Main belt comets

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Main belt comets are a group of small bodies in the solar system that cannot be clearly assigned to either comets or asteroids . They are mainly located in the main belt , show comet-like activity and cannot be dynamically distinguished from the asteroids. The active asteroid (7968) Elst-Pizarro is currently the best-studied object of this group.

discovery

In August 1996, the Belgian astronomer Eric Walter Elst reported on the discovery of a comet in pictures taken by his Chilean colleague Guido Pizarro . Using additional images, Brian Marsden from the USA succeeded in calculating the comet's orbit around the sun and assigning it to an already known object. It coincided with the orbit of the asteroid 1979 OW7, which had been discovered in 1979. It orbits the Sun within the orbits of Mars and Jupiter in the asteroid belt. The asteroid was then classified as Comet 133P-Elst-Pizarro.

Emergence

The question has not yet been finally clarified whether the main belt comets originated where they are today or whether they were transported to their present location from another area in the solar system. Computer simulations show that objects from the Kuiper Belt outside of Neptune's orbit can be transported on stable orbits in the main belt. Originally, meteoric objects were outside of today's planetary orbits. After the formation of the solar system, the large planets changed their orbits and this made a ring of comet-like objects unstable. Many such comets, which initially crossed Jupiter's orbit, were able to achieve stable orbits in the main belt through a combination of dynamic processes .

Activity mechanisms

So far, no universal mechanism is known that could be responsible for all meteoric asteroids. The researchers discuss a number of different processes that could be considered for some objects:

  • As with comets, the activity of some celestial objects could be driven by subliming water.
  • The objects could become unstable as a result of their rotation , so that the fragments would be hurled off their surface.
  • Another mechanism of activity is that small celestial bodies hit its surface and leave an impact crater. Large amounts of dust and debris would then be released from it.
  • Some objects get so close to the sun that their surface becomes very hot. At such high temperatures, fractures can occur in the rock, from which dust is released into space. If there are also water-containing minerals there, they can release water at the high temperature.
  • Processes that take place directly on dust particles on the surfaces. The solar radiation causes the dust particles to be lifted from the surface. The particles can be electrically charged by the photoelectric effect and by the plasma of the solar wind and transported away by electrostatic repulsion.

Objects

Surname discovery Core diameter (km)
Elst-Pizarro 1979 1.6 x 2.3
238P Read 2005 0.6
118401 Linear 2005 1.5 x 2.6
PR1 Garrad 2008 0.4

literature

  • Stars and Space 2015 Active Asteroids , Verlag Spektrum der Wissenschaft, Heidelberg

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