In the search for life, astronomers follow the water. Ten years ago, the search led them to Saturn's moon Enceladus, where they discovered several plumes on the south pole spewing water into space. In 2014, scientists finally found their source: a huge lake about 20 miles under the surface ice. Luciano less of the University of Rome La Sapienza and his colleagues suspected such an underground reservoir might exist, so they used NASA's Cassini probe to investigate. The spacecraft measured Enceladus' gravitational tug at various points during three passes just 30 to 60 miles from the surface. The stronger gravity's pull, the more mass lay directly below.
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