Explanation:
Small saturnian moon
Epimetheus
(ep-ee-MEE-thee-us)
is at most 116 kilometers across.
Its cratered surface and irregular shape are highlighted
by dramatic shadows in
this
composite close-up image from the Cassini spacecraft.
However, orbiting 91,000 kilometers above
Saturn's cloud tops,
Epimetheus
is not alone.
Similar in size, saturnian moon
Janus
occupies an orbit separated from
Epimetheus' by only about 50 kilometers.
The two actually approach each other once every four years,
but instead of colliding, the moons
deftly exchange orbits
and
move apart again!
In fact, co-orbiting Epimetheus and Janus both consist mostly of
porous
water ice and could have
formed from the breakup of a single parent body.
The small moons are also believed to play a role
in maintaining the outer edge of
Saturn's A ring.
