Crashing on the Moon
The European Space Agency’s SMART-1 experimental spacecraft will have a planned (meaning expected) crash landing on the surface of the Moon sometime this weekend. A couple of years ago, of course, we had the planned (really meaning planned, as that was the whole point of the mission) impact of part of the Deep Impact spacecraft into the nucleus of a comet so that the resulting debris from the interior could be studied. While the SMART-1 impact is not part of a planned scientific experiment, it will provide another useful data point on the study of cratering in the solar system. Craters abound on planets, moons, asteroids, and comets. They provide a nice historical record of the abuse that those objects have suffered over the ages. By untangling the pattern of craters on the surface of an object such as the Moon, we can learn what the history of debris in the solar system has been. For example, the Moon’s craters appear to show that there was a great cataclysm of impacts some 700 billion years after the formation of the planets was mostly complete. While the SMART-1 impact won’t shed any light on the mystery of this so-called Late Heavy Bombardment, it will help us understand how big a crater is produced in a particular impact. Usually we have to use computer models to estimate the size and speed of an object that produced any particular crater. In this case, we will know the mass and speed of the impacting object at high precision, and future lunar orbiters, in particular the Lunar Reconaissance Orbiter scheduled for launch in 2008, will be able to see the crater that it produces.