Near Earth Object

A Near-Earth Object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's, and the object is larger than 140 meters (460 feet) across, it is considered a potentially hazardous object (PHO), and some of these if they hit Earth can lead to an Extinction Level Event (ELE).

The asteroid Apophis will make an uncomfortably close pass in 2029. Apophis is about 1,000 feet across, the size of a large football stadium, and will come so close to the earth that it will actually pass beneath some of our satellites. Depending on how the orbit of the asteroid is distorted by this close pass, it may swing back to the earth in 2036, where there is a tiny chance (1 out of 100,000) that it might hit the earth. If this were to happen, it would hit with the force of 100,000 Hiroshima bombs, sufficient to destroy an area as large as France with firestorms, shock waves, and fiery debris. By comparison, a much smaller object, probably the size of an apartment building, slammed into Tunguska, Siberia, in 1908, with the force of about 1,000 Hiroshima bombs, wiping out 1,000 square miles of forest and creating a shock wave felt thousands of miles away.

This is a major concern for the possible extinction of a Type 0 civilization, and Type I civilizations will have planetary defense systems against NEOs.