Rough Science Death Valley: Mike's Impact Diary

Production team

Day One & Two

If someone had told me that you can estimate the size of the meteor that created a particular impact crater just by dropping a 1.75 kilo steel ball into sand, I’d have told them they were talking rubbish. But it can be done.

The first two days of this challenge involved me doing just that. For this programme, Kathy, Iain and I have been given the job of working out the size (diameter) of the meteorite that produced the particularly large impact crater in the Nevada Desert.

While Kathy and Iain were away in Nevada working out the actual size of the crater, my job was to create a series of much smaller craters using a much smaller meteorite.

All I had to do was drop a steel ball of known weight from known heights and plot the diameter of the impact craters that I formed against the energy of the impact, which can be calculated since you know the height from which you’re dropping the ball.

By going to greater and greater heights you can get more and more impact energy. From just a few data points, it’s possible to estimate the size of the meteorite that will produce a particular crater size. The idea is to extrapolate from my small-scale results to the larger scale of the Nevada crater.

OK, there are other processes going on in real meteorite impacts, such as the meteorite exploding – something that we could never reproduce experimentally under Rough Science conditions. Even so, this extrapolation method might still work well enough for our purposes.

Day Three

By the middle of day three I’ve got enough data points to be able to plot a graph of log (crater diameter) against log (energy of impact). Using Kathy and Iain’s estimate of the diameter of the real Nevada impact crater, we will be able to extrapolate from my graph in order to determine the energy of the meteorite that caused it.

Knowing the impact energy, and the approximate speed of impact (which we can guestimate), will give us the mass of the meteorite. If we also guestimate the density of the meteorite (most of them are composed of iron and nickel, so a reasonable estimate should be possible), we can work out the volume of the meteorite. From there it’s easy enough to calculate its diameter.

I’m absolutely astonished when we find out at the end of the day that we’re not all that far out from the meteorite diameter value which the professionals have estimated for the Nevada crater.

Okay, we’ve made lots of assumptions and approximations along the way, not the least of which was ignoring the explosion that accompanies real meteorite impacts.

Maybe the errors we’ve made in our measurements have all cancelled themselves out, but I’m impressed nevertheless. I'd never have thought it possible…