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:
“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)
“Somebody once said that I am incapable of drawing a man, but that I draw abstract things like despair, disillusion, despondency, sorrow, lapse of memory, exile, and that these things are sometimes in a shape that might be called Man or Woman.”
—James Thurber (1894–1961)
“Fortuitous circumstances constitute the moulds that shape the majority of human lives, and the hasty impress of an accident is too often regarded as the relentless decree of all ordaining fate.”
—Augusta Evans (1835–1909)