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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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Dawn Finds Similarities Between Ceres and Saturn’s Moons

Ceres (left, Dawn image) compared to Tethys (right, Cassini image) at comparative scale sizes. (Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA and NASA/JPL-Caltech/SSI. Comparison by J. Major.)

Ceres (left, Dawn image) compared to Tethys (right, Cassini image) at comparative scale sizes. (Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA and NASA/JPL-Caltech/SSI. Comparison by J. Major.)

Around 600 miles wide, covered in craters and cliffs, a composition of rock and water ice… these are descriptions of both several of Saturn’s moons and the dwarf planet Ceres, based on recent observations by NASA’s Dawn spacecraft. New topographical maps show that, in terms of surface features anyway, Ceres shares similarities with Saturn’s icy satellites.

“The craters we find on Ceres, in terms of their depth and diameter, are very similar to what we see on Dione and Tethys, two icy satellites of Saturn that are about the same size and density as Ceres,” said Paul Schenk,  Dawn science team member and a geologist at the Lunar and Planetary Institute (LPI) in Houston, TX. “The features are pretty consistent with an ice-rich crust.”

Read more in my article on Universe Today.

Hyperion in Color: a Composite from Cassini’s Last Visit

RGB color-composite of Hyperion from Cassini's May 31, 2015 flyby. NASA/JPL-Caltech/SSI. Edited by Jason Major.

RGB color-composite of Hyperion from Cassini’s May 31, 2015 flyby. NASA/JPL-Caltech/SSI. Edited by Jason Major.

Here’s a color view of Hyperion made from raw images acquired in optical wavelengths by Cassini during its flyby on May 31, 2015 – the last pass it will make by this moon during its mission. Read more about this flyby here.

Cassini To Make Its Last Pass Of Hyperion

Mosaic of Hyperion from Cassini images acquired Sept. 26, 2005. (NASA/JPL/SSI)

Mosaic of Hyperion from Cassini images acquired Sept. 26, 2005. (NASA/JPL/SSI)

This coming Sunday, May 31, the Cassini spacecraft will perform its last close pass of Hyperion, Saturn’s curiously spongelike moon. At approximately 9:36 a.m. EDT (13:36 UTC) it will zip past Hyperion at a distance of about 21,000 miles (34,000 km) – which may sound like a lot but but it’s even closer (by 17,500 miles/28,160 km) than it was when the image above was acquired.

Cassini will not come that close to Hyperion or make any flybys of it at all for the remainder of its mission, which will come to an end when it dives down into Saturn’s atmosphere in September 2017.

Read more in my article on Universe Today.

UPDATE 6/1/15: The images from the flyby are in! See a few of them below…

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Icy Tendrils in Saturn’s E Ring Traced Back to Enceladus

Cassini images of Enceladus in the E ring (top left, upper center) and computer-generated models of the same scenes. Views from 2006 and 2013, respectively. (NASA/JPL-Caltech/Space Science Institute)

Cassini images of Enceladus in the E ring (top left, upper center) and computer-generated models of the same scenes. Views from 2006 and 2013, respectively. (NASA/JPL-Caltech/Space Science Institute)

As the ice-encrusted moon Enceladus makes it way along its orbit around Saturn it gets repeatedly squeezed by the giant planet’s gravity, like a frozen stress ball with water-filled insides. This constant squeezing and relaxing generates friction heat in the moon’s crust, which could be responsible for keeping some of its internal water liquid and spraying it out into space from long canyons that cut across its southern pole. And sometimes more ice gets shot out than at other times, forming a trail of long tendrils that stretch into the “E” ring – a hazy, diffuse doughnut around Saturn made from Enceladus’ icy exhaust.

These tendrils had been observed by the Cassini spacecraft since 2006, but only now have they been positively confirmed to be the results of specific geysers on the 318-mile-wide moon.

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Cassini Spots the Sombrero Galaxy from Saturn

M104 imaged five years apart from Cassini on April 12, 2015 (left) and from the Subaru Telescope on April 12, 2015 (right). Credits: NASA/JPL/SSI/J. Major and NAOJ.

M104 imaged five years apart – from Cassini on April 12, 2015 (left) and from the Subaru Telescope on April 12, 2015 (right). Credits: NASA/JPL/SSI/J. Major and NAOJ.

We’re all used to seeing fantastic images of Saturn and its family of moons from NASA’s Cassini spacecraft, which has spent the last decade in orbit around the ringed world. But every now and then Cassini aims its cameras outwards, capturing images of the sky beyond Saturn – just like we might look up at the stars from here on Earth. And while it’s not designed to be a deep-space observatory like Hubble or Subaru (or even like a modest backyard telescope, really) Cassini can still resolve many of the same stars we can easily see in the night sky… and, on April 12, 2015, it spotted something much farther away: the Sombrero Galaxy (M104), 29 million light-years distant!

Coincidentally Cassini grabbed its image of M104 exactly five years after it was imaged with Japan’s Subaru Telescope, located atop Mauna Kea.

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