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: Moon Moon
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)
“But her shape is the least of my madness; she has things by which it is more pleasing to die.”
—Propertius Sextus (c. 50–16 B.C.)
“There are moments when very little truth would be enough to shape opinion. One might be hated at extremely low cost.”
—Jean Rostand (1894–1977)