Cosmic Rays Change Composition Midway
Cosmic rays are not light but charged particles bombarding Earth from all directions. Most of them are protons (hydrogen nuclei), but heavier nuclei also show up: helium, nitrogen, iron.
Neutrons Leave a Trace
A dark matter detector is like a super-sensitive microphone listening for silence. It picks up tiny heat jolts, phonons, that occur when a particle grazes a crystal. But instead of silence, the instruments have been hearing noise for years: a slew of weak signals below a few hundred electronvolts.