Janus & Epimetheus:
Co-orbital Moons of Saturn
- Two smaller, innermost moons to Saturn:
- Janus (pronounced JAY-nus)
- Epimetheus (ep-ee-MEE-thee-is)
- Janus and Epimetheus orbit at almost exactly the same distance from Saturn.
- Their orbit is just on the fringes of Saturn's rings.
- Janus was first observed from Earth in the 1960s.
- The Voyager probes recorded a great deal of data about Saturn's system of rings and moons.
- Effort was required to determined which of the two moons was the original Janus.
- The moons were determined to have common characteristics:
- Low density
- Comprised of ice
- Similar size
- Janus is about 220 x 160 km (137 x 99 miles) in size.
- Epimetheus is about 140 x 100 km (87 x 62 miles).
- Close encounters of the two are frequent.
- In 1989 it was determined that they cannot approach each other any closer than 21,000 km (13,000 miles).
- At this time Janus would look about 0.6° in angular size from Epimetheus.
- That is a bit bigger than the apparent size of our moon.
- Also at this point they "do a fantastic dance around each other exchanging paths.
- Some researchers believe they are crushed fragments of a once-larger icy satellite, like nearby Mimas, that orbited in this vicinity.
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