A closer look

Forget risking a grad student's life inside an active caldera. Physicists instead rely on the cosmic detritus of exploding stars. High-energy muons constantly rain down on Earth, passing effortlessly through solid rock. By catching the few muons that get absorbed by ultra-dense magma, scientists create three-dimensional X-ray maps of a volcano's internal plumbing, essentially watching a mountain digest its own molten guts before an eruption.