|Cosmic ray tracks in an Apollo space helment, amplified 10-millionfold by chemical etching.|
. . . in other words, a subatomic particle with macroscopic kinetic energy equal to that of a baseball (142 g or 5 ounces) traveling at 96 km/h (60 mph).At some point I had the idea that cosmic rays were iron particles, and that might occasionally be the case, but they are more likely to be protons.
It was most probably a proton with a speed very close to the speed of light.
So I'm wondering if the astronaut noticed when this particle hit his helmet. Maybe it wasn't an ultra-high energy cosmic ray, maybe it was just regular cosmic ray, and he just thought someone was throwing spitballs at him. Jimmy! Stop that!
Update January 2017 replaced missing picture.