|Volume: 03, Issue: 14||07/13/2005|
Spongy-Looking Hyperion Tumbles into ViewThe Cassini spacecraftís first brush with Saturnís moon Hyperion revealed several interesting features. Hyperion isnít what one would typically envision for a moon: its shape is not symmetrical or spherical, and its pockmarked surface adds to the unique look. New views acquired by Cassini offer the best looks yet at the icy, oddly-shaped moon.
Hyperion has a battered appearance. Jagged outlines visible on the moon's surface are indicators of large impacts that have chipped away at its shape like a sculptor. In addition, craters are visible on the moonís surface. The fresh appearance of most of these craters, combined with their high spatial density, makes Hyperion look something like a sponge.
The moon's spongy-looking exterior is an interesting coincidence, as much of Hyperionís interior appears to consist of voids. Hyperion is close to the size limit where, like a child compacting a snowball, internal pressure due to the moonís own gravity will begin to crush weak materials like ice, closing pore spaces and eventually creating a more nearly spherical shape.
At present, however, preliminary estimates of its density show that Hyperion is only about 60 percent as dense as solid water ice, indicating that much of its interior (40 percent or more) must be empty space. This makes the moon more like an icy rubble pile than a solid body.
During this flyby, Cassini captured images from distances ranging approximately 506,000 to 104,000 miles from Hyperion. Cassini will complete another flyby of Hyperion on Sept. 26, 2005, coming within 317 miles of the moon.
The next item on Cassiniís agenda is the spacecraftís closest flyby yet. On July 14, Cassini will come within 109 miles from the surface of the wrinkled, icy moon Enceladus.
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