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There are 62 confirmed moons orbiting Saturn. Of these, 53 are officially named. And most of you probably don’t know the names of more than a handful. Most of us have heard of Titan (largest moon in the solar system) and Enceladus (the moon with spewing plumes of icy material).
NASA’s Cassini spacecraft captured the image on July 26, 2015 from a distance of 500,000 miles. The image scale is 3 miles per pixel.
Did you know Epimetheus shares a nearly identical orbit with another nearby moon? The neighboring moon is called Janus and stunned astronomers (when they first discovered it) who couldn’t believe two moons could share such similar orbits without smashing into one another. Both moons lie in orbits about 94,100 miles from Saturn. And one of the moons orbits 31 miles higher from the planet than the other. The moon that orbits farther away moves just a bit slower than the other.
Which moon is it? That’s where things get interesting. Every four Earth years, the inner moon catches up to the outer one. Gravity between the two moons pulls the inner moon into a higher orbit. This same gravity interaction drags the outer moon into a lower orbit.
Epimetheus and Janus after switching orbits.
The theory between Epimetheus and Janus suggests they are the remnants of one moon. Whatever happened, both moons have been this way for a long time. Ancient craters dot the surfaces of each. And, groove-like features indicate glancing blows from other objects.
Cassini and Epimetheus
Cassini has ventured close to Epimetheus several times since it entered Saturn’s orbit in 20014. But no target flybys are scheduled. According to NASA/JPL, Cassini will make its closest approach to the moon on December 6th. Cassini will be just 1,629 miles away from Epimetheus then.
To put that in perspective, New Horizons soared by Pluto at a distance of around 7,800 miles. It’s close, but Cassini has flown much closer to moons before. On October 28th, the spacecraft was just 30 miles above Enceladus’ south polar region.
Cassini returns to Enceladus on December 19th for the last targeted flyby of the moon. The spacecraft will continue to observe the moon’s south polar terrain to better understand heat flow from the interior of Enceladus.