Pluto

Pluto is a body in the Sol system. From 1930 to 2006, Pluto was considered the 9th planet in the solar system, at which point it was reclassified as a dwarf planet. The planet was named after the Roman god of the underworld. The planet is approximately a fifth of the size of Luna, and is comprised mainly of rock and ice. It has an eccentric orbit that brings it closer to the sun than the planet Neptune.

The USS Galaxy (NCC-70637) spent some time in orbit around Pluto, and sent updates on the performace of her systems to the USS Enterprise (NCC-1701-D) during this time. (Star Trek: The Next Generation Technical Manual).