3908 Nyx is an Amor and Mars-crosser asteroid. It was discovered by Hans-Emil Schuster on August 6, 1980, and is named after Nyx, the Greek goddess of the night, after which Pluto's moon Nix is also named. It is 1–2 km in diameter and is a V-type asteroid, meaning that it may be a fragment of the asteroid 4 Vesta.
In 2000, radar observations conducted at the Arecibo and Goldstone observatories produced a model of Nyx's shape; the asteroid can best be described as spherical but with many protruding lumps.
To avoid confusion with 3908 Nyx, Pluto's moon Nix was changed from the initial proposal of the classical spelling Nyx, to Nix.