Short answers, pulled from the story.
Giovanni Domenico Cassini discovered the moon Rhea on the 23rd of December 1672. He used a telescope crafted by Giuseppe Campani to spot this faint point of light moving against the stars.
Rhea possesses a mean diameter of 1,528 kilometers yet maintains a surprisingly low density of about 1.236 grams per cubic centimeter. This measurement suggests the moon consists of roughly three-quarters water ice and only one-quarter rock material with an almost homogeneous interior.
The surface temperature on Rhea drops to minus 174 degrees Celsius under direct sunlight and falls as low as minus 220 degrees Celsius in shadowed regions. This extreme cold preserves a heavily cratered landscape that resembles the terrain found on Dione.
NASA announced the discovery of an extremely tenuous atmosphere around Rhea on the 27th of November 2010. This exosphere consists primarily of oxygen and carbon dioxide molecules distributed in a ratio of roughly five to two.
Scientists initially claimed Rhea might possess a weak ring system following observations by Cassini in 2008 but later concluded no physical evidence existed. Targeted observations from multiple angles failed to reveal any rings despite earlier magnetic field disturbances.