Planetary scientists are often found droning on about meteorites, but what makes them so interesting and useful to study? To explain this, we have to understand what a meteorite actually represents to scientists. This can be most easily described by using photography as a parallel.
Photographs are snapshots in time, and we use them to remind ourselves about what the time they were taken was like. Now, imagine someone gave you a photograph that you had never seen before; you don’t know the people within the frame and as such, their life, nor do you know the location it was taken. But wait, because you may be able to work out some of these mysteries by analysing the details of the photograph. You could guess at the age of the photo, based on the clothing they were wearing or the colouration of the photo. You might be able to identify landmarks in the background, to help work out where it was taken. You may even be able to theorise about the activity that was going on at the time the photo was taken. All of these have direct parallels to the way scientists use meteorites.
When dust, rock grains and metals accrete to form a meteorite, they are essentially taking a photograph of the place they were formed. The material that was present and the amounts of it that were available, the gases that were present in the environment at the time, even the processes that were affecting the material, these are all preserved within a meteorite. The information contained may not be immediately visible, in fact it quite often requires hi-tech instrumentation to access, but it is there nonetheless. Quite a large amount of information is found in the gases contained inside the meteorite. These gases have unique properties which preserve different information about the meteorite’s origins.
The parallel can be taken even further if we consider what happens to both meteorites and photographs if they are exposed to environments that would alter them. If we were to expose a photo to a flame, there wouldn’t be much left to tell us about the origins of the photo. Equally, exposing a meteorite to heat quite often leads to some of these trapped gases escaping, altering what we are able to tell about the meteorite’s origins. This is particularly the case if the meteorite melts. In the same way that pigments and paper decay when exposed to things like water and oxygen, so do the minerals within meteorites.
Like the historians trying to unravel the past, if we hope to understand how we came to be on earth, how the planets and maybe even the stars formed, our best source of information may well be the ‘photographs’ of the solar system that we call meteorites.