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:
“Political image is like mixing cement. When it’s wet, you can move it around and shape it, but at some point it hardens and there’s almost nothing you can do to reshape it.”
—Walter F. Mondale (b. 1928)
“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)
“There are men from whom nature or some peculiar destiny has removed the cover beneath which we hide our own madness. They are like thin-skinned insects whose visible play of muscles seem to make them deformed, though in fact, everything soon turns to its normal shape again.”
—E.T.A.W. (Ernst Theodor Amadeus Wilhelm)