The Oh-My-God cosmic ray particle is a single ultra-relativistic proton (?) carrying 50 joules of energy. Is it sufficiently energetic to kill an astronaut in the unlikely event of hitting the person? More precisely, I'm asking: i) Does most of the energy get absorbed by the human body, or penetrate the body without doing harm? (Since protons are highly ionizing, I guess a significant amount of energy would be dumped inside the body with a shower of secondary particles, but I have no idea exactly how much it will be.) ii) Is the release of energy from this particle localized to a small area, or spread out in the human body? (Even if the radiation dose is large, the person can survive if it's localized. For example, the radiation could destroy one of his fingers leaving other part of the body intact.