largest moon, Titan, and attempt to land on its surface.

Cassini is named for the 17th-century Italian astronomer who discovered four of Saturn's moons and, more famously, the strange gap in the planet's ring system that is now named for him.

Huygens is named for the Dutch scientist and mathematician who helped improve the quality of telescopes, also in the 17th century.

NASA officials have called Cassini-Huygens "one of the most ambitious missions ever launched into space".

Loaded with 18 exquisitely sensitive instruments — 12 on the orbiter and six on the probe — that are capable of performing a variety of scientific measurements, the twin craft have been equipped to investigate all the important characteristics of the Saturn system that their builders could anticipate.

Given the capability of the spacecraft, and given Saturn's formidable list of unique characteristics, the tenure of Cassini-Huygens within the Saturnian system promises to flood earthbound scientists, both with discoveries to savour and with more mysteries to ponder.

Even what scientists already know is amazing:

• Second-largest Saturn is perhaps the most arresting sight in the solar system. Its stunning rings are 185,000 miles in diameter -- more than twice the size of Jupiter -- but only about a half-mile thick.

• Its 31 known moons include Titan, which is larger than Mercury and is the only moon in the solar system with its own atmosphere -- which is thicker than Earth's atmosphere.

• Saturn has the distinction of being the only known planet that is less dense than water. That means if it could be placed in a gigantic bathtub it actually would float.

• Saturn has an extremely stormy atmosphere, outclassing even Jupiter, with winds clocked at more than 1,100 miles per hour near its equator.

• The surface of Mimas has been scarred by a crater so big the impact nearly shattered Saturn's small moon. Scientists think Mimas might have sustained even larger impacts during the solar system's history, and perhaps was broken up and gravitationally reassembled several times.

• Another of Saturn's moons, Iapetus, is bright and icy on one side and dark and dusty on the other.

The rings are what set Saturn apart from the rest of the planets in the solar system.

Made up by billions and billions of ice and rock particles of all sizes -- from small debris to boulders as big as houses -- the rings orbit Saturn at varying speeds. They are so big they would fill three-quarters of the distance between Earth and the moon.

Although popular satellite images show only five main rings -- named "A" through "E" -- and a secondary, "F" ring, there really are hundreds of rings, all thought to be pieces of shattered comets, asteroids or moons that broke apart because they swung a little too close to Saturn.

Actually, Saturn's thin F ring could prove to be the most fascinating -- and the key to the entire ring system -- because it seems to be held in place by two tiny "shepherd" moons.

Named Prometheus and Pandora -- in keeping with the tradition of drawing from mythology for newly discovered solar system members -- the moons act like a pair of herding sheepdogs.

Planetary scientists, such as David Grinspoon of the Southwest Research Institute in Boulder, Colorado, are beginning to think Saturn's ring system is a relatively temporary phenomenon.

It might be, Grinspoon said, that humans are merely fortunate to be living at a time when Saturn's rings are so glorious. Perhaps in a matter of some millions of years, they will dissipate, relegating Saturn to the second-class status now occupied in the solar system by Uranus and Neptune.

Or, the rings have persisted only because Prometheus and Pandora preserve their integrity.

Cassini will attempt to learn more about the dynamics of the rings during its operational lifetime, along with exploring the host of intriguing facets that make up the real "Lord of the Rings."