080828 Cassini pinpoints source of Enceladus jets

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Cassini pinpoints source of Enceladus jets
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: August 28, 2008

Thanks to an amazing new array of photographs of Saturn’s geologically active moon Enceladus, Cassini has pinpointed precisely the source of the icy jets seen erupting from the surface in previous fly-bys.

Map of the south polar region of Enceladus showing the correlation between jet sources identified in Cassini imaging data (and correlating to the roman numeral identification of the new images) and hot spots on the surface. Image: NASA/JPL/Space Science Institute.

Carefully targeted pictures uncover exquisite details in the
prominent south polar tiger stripe fractures from which the jets of icy particles, water vapour and traces of organics emanate. The photographs – captured as Cassini sped past the moon at a staggering 64,000 kilometres per hour – show the fractures are about 300 metres deep, with V-shaped inner walls. The outer flanks of several of the fractures show vast deposits of fine material, while large blocks of ice, tens of metres in size, litter the terrain surrounding the larger fractures.

"There appears to have been extensive fallout of icy particles to the ground, along some of the fractures, even in areas that lie between two jet source locations, though any immediate effects of presently active jets are subtle," says Carolyn Porco, Cassini imaging team leader.

Four source locations for the jets in tiger stripes Baghdad Sulcus, Cairo Sulcus and Damascus Sulcus are circled in this image and superimposed on the new high resolution imagery of Enceladus. Roman numerals correspond to locations indicated on the map above. Image: NASA/JPL/Space Science Institute.

Scientists are now focusing their efforts on the nature and intensity of the jetting process and its effects on the surrounding terrain. This information, coupled with observations by Cassini's other instruments, may answer the question of whether reservoirs of liquid water exist beneath the surface.

"This is the mother lode for us," says Carolyn Porco, Cassini imaging team leader. "[The images show] a place that may ultimately reveal just exactly what kind of environment, habitable or not, we have within this tortured little moon."

Combined with broader images showing the whole region, the new high-resolution snapshots provide critical documentation for understanding what may be powering the activity on Enceladus, and for the first time, planetary scientists are beginning to understand how freshly erupted surface deposits differ from older deposits. One current idea suggests that once warm vapour rises from underground to the cold surface through narrow channels, the icy particles may condense and seal off an active vent. Fresh jets may then appear elsewhere along the same fracture. The latest set of images clearly show evidence for the eruptions moving up and down the lengths of the tiger stripes over geologic time.