NASA's Cassini spacecraft has been studying Saturn and its moons including Dione, Titan and Rhea for the last 11 years. On Aug. 17, the probe passed 295 miles above the surface of Dione marking its fifth close encounter with the natural satellite.
Measuring about 698 miles in diameter, Dione is the 15th biggest moon in the Solar System. It is more massive compared with all known moons that are smaller than itself combined.
Dione, which orbits Saturn every 2.7 days, laps around the planet at about the same distance as the moon orbits planet Earth. During its last close rendezvous with this alien world, Cassini captured images of the small and icy moon, two of which show Dione's surface at the best resolution ever.
Scientist looked forward for these high-resolution images, particularly those of the moon's north pole in the hope of knowing if Dione has geological activity.
"Dione has been an enigma, giving hints of active geologic processes, including a transient atmosphere and evidence of ice volcanoes," said Bonnie Buratti, a member of the Cassini science team at NASA's Jet Propulsion Laboratory. "But we've never found the smoking gun. The fifth flyby of Dione [was] our last chance."
NASA released the images taken by the spacecraft on Friday. Interestingly, the primary scientific focus of the flyby was not actually imaging but gravity science, which made capturing the images of Dione tricky because the probe's camera was not in control of where the spacecraft pointed.
"I am moved, as I know everyone else is, looking at these exquisite images of Dione's surface and crescent, and knowing that they are the last we will see of this far-off world for a very long time to come," said Cassini imaging team lead Carolyn Porco, from the Space Science Institute. "Right down to the last, Cassini has faithfully delivered another extraordinary set of riches. How lucky we have been."
Cassini is now busy accomplishing what are considered as the last tasks in its to do list as it is now headed for a destructive dive into Saturn come September 2017.
Cassini mission deputy project scientist Scott Edgington said that the latest flyby is the last chance scientists had in many years to come to see Dione up close. He added that the spacecraft has offered insights into the mysteries of the icy moon as well as gave new questions for researchers to ponder.