Class J planets range in age from 2 to 10 billion years old. Their diameters range in size from 50,000 to 140,000 km. They are mostly located in the cold zone region of a star's solar system, although some have been found to exist in hot regions. Their surfaces are tenuous, comprised of gaseous hydrogen and hydrogen compounds. The atmosphere within the planet vary in temperature, pressure and composition. Hydrocarbon-based life has been known to exist in these planets. (Star Trek: Star Charts)