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:
“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)
“It is only a short step from exaggerating what we can find in the world to exaggerating our power to remake the world. Expecting more novelty than there is, more greatness than there is, and more strangeness than there is, we imagine ourselves masters of a plastic universe. But a world we can shape to our will ... is a shapeless world.”
—Daniel J. Boorstin (b. 1914)
“What man dare, I dare.
Approach thou like the rugged Russian bear,
The armed rhinoceros, or the Hyrcan tiger;
Take any shape but that, and my firm nerves
Shall never tremble. Or be alive again
And dare me to the desert with thy sword.”
—William Shakespeare (1564–1616)