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LOS ANGELES (AP) - Three years after gigantic geysers were spied on an icy Saturn moon, the international Cassini spacecraft is poised to plunge through the fringes of the mysterious plumes to learn how they formed.
Wednesday’s flyby will bring Cassini within 30 miles of the surface of Enceladus (en-SELL’-uh-duhs) at closest approach. The unmanned probe will be about 120 miles above the moon as it sweeps through the edge of the geysers and measures their chemical makeup.
The carefully orchestrated event will take Cassini “deeper than we’ve been before,” mission scientist Carolyn Porco of the Space Science Institute said in an e-mail.
Scientists long believed Enceladus, the shiniest object in the solar system, was cold and still because it resides hundreds of millions of miles from the sun. But recent evidence shows the Arizona-sized satellite is geologically active with a significant atmosphere and a relatively warm south pole.
In 2005, Cassini surprised scientists when it snapped images of geyser-like eruptions of ice particles and water vapor spewing from the south pole. The dramatic images effectively put Enceladus on the short list of places within the solar system most likely to have conditions suitable for extraterrestrial life.
Scientists generally agree the presence of water, organic compounds and a stable heat source are needed to support primitive life.
Previous measurements by Cassini showed the eruptions were frequent, with gases and particles venting from the surface at about 800 mph and forming plumes hundreds of miles high.
The source of the geysers is a mystery, but some theorize reservoirs of liquid water below the surface likely are supplying the ice and vapor seen in the plumes.
Until now, scientists have not been able to measure the plumes’ makeup in detail. Using its particle analyzers, Cassini will calculate the density, size and speed of the various gases and particles. The spacecraft’s cameras will also image the moon during the flyby.
Of particular interest is whether the plumes contain ammonia, which can keep water in liquid form and would bolster the theory that liquid water lies beneath.
“There’s not much for us … to do regarding the upcoming flyby except to hold our breaths and cross our fingers,” John Spencer of the Southwest Research Institute in Boulder, Colo., wrote on the Cassini blog.
The close encounter poses little danger to Cassini because the plume particles are small compared with the dust-sized debris the spacecraft is used to flying through while orbiting Saturn, scientists said.
The Cassini mission is a collaboration between NASA and the European and Italian space agencies.
On the Net:
Cassini mission: http://saturn.jpl.nasa.gov/home/index.cfm

via AOL

NASA’s Cassini spacecraft circling the planet Saturn will plunge through the outer fringes of an icy plume spewing out from cracks in one of the ringed world’s many moons on Wednesday.

Cassini will zip through the edges of immense frozen water vapor geysers gushing from fractures in the south polar region of Saturn’s moon Enceladus. The flyby is Cassini’s first of four swings past icy Enceladus this year, where the spacecraft will use onboard instruments to “sniff and taste” the satellite’s Old Faithful-like water-ice eruptions, mission managers said.

“This daring flyby requires exquisite technical finesse, but it has the potential to revolutionize our knowledge of the geysers of Enceladus,” said Alan Stern, associate administrator of NASA’s science mission directorate, in a statement.

At its closest approach, Cassini will skim just 32 miles above the surface of Enceladus before passing through the moon’s icy plume at an altitude of about 120 miles. The spacecraft will zoom past Enceladus at about 32,234 mph, snapping photos on approach and departure that will return the first-ever views of some northern regions, NASA officials said.

But Cassini will use particle analyzers during the flyby itself to determine the exact make up of the moon’s odd plume material, which contains water vapor and traces of carbon dioxide, methane and other gases.

“We want to know if there is a difference in composition of gases coming from the plume versus the material surrounding the moon,” said Hunter Waite, principal investigator for Cassini’s Ion and Neutral Mass Spectrometer at the Southwest Research Institute. “This may help answer the question of how the plume formed.”

NASA/JPL/SSIWispy fingers of bright, icy material reach tens of thousands of kilometers outward from Saturn’s moon Enceladus into the E ring, while the moon’s active south polar jets continue to fire away.Cassini first spotted Enceladus’ icy plume in 2005, when its onboard instruments recorded water vapor geysers rushing out to distances of up to three times the 310-mile wide moon’s diameter. The ice particles themselves are tiny, just one ten-thousandth of an inch or about the size of the width of a human hair but jet out of Enceladus at about 800 mph.

The apparently continuous eruptions appear to periodically give Enceladus a fresh coat of surface material and spew out ice dust that bolsters Saturn’s faint E-ring.

Cassini researchers already know that there are at least two types of particles pure water-ice and water-ice intermixed with other material in Enceladus’ plume.

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“We think the clean water-ice particles are being bounced off the surface and the dirty water-ice particles are coming from inside the moon,” said Sascha Kempf, deputy principal investigator for Cassini’s Cosmic Dust Analyzer at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. “This flyby will show us whether this concept is right or wrong.”

Cassini mission managers will watch how their spacecraft weathers Wednesday’s Enceladus flyby to aid planning for additional swings past the Saturnian moon. Cassini is due to make seven trips past Enceladus during its extended mission, and could swing closer to the moon should this weeks’ rendezvous go well, NASA officials said.

via MSN