Water Plumes of Enceladus(a brief discussion is in your textbook; most of the following is from a NY Times slide show;homework question is on the last slide.)Until a few years ago, Enceladus, hereseen above Saturn's rings, was anondescript 310-mile-wide iceball, oneof dozens of moons around Saturn. Thisimage was taken by NASA's Cassinispacecraft at a distance of 1.3 millionmiles.1Then, in 2005, Cassini spotted somethingcoming off the bottom of Enceladus -- aplume of icy particles. On the left, amonochrome version shows hints of theplume; the colorized version on the rightmakes the extent of the plume moreobvious.Water Plumes of EnceladusImages of the south polar region showedintriguing "tiger stripe" fractures,including four prominent ones seen inthe lower right. The greenish areas in thisfalse-color image are believed to beboulders and deposits of coarser-grainedice.1After studying the plumes for months,scientists working on the mission reportedin March 2006 that they believed theplumes originated from geysers eruptingfrom underground reservoirs of liquidwater where temperatures warmed abovethe melting point of ice. Using images likethis false-color one, scientists latertriangulated eight specific origin sites ofthe plume jets, and all eight lay within thetiger stripes.Water Plumes of EnceladusCassini's spectrometer -- basically, heat sensor -- capturedthe first view of Enceladus in infrared light in Nov. 2006,right. Another image was taken July 2005, left. The dataindicated that the warm areas coincided with the tigerstripes. The distribution of temperatures changed littleduring those 16 months.1This image shows close-ups of two of the tigerstripes, named Baghdad and Cairo. The yellowcircles identify origins of two of the jets.Water Plumes of EnceladusThis artist's drawing shows one proposed "shear heating"model for Enceladus' jets. According to this model, tidalforces caused by Saturn's gravity as Enceladus loops aroundSaturn once every 1.37 days cause the sides of vertical faultsto rub against each other. That friction warms the ice enoughto produce the jets of ice and water vapor.1Even before discovery of the jets, planetary scientists suspectedthat Enceladus might be the source of the particles that make upSaturn's E-ring. In this Cassini image, the wispy fingers ofparticles from Enceladus stretch out thousands of miles.Homework question:Why does anyone think the geysers of Enceladus are water?I.e. why not some other liquid?Use the resources at your disposal--make sure your source is up-to-date.Check the links at the course
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