Nature imitates art! Kinda!
I am endlessly fascinated by impact craters. You might think they all look alike, but they don't. They have different shapes, structures, shading, even (sometimes) colors. And these features can tell us a lot about the object that caused the impact as well as the structure of the surface they hit.
For example, here's a nifty crater on the Moon as seen by the Lunar Reconnaissance Orbiter:
That image is 500 meters (.3 miles) across, so this is a decent-sized hole [click it to enlunanate]. Note the rubble; that's a clear indication that the surface of the Moon where the object hit was rocky as opposed to sandy. You only get fractured boulders like that when the impacted surface has some cohesion. Most of the Moon is covered with a layer of dust called regolith, but here, under that powdery surface, was rock.
I'm not a geologist, so that wasn't the first thing I thought of when I saw this picture. What I did think of was how familiar this crater looked to me. And it didn't take me long to figure out why...
That's a picture of me standing at the bottom of a crater I helped make. I didn't dig it, but I did press the button that detonated the equivalent of 1.5 tons of TNT! I did this for the first episode of "Bad Universe", to simulate what would happen when an asteroid hits the ground. Look how similar the two craters are; there was lots of rubble in our man-made hole, and the resemblance is also striking when you see our crater from a distance:
Note the streaks of debris on the ground around the crater, much like the one on the Moon. It's cool how well blowing up stuff on Earth can mimic an impact on the Moon.
Interestingly, the desert where we detonated the explosion was part of a well-used explosives range, so the surface was mostly compacted dirt. That doesn't have the same cohesion as rock, yet the craters are remarkably similar. Clearly impacts are not quite so cut-and-dried as simple explosions on Earth -- the Moon has no air to carry a shock wave, for example -- but pulling the trigger on a ton or two of TNT does do a good job of simulating the event.
Also? It was hugely awesome to blow that hole. That's a perk of being a scientist sometimes.
Image credits: NASA/GSFC/Arizona State University; Discovery Channel
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