X Crater: First Class

When an asteroid or comet impacts a planet, the explosion ejects huge amounts of material, sending it flying in all directions. But there are also plumes of material, long fingers of rock and dust that stream out as well. The boulders and such inside this plume then fall back to the ground, making liner chains of secondary craters. We see lots of these on our Moon, moons in the outer solar system, and Mercury, too.

If these features are long enough, it’s inevitable two chains from two different primary craters would cross somewhere. And it turns out this has been seen… but where?

Well, X marks the spot!

This MESSENGER image of Mercury shows exactly that: two crater chains from two separate impacts crossing over each other (and a third, shorter chain is at the bottom, too). They’re almost exactly perpendicular to each other, which is cool, and the intersection happens to lie in a big, shallow crater about 120 km (72 miles) across that fills this image. Unfortunately, MESSENGER hasn’t been orbiting Mercury long enough to have surveyed the whole planet yet, so I wasn’t able to ...

Full story at http://blogs.discovermagazine.com/badastronomy/2011/05/09/x-crater-first-class/