Io

Io (aka Sol Va) was a natural satellite, or moon, of Jupiter.

Io had only one Earth colony, devoted to mining. It had a population of 900,000. (Star Fleet Universe: Gazetteer Based on F&E Map, 14 August 2012 revision)

Namesake starships
In the late 24th century, a class of starships named after natural satellites in the Sol system was commissioned. One of these was the USS Io, launched in 2379 under the command of Captain T'Vrea. (' novels ' and )