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
Phaeton (hypothetical planet) the protoplanetary disk, and in this region the incorporation of protoplanetary remnants into the planets was prevented by large gravitational perturbations induced by Jupiter during the formative period of the solar system. Some scientists and non-scientists continue to advocate for the existence and destruction of a Phaeton-like planet. Zecharia Sitchin suggested that the goddess known to the Sumerians as Tiamat in fact relates to a planet that was destroyed by a rogue planet known as Nibiru, creating both Earth and the asteroid belt. His work is widely regarded as pseudoscience. The astronomer and author Tom Van Flandern held that Phaeton