Some days I think that JPL is the only part of NASA that is worth anything. They are the guys who ran the hugely-successful Deep Impact mission, the beyond-all-expectations Spirit and Opportunity Mars rovers, the Mars Pathfinder rover mission, and were involved in the NEAR Eros mission (as a junior partner to the Johns Hopkins University Applied Physics Lab, where Mike Griffin worked before becoming NASA Administrator).
JPL is also responsible for the Cassini probe currently orbiting Saturn. I posted some pictures taken by Cassini last month, but now there are some more I'd like to share.
First up is a picture taken on September 22nd of Dione and Tethys. In this shot, Dione looks huge compared to Tethys, but Dione is only a little bigger: Dione is 1126 km across, and Tethys is 1071 km across. Dione looks much bigger in this image because the Cassini spacecraft is only 860000 km away (a little over twice the distance from the Earth to the moon) but 1.5 million km from Tethys (almost 4 times the distance from the Earth to the moon).
Next is a picture of Hyperion taken on September 26th from a distance of 62000 km. Hyperion has an unusual appearance. It is probably an icy body, and when it gets hit by darker, carbonaceous impactors, the cratered areas absorb more heat than the surrounding areas. These darker, warmer impact zones would then slowly melt their way toward Hyperion's center of mass, creating the radial-tunnels appearance. Hyperion's axis of rotation wobbles a lot, giving it a chaotic rotation; its orientation in space is totally unpredictable.
The final image posted here is of Pandora, taken on September 5th from a distance of about 52000 km. Pandora is a fairly small body, only 84 km across, and is the outer shepherd moon constraining Saturn's F ring. Pandora and its orbital partner Prometheus interact gravitationally with each other, giving both moons chaotic orbits around Saturn - the first such orbits found in the solar system.
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