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Spacecraft zips over Saturn's geyser-spurting moon

WASHINGTON (Reuters) - A spacecraft whizzed past Saturn’s moon Enceladus on Wednesday and through a huge geyser spurting from its south pole, collecting samples of ice and gas shooting about 500 miles (800 km) into space.

Scientists involved in the joint U.S.-European mission are hoping observations and samples collected by the Cassini spacecraft will enable them to better understand one of the most dramatic geological features of the entire solar system.

Geysers reminiscent of the famed Old Faithful at Yellowstone National Park in the United States -- only on a massive scale -- are shooting continuously off Enceladus at about 900 miles per hour (1,450 kph). It is one of about 60 moons of Saturn.

Some scientists think the source of the geysers may be heated liquid water -- perhaps even an ocean -- under the frozen surface of Enceladus (pronounced en-SELL-ah-dus).

The geysers may also be the source of the particles in one of Saturn’s rings.

Amanda Hendrix, a scientist involved in the mission from NASA’s Jet Propulsion Laboratory in Pasadena, California, said Cassini was passing as close as 30 miles (50 km) above the surface, although not that close around the geysers.

Hendrix said Cassini was about 120 miles (200 km) above the moon’s surface as it flew through the edge of a plume erupting from the south pole.

Hendrix said its findings were not immediately available, but preliminary results could be made public on Thursday.

“We will measure ice particles and vapor, and different kinds of gases -- water vapor for sure, and we’ll see what other kinds of gases are present,” Hendrix said.

Cassini’s instruments will try to determine the density, size, composition and speed of the gas and particles shooting off the surface. In addition to ice, the plumes seem to contain carbon dioxide, methane and ammonia in small amounts.

The possibility of heated water has some scientists wondering whether Enceladus might harbor conditions that could support life, even if only microbial organisms. Liquid water is thought to be a necessary ingredient for life.

“If there is hot, liquid water under the surface, then that does bring in the question of whether life could exist there,” Hendrix said.

“Since we’re sensing the composition of the plume, really what we’re sensing is the composition of the sub-surface region -- because the gas and the particles are coming from underneath the surface,” Hendrix added.

Enceladus, with a diameter of 310 miles (500 km), is one of the solar system’s brightest objects. Encased in ice, it reflects almost 100 percent of the sunlight that strikes it. It is one of Saturn’s innermost moons.

The U.S. space agency does not believe that flying through the plume posed much threat to the spacecraft because the particles are so small. Cassini often passes through regions made up of dust-size particles in its ongoing mission around Saturn.

Cassini in 2005 revealed for the first time that geysers were erupting off Enceladus. The spacecraft is due to fly by Enceladus three more times in 2008.