A Class D planet is a moon or asteroid. They have an age that ranges from 2-10 billion years and a diameter between 100 and 1,000 km. They are located throughout the solar system. Moons and asteroids are categorized by being geologically inactive and usually pockmarked with craters. They are often so small that they cannot maintain any kind of atmosphere. Class D planets cannot sustain any known form of life, besides that of Silicon based life forms, E.I. Space Slug/Mynock.