The Earth is a Unique Planet The Earth has many special features that set it apart from its planetary siblings within the Solar System. It has a unique position relative to the Sun; it is the only planet within the Habitable Zone. Moreover, the Earth is fortunate that a series of circumstances (its relation to the gas giant planets, a large moon and a particularly stable orbit, an atmosphere and a magnetic field) have combined to enhance the long-term stability of the planet, allowing an extended period over which life could develop and evolve. Conditions on the Earth are maintained between the atmosphere developing into a runaway greenhouse and the Earth becoming a ball of ice by the process of plate tectonics, which keeps the carbon balance between the atmosphere, the hydrosphere (the water, i.e. oceans, lakes and rivers) and the lithosphere (the continents). All these circumstances conspire to render the Earth and the development of higher forms of life unique, almost certainly in the Solar System - and possibly in the Universe.

This photograph shows the partly-illuminated Earth rising over the lunar horizon. The Earth is approximately 400,000 km away. This image was taken during the Apollo 11 mission.