So some meteor impacts are big enough to register on the Richter Scale. Tunguska was one of these, but the scale hadn’t been invented yet. But to find the most ground-shaking event we’ve ever seen, you need to look to Mercury.
The circled area is the Caloris Basin. It doesn’t look like much, but it’s been filled in by lava that happens to be the same color as the rest of the surface. It’s actually an enormous impact crater over 1000 miles across which we’ve know about for decades. The MESSENGER probe has found some very exciting discoveries just in its first flyby earlier this year. One of those discoveries is how powerful of a hit Mercury really took.
The science team working on MESSENGER have analyzed the breaks in the crust on THE OTHER SIDE OF THE PLANET that were formed when the impactor collided.
There are breaks in the surface we can use to measure how strong the ripple effect that covered the entire planet and pushed through the core really was. Mathematical modeling has now shown us that the motions of the quake would have pushed the surface over a half-mile of displacement vertically starting about 15 minutes after the initial impact. I can’t even guess what that would read on the Richter Scale! Imagine, a half-mile — one kilometer — straight up! That’s a quake for the ages.
There have been other impacts in the solar system at least as large and larger than this one, but Mercury is smaller than all the other worlds, even smaller than some moons. An impactor like that one would certainly cause global extinction on the Earth, but on Mercury it was REALLY a bad day!