Several of the mapping tasks here at CQ include marking the size and position of impact craters. Why is this so important, and how does so much science come out of these measurements? We’ll answer these questions in a series of posts about impact craters, starting here with Impact Events.

Impact craters are the scars left behind by impact events. An impact event occurs any time something in outer space runs into something else, and that actually happens all the time. What we might think of as empty, open space isn’t actually empty – there are a lot of rocks (and dust) of different sizes and compositions out there. Some rocks eventually find themselves on a collision course with another rock. The big one in the impact is called the “target” body, and the smaller one the “impactor.” These targets and impactors can be planets, asteroids, comets, and moons.

An artist’s conception of a major impact event, with the early Earth as the target body. Such massive impacts no longer occur, but plenty of small ones do. Image Credit: Don Davis (work commissioned by NASA)

So where did all this material come from? When the solar system first formed, most material was gathered up quickly, forming the planets and their moons. What remained rained down on the new bodies in the solar system, leaving what we now see as ancient impact scars. Most of the impact craters we see on the inner planets (Mercury, Venus, Earth, Mars) and the Moon are the result of impacts by asteroids and comets. While the bulk of that dust, rock, and ice from the early days of the solar system is gone, there is still plenty left to create impact events even today.

Impact craters are therefore key to the investigation of impact events. We can learn a great deal about the nature of the impact event – when it happened, how energetic it was, and how it changed the target body – by studying the crater left behind. We can research both events in the past, and in our present, allowing us to see how the solar system has changed with time.