Pioneer 11 encounters Saturn 1979

Launched April 6, 1973, Pioneer 11 became the first space probe to encounter Saturn on September 1, 1979.  It followed Pioneer 10 through the asteroid belt and past Jupiter, but then headed toward Saturn.  During its flyby, it discovered a new ring and almost collided with a new moon discovered the day before, Epimetheus.  After the Voyager flybys, it was discovered that Janus (already known moon) and Epimetheus occupy the same orbit and are about the same size, so it could have been either one.

On September 29, 1995, NASA announced it was closing the project after over 22 years.

Epimetheus, Saturn's moon, up close!

While the Cassini spacecraft prepares for her swan song and death dive into the Saturnian atmosphere, she is still orbiting the planet and taking pictures of everything.  In February, Cassini performed a flyby of the inner moon Saturn XI or Epimetheus.

The moon Janus was discovered in December 1966 by two separate astronomers and believed there to be only one moon.  In 1978, two more astronomers determined that 1966 observations were best explained by two distinct objects, sharing very similar orbits.  Voyager 1 confirmed this in 1980, so the two astronmers Stephen Larson and John Fountain are credited with Epimetheus' discovery.

Epimetheus is only about 70 miles in diameter which means it is too small to have an atmosphere or to be geologically active.  It has two named craters, Hilairea and Pollux, characters from Castor and Pollux of Greek mythology.

Cassini spacecraft taking hi-resolution pics of Saturn's moons

Atlas

 

This small moon is only 30 kilometers, or 19 miles across.  Atlas orbits Saturn in a region called the Roche Division, between the planet's A and F rings, at the outer edge of the main ring system. The outer A ring is seen at the bottom of this view.

 

 

Epimetheus

 

A little larger than Atlas, Epimetheus is 116 kilometers, or 72 miles across.

 

Prometheus

 

Prometheus, 86 kilometers, or 53 miles across, orbits Saturn just inside the F ring, seen at the top of the picture.

 

Tethys

 

Tethys (531km or 319 miles) is dwarfed by Saturn and its rings.  A crescent view like this is impossible to see from Earth.  Reflected light from the rings illuminate Tethys' northern hemisphere.

 

nasa.gov