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Light and Dark: the Two Faces of Dione

Global map of Dione’s surface. NASA/JPL-Caltech/SSI/LPI

Saturn’s moon Dione (pronounced DEE-oh-nee) is a heavily-cratered, 700-mile-wide world of ice and rock, its surface slashed by signature “wispy lines” that mark the bright faces of sheer ice cliffs. But Dione has some strange colorations too, evident here in a global map created in 2014 from Cassini images. Its leading half—the side that faces “forward” as it moves around Saturn in its tidally-locked orbit—is pale and bright, while its trailing hemisphere is stained a brownish color, the result of surface interaction with  charged particles in Saturn’s magnetic field.

Read more from ESA here: Space in Images – Global colour mosaic of Dione and see more pictures and news about Dione here.

Rhea Eclipses Dione While Cassini Watches

Saturn's moons Rhea (front) and Dione (back) pass each other on Oct. 11, 2015. (NASA/JPL-Caltech/SSI/Jason Major)

Saturn’s moons Rhea (front) and Dione (back) pass each other on Oct. 11, 2015. (NASA/JPL-Caltech/SSI/Jason Major)

It’s been a while since I last made one of these: it’s an animation comprising 27 images acquired by Cassini in various color channels on October 11, 2015. It shows Saturn’s second-largest moon Rhea passing in front of the smaller and more distant* Dione, both partially illuminated by sunlight. I cleaned up some image artifacts from each frame and adjusted the levels to make the blacks black and not banded, like is often found in images like these. I also added a bit of a glow to the moons, to enhance the sense of light (and bring out some of the detail in the darker areas.)

There’s nothing particularly scientific here, just an enjoyment of the endless and ongoing dance of the spheres!

Check out an older moon animation of Rhea here.

*Dione is more distant from the Cassini spacecraft in these views; it’s actually closer to Saturn in its orbit than Rhea.

Cassini Bids Farewell to Dione with Some Fantastic Final Views

Mosaic of Saturn's 700-mile-wide moon Dione made from nine images acquired on Aug. 17, 2015. Saturn itself covers the entire background. (NASA/JPL/SSI)

Mosaic of Saturn’s 700-mile-wide moon Dione made from nine images acquired during its “D-5” flyby on Aug. 17, 2015. Saturn itself covers the entire background. (NASA/JPL/SSI)

NASA’s venerable Cassini spacecraft may still have another two years left in its exploration of the Saturn system but on Monday, August 17, it had its final intimate visit with Dione, one of Saturn’s largest natural satellites at nearly 700 miles (1,126 km) across. On that day Cassini passed within 300 miles (480 km) of Dione at 2:33 p.m. EDT (18:33 UTC), not its closest flyby ever but certainly near enough to get some truly spectacular views of the icy moon’s ancient and cratered surface.

Check out some of Cassini’s last close-up images of Dione below:

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Dione to Join the List of Moons with Underground Oceans?

Angled sunlight brings Dione's "wispy lines" into relief

A slushy, icy ocean may be hiding beneath Dione’s cratered crust

Earth may display its seas on its surface for all the Universe to see, but further out in the Solar System liquid oceans are kept discreetly under wraps, hidden beneath cratered surfaces of ice and rock. And while Saturn’s moon Enceladus sprays its salty subsurface ocean out into space, other moons are less ostentatious — Europa, Ganymede, Titan… all are thought to have considerable underground oceans of liquid water, based on measurements of their mass, density, and shape.

Now, scientists are suggesting that Saturn’s 700-mile-wide moon Dione may also have a subsurface ocean… and may have even once exhibited icy geysers like its smaller sibling Enceladus.

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Dione in Color

Although made mostly of ice and rock, Saturn’s moon Dione (pronounced DEE-oh-nee) does have some color to it — although mostly chilly hues of steel blue, as seen in this color-composite made from raw images acquired by Cassini on July 23.

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A Little Pas de Deux: Tethys and Dione

Saturn's moons Tethys and Dione pass each other from Cassini's point of view. (CLICK TO PLAY)

Saturn’s moon Tethys, its giant Odysseus crater in plain view, passes in front of of the slightly darker Dione in this animation made from several raw images acquired by Cassini earlier this month. Pretty cool!

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