Hansen-Stellar Occultation (5MB video)
On March 11, 2016, Enceladus passed in front of Epsilon Orionis (the central star in Orion’s Belt), and UVIS watched as the light from the star was altered as it passed through the plume. Such observations, known as stellar occultations, provide information about the density and composition of the plume.
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/
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