The Cassini spacecraft's tour of Saturn has been one of NASA's most successful planetary missions. The spacecraft's amazing discoveries and images have revolutionized our knowledge of the ring world and its moons. The spacecraft has recently uncovered evidence that Saturn's moon, Enceladus, harbors a large underground ocean.
One of Cassini's major highlights was the 2005 discovery of water-ice geysers erupting from the surface of Saturn's moon Enceladus. This small moon is only one-seventh the size of Earth's moon. The geysers, which jet out at a distance three times the diameter of Enceladus, shoot particles into Saturn's expansive ring system. Based on this discovery, scientists believe that liquid water may be found just beneath the surface of Enceladus. New data from Cassini on Enceladus' gravity field support the theory that an ocean is hidden inside the moon.
Gravity measurements suggest to scientists that a large ocean about 6 miles deep lies beneath an ice shell about 19 to 25 miles thick. Differences in the moon's gravity field, such as those caused by mountains on the surface or variations in underground composition, can be detected as minute changes in the spacecraft's velocity. These changes in velocity can be as little as less than one foot per hour. This precision has yielded evidence of a zone below the moon's south pole with higher density than other portions of the interior.
Cassini was launched in 1997 from Cape Canaveral, Fla. After traveling seven years and 2.2 billion miles, the spacecraft reached orbit around Saturn in June 2004. During the past 10 years, Cassini has flown near Enceladus 19 times with three flybys between 2010-12.
Scientists have been excited about Cassini's discovery of Enceladus' water geysers in 2005 and the likelihood of a hidden ocean because of the possibility that the moon's wet environment could be a potential home for microbial life.