Class Y planet

File:Demon class planet.jpg

Surface of a class Y planet

In the Federation standard system of planetary classification a class Y (known informally as demon class) planet was characterized by a toxic atmosphere, surface temperatures exceeding five hundred Kelvin and thermionic radiation discharges. They were sometimes nicknamed demon class planets due to their extremely inhospitable nature to most humanoid life. Even entering orbit of a class Y planet could be hazardous to starships. (VOY: "Demon")

In 2374, the USS Voyager was forced to land on a class Y planet in the Vaskan sector after detecting desperately needed deuterium on the surface. There, they discovered the deuterium was in fact contained in a biomimetic lifeform called the "Silver Blood", which duplicated the crew and ship. (VOY: "Demon")

A year later, the crew of the Silver Blood USS Voyager began to deteriorate on their way to the Alpha Quadrant. After discovering their true natures, the crew attempted to take shelter on another class Y planet but were turned away by a mining concern. The mimetic Voyager disintegrated en route to its original homeworld. (VOY: "Course: Oblivion")

In 2377, the hologram Iden identified a class Y planet as an ideal new home for his group of freed prey holograms. He named the planet Ha'Dara, Bajoran for "home of light". (VOY: "Flesh and Blood")

Information taken from Star Trek: Star Charts indicates class Y worlds have an age between two and ten billion years and a diameter between 10,000-15,000 kilometers. They can be located anywhere within a star system.