Rubble pile

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Rubble pile ( English for debris heap ) is in the Planetologie an informal name for an asteroid is composed of many smaller "chunks" and only by the gravitational is loosely held together (in contrast to the monolith ).

Rubble piles presumably make up a significant proportion of the asteroids, although evidence is still pending. This would have a significant impact on the possibly necessary deflection of an asteroid on a collision course with Earth. In addition, it would have considerable effects on the characteristics of a collision, since such a pile of rubble can lead to an accumulation of explosions of small bodies in the earth's atmosphere , in contrast to the breakdown of the atmosphere by a monolith with a subsequent explosion in the earth or in the ocean.

properties

  • Because of the voids between its components, a rubble pile should have a relatively low density (see bulk density and true density ).
    • Many asteroids are considerably less dense than meteorites (which are likely fragments of asteroids and usually have 3 to 5 g / cm³) and are therefore likely to be rubble piles , e.g. B. Eugenia (1.12 g / cm³) and Mathilde (1.3 g / cm³). They are therefore only slightly denser than water (1 g / cm³).
    • Some small moons even have a density that is lower than that of water, such as Saturn's moons Pandora (0.49 g / cm³) and Helene (0.5 g / cm³).
    • Other asteroids, on the other hand, can not have larger cavities due to their relatively high density , e.g. B. Vesta (3.7 g / cm³) or Pallas (3.28 g / cm³), and thus not be rubble piles .
  • A rubble pile cannot rotate around its own axis as fast as it wants, since above a certain limit speed the centrifugal force becomes stronger than gravity and tears the body apart. This should be the case for rotation periods of less than approx. 2.2 hours.
    • In fact, few asteroids rotate faster. They are very small with a diameter of less than 150 m.
    • The known rotation speeds of all other asteroids are lower than the limit speed mentioned above. This is considered a strong indication that many, if not most of the asteroids are rubble piles .

literature

  • Alan W. Harris: The Rotation Rates of Very Small Asteroids: Evidence for 'Rubble Pile' Structure . In: Lunar and Planetary Science . 27/1996. P. 493, ISSN  0197-274X ( bibcode : 1996LPI .... 27..493H )
  • Günther Glatzel: Titan and Phobos: grainy inside . The use of the radar Doppler shift to determine the internal structure of "Rubble Piles" using the example of the Saturn moon Titan and the Martian moon Phobos (which in turn is considered to be a possible captured asteroid). Online article at Raumfahrer.net, added Dec. 27, 2013
  • Deller, Jakob (2015) Hyper-Velocity Impacts on Rubble Pile Asteroids . PhD thesis, University of Kent, International Max Planck Research School for Solar System Science. Online at kent.ac.uk (PDF)
  • Kevin J. Walsh: Rubble Pile Asteroids. Annual Review of Astronomy and Astrophysics, 2018, Vol. 56: 593-624, @arxiv