Thursday, December 6, 2007

Strangely, some of Saturn's Moons are Disk Shaped





Saturn's rings orbit the planet in a flat disk that corresponds to the planet's equator. Likewise, Earth and the other planets orbit the sun in a fairly flat plane that relates to the sun's equator. The planets, at least the rocky ones, are thought to have formed when bits of material orbiting the newborn sun stuck together, forming larger and larger objects that collided and coalesced.

Observations by NASA's Cassini spacecraft revealed the Saturnian moons Atlas and Pan, each roughly 12 miles from pole to pole, have massive ridges bulging from their equators some 3.7 to 6.5 miles high, giving them the flying-saucer appearance.

In principle, fast rates of spin might have stretched Atlas and Pan out into such unusual shapes, just as tossing a disk of pizza d ough flattens it out. But neither moon whirls very quickly, each taking about 14 hours to complete a rotation. Earth, far bigger, rotates in 24 hours, of course.