Post by glaucus on Feb 17, 2019 3:08:18 GMT
A minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor exclusively classified as a comet. Minor planets can be dwarf planets, asteroids, trojans, centaurs, Kuiper belt objects, and other trans-Neptunian objects.
There are various broad minor-planet populations:
Asteroids; traditionally, most have been bodies in the inner Solar System.
Near-Earth asteroids, those whose orbits take them inside the orbit of Mars. Further subclassification of these, based on orbital distance, is used:
Apohele asteroids orbit inside of Earth's perihelion distance and thus are contained entirely within the orbit of Earth.
Aten asteroids, those that have semi-major axes of less than Earth's and aphelion (furthest distance from the Sun) greater than 0.983 AU.
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.
Amor asteroids are those near-Earth asteroids that approach the orbit of 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;
Earth trojans, asteroids sharing Earth's orbit and gravitationally locked to it.
Mars trojans, asteroids sharing Mars's orbit and gravitationally locked to it.
Asteroid belt, whose members follow roughly circular orbits between Mars and Jupiter. These are the original and best-known group of asteroids.
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.
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.
Trans-Neptunian objects, bodies at or beyond the orbit of Neptune, the outermost planet.
The Kuiper belt, objects inside an apparent population drop-off approximately 55 AU from the Sun.
Classical Kuiper belt objects like Makemake, also known as cubewanos, are in primordial, relatively circular orbits that are not in resonance with Neptune.
Resonant Kuiper belt objects
Plutinos, bodies like Pluto that are in a 2:3 resonance with Neptune.
Scattered disc objects like Eris, with aphelia outside the Kuiper belt. These are thought to have been scattered by Neptune.
Resonant scattered disc objects.
Detached objects such as Sedna, with both aphelia and perihelia outside the Kuiper belt.
Sednoids, detached objects with perihelia greater than 75 AU (Sedna and 2012 VP113).
The Oort cloud, a hypothetical population thought to be the source of long-period comets that may extend out to 50,000 AU from the Sun.
en.wikipedia.org/wiki/Minor_planet
