Amor Asteroid - Definition 1

Definition 1

(The source of this definition was not given by the author(s), but it is being kept in case someone can find a source. Definition 2 has a source.)

There are three general criteria an asteroid must meet to be considered a member of the Amor asteroid class.

• The asteroid must be able to come near the Earth. To be considered "near", the asteroid must come closer to the Earth than any other major planet. The closest planet to Earth is Venus, which can get as close to 0.27 AU from the Earth at its closest. This value is rounded up to 0.30 AU. Therefore, an Amor asteroid must be able to get as close or closer to the Earth than 0.30 AU.

• The asteroid's orbit must be outside the orbit of the Earth (like the majority of asteroids). Asteroids that get close to the Earth whose orbits are inside the Earth are considered Apohele asteroids (although not all Apoheles necessarily get close to the Earth).

• The asteroid's orbit must not cross Earth's orbit. The most commonly used definition (which Wikipedia uses) defines this as being unable to get closer to the Sun than the Earth's average distance from the Sun (1.000 AU). A more strict definition interprets this as "at any point along the asteroid's orbit, the Earth's orbit is closer to the Sun". This takes into consideration the fact that the Earth's orbit ranges between 0.983 and 1.016 au from the Sun. It is more difficult to sort out the Amor asteroids from the non-Amor asteroids using this definition, however.

These three criteria are boiled down to a single test for membership. If the asteroid has a perihelion between 1.000 AU and 1.300 AU, it is considered an Amor asteroid. Any asteroid with this trait is considered an Amor class asteroid, regardless of its semi-major axis, eccentricity, aphelion, inclination, physical properties, orbital stability, or place of origin.