Planets are not the only bodies orbiting the Sun. The Solar System also contains innumerable smaller bodies: meteoroids, asteroids and comets. We now turn to a study of these.

We have already commented on how common craters are in the Solar System. Our Moon is covered with them, as are many other moons and planets. Indeed, the Earth is unusual in having so very few craters. As we have already mentioned, this is not because the Earth never had craters: it is because they have been “erased” by erosion and other geological processes.

Once in a long while these impacts are catastrophic. Indeed, we believe it was just such an impact that led to the extinction of the dinosaurs. Only highly sensitive and highly accurate observations are capable of telling us whether an incoming body poses a similar threat today. Efforts are under way to study the feasibility of deflecting any such potentially threatening objects that we might discover.

Meteors

Meteor showers

Several times each year a meteor shower occurs. Perhaps you have seen one. They can be very beautiful as, utterly soundlessly, meteors streak across the sky. Sometimes a particularly large one will leave a faint glowing trail. The meteoroids that produce these showers are tiny – about the size of snowflakes. Because they are so small they entirely burn up in their fiery passage through the atmosphere: none of them survives to reach the ground. During a particularly intense shower you might see one a minute, although occasionally even greater rates are seen.