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Monday, August 18, 2008

NASA Has Its Closest Look at Geysers on Saturn Moon

By KENNETH CHANG

NASA

An image of fissures along the surface of Enceladus, a frozen moon of Saturn, taken on Monday by the Cassini spacecraft. More Photos »

Exquisite close-ups of fissures on a tiny frozen moon of Saturn will provide the latest clues in solving the riddle of how a 310-mile-wide ice ball could possibly be shooting geysers of vapor and icy particles.

Since the discovery of the jets in 2005, the moon, Enceladus, has jumped to near the top of the list of potential places for life in the solar system. A warm spot near Enceladus’s south pole powers the jets and may also melt below-surface ice into water, a necessity for living organisms.

On Monday, the NASA spacecraft Cassini made its latest flyby of Enceladus (pronounced en-SELL-ah-dus), passing 30 miles above the moon’s surface at 64,000 miles per hour.

Despite the high speed, Cassini was able to take razor-sharp images that, at seven meters per pixel, offer a resolution 10 times greater than earlier views. Scientists can now clearly see the V-shaped walls of the fractures, which are nearly 1,000 feet deep. Team members likened the accomplishment to taking a photo of a roadside billboard using a telephoto lens held out the window of a speeding car.

“If there is one set of images from this mission that illustrates how skilled we have become as planetary explorers, this is it,” said Carolyn Porco, leader of Cassini’s imaging team. “They are the most astounding images of any planetary surface that our cameras have so far taken.”

The observations should help scientists understand how geological processes can persist on such a small body, which is being heated by tidal distortions induced by Saturn.

A series of long fissures known as tiger stripes scars Enceladus’s south polar region, and earlier observations allowed the Cassini scientists to triangulate the origin of the jets within the fissures and show that the warm spots coincide with them.

In a flyby in March, Cassini flew through the plume and detected organic molecules, the carbon-based molecules that could provide the building blocks for life. Cassini also detected water vapor, carbon dioxide and carbon monoxide. The composition was surprisingly similar to that of a comet, scientists said.

At first glance, nothing in the landscape differentiates the active jet areas from other parts of the fissures. “We have a lot of interpretation to do,” Dr. Porco said. “The effects appear to be subtle.”

Comparison with other data taken during the flyby — like temperatures — should provide more clues.

The researchers see smooth areas on Enceladus that appear to be piles of ice particles that have fallen back to the surface. “Like snow,” Dr. Porco said. “We’re pretty sure we’re seeing that in these pictures.”

Paul Helfenstein, the team member who developed the technique for taking the high-speed, up-close pictures, said: “We can actually count boulders on the surface. We can look at details and distinguish fresh deposits.”

In the fall, Cassini is to make an even closer near-miss of Enceladus, passing within 15 miles of the moon’s surface.

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