Qite Li

Inside an atomic nucleus, particles aren't just tossed together any which way. Sometimes two protons and two neutrons huddle into a tight quartet — a mini-collective known as an alpha cluster. Think of it as a family that sticks together in a crowded building. Knocking this quartet out of the nucleus and seeing how it lived there is a job for a fast proton.

The Moon is an airless sphere of dense rocky grit called regolith. When fast particles from space slam into it, muons are born in the soil — unstable relatives of electrons, but two hundred times heavier. Most fly downward and fade away in the depths. But those that pop upward into the vacuum can travel tens of kilometers before decaying.