On October 19th, 1991, a single atomic nucleus, smashed into the Earth's atmosphere at 1.5 quintillionths of a meter per second less than the speed of light. That is 99.999,999,999,999,999,999,999,999,51% the speed of light. It quickly disintegrated into a shower of light and subatomic particles, seen by the Fly's Eye Observatory. This was known as the Oh My God Particle.
The single particle had an estimated 50 joules of energy, about the same energy as a baseball thrown at 100 km/h.