|Saturn's moon Hyperion. |
Image Cassini APOD
Wildly rotating and only 250 kilometers in diameter Hyperion may be full of cavities, a true space sponge!
An image from the 2005 pass, shown above in false color, shows a remarkable world strewn with strange craters and a generally odd surface... and has a density so low that it might house a vast system of caverns inside.
from text in APOD