Cassini Spacecraft Glides Over Icy Saturn Moon

This story was updated at 5:00 p.m. ET on April 28.

The Cassini spacecraft exploring Saturn got a new taste of the ringed planet's moon Enceladus late Tuesday when it flew over the icy satellite in a gravity experiment.

NASA's Cassini probe glided low over Enceladus Tuesday night to perform an experiment designed to probe the moon's interior composition. At closest approach, Cassini flew just 60 miles (100 km) above the surface of Enceladus at a speed of 15,000 mph relative to the moon.

The flyby, which took Cassini through the water-rich plume flaring out from Enceladus' south polar region, occurred on April 27 at 8:10:17 p.m. EDT (0010:17 GMT on April 28).

Scientists planned to use Cassini's radio science instrument to measure the gravitational pull of Enceladus against the steady radio link to NASA's Deep Space Network here on Earth. Detecting any changes will help scientists understand what lies beneath Enceladus' famous "tiger stripe" fractures, which spew water vapor and organic particles from the moon's south polar region.

The experiment was also expected to help scientists learn if the south polar region's sub-surface resembles a lava lamp. Scientists have hypothesized that a bubble of warmer ice periodically travels up to the crust and repaves it, explaining the quirky heat behavior and intriguing surface features of this region.

While Cassini's low flyby would have been ideal for snapping new photos of Enceladus, the primary objective of the mission was to collect information for the gravity experiment.

"Radio science was prime through this flyby, meaning that it got to control spacecraft pointing, which precluded pointing the optical instruments at Enceladus," said Robert Mitchell, Cassini program manager. "So, unfortunately, the imaging camera did not take up-close pictures."

The Cassini probe launched in 1997 and arrived at Saturn in 2004, where it dropped the European Huygens probe on the cloudy surface of the planet's largest moon Titan. Cassini was slated to be decommissioned in September of this year, but has received an extended mission that now runs through 2017.

The Cassini-Huygens mission is a joint project of NASA, the European Space Agency and the Italian Space Agency. It is managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif.

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