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The Amor asteroids are a group of near-Earth asteroids named after the asteroid 1221 Amor. They approach the orbit of Earth from beyond, but do not cross it. Most Amors cross the orbit of Mars. The two moons of Mars, Deimos and Phobos, may be Amor asteroids that were captured by Mars's gravity. The most famous member of this group is 433 Eros, which was the first asteroid to be orbited and then landed upon by a human probe (NEAR Shoemaker). == Definition 1 == There are three general criteria which an asteroid must meet to be considered a member of the Amor asteroid class: * The asteroid's orbit must periodically bring it near Earth. To be considered "near", the asteroid must come closer to Earth than to any other major planet. The closest planet to Earth is Venus, which can come as close as 0.27 AU; this value is rounded up to 0.30 AU for the purpose of this definition. Therefore, an Amor asteroid must come within 0.30 AU of Earth's orbit. * The asteroid's orbit must be outside the orbit of Earth (like the majority of asteroids). Asteroids that come close to Earth whose orbits are inside Earth's orbit are considered Apohele asteroids (although not all Apoheles necessarily get close to Earth). * The asteroid's orbit must not cross Earth's orbit. The most commonly used definition of this (which Wikipedia uses) is that it never orbits closer to the Sun than Earth's average distance from the Sun (1.000 AU). A more strict definition is that "at any point along the asteroid's orbit, Earth's orbit is closer to the Sun". This takes into consideration the fact that 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 boil down to a single test for membership: If an asteroid has a perihelion between 1.000 AU and 1.300 AU, it is 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Amor asteroid」の詳細全文を読む スポンサード リンク
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