Oso I is a terrestrial planet on the Oso system, and is the first world from its sun. Tidally locked, one of its sides permanently faces its star, leaving the other side dark and cold. The warm side of Oso I is covered in a sea of lava that ends at the dividing line between night and day. Early surveys found that the reddish-black crust on the cool side was rich in iron.
Before the Osoians were discovered on neighboring planet Oso II, Oasis Resort had given a press conference announcing speculative plans to create a luxury hotel with "sweeping views of the awe-inspiring lava sea" on a chain of islands near the solar terminus. They were forced to cancel their scheme when the Fair Chance Act was applied.