vendredi 21 août 2015

Cassini's Final Breathtaking Close Views of Dione












NASA - Cassini Mission to Saturn patch.

August 21, 2015


Image above: This view from NASA's Cassini spacecraft looks toward Saturn's icy moon Dione, with giant Saturn and its rings in the background, just prior to the mission's final close approach to the moon on August 17, 2015. Image Credit: NASA/JPL-Caltech/Space Science Institute.

A pockmarked, icy landscape looms beneath NASA's Cassini spacecraft in new images of Saturn's moon Dione taken during the mission's last close approach to the small, icy world. Two of the new images show the surface of Dione at the best resolution ever.


Image above: Dione hangs in front of Saturn and its icy rings in this view, captured during Cassini's final close flyby of the icy moon. Image Credit: NASA/JPL-Caltech/Space Science Institute.

Cassini passed 295 miles (474 kilometers) above Dione's surface at 11:33 a.m. PDT (2:33 p.m. EDT) on Aug. 17. This was the fifth close encounter with Dione during Cassini's long tour at Saturn. The mission's closest-ever flyby of Dione was in Dec. 2011, at a distance of 60 miles (100 kilometers).


Image above: Saturn's moon Dione hangs in front of Saturn's rings in this view taken by NASA's Cassini spacecraft during the inbound leg of its last close flyby of the icy moon. Image Credit: NASA/JPL-Caltech/Space Science Institute.

"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," said Carolyn Porco, Cassini imaging team lead at the Space Science Institute, Boulder, Colorado. "Right down to the last, Cassini has faithfully delivered another extraordinary set of riches. How lucky we have been."

Raw, unprocessed images from the flyby are available at: http://saturn.jpl.nasa.gov/mission/flybys/dione20150817/


Image above: NASA's Cassini spacecraft captured this parting view showing the rough and icy crescent of Saturn's moon Dione following the spacecraft's last close flyby of the moon on Aug. 17, 2015. Image Credit: NASA/JPL-Caltech/Space Science Institute.

The main scientific focus of this flyby was gravity science, not imaging. This made capturing the images tricky, as 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," said 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 some of the images."


Image above: NASA's Cassini spacecraft gazes out upon a rolling, cratered landscape in this oblique view of Saturn's moon Dione. Image Credit:NASA/JPL-Caltech/Space Science Institute.

Cassini scientists will study data from the gravity science experiment and magnetosphere and plasma science instruments over the next few months as they look for clues about Dione's interior structure and processes affecting its surface.

Only 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 moon Enceladus on Oct. 14 and 28, and Dec. 19. During the Oct. 28 flyby, the spacecraft will come dizzyingly close to Enceladus, passing a mere 30 miles (49 kilometers) from the surface. Cassini will make its deepest-ever dive through the moon's plume of icy spray at this time, collecting valuable data about what's going on beneath the surface. The December Enceladus encounter will be Cassini's final close pass by that moon, at an altitude of 3,106 miles (4,999 kilometers).


Image above: This view from NASA's Cassini spacecraft shows terrain on Saturn's moon Dione that is entirely lit by reflected light from Saturn, called Saturnshine. Image Credit: NASA/JPL-Caltech/Space Science Institute.

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 30,000 miles (50,000 kilometers). 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.


Image above: This view of Dione from Cassini includes the mission's highest-resolution view of the icy moon's surface as an inset at center left. Image Credit: NASA/JPL-Caltech/Space Science Institute.

During the mission's final year -- called its Grand Finale -- Cassini will repeatedly dive through the space between Saturn and its rings.


Image above: A region on Dione where features in shadow are illuminated by reflected light from Saturn. Inset above center is one of Cassini's highest-resolution views of Dione's surface. Image Credit: NASA/JPL-Caltech/Space Science Institute.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory in Pasadena, California, manages the mission for the agency's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena. The Cassini imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about Cassini, visit:

http://www.nasa.gov/cassini

http://saturn.jpl.nasa.gov

http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

Images (mentioned), Text, Credits: NASA/JPL/Preston Dyches.

Greetings, Orbiter.ch

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