Cassini Prepares for Monday Flyby of Saturn Moon
This three-image mosaic is the highest resolution view yet obtained of Enceladus' north polar region. The view looks southward over cratered plains from high above the north pole of Enceladus. NASA's Cassini probe caught this view during a March 12, 2008 flyby.
Credit: NASA/JPL/Space Science Institute

NASA's Cassini spacecraft is going to get another up-close-and-personal look at Saturn's moon Enceladus on Monday. Scientists hope the glimpse at fractures on the icy moon's surface will provide clues as to how the jets spewing from them form.

The spacecraft will zoom past the tiny moon just 30 miles (50 kilometers) over the surface. Immediately after closest approach, Cassini will train its cameras onto the fissures that run along Enceladus' south pole.

Jets of icy water vapor, first discovered by Cassini in 2005, erupt hundreds of miles into space from these large cracks. The eruptions create a giant halo of ice and gas around Enceladus that helps supply material to Saturn's E-ring.

Cassini's cameras, which collect light in the infrared, visible and ultraviolet wavelengths, will aim to take high resolution images, as fine as 23 feet (7 meters) per pixel, of the known active spots on three of the prominent "tiger stripe" fractures.

"Our main goal is to get the most detailed images and remote sensing data ever of the geologically active features on Enceladus," said Paul Helfenstein, a Cassini imaging team associate at Cornell University in New York. "From this data we may learn more about how eruptions, tectonics and seismic activity alter the moon's surface."

Infrared observations, which detect temperatures on the surface, could help scientists determine if water, in vapor or liquid form, lies close to the surface.

"We'd like to refine our numbers and see which fracture or stripe is hotter than the rest because these results can offer evidence, one way or the other, for the existence of liquid water as the engine that powers the plumes," said Cassini team member Bonnie Buratti of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Cassini's observations should also help determine the size of the ice grains that spew from the jets, as well as distinguish any other elements mixed in with the ice, such as oxygen, hydrogen or organics.

"Knowing the sizes of the particles, their rates and what else is mixed in these jets can tell us a lot about what's happening inside the little moon," said Cassini team member Amanda Hendrix, also of JPL.

This next flyby follows a previous close approach in March during which Cassini was to sample the material emanating from the plumes. A software glitch kept the spacecraft from carrying out its sampling mission, but it did return the most detailed images of the moon to date.

Monday's flyby will be followed by two more in October. The attempt on Oct. 9 will also try to sample one of the icy plumes, while the Oct. 31 flyby will image the surface again. Cassini, currently on an extended two-year mission following the June 30 completion of its four-year primary mission, entered orbit at Saturn July 1, 2004.