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Cassini Space Probe is Settling in Around Saturn

Posted on: Wednesday, 2 August 2006, 06:00 CDT

By Dan Vergano

The Cassini spacecraft orbiting Saturn and headed for a series of close encounters with Titan, the planet's largest moon, also appears aimed for an extended stay at the ringed planet, the mission's chief says.

"The spacecraft is doing just remarkably well, performing practically flawlessly," says Cassini program manager Bob Mitchell of NASA's Jet Propulsion Laboratory.

Launched in 1997, the $3 billion international spacecraft arrived at Saturn just over two years ago, making a daring dash across the planet's rings to settle into orbit on a four-year mission.

At the mission's halfway point, the spacecraft launched the Huygens probe to Titan last year and has explored Saturn's rings in great detail, finding evidence of spokes and other unexpected shapes in the planet's six bands.

Next year, the space agency and its partners will decide whether to extend Cassini's mission. NASA has financed the orbit and the necessary science planning, Mitchell says. "Nothing is guaranteed," he says, but given the prospects of more discoveries and the spacecraft's good health, "at this point, the chances of not extending the mission seem pretty remote."

Only last week, Cassini reported the first definitive evidence that there are lakes of liquefied methane, known on Earth as natural gas, near Titan's north pole. One of the largest moons in the solar system at 3,200 miles across, Titan is a mini-world with a methane-rich atmosphere about 60% more dense than Earth's. Resolving a small mystery, "we can now say with confidence it appears these lakes are recharging Titan's atmosphere," says JPL's Steve Wall, deputy team leader of the radar imaging team.

The lake discovery came on a 590-mile-high flyby past the moon, one of the mission's 52 planned close encounters with Saturn's moons. Titan has another 29 flybys coming, says Mitchell, starting on Sept. 7 and coming in roughly two-week intervals thereafter. "Things are picking up," he says.

Titan's thicker-than-expected atmosphere has kept the flybys all above 590 miles out of fear that a dip too deep would skew the spacecraft's direction, sending it into "safe" mode and ending observations. So far, Cassini has mapped about 20% of Titan with radar, Wall says. He is confident that the radar will be able to pick out waves on Titan's lakes in an October flyby.

Although Cassini has shown that Titan has lakes, hills and weather, it is still a bizarrely alien world. Surface temperatures average around minus 290 degrees and the landscape is a mixture of frozen ice and tarry sludge. Rain there falls largely from clouds of liquefied methane.

For many planetary scientists, last year's discovery that the small moon Enceledus shoots a watery geyser from its south pole was a highlight of Cassini's stay at Saturn.

Most surprising, liquid water may hide within 30 feet of Enceledus' surface. University of Arizona scientist Jeffrey Kargel wondered in Science magazine whether the moon "might be life's most distant outpost."

The geyser find confirms that Enceledus is the source of Saturn's "E" ring, a broad and wispy band that circles some 110,000 miles above the planet.

Intrigued by the possibility that some sort of volcanic activity may warm water within Enceledus to a liquid state, mission scientists hope to pass very close to its south pole on a flyby planned for next year. Smaller than New Mexico, Enceledus exerts very little gravitational pull on Cassini, allowing a close pass over its surface.

"Some of the scientists want to fly right through the (geyser) plume," Mitchell says. "We are still deciding, but it's a safe bet it will be a close one."

Source: USA TODAY

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