Preschool Space Fast Facts

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Solar system objects

The wide variety of objects that exist in the solar system fall into several categories. In recent years many of these categories have been found to be less clear-cut than once thought.

  • The Sun is a spectral class G2 star that contains 99.86% of the system's mass.
  • The planets of the solar system are those nine bodies traditionally labelled as such: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
  • Sizeable objects that orbit these planets are moons. For a complete listing, see that article.
  • Dust and other small particles that orbit these planets form planetary rings.
  • Space debris of artificial origin that can be found in orbit around Earth.
  • Planetesimals, from which the planets were originally formed, are sub-planetary bodies that accreted during the first years of the solar system and that no longer exist. The name is also sometimes used to refer to asteroids and comets in general, or to asteroids below 10km in diameter.
  • Asteroids are objects smaller than planets that lie roughly within the orbit of Jupiter and are composed in significant part of nonvolatile minerals. They are subdivided into asteroid groups and asteroid families based on their specific orbital characteristics.
    • Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners.
    • Trojan asteroids are located in either of Jupiter's L4 or L5 points, though the term is also sometimes used for asteroids in any other planetary Lagrange point as well.
      Meteoroids are asteroids that range in size from roughly boulder sized to particles as small as dust.
  • Comets are composed largely of volatile ices and have highly eccentric orbits, generally having a periapsis within the orbit of the inner planets and an apoapsis beyond Pluto. Short-period comets exist with apoapses closer than this, however, and old comets that have had most of their volatiles driven out by solar warming are often categorized as asteroids. Some comets with hyperbolic orbits may also originate outside the solar system.
  • Centaurs are icy comet-like bodies that have less-eccentric orbits so that they remain in the region between Jupiter and Neptune.
  • Trans-Neptunian objects, which are icy bodies whose mean orbital radius lies beyond Neptune's. These are further subdivided:
    • Kuiper belt objects have orbits lying between 30 and 50 AU. This is thought to be the origin for short-period comets. Pluto is sometimes classified as a Kuiper belt object in addition to being a planet, and a class of Kuiper belt objects with Pluto-like orbits are called Plutinos. The remaining Kuiper belt objects are classified as Cubewanos in the main belt and scattered disk objects in the outer fringes.
    • Oort cloud objects, currently hypothetical, have orbits lying between 50,000 and 100,000 AU. This region is thought to be the origin of long-period comets.
    • The newly discovered object Sedna, with a highly elliptical orbit extending from about 76 to 850 AU, does not obviously fit in either category, although its discoverers argue that it should be considered a part of the Oort cloud.
  • Small quantities of dust are present throughout the solar system and are responsible for the phenomenon of zodiacal light. Some of the dust is likely interstellar dust from outside the solar system.

These fast facts were based off of a Wikipedia Document on Space.

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