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Cassini makes final flyby of Saturn's moon Dione

Morgan Rehnberg, Correspondent
Aug 24, 2015, 20:08 UTC

Sen—It may have two years left in its mission, but NASA’s Cassini spacecraft is already bidding members of the Saturn system farewell. This week that list grew to include the moon Dione, one of a host of icy worlds surrounding the sixth planet.

With many questions about the moon still unanswered, many of Cassini’s scientific instruments were zeroed in as the spacecraft arrived for its fifth targeted—and second closest—encounter. Skimming less than 500 kmfrom the surface of this 1123 km-wide object, the Imaging Science Subsystem was poised for some dramatic views.

In addition to its visible, infrared, and ultraviolet imaging systems, Cassini trained its thermal camera on some unusually warm regions of the surface noticed on previous visits and deployed the Cosmic Dust Analyzer in search of particles emanating from the moon. It also continued to develop a gravity mapof Dione, which will help scientists deduce its internal structure.


A spectacular view of Saturn's icy moon Dione, with giant Saturn and its rings in the background, just prior to the mission's final close approach to the moon on August 17, 2015. Image credit: NASA/JPL-Caltech/Space Science Institute

So what has Cassini taught us about this icy world? Like many of the other Saturnian satellites, Dione has been revealed as a more complex and active world than previously imagined. Its surface is marred not just by the typical accumulation of craters but also by chasms and ridges indicative of a more volatile past. Indeed, like its neighbor Enceladus today, Dione may once also have supported an ocean of liquid water beneath its surface. Perhaps it, too, had plumes that created their own now-lost ring of Saturn.

TheCassini-Huygens missionis a collaborative effort between NASA, ESA, and the Italian Space Agency. Launched in 1997, it reached Saturn in 2004 and has since been studying the planet, its moons, and its rings. In 2005, the Huygens probe made the first landing on Titan, Saturn’s largest moon. After completing its second mission extension in 2017, Cassini will make a series of close passes to the planet and then end its time at Saturn by plunging into the planet’s atmosphere.