Rubble Pile

Rubble Pile (English for rubbish heap ) is in the Planetology an informal name for an asteroid, which consists of numerous smaller " chunks " and only by gravity is loosely held together ( in contrast to the monolith ). It is believed that rubble piles represent a significant part of the asteroid, where a proof is still pending. This would have a significant impact on the potential requirement for deflecting an asteroid on a collision course with Earth. It would secondly a significant impact on the characteristics of a collision, since such a pile of rubble can lead to an accumulation of small body explosions in the atmosphere, in contrast to penetrate the atmosphere through a monolith with subsequent explosion in the earth or in the ocean.

Properties of rubble piles

  • Because of the voids between its components a rubble pile should have a relatively low density (see bulk density and true density ). Meteorites are probably fragments of asteroids. Their density is usually 3-5 g / cm ³.
  • Many asteroids are much lighter and are therefore likely to rubble piles eg Eugenia has a density of 1.12 g / cm ³ and Mathilde 1.3 g / cm ³. They are thus only slightly heavier than water (1 g / cm ³).
  • Some small moons even have a density that is less than that of water. Around Saturn's moons Pandora and Helene with a density of only 0.49 g / cc and 0.5 g / cm ³.
  • Other asteroids, however, can have no major cavities: the density of Vesta, for example, is 3.7 g / cm ³, the Pallas of 3.28 g / cm ³.
  • A rubble pile can not rotate at any speed around its own axis, because above a certain threshold speed, the centrifugal force is stronger than gravity and the body is torn apart. This should be less of period durations than about 2.2 hours, the case. In fact, only a few very small asteroids rotate faster. They are smaller than about 150 m in diameter.
  • The known rotational velocities of all other asteroids are lower than the above Limit speed. This is a strong indication that many, if not most asteroids are rubble even piles.
Impact depth Particle density Pandora (moon) Helene (moon) (4) Vesta (2) Pallas
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