Table of Phoebe Facts
|Discovered by||William Pickering|
|Year of Discovery||1898|
|Orbit (mean distance from Saturn)||12 952 000 km|
|Radius||115 x 110 x 105 km|
|Mass||7.2 x 1018 kg|
|Mean Density (water = 1000)||1330 kgm-3|
|Rotational Period||9 hours 30 minutes|
|Orbital Period (retrograde)||550 days 11 hours|
Phoebe is different to most other moons of Saturn for a number of reasons.
- Its orbit is retrograde, meaning it orbits Saturn in the opposite direction to most of the other moons.
- The orbit does not lie in Saturn's equatorial plane, but in the ecliptic plane.
- The rotational period and orbital period are different and not phase linked. This means the face presented to Saturn is constantly changing
- The surface is relatively dark.
The conclusion from all these differences is that Phoebe is a captured asteroid, possbile belonging to the class of Centaurs. (Centaurs are Kuiper Belt objects that migrated into the inner solar system.) If this is the case then study of Phoebe could provide vital clues as to the conditions in the early history of the solar system.
There are many unanswered questions about Phoebe. The Voyager 2 images, taken from a distance of 2.2 million km, raise many more questions than answers. The moon is thought to be roughly circular with some surface feature, althought the size and scale of such features can only be guessed at. The internal structure is also a mystery. Determining this would help scientist understand more about the origins of the moon.