Emily LakdawallaJan 20, 2011

Two fine color Cassini animations: Prometheus rotating, Tethys and Dione dancing

Cassini flew rather close to Prometheus on January 27, 2010, passing within 40,000 kilometers. At the time I made my own rather poor color version of one set of the images. But now that the high-quality, archived versions of the images have become available at the Planetary Data System, Daniel Macháček has reached into the dark side of Prometheus and pulled out an incredible amount of detail where the potato-shaped moon is illuminated by Saturnshine. He produced an animation that morphs among the three sets of four-filter color images that Cassini snapped during the flyby:

Saturnian moon Prometheus Animation of Saturn's moon Prometheus from three images (+9 images for color) taken by the Cassini spacecraft. All images were rotated by 180° and equalized so that regions illuminated by Saturn are visible. The images in the animation were acquired on 27 January 2010. NASA / JPL-Caltech / SSI / Daniel Macháček

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While I am posting cool Cassini animations, here's another color animation (this one made from raw images) by Ian Regan of Tethys and Dione passing in the night. The sequence was captured by Cassini on December 6 and includes a total of 75 images captured sequentially through red, green, and blue filters. Cassini's taken these "mutual event" movies since early in the mission but it's only since a year or so ago that they switched to taking them with color filters rather than the clear filter; the result is images that have the science value they need (these animations are taken in large part to help increase the precision of our measurement of the moons' orbits), plus they have extra added public interest value because they have the color information needed to represent them as "true color." The color is cool but it's a huge amount of extra added work to convert each 3-image set into single color frames; I'm happy Ian stepped in to do this!

Before you click the play button, try to guess which moon is in front! Dione is the darker of the two.

Tethys and Dione This natural color, time-lapse movie comprised of images from the Cassini spacecraft taken in December 2010 shows Dione moving from left to right, passing behind its sister moon Tethys, which remains in the center of the frame. NASA / JPL-Caltech / SSI / Ian Regan

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