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Q & A: A Great Many Asteroids

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Most recent answer: 10/22/2007
how many asteroid are there in the solar system?
- Nicholas seah (age 10)
Tampines North Primary School, SIngapore
Nicholas -

A little background helps to show why the answer to this question is complicated but interesting. Asteroids are rocky objects in the solar system. They are mostly found in what is called the Main Belt of asteroids (a.k.a. the Asteroid Belt) which lies between Mars and Jupiter. In movies (e.g., The Empire Strikes Back), asteroids are often shown as huge, mountain-sized objects. Indeed, a few of them are this large. But they come in many sized, and in fact most asteroids are much smaller. Going to the excellent SEDS website

we find that:

"There are 26 known asteroids larger than 200 km in diameter. Our census of the largest ones is now fairly complete: we probably know 99% of the asteroids larger than 100 km in diameter. Of those in the 10 to 100 km range we have cataloged about half. But we know very few of the smaller ones; perhaps as many as a million 1 km sized asteroids may exist."

Although asteroids are not nearly a close together in space as movies and video games suggest, they still can and do collide, and the rubble comes in all sizes, from rocks (which are the meteorites we find on earth) down to tiny microscopic dust particles. Indeed, these dust particles are so interesting that there is a NASA space
mission going on right now which will retrieve some of this space dust (asteroid and comet debris) and bring it back to Earth for study:

Finally, the really interesting aspect of all of this is that we believe that asteroids are the leftover "building blocks" of planets. This means that asteroids, as well as meteors and interplanetary dust, provide us a record of material from the early development of the solar system. This is why these are so important to study: they can tell us a lot about where we came from.


(published on 10/22/2007)

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