NASA’s Cassini robotic orbiter captured these images of Mimas and Epimetheus during a close flyby on January 30, 2017.
This image of Saturn’s moon Epimetheus was taken on January 30, 2017 and received on Earth February 1, 2017. The image was taken using the CL1 and GRN filters. Image credit: NASA / JPL-Caltech / SSI.
Also known as Saturn XI and S/1980 S3, Epimetheus is an inner satellite of Saturn. It was discovered by astronomer Richard Walker on December 18, 1966.
Epimetheus is a potato-shaped object with dimensions approximately 84 x 65 x 65 miles (135 x 108 x 105 km, respectively).
It orbits 94,000 miles (151,000 km) away from Saturn, taking 17 hours to circle the gas giant, in the gap between the F and G rings, but it doesn’t do this alone.
Epimetheus and the neighboring Saturnian moon Janus have been referred to as the Siamese twins of Saturn because they orbit the parent planet in nearly the same orbit.
According to planetary scientists, these two moons may have formed by the break-up of one object.
Epimetheus is phase locked with Saturn — one side always faces toward the gas giant.
This small moon is thought to be composed of water ice, but its density of less than 0.7 is much less than that of water.
Thus, the object is probably a rubble pile — a collection of numerous boulders, rocks, and dust loosely held together by gravity.
This image of Epimetheus was taken on January 30, 2017 and received on Earth February 1, 2017. The image was taken using the CL1 and CL2 filters. Image credit: NASA / JPL-Caltech / SSI.
Mimas is the innermost and smallest of Saturn’s main moons.
It was discovered on Sept. 17, 1789 by the English astronomer William Herschel and named for one of the Giants of Greek mythology.
Also known as Saturn I, Mimas is roughly 246 miles (396 km) across.
It revolves around Saturn in a prograde, near-circular orbit at a mean distance of about 117,000 miles (189,000 km).
This image of Saturn’s moon Mimas was taken on January 30, 2017 and received on Earth February 1, 2017. The camera was pointing toward Mimas at roughly 26,700 miles (43,000 km) away, and the image was taken using the CL1 and GRN filters. Image credit: NASA / JPL-Caltech / SSI.
This image of Mimas was taken on January 30, 2017 and received on Earth February 1, 2017. The camera was pointing toward Mimas at roughly 26,700 miles (43,000 km) away, and the image was taken using the CL1 and CL2 filters. Image credit: NASA / JPL-Caltech / SSI.
Because of tidal interactions with the gas giant, Mimas rotates synchronously with its orbital motion, always keeping the same hemisphere toward the planet and always leading with the same hemisphere in orbit.
Mimas’ surface is icy and heavily cratered. One of the craters, Herschel, is surprisingly large in comparison to the size of the moon. It is roughly 81 miles (130 km) wide, one-third the diameter of this moon.
