Brown dwarf

A brown dwarf was a stellar object that had characteristics of both a star and a planet.

wanted to investigate a brown planetary system in 2152 when the ship was infested by a symbiotic lifeform and the investigation was interrupted. 

According to Data in 2365, the abundance of dysprosium in a brown dwarf star was different than regular stars, when factored with terbium, holmium, erbium, and europium.