Geology of solar terrestrial planets Earth, and Mars) have substantial atmospheres; all have impact craters and tectonic surface features such as rift valleys and volcanoes. The term "inner planet" should not be confused with "inferior planet", which refers to any planet that is closer to the Sun than the observer's planet is, but usually refers to Mercury and Venus. The Solar System is believed to have formed according to the nebular hypothesis, first proposed in 1755 by Immanuel Kant and independently formulated by Pierre-Simon Laplace. This theory holds that 4.6 billion years ago the Solar System formed from the gravitational collapse of a giant molecular
Satellite system (astronomy) the largest satellite system, the Jovian system, with 79 known moons (including the large Galilean moons) and the Saturnian System with 62 known moons (and the most visible ring system in the Solar System). Both satellite systems are large and diverse. In fact all of the giant planets of the Solar System possess large satellite systems as well as planetary rings, and it is inferred that this is a general pattern. Several objects farther from the Sun also have satellite systems consisting of multiple moons, including the complex Plutonian system where multiple objects orbit a common center of mass, as