Geology of solar terrestrial planets of heavier elements contained in the solar nebula. The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of minerals with high melting points, such as the silicates which form their solid crusts and semi-liquid mantles, and metals such as iron and nickel, which form their cores. The Mariner 10 mission (1974) mapped about half the surface of Mercury. On the basis of that data, scientists have a first-order understanding of the geology and history of the planet. Mercury's surface shows intercrater plains, basins, smooth plains, craters, and
Lucky Starr and the Moons of Jupiter of Eternity". Consequently, there are small inconsistencies between the various novels. In the first, Ganymede is mentioned as a settled world of the Solar System, although in later novels Ganymede has no permanent settlement, and has even served as the location of a secret Sirian base. The first man on Mars is named Wingrad in "David Starr, Space Ranger", but is named Ching in "Moons of Jupiter". The name of the state that rules the Solar System also changes from novel to novel. In "Pirates of the Asteroids", it is the Terrestrial Empire; in "Oceans of Venus", it is the