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Asteroid Types

  • Asteroids; traditionally, most have been bodies in the inner Solar System.[6]
    • Main-belt asteroids, those following roughly circular orbits between Mars and Jupiter. These are the original and best-known group of asteroids or minor planets.
    • Near-Earth asteroids, those whose orbits take them inside the orbit of Mars. Further subclassification of these, based on orbital distance, is used:[12]
      • Aten asteroids, those that have semi-major axes of less than one Earth orbit and aphelion (furthest distance from the Sun) greater than 0.983 AU.
      • Amor asteroids are those near-Earth asteroids that approach the orbit of the Earth from beyond, but do not cross it. Amor asteroids are further subdivided into four subgroups, depending on where their semimajor axis falls between Earth’s orbit and the asteroid belt;
      • Apollo asteroids are those asteroids with a semimajor axis greater than Earth’s, while having a perihelion distance of 1.017 AU or less. Like Aten asteroids, Apollo asteroids are Earth-crossers.
      • Apohele asteroids orbit inside of Earth’s perihelion distance and thus are contained entirely within the orbit of Earth.
    • Earth trojans, asteroids sharing Earth’s orbit and gravitationally locked to it. As of 2011, the only one known is 2010 TK7.[13]
    • Mars trojans, asteroids sharing Mars’s orbit and gravitationally locked to it. As of 2007, eight such asteroids are known.[14]
    • Jupiter trojans, asteroids sharing Jupiter’s orbit and gravitationally locked to it. Numerically they are estimated to equal the main-belt asteroids.
  • Distant minor planets; an umbrella term for minor planets in the outer Solar System.
    • Centaurs, bodies in the outer Solar System between Jupiter and Neptune. They have unstable orbits due to the gravitational influence of the giant planets, and therefore must have come from elsewhere, probably outside Neptune.[15]
    • Neptune trojans, bodies sharing Neptune’s orbit and gravitationally locked to it. Although only a handful are known, there is evidence that Neptune trojans are more numerous than either the asteroids in the asteroid belt or the Jupiter trojans.[16]
    • Trans-Neptunian objects, bodies at or beyond the orbit of Neptune, the outermost planet.