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Entranced by a transit of Dione

Saturn’s 698-mile-wide moon Dione crosses the face of the giant planet in a phenomenon known as a transit. Transits play an important role in astronomy and can be used to study the orbits of planets and their atmospheres, both in our solar system and in others. By carefully observing and timing transits, scientists can more precisely determine the orbital parameters of planetary moons.

Observing

See the Moon meet Saturn and a star disappear on 22 August

As dusk fades to dark on Saturday, 22 August, observers in the British Isles and Western Europe with clear skies can see the first quarter Moon close above planet Saturn low to the southwest. But for those skywatchers with binoculars and small telescopes, an additional treat is in store as the Moon passes in front of (occults) a naked-eye star.

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Chasms on Dione

While not bursting with activity like its sister moon Enceladus, the surface of Saturn’s moon Dione is definitely not boring. Some parts of the surface are covered by linear features, called chasmata — bright icy cliffs among myriad fractures — which provide dramatic contrast to the round impact craters that typically cover moons.

News

Cassini’s last close flyby of Saturn’s moon Dione

NASA’s Cassini spacecraft will zip within 295 miles of Saturn’s moon Dione on Monday, 17 August — the final close flyby of this icy satellite during the probe’s long mission. After close flybys of other moons in late 2015, Cassini will depart Saturn’s equatorial plane to begin a year-long setup of the mission’s grand finale: repeatedly diving through the space between Saturn and its rings.

News

Scientists solve age-old planetary ring riddle

An international team of scientists has solved an age-old scientific riddle by discovering that planetary rings, such as those orbiting Saturn, have a universally similar particle distribution. The study also suggests that Saturn’s rings are essentially in a steady state that does not depend on their history.

News

Unusual red arcs discovered on icy Saturnian moon

Like graffiti sprayed by an unknown artist, unexplained narrow, arc-shaped, reddish streaks are visible on the surface of Saturn’s icy moon Tethys in new, enhanced-colour images from NASA’s Cassini spacecraft. The red arcs are among the most unusual colour features on Saturn’s moons to be revealed by Cassini’s cameras.

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Bright impact basin on Saturn’s icy moon Tethys

In this NASA/ESA Cassini mission image of Saturn’s 660-mile-wide moon Tethys, the giant impact basin Odysseus stands out brightly from the rest of the illuminated icy crescent. Some 280 miles across, Odysseus is one of the largest impact craters on Saturn’s icy moons, and may have significantly altered the geologic history of Tethys.