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Scientists, led by David Nesvorny from the Southwest Research Institute, Colorado, have discovered the youngest known family of asteroids in the main asteroid belt between Mars and Jupiter. Asteroid families are groups of asteroids that have similar orbits and formed by the break-up of a large asteroid in a collision. By tracing back the path's of the 39 asteroids in the newly discovered family the collision that caused the break-up has been dated at 5.8 million years. This is practically yesterday compared to the 4.5 billion year history of the main asteroid belt. The family has been named after its largest member asteroid, Karin, which is 19 km in diameter.
A large number of asteroid families have already been identified in the main asteroid belt and some consist of hundreds of asteroids. The Karin family is, however, by far the youngest, most of the others having been formed by collisions that occurred tens to hundreds of millions of years ago. Ever since the formation of the asteroid belt 4.5 billion years ago collisions have occurred between asteroids since their orbits are disturbed by the gravity of the giant planet Jupiter. The main belt asteroids have, therefore, been gradually grinding themselves away into smaller and smaller fragments. Not only do the families of asteroids, with their similar orbits, testify to collisions within the main belt but images of asteroids taken by spacecraft such as Galileo and NEAR show that most are deeply scarred by impact craters.
The newly discovered Karin family is significant since because it is so young its member asteroids have not be worn down by further collisions and so they can tell us how many asteroids of a particular size are produced when an asteroid breaks up. The largest asteroid in the family, for example, is 19 km in diameter and yet perhaps millions of 100 m fragments would have been produced in the collision. Although breaking up a potentially hazardous asteroid would be the last resort because some pieces could still collide with the Earth, the information from the Karin family will help scientists estimate the size of the fragments. Asteroids in the Karin family are, however, main belt asteroids and thus have orbits that do not come anywhere near our planet. Only a small proportion of main belt asteroids become NEOs. The discovery of the Karin asteroid family was published today in the Journal Nature.
More info: The Journal Nature
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