Secrets of Saturn Moon's Interior Probed by Cassini Spacecraft
NASA's Casini spacecraft obtained this raw image of Enceladus on April 26, 2010. The camera was pointing toward Enceladus at approximately 946,585 kilometers away, and the image was taken using the CL1 and IR3 filters. This image has not been validated or calibrated. A validated/calibrated image will be archived with the NASA Planetary Data System in 2011.
Credit: NASA/JPL/Space Science Institute

Scientists are eagerly poring over new observations of Saturn's moon Enceladus ?beamed to Earth from NASA's Cassini spacecraft from a flyby last week that measured the moon's gravitational tug in an experiment to determine its interior structure and composition.

The flyby, which occurred April 27 at 8:10:17 p.m. EDT (0010:17 GMT on April 28), took Cassini through the water-rich plume that flares out from Enceladus' south polar region. At closest approach, Cassini was about 100 kilometers (60 miles) above the surface of Enceladus, at a speed of 15,000 mph relative to the moon.

In a new Enceladus photo released by NASA, the moon looks like a crisp orb in space with one end ? the south pole known to be home to icy geysers ? appearing hazy through the plumes there.

Cassini's low flyby would have been ideal for snapping new photos of Enceladus, but the primary objective of the mission was to collect information for the gravity experiment. The new photo, for example, is a raw, unprocessed image.

"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."

Instead, the imaging camera was only able to obtain more distant pictures.

As part of Cassini's 26-hour gravity observation, a steady radio link to NASA's Deep Space Network on Earth enabled Cassini scientists to use the radio instrument to measure the variations in the gravitational pull of Enceladus.

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. 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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