How long is a day on Oberon?

About 323.1 Earth hours · orbits Uranus every 13.5 days

Uranus's outermost major moon, heavily cratered with a mysterious dark surface

Oberon is the most heavily cratered moon of Uranus, with some craters over 4 billion years old! It also has mysterious dark material on its surface - possibly carbon-rich organic compounds created over billions of years!