Class S and Class T planets are super gas giants. They range in age from 2 to 10 billion years old. Their diameters range in size from 10 to 50 million km (Class S) and 50 to 120 million km (Class T). They are usually located in a solar system's coldzone, however they can be in any region. Their surface is tenuous, composed of hydrogen, and hydrogen compounds. They radiate considerable heat and tremendous gravity. The atmosphere varies in temperature, pressure and composition at different layers. There may also be water vapor present. Life forms may only exist as single-celled organisms if any exist at all. They may have hundreds or thousands of moons, some of which may be terrestrial planets of Class M, Class O and Class P.