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Surface of a class Y planet

A class Y planet from orbit

"Need I remind you, ensign, that there is no environment less hospitable to Human life than a class Y?"

In the Federation standard system of planetary classification, a class Y planet was characterized by a toxic atmosphere, sulfuric deserts, surface temperatures exceeding five hundred Kelvin, and thermionic radiation discharges. Due to the inhospitable and dangerous nature, and often hellish appearance, of such planets they were also nicknamed "Demon class" by Starfleet. Even entering a standard orbit of a class Y planet could be hazardous to starships. (VOY: "Demon", "Flesh and Blood")

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 that the deuterium contained 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 vessel claiming to protect the Ord'mirit Mining Treaty. 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")

Theta Zeta, a class Y planet in the Verubin Nebula, was ground zero for the Burn in 3069. (DIS: "Su'Kal", "That Hope Is You, Part 2")

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 and 15,000 kilometers. They can be located anywhere within a star system.

List of class Y worlds

Image Name Location Notes Source
HaDara.jpg Ha'Dara Delta Quadrant VOY: "Flesh and Blood"
Class y planet.jpg Ord'mirit planet Delta Quadrant VOY: "Course: Oblivion"
Demon planet display.jpg Silver Blood homeworld Vaskan sector, Delta Quadrant Homeworld of the Silver Blood, a biomimetic lifeform. VOY: "Demons"
Theta Zeta.jpg Theta Zeta Verubin Nebula Described as both a planet and a planetoid. DIS: "Su'Kal"

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