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Space is empty ... lots of empty. Apparently so empty that the risk of collision between a spacecraft of our times, and an asteroid in the asteroid belt is said to be infinitesimal.

Running a search for asteroid collision brings up any number of talk about an asteroid/comet colliding with Earth. There doesn't appear to be much known about Asteroid-Asteroid collisions though

  • How frequently does an asteroid collide with another?
  • Are there any such asteroid-asteroid collisions calculated to be visible in the near future?
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Both questions are really hard to answer. You can only estimate how often this happens.

There is no monitoring system, which constantly observes the entire sky. There is an unknown number of asteroids and comets in the solar system. Right now, the rate of newly discovered objects increases exponentially (due to better and better technology). Today's number of uniquely identified objects is in the range of half a million to one million objects (620284 as of July 22 2013). They are listed by the Minor Planet Center. While there actually are estimated values of the total amount of objects in our solar system, nobody can be sure about it at the current state of science, technology and monitoring. There are some attempts like observing and counting present impacts and dating existing craters on the Moon, but this only helps for the class of objects, which intersect Earth's orbit around the sun. For instance, it excludes objects in the asteroid belt or Kuiper belt.

Keeping in mind those numbers, inter-asteroid / asteroid-comet / inter-comet collisions are extremely rare. They are in fact so rare, that there is basically no statistics about it. It is hard or near impossible to put a number of that.

However, there are attempts to predict collisions. Keeping in mind that orbital parameters of small and distant objects can only be determined with some uncertainty, the idea is to go through the database of known objects and predict when a pair of objects comes into a certain proximity. This gives candidates for collision events. They are rather interesting for researchers, who are studying the structure or chemical composition of such objects. Another however, the amount of collisions actually happening after such a prediction is still incredibly low.

If you are interested in such events, it is a good idea to set a number of Google alerts on some relevant key words and follow as many astronomers mailing lists as possible. This may sound like stupid advice, but it is as good as it can get. Sometimes, there are announcements. You just need to find them at the right time.

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  • $\begingroup$ arxiv.org/abs/1211.6275 $\endgroup$
    – Deer Hunter
    Aug 20, 2013 at 9:53
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    $\begingroup$ +1 and just to re-emphasise how hard it is to monitor all the small objects, even those potentially hitting the Earth, those scientists and observers that predicted so well the asteroid 2012 DA14 to pass the Earth by a width of a hair, were the same scientists and observers that failed to even detect the Chelyabinsk meteor that hit Russia earlier that very same day. That said, any numbers we might have on asteroids hitting each other would be rough estimates at best, even if they'd be good to know. $\endgroup$
    – TildalWave
    Aug 20, 2013 at 10:51
  • $\begingroup$ Good discussion, but it would really be better to give a number, even if it has large uncertainties associated with it. $\endgroup$
    – pericynthion
    Mar 6, 2017 at 19:37
  • $\begingroup$ We don't know enough to give a number with a large uncertainity. A unknown asteroid means a unknown orbit and we cant say anything about the collision probability between unknown asteroids. $\endgroup$
    – Uwe
    Mar 7, 2017 at 21:47

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