The Cassini spacecraft has discovered the long, cracked featuresdubbed "tiger stripes" on Saturn's icy moon Enceladus are very young --between 10 and 1,000 years young.
These findings support previous results showing the moon's southernpole is active. The pole had episodes of geologic activity as recentlyas 10 years ago. These cracked features are approximately 130kilometers long (80 miles), spaced about 40 kilometers (25 miles) apartand run roughly parallel to one another.
The cracks act like vents. They spew vapor and fine ice waterparticles that have become ice crystals. This crystallization processcan be dated, which helped scientists pin down the age of the features.
"There appears to be a continual supply of fresh, crystalline ice atthe tiger stripes, which could have been very recently resurfaced,"said Dr. Bonnie Buratti. She is a team member of the Cassini visual andinfrared mapping spectrometer at NASA's Jet Propulsion Laboratory,Pasadena, Calif. "Enceladus is constantly evolving and getting amakeover."
This finding is especially exciting because ground-based observershave seen tiny Enceladus brighten as its south pole was visible fromEarth. Cassini allows scientists to see close up that the brighteningis caused by geologic activity. When NASA's Voyager 2 spacecraft flewover the moon's north pole in 1981, it did not observe the tigerstripes.
Cassini's visual and infrared mapping spectrometer shows water iceexists in two forms on Enceladus: in pristine, crystalline ice andradiation-damaged amorphous ice.
When ice comes out of the "hot" cracks, or "tiger stripes," at thesouth pole, it forms as fresh, crystalline ice. As the ice near thepoles remains cold and undisturbed, it ages and converts to amorphousice. Since this process is believed to take place over decades or less,the tiger stripes must be very young.
"One of the most fascinating aspects of Enceladus is that it is sovery small as icy moons go, but so very geophysically active. It's hardfor a body as small as Enceladus to hold onto the heat necessary todrive such large-scale geophysical phenomena, but it has done justthat," said Dr. Bob Brown. Brown is a team leader for the visual andinfrared mapping spectrometer at the University of Arizona, Tucson."Enceladus and its incredible geology is a marvelous puzzle for us tofigure out."
Adding to the already mounting evidence for an active body is thecorrelation of results from multiple instruments. Cassini's camerasprovided detailed images of the south polar cap, in which the tigerstripe fractures were found to be among the hottest features.
The timing of the craft's ion and neutral mass spectrometer and thecosmic dust analyzer observations seems to indicate the vapor and finematerial are originating from the "hot" polar cap region. These dataalso indicate the production of water vapor and ejection of finematerial are connected, as they are in a comet. This suggests thatvapor and dust-sized icy material are coming from the tiger stripes.
Enceladus is on a short list of bodies in our solar system wherescientists have found internal activity. The others are the volcanoeson Jupiter's moon Io and geysers on Neptune's moon Triton.
Data for these measurements were taken during Cassini's closestflyby on July 14, 2005. The spacecraft came within 175 kilometers (109miles) of the surface of Enceladus. Enceladus is 500 kilometers (314miles) across and has the most reflective surface in the solar system.
The Cassini-Huygens mission is a cooperative project of NASA, theEuropean Space Agency and the Italian Space Agency. The Jet PropulsionLaboratory, a division of the California Institute of Technology inPasadena, manages the mission for NASA's Science Mission Directorate,Washington.
For information about the Cassini-Huygens mission on the Web, visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov . For information about NASA and agency programs on the Web, visit http://www.nasa.gov/home/index.html .
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