Near Earth Objects

The Barringer Crater
Meteor Crater in Arizona
Credit: D. Roddy, US Geological Survey

Near Earth Objects (NEOs) are objects in space on orbits which come near to the Earth. They are often comets or asteroids. Most NEOs were once part of the asteroid belt. Then gravity from the Sun or inner planets pulled them out of place. Or they collided with another asteroid which knocked them towards the Sun.

An NEO has an orbit which takes it within 1.3 AU of the Sun. The largest known NEO is over 40 km in diameter. Astronomers have found thousands of NEOs with diameters larger than 1 km. Anything smaller is too hard to see.

Meteoroids are pieces of rock from an asteroid or comet. Lots of meteoroids enter Earth's atmosphere each day. Their superfast speed through the air causes them to burn up as they fall. The glow we see from this is called a meteor (or shooting star). Some rocks survive to hit the ground. We call these meteorites. Most are the size of a pebble by the time they reach the Earth's surface.

A large NEO could collide with the Earth in the future. The impact would cause widespread damage. The most dangerous, or hazardous, objects are the biggest and closest ones to the Earth. A hazard it does not mean it will hit the Earth. Astronomers track NEOs in case they are a threat to Earth in the future. Scientists want to "push" any hazardous NEOs out of the way. We need to spot these hazards early to do this. By seeing them early we can prevent a disaster. Remember that a large asteroid colliding with the Earth is not likely!