Small body (astronomy)

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Asteroid (243) Ida (60 × 25km) with moon Dactyl . It orbits thousands of similar size in the asteroid belt between Mars and Jupiter's orbit
A meteorite of the Perseids with a size of about one centimeter when entering the earth's atmosphere in ten times slow motion (event duration one second)

Small bodies are a class of celestial bodies in orbits around the sun, redefined by the International Astronomical Union (IAU) on August 24, 2006 in Prague . With a diameter of less than 300 km, they are too small to be spherical.


The term small bodies are asteroids , comets and meteoroids summarized that the sun orbiting and - unlike dwarf planets  can form because of their low mass and gravitational no spherical shape -.

A small body that outgasses near the sun and forms a coma or tail is a comet. If the tail and coma disappear, so that the body appears as a sharply outlined structure in the telescope, it can no longer be distinguished from an asteroid.

If a small body is smaller than a few meters, it is called a meteoroid. Far away from the earth, it is too small for direct observation. Instead, it makes itself noticeable as a meteor if it enters the earth's atmosphere, and as meteor dust . If it does not completely burn up as a shooting star , it will reach the surface of the earth as a meteorite .


Small bodies occur mainly in three regions in the solar system :

  • In the asteroid belt , between the inner (earth-like) and outer, Jupiter-like planets - as rock-like asteroids ( planetoids ).
  • In the Kuiper Belt , which is located outside of Neptune's orbit - as strongly icy asteroids and potential mid-period comets.
  • In the Oort cloud , which forms the outer, spherical zone of the solar system - as a theoretical reservoir for long-period comets.


Asteroids and comet nuclei are primarily considered to be primeval material remnants that are left over from the formation of the planetary system because they did not merge with other planetesimals to form protoplanets or planets . In addition, some are fragments that have arisen from the collision between larger small bodies or from the disintegration of a cometary nucleus into a meteor shower. Such events are also the main cause of the formation of meteoroids. But such smaller objects can also enjoy a impact on a larger body such as a planet or moon are beaten from its surface.

See also


  • Ingrid Mann: Small bodies in planetary systems. Springer, Berlin 2009, ISBN 3-540-76934-X
  • Bonnie A.Steves, Archie E. Roy: The dynamics of small bodies in the solar system-a major key to solar system studies. Reidel, Dordrecht 1999, ISBN 0-7923-5466-4 .
  • Tadashi Mukai, (et al.): Sample return missions to small bodies. Pergamon, Oxford 2000
  • Jeffrey Bennett, Megan Donahue et al .: Astronomy. The cosmic perspective (Ed. Harald Lesch), Chapter 12 (asteroids etc.); 5th edition, Pearson Studium Verlag, Munich 2010, ISBN 978-3-8273-7360-1
  • John S. Lewis: Mining the sky - untold riches from the asteroids, comets, and planets. Addison-Wesley, Reading 1997, ISBN 0-201-32819-4

Web links

Commons : Small bodies  - collection of images