Protons from outer space crash into the Earth's atmosphere at a high rate. These protons create particles that eventually decay into other particles called muons. This cosmic debris travels through the atmosphere. Every second, dozens of muons pass through your body. If a muon is created 30 km above the Earth's surface, what minimum speed and kinetic energy must the muon have in order to hit Earth's surface? A muon's mean lifetime (at rest) is 2.20 μs and its mass is 105.7 MeV/c2.