From Halopedia, the Halo wiki
There are no facilities on the dwarf-planet's surface; however, several military and scientific stations orbit Pluto, including the Kelvin Research Station, UNSC Monitoring Station Delta Five, and the remote scanning outpost, Democritus.
Pluto was discovered in the early 20th-century. It was originally considered a planet and thought to be causing issues in Neptune's orbit but was then downgraded to a dwarf planet when Pluto was determined to be ill-suited for that.
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