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SYFY WIRE Bad Astronomy

Desktop Project Part 1: A weird Moon crater

By Phil Plait

[Over the past few weeks, I've collected a metric ton of cool pictures to post, but somehow have never gotten around to actually posting them. Sometimes I was too busy, sometimes too lazy, sometimes they just fell by the wayside... but I decided my computer's desktop was getting cluttered, and I'll never clean it up without some sort of incentive. I've therefore made a pact with myself to post one of the pictures with an abbreviated description every day until they're gone, thus cleaning up my desktop, showing you neat and/or beautiful pictures, and making me feel better about my work habits. Enjoy.]

First up in my Desktop Project is a weird crater on the Moon, seen by the Lunar Reconnaissance Orbiter:

What a strange little thing! [Click to enlunenate.]

It's about 140 meters across the rim, and it's located in Plato, a big, relatively flat walled plain -- basically, a crater that got mostly filled in with lava long ago -- about 110 km (70 miles) across. You can see rubble and other debris scattered around it (in this image, sunlight is coming from below and to the left), and the interior is just odd.

This is called a bench crater, where you get roughly concentric features inside the crater itself. It's probably from a high-velocity impact by a small (5-meter or so) asteroid, and the terrain where it hit probably has a thin layer of compacted regolith -- the powdery surface material covering a lot of the Moon. This loose material blasted out more than the harder rock below, so you get this weird two-tiered structure.

Craters can be pretty complex; you might think you just get bowl, but in fact the impact speed, angle, the terrain, and the overall size of the impactor make a huge difference in crater structures.

Also? The first thing I thought of when I saw this picture was that it looked like the plaster cast they made of the giant ant footprint in one of my favorite movies of all time, "Them!" And that makes me a bigger dork than you can ever hope to be.

Image credit: NASA/GSFC/Arizona State University

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