August 1, 2013
Enceladus Jets Are Controlled By Saturn: Cassini
April Flowers for redOrbit.com - Your Universe Online
The proximity of Saturn's moon Enceladus to the ringed planet can change the intensity of the jets of water ice and organic particles that shoot out from the moon, according to data from NASA's Cassini spacecraft.The findings, published in Nature, add to the growing evidence a liquid water reservoir or ocean lurks under the icy surface of the moon. The Cassini data is the first clear observation the bright plume emanating from Enceladus' south pole varies in a predictable manner.
"The jets of Enceladus apparently work like adjustable garden hose nozzles," said Matt Hedman, a Cassini team scientist based at Cornell University. "The nozzles are almost closed when Enceladus is closer to Saturn and are most open when the moon is farthest away. We think this has to do with how Saturn squeezes and releases the moon with its gravity."
Cassini has been orbiting Saturn since 2004. In 2005, the spacecraft discovered the jets that form the plume, with water ice and organic particles that spray out from several narrow fissures nicknamed "tiger stripes."
"The way the jets react so responsively to changing stresses on Enceladus suggests they have their origins in a large body of liquid water," said Christophe Sotin, Cassini team member at NASA's Jet Propulsion Laboratory (JPL). "Liquid water was key to the development of life on Earth, so these discoveries whet the appetite to know whether life exists everywhere water is present."
Scientists have hypothesized for years that the intensity of the jets most likely varied over time. Until now, no one had been able to show they changed in a recognizable pattern. The new study, using Cassini's visual and infrared mapping spectrometer (VIMS), was able to see the changes by examining infrared data of the plume as a whole and examining data gathered over a long period of time.
The VIMS instrument enables the analysis of a wide range of data including the hydrocarbon composition of the surface of another Saturnian moon, Titan, and the seismological signs of Saturn's vibrations in its rings. Between 2005 and 2012, VIMS collected more than 200 images of the Enceladus plume.
According to the data, the plume was dimmest when the moon was at the closest point in its orbit to Saturn, gradually brightening until Enceladus was at the most distant point. At this point in the orbit, the plume was three to four times brighter than the dimmest detection - comparable to moving from a dim hallway into a brightly lit office.
The scientists were able to deduce a stronger gravitational squeeze near the planet reduces the opening of the tiger stripes and the amount of material spraying out by adding the brightness data to previous models of how Saturn squeezes Enceladus. The team believes as the gravity from Saturn relaxes farther away from the planet, the tiger stripes become more open, allowing the spray to escape in larger quantities.
"Cassini's time at Saturn has shown us how active and kaleidoscopic this planet, its rings and its moons are," said Linda Spilker, Cassini project scientist at JPL. "We've come a long way from the placid-looking Saturn that Galileo first spied through his telescope. We hope to learn more about the forces at work here as a microcosm for how our solar system formed."