Class A - Geothermal
Age: 0-2 billion years
Diameter: 1,000 - 10,000 km
Location: Ecosphere or Cold Zones
Surface: Partially molten
Atmosphere: Primarily hydrogen compounds
Evolution: Cools to become a Class-C planet
Life-Forms: None known
Class A planets are generally found within a star's habitable or cold zone. They are smaller than Earth, ranging in size from 1,000 to 10,000 kilometers in diameter. Their surface is partially molten, with an atmosphere composed primarily of hydrogen compounds, making them unsuitable for humanoid life forms. They cool to become class C planets.
Gothos, the iron-silica planet created by Trelane in "The Squire of Gothos" (TOS), is a Class A planet. The surface of Gothos contains no vegetation or even detectable soil. Cursed with a toxic atmosphere, the planet is plagued by storms and continuous volcanic eruptions. Gothos was only capable of supporting life forms because Trelane artificially created a small area of Class M conditions.