Since 2004, NASA’s Cassini spacecraft has been orbiting Saturn and its moons. On Monday, it soared past Saturn’s moon Dione for the last time. Yesterday’s flyby brought Cassini within 295 miles of Dione’s surface at 2:33 p.m. ET.
Yesterday’s flyby was the fifth and final targeted encounter with Dione. Targeted encounters require a burn to get the spacecraft in just the right position to set up a flyby. On August 9th, Cassini executed a 12-second burn to set up the August 17th encounter.
Out of all of Cassini’s close encounters with Dione, none was closer than the encounter in December 2011. At just 60 miles above the moon’s surface, Cassini was able to reveal exactly what the Voyager mission was seeing on Dione’s bright, wispy surface. When Voyager first imaged Dione, some suspected the wispy terrain were surface deposits of frost.
Cassini revealed them as bright icy cliffs.
The pattern of these features may indicate a stress pattern related to Dione’s orbital evolution and tidal stresses over time.
During yesterday’s flyby, Cassini’s team planned to gather gravity-science data of Dione. This type of data has only been gathered on a handful of Saturn’s 62 known moons.
“Dione has been an enigma, giving hints of active geologic processes, including a transient atmosphere and evidence of ice volcanoes. But we’ve never found the smoking gun. The fifth flyby of Dione will be our last chance,” Buratti says.
With Dione in its rear view, Cassini is setting up for its final year. It will finish a series of close moon flybys later this year. In late 2015, it will position itself for its most bold mission yet. The spacecraft will leave Saturn’s equatorial plane (where most of Saturn’s moons orbit) and edge closer to Saturn and its rings. It’s final year will be marked by repeatedly diving between the gas giant and its breathtaking rings before crashing into Saturn’s atmosphere in 2017.
The Best Images of Dione
Cassini’s multiple visits to Dione have yielded breathtaking images. You can check them out here. I’ll be highlighting some of my favorites below.
Dione (left) and Mimas (right) with Saturn in the background
Nope, I didn’t add Rhea (top) into the GIF. Cassini was 68,000 miles away from Dione when it snapped the series of images above. Rhea (949 miles across) is bigger than Dione (698 miles across), but Dione appears larger because it is much closer to Cassini at the time the images were captured.
During Cassini’s closest flyby, it snapped this image of Dione and two smaller moons, Epimetheus and Prometheus. Epimetheus is on the right while Prometheus sits just above Saturn’s rings near the center.
Check out the night side of Saturn and Dione hanging out in the top right.
Get Your Telescope Out This Week
National Geographic points out that backyard skywatchers can get a glimpse of Saturn’s Cassini division (the largest dark gap between Saturn’s rings) this week. Saturn’s bright rings are facing Earth right now.
Here’s a top-down view of Saturn from Cassini.
It won’t look this good through your telescope, but you should be able to easily make out the Cassini division in clear, dark skies.