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What's New?
Cassini 'tastes' organic brew at Saturn’s geyser moon
March 26, 2008. Streams of high-density gas detected by Cassini’s Ultraviolet Imaging Spectromer (UVIS) on Saturn’s moon Enceladus match the locations of dust jets determined from Cassini images, labeled here with Roman numerals. The spectrograph pinpointed the locations of individual gas streams in the plume in a ‘stellar occultation’ which involves measuring the light of a star, (in this case, zeta Orionis), as it passed behind the plume from Cassini’s viewpoint. The blue line in this projection shows the path of the starlight through the plume,over the south polar region of Enceladus. The instrument looked at the star across this path in the direction indicated by the short blue lines.
Some of the dust jets appear to merge together in UVIS stellar occultation data. The dimming of starlight labeled “a” was caused by dust jets V and VII. The dimming of starlight marked as feature “b” is probably off-set too far to be associated with dust jet I, because the jet is not perfectly vertical. Dimming of starlight labeled “c” corresponds to dust jet VI, and “d” is dust jet III, with dust jet II in between. The individual jets come from sources with an area of less than 300 by 300 meters (1,000 feet square) – about the size of half a tennis court -- probably stretched out rectangularly along the tiger stripes. The new UVIS data indicate that the water molecules are blasting off from Enceladus at faster than 600 meters per second (about 1,300 miles per hour.
Credit: NASA/JPL/University of Colorado/
Two views of Iapetus
Saturn's odd, two-toned, walnut-shaped moon, Iapetus, has a ridge of surprisingly large mountains — the so-called "belly-band" — that lies directly on top of the equator. The moon also has a distinct difference in the brightness of its leading and trailing hemispheres, one as bright as snow and the other dark as tar. The ultraviolet-light image taken with UVIS (left) was taken during a flyby in December 2004. A visible light image taken on the same date is shown on the right for reference. The ultraviolet image indicates water ice abundance across the surface: the bright north polar terrain (shown in red) is the iciest region in this view. Away from the pole, as the color shifts to blue, less water ice is present in the surface. The darkest terrain, which includes very little water ice, is shown in light blue. The dark sky background viewed during the observation is shown as purple in this color scheme.
Cassini will make its only close flyby of Iapetus on Sept. 10, 2007, at about 1,640 kilometers (1,000 miles) from the surface which will be 100 times closer than Cassini's 2004 encounter, and will be the last time the spacecraft will aim its instruments at this moon. The irregular shape, the mountain ridge and Iapetus' brightness contrast are among the key mysteries scientists are trying to solve.
Credit: NASA/JPL/University of Colorado/Space Science Institute (PIA09970)
