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
Solar conjunction the line of sight to an interior planet (Mercury or Venus) being very close to the solar disk. If the planet passes directly in front of the sun, a solar transit occurs. Solar conjunction Solar conjunction occurs when a planet or other solar system object is on the opposite side of the sun from the Earth. From an Earth reference, the sun will pass between the Earth and the object. Communication with any spacecraft in solar conjunction will be severely limited due to the sun's interference on radio transmissions from the spacecraft. When in reference to Satellite Communications, solar conjunction