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Why Meteoroids Explode Before Hitting the Earth (qz.com)
According to a new study from Purdue University, scientists have figured out why meteoroids explode before hitting the Earth. "The research, published in the December issue of the journal Meteoritics & Planetary Science, shows that as meteoroids plunge, the high-pressure air they push against find its way into the objects' pores and cracks, forcing their bodies apart from the inside," reports Quartz. "The result is a kind of detonation that looks like an explosion." From the report: To explain the astrophysics, researchers focused their work on a widely viewed February 2013 meteoroid explosion place over Chelyabinsk, Russia, a city of 1.1 million north of the Kazakhstan border. Researchers ran a computer program that allowed for them to simulate what happened to the meteoroid in the atmosphere. "Our simulations reveal a previously unrecognized process in which the penetration of high-pressure air into the body of the meteoroid greatly enhances the deformation and facilitates the breakup of meteoroids similar to the size of Chelyabinsk," the study states. The researchers added that while the air pressure is effective at breaking apart small meteoroids, larger ones would likely withstand the force as they come to Earth.
Have you ever used a pressure washer? I own a mid grade entry level one with 3500 psi. You have to be very careful not to spray too hard into a crack or it will rip whatever it is apart. 3500 might not sound like a lot, but square area is deceptive. Say 300 psi gets into the crack, but the crack is 6 inches deep and 12 inches wide that's 21,600 lbs pushing on each side. But it gets worse, the stress has to flow from one side to the other of the crack, around the propagating crack tip. The sides of the crack act as a lever to concentrate the force many times higher if the crack tip is sharp and enough force is used to slightly bend the material. It's similar to fracking, the pressure may be moderate to high but the surface area is very large and it creates a super large force through several different effects that is capable of breaking rock.