Yesterday Cassini passed unusually close by Hyperion, the oddly shaped moon that orbits Saturn just beyond Titan. Among the many cool images captured during this flyby were three that I used to make this neato view of Hyperion's crescent. Actually, I needed four pictures, because the three-image mosaic cut off the "nose" of Hyperion, the bit of limb on the right.
NASA / JPL / SSI / mosaic by Emily Lakdawalla
As Cassini approached Hyperion for a close encounter on August 25, 2011, it snapped a three-image mosaic of the sponge-like moon at a crescent phase. The mosaic did not quite cover the entire visible crescent, so a wide-angle image (with a resolution 10 times lower than the other images) was used to fill in a small area on the "nose."
A bit of trivia: Hyperion is only about half the diameter of Vesta, and has the weird property of having a density barely more than half that of water ice. Since there's nothing much in the solar system that's less dense than water ice when solid, that means Hyperion's interior must be nearly half empty space, with lots of open pores between ice grains.
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