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:
“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.)
“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)
“Surely among a rich man’s flowering lawns,
Amid the rustle of his planted hills,
Life overflows without ambitious pains;
And rains down life until the basin spills,
And mounts more dizzy high the more it rains
As though to choose whatever shape it wills....”
—William Butler Yeats (1865–1939)