Sharpshooting Enceladus

Cassini spacecraft reveals location of icy geysers on one of Saturn’s moons

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Swooping within 49 kilometers of Saturn’s tiny, geologically active moon Enceladus, the Cassini spacecraft has pinpointed the locations of the icy geysers that erupt from the southern hemisphere of this wrinkled moon’s surface.

| Cassini shot past the surface of Saturn’s moon Enceladus on August 11, recording seven high-resolution images that home in on warm regions within the moon’s tiger-stripe fractures, also known as sulci. This composite image shows two of the stripes; circles indicate the location of geysers that emanate from these fractures. NASA/JPL/Space Science Institute
CLOSE RANGE The Cassini spacecraft recently got very cozy with Saturn’s moon Enceladus. The craft approached within 49 kilometers of the moon’s surface and snapped photos that pinpoint specific locations of icy geysers within the moon’s fractures. NASA/JPL/Space Science Institute
| This close-up of an Enceladus tiger-stripe fracture known as Damascus Sulcus shows the location of two geysers (yellow circles). NASA/JPL/Space Science Institute

Images taken by Cassini during an Aug. 11 flyby have revealed new details about the south polar fractures, dubbed tiger stripes, from which the geysers emanate. The images reveal that the fractures are about 300 meters deep and have V-shaped inner walls. Some fractures are flanked by large deposits of fine material, another indication that those trenches are the geysers’ source. Blocks of ice, house-sized and larger, litter the surrounding, more finely fractured terrain.

The geysers blast icy particles, water vapor and trace amounts of organic compounds into space, and researchers are hoping to use the images and other Cassini data to determine whether these vents originate from a subsurface ocean. The craft’s recent detection of sodium in Saturn’s icy E ring, whose ice particles are supplied by Enceladus, suggests that the moon has an underground reservoir of salty water.

Icy particles line some of the fractures, even the regions between geysers. One explanation is that when warm vapor from an underground source rises to the cold surface, ice particles condense and settle on the ground, sealing off a vent. New jets may then erupt from other locations along the same fracture.

“At the limited spatial resolution on the tiger stripes that we had from previous flybys, we could not previously identify any unique morphological [shape], albedo [reflectivity] or color details that would allow us to distinguish the active vent locations from the rest of their tiger stripes,” notes Cassini researcher Paul Helfenstein of Cornell University.

The Aug. 11 passage was Cassini’s fifth close flyby of Enceladus and the nearest yet to the moon’s surface. From Cassini’s point of view, Enceladus streaked past at a relative speed of 64,000 kilometers per hour, making it extremely challenging to take sharp, smear-free images.

Helfenstein devised a strategy of pointing the craft far ahead of Enceladus and then turning the craft as quickly as possible in the direction of the moon’s path. That enabled the craft to take seven high-resolution images of the tiger stripes in rapid succession

Cassini will next pass by Enceladus on October 10, when the craft should venture even closer, within 25 kilometers of the moon’s surface. Five other flybys are planned.

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