Shape
Proteus is the largest irregularly shaped natural satellite. All other known natural satellites the size of Miranda and above have lapsed into a rounded ellipsoid under hydrostatic equilibrium. The planets are not truly spherical but oblate spheroids, squatter at the pole than at the equator, but with a constant equatorial diameter. The larger natural satellites, however, since they are all tidally locked, are scalene, squat at the poles but with the equatorial axis directed at their planet longer than the axis along their direction of motion. The most distorted natural satellite is Mimas, where the major axis is 9% greater than its polar axis and 5% greater than its other equatorial axis, giving it a notable egg shape. The effect is smaller with the largest natural satellites, where self gravity is greater relative to tidal distortion, especially when they orbit a less massive planet or at a greater distance, as the Moon does.
| Name | Satellite of | Difference in axes | |
|---|---|---|---|
| (km) | (% of mean diameter) | ||
| Mimas | Saturn | 33.4 (20.4, 13.0) | 8.4% (5.1%, 3.3%) |
| Enceladus | Saturn | 16.6 | 3.3% |
| Miranda | Uranus | 14.2 | 3.0% |
| Tethys | Saturn | 25.8 | 2.4% |
| Io | Jupiter | 29.4 | 0.8% |
| The Moon | Earth | 4.3 | 0.1% |
Read more about this topic: Natural Satellite
Famous quotes containing the word shape:
““Must a name mean something?” Alice asked doubtfully.
“Of course it must,” Humpty Dumpty said with a short laugh: “my name means the shape I am—and a good handsome shape it is, too. With a name like yours, you might be any shape, almost.””
—Lewis Carroll [Charles Lutwidge Dodgson] (1832–1898)
“Irish poets, learn your trade,
Sing whatever is well made,
Scorn the sort now growing up
All out of shape from toe to top.”
—William Butler Yeats (1865–1939)
“I know that each stage is not going to last forever. I used to think that when he was little. Whenever he was in a bad stage I thought that he was going to be like that for the rest of his life and that I’d better do something to shape him up. When he was in a good state, I thought he was going to be a perfect child and I would never have to worry; he was always going to stay that way.”
—Anonymous Parent of An Eight-Year-Old. As quoted in Between Generations by Ellen Galinsky, ch. 4 (1981)