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:
“Thus when I come to shape here at this table between my hands the story of my life and set it before you as a complete thing, I have to recall things gone far, gone deep, sunk into this life or that and become part of it; dreams, too, things surrounding me, and the inmates, those old half-articulate ghosts who keep up their hauntings by day and night ... shadows of people one might have been; unborn selves.”
—Virginia Woolf (1882–1941)
“After that it came to my door. Now it lives here.
And of course: it is a soft sound, soft as a seal’s ear,
that was caught between a shape and a shape and then returned to me.”
—Anne Sexton (1928–1974)
“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.)