NASA's Cassini spacecraft, which has been sailing around the Saturn system for more than 11 years, will make its final close approach to the ocean-bearing moon Enceladus on Saturday.
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One of the most significant findings of the entire Cassini mission, which is due to end in September 2017, is that the small moon has plumes of organics-laced vapor and ice shooting out into space from cracks in the southern polar region.
Scientists believe the plumes stem from a global ocean sealed beneath Enceladus' icy surface, and that the ocean is in contact with rock, which on Earth at least sets the stage for chemistry and environments suitable for life.
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Cassini is due to pass 3,106 miles from Enceladus at 12:49 p.m. EST. Scientists want to use the flyby to study how much heat is coming up through the ice from the moon's interior. The measurements will help researchers figure out what is driving Enceladus' plumes.
"Understanding how much warmth Enceladus has in its heart provides insight into its remarkable geologic activity," Cassini project scientist Linda Spilker, with NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement.
Cassini will continue to observe Enceladus during the remainder of its mission, but it will be at least four times farther away than Saturday's close approach.
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Cassini has been as close as 16 miles above Enceladus, a pass completed in October 2008. Saturday's flyby is Cassini's 22nd visit to Enceladus.
"We won't get this close to Enceladus again with Cassini, but our travels have opened a path to the exploration of this and other ocean worlds," Spiker said.