Near-Earth object
A near-Earth object is an asteroid or comet whose orbit brings it to within about 1.3 au of the Sun.
A near-Earth object, or NEO, is any asteroid or comet whose closest approach to the Sun is less than 1.3 astronomical units. This includes near-Earth asteroids and near-Earth comets. More than 35,000 near-Earth asteroids are known, and new ones are found every day.
NEOs are divided into groups by their orbits. Amors approach from outside Earth's orbit without crossing it. Apollos cross Earth's orbit with orbits larger than ours. Atens cross it with orbits smaller than ours. Atiras orbit entirely inside Earth's orbit.
Most NEOs come from the main asteroid belt, pushed inwards by resonances with Jupiter and Saturn. They survive in near-Earth orbits for only about 10 million years on average before hitting a planet, falling into the Sun or being thrown out of the Solar System. That means they are constantly replenished, and they are the direct parents of most meteorites.
Related terms
Level: Explorer Ages 10 and up