Brand new images of the pockmarked, icy landscape of Dione, mark the Cassini spacecraft’s final close approach of the small Saturn moon. Two of the images reveal the surface of the frozen world at the best resolution ever seen.
The Cassini spacecraft, which passed 474 kilometres (295 miles) above Dione’s surface on 17 August, has skimmed the moon four times before during its long tour of the Saturn system. While the resolution of the new images is breathtaking, this isn’t the mission’s closest-ever flyby of Dione – Cassini managed to get 100 kilometres (60 miles) above the moon’s surface back in December 2011.
Carolyn Porco, who leads the Cassini imaging team at the Space Science Institute in Boulder, Colorado, is proud of what the spacecraft has accomplished since its launch in October 1997. “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,” she says. “Right down to the last, Cassini has faithfully delivered another extraordinary set of riches. How lucky we have been.”
The main aim of the flyby was to take gravity measurements rather than imaging the moon – this meant that capturing shots of the surface was tricky since 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,” says 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 the images.”
Over the next few months, Cassini scientists will be taking a look at measurements from the gravity science experiment as well as the magnetosphere and plasma science instruments as they hunt for clues surrounding Dione’s interior structure and the processes affecting its surface.
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 Enceladus on 14 and 28 October as well as 19 December. During the 28 October approach, the spacecraft will pass a mere 49 kilometres (30 miles) above the surface. Cassini will also make its deepest-ever dive through the moon’s plume of icy spray during this time, collecting valuable data about what’s happening beneath the surface.
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 50,000 kilometres (30,000 miles). 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 – the spacecraft will repeatedly dive through the gap between Saturn and its rings.
You can check out the full gallery of Cassini’s new images of Dione by visiting the Cassini Imaging Central Laboratory for OPerationS (CICLOPS) website.