Aten asteroid

Aten asteroids are a class of near-Earth asteroids whose orbits are primarily within Earth's orbit but may extend beyond it at their farthest point from the Sun. They are defined by having a semimajor axis of less than one astronomical unit.1

There are two main families of asteroids that cross Earth's orbit:
* Aten asteroids: Spend most of their time inside Earth's orbit. Their mean distance from the Sun is less than 1 AU, and their aphelion distances are greater than or equal to Earth's perihelion distance.12
* Apollo asteroids: Are mostly beyond Earth, with only the innermost point of their orbit inside ours. Their mean distances from the Sun are greater than or equal to 1 AU, and their perihelion distances are less than or equal to Earth's aphelion distance.12

Astronomers actively search for these asteroids due to the potential risk of collision with Earth.3