Fig (1)
This three-image mosaic is the highest resolution view ever acquired of the north polar region of Saturn’s moon Enceladus.
Credit: NASA/JPL/Space Science Institute

On 12 March 2008, NASA's Cassini spacecraft performed a daring flyby of Saturn's moon Enceladus, flying about 15 km/s through icy plumes emanating from the south polar region of the moon. At closest approach, Cassini flew within only 50 km above the surface of Enceladus (505 km across); obtaining valuable samples that might indicate the presence of a water ocean or organics beneath the moon’s icy crust.

These plumes resemble terrestrial geysers, a volcanic phenomenon in which a hot column of water and steam erupts periodically from below the ground.

Scientists believe the geysers of Enceladus could provide evidence that liquid water exists beneath the icy crust of Enceladus. The geysers erupt from fractures extending across the moon's south pole, spewing out water vapor at approximately 400 m/s.

Fig (2)
This illustration shows how the ice particles and water vapor observed spewing from geysers on Saturn's moon Enceladus may be related to liquid water beneath the surface. The large number of ice particles and the rate at which they are produced require relatively high temperatures, close to the melting point of water. These warm temperatures indicate that there may be an internal lake of liquid water at or near the moon's south pole, where the geysers are present.
Credit: NASA/JPL

The new data provide a new view of the fractures that modify the surface, and will yield a better understanding of the geologic evolution of the moon's north pole and south pole.
New images demonstrate that compared to much of the southern hemisphere on Enceladus, the south polar region in particular, the north polar region is much older and pitted with craters of various sizes. These craters show different stages of disruption and alteration by tectonic activity, and probably from past heating from below.

"These new images are showing us in great detail how the moon's north pole differs from the south, an important comparison for working out the moon's obviously complex geological history," said Carolyn Porco, leader of Cassini’s imaging team. "And the success of yesterday's daring and very low-altitude flyby means this coming summer's very close encounter, when we get exquisitely detailed images of the surface sources of Enceladus' south polar jets, should be an exciting 'next big step' in understanding just how the jets are powered."

This flyby and another one planned for 9 October 2008 were so designed to allow Cassini's particle analyzers to dissect the "body" of the plume for information on the density, size, composition and speed of its particles.

Cassini's instruments discovered evidence for the geyser-like jets on Enceladus in 2005, finding that the continuous eruptions of ice water create a gigantic halo of ice dust and gas around Enceladus, which helps supply material to Saturn's E-ring.

Three more flybys of Enceladus are planned for 2008. In June 2008, Cassini will complete its prime four-year mission to Saturn. An extension of Cassini’s mission is proposed, and there would be more Enceladus flybys during this mission extension.

Further Reading

NASA’s JPL News Release
http://www.jpl.nasa.gov/news/news.cfm?release=2008-044

Cassini’s Official Websites
http://www.nasa.gov/mission_pages/cassini/main/index.html
http://saturn.jpl.nasa.gov/

Aymen Mohamed Ibrahem
Senior Astronomy Specialist