Asteroids - How?

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Next Chapter: Asteroids - Types

When the Earth and the rest of the planets were forming all those billions of years ago, the Solar System was full of asteroids. The asteroids were created from a dusty, gaseous disc that had formed around the young Sun. These asteroids then began to merge to form bigger and bigger objects called planetesimals, which then grew into planets like Earth and Mars. Life in this construction yard wasn’t fun; colliding with other asteroids and gathering up debris, all the while trying to avoid getting pulverised by a larger object.

The rocks in the Asteroid Belt are the leftover rubble from this construction period. Therefore asteroids are the building blocks of planets, which means they are made of the pure material from which the Solar System formed. Consequently, by studying what asteroids are made of, we can find out about the materials that originally built the Earth.

There are three ways we can discover what asteroids are made from. One way is by sending space probes to investigate them, taking pictures or even landing on them. This is what NASA’s NEAR-Shoemaker spacecraft (Near Earth Asteroid Rendezvous; Shoemaker refers to Gene Shoemaker, the legendary planetary scientist and asteroid and comet discoverer) did when it arrived at the asteroid Eros in the year 2000. Alternatively, sometimes asteroids come to us, in the form of tiny chunks of rock blasted off their surfaces that then fall to Earth as meteorites. However, space missions are expensive and are few and far between, while you need a certain degree of luck to find meteorites. Astronomers therefore use a third method for measuring what asteroids are made of, and this method is called spectroscopy.

Different materials absorb and reflect light from the Sun at different wavelengths. By identifying these different wavelengths astronomers can work out the make-up of an asteroid’s surface.

Next Chapter: Asteroids - Types