Rhea

It is the 2nd largest moon of saturn at 1524.4 kilometers in diameter.

Discovery & explorations
Rhea was discovered by Giovanni Domenico Cassini on December 23rd, 1672 and is part of the Sidera Lodoicea. It wasn't named until 1847 when John Herschel suggested the name "Rhea".

The first non-telescopic images of Rhea were obtained in 1980 when the Voyager 1 spacecraft reached Saturn.

The Cassini spacecraft arrived to Saturn in 2004 and gained lots more images and did lots more measurements on Rhea than the voyager spacecrafts did as the voyagers only flew by rhea but cassini orbited Saturn for almost 15 years.

Cassini flew by Rhea closely 5 times - November 26, 2005 at a distance of 500km, August 30, 2007 at a distance of 5,750 km, March 2, 2010 at a distance of 100 km, January 11, 2011 at 69 km, and March 9, 2013 at 992 km. Rhea has been also imaged many times from long to moderate distances by the spacecraft.

Rings
Rhea is the only moon in the solar system with a ring, but the rings are extremely faint - uncomparable to Saturn's or Uranus' rings.