This was the fifth close encounter with Dione during NASA’s Cassini mission’s long tour at Saturn. The mission’s closest-ever flyby of Dione was in December 2011, at a distance of 60 miles (100 kilometres).
“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 Carolyn Porco, Cassini imaging team lead at the Space Science Institute, Boulder, Colorado. “Right down to the last, Cassini has faithfully delivered another extraordinary set of riches. How lucky we have been.”Processed images from the flyby are available by clicking here, while raw, unprocessed images from the flyby are available here.
The main scientific focus of this flyby was gravity science, not imaging. This made capturing the images tricky, as Cassini’s camera was not controlling where the spacecraft pointed.“We had just enough time to snap a few images, giving us nice, high-resolution looks at the surface,” said Tilmann Denk, a Cassini participating scientist at Freie University in Berlin. “We were able to make use of reflected sunlight from Saturn as an additional light source, which revealed details in the shadows of some of the images.”
Cassini scientists will study data from the gravity science experiment and magnetosphere and plasma science instruments over the next few months as they look for clues about Dione’s interior structure and processes affecting its surface.Only a handful of close flybys of Saturn’s large, icy moons remain for Cassini. The spacecraft is scheduled to make three approaches to the geologically active moon Enceladus on 14 and 28 October, and 19 December. During the 28 October flyby, the spacecraft will come dizzyingly close to Enceladus, passing a mere 30 miles (49 kilometres) from the surface. Cassini will make its deepest-ever dive through the moon’s plume of icy spray at this time, collecting valuable data about what’s going on beneath the surface. The December Enceladus encounter will be Cassini’s final close pass by that moon, at an altitude of 3,106 miles (4,999 kilometres).After December, and through the mission’s conclusion in late 2017, there are a handful of distant flybys planned for Saturn’s large, icy moons at ranges of less than about 30,000 miles (50,000 kilometres). Cassini will, however, make nearly two dozen passes by a menagerie of Saturn’s small, irregularly shaped moons — including Daphnis, Telesto, Epimetheus and Aegaeon — at similar distances during this time. These passes will provide some of Cassini’s best-ever views of the little moons.
During the mission’s final year — called its Grand Finale — Cassini will repeatedly dive through the space between Saturn and its rings.
We may be losing Jupiter in the west at dusk, but two other planets are well placed in the late evening. Skywatchers in the UK and Western Europe should look low in the southern sky around 12am local time on 17, 18 and 19 June to see the waxing gibbous Moon in the vicinity of planets Mars and Saturn, plus first-magnitude star Antares in the constellation of Scorpius.
Although Saturn’s moons Dione (near) and Enceladus (far) are composed of nearly the same materials, Enceladus has a considerably higher reflectivity than Dione. As a result, it appears brighter against the dark night sky. This image was taken by NASA’s Cassini spacecraft in visible light with the narrow-angle camera on 8 September 2015.