J. M. Conrad

The MicroBooNE detector is a large tank of liquid argon that catches particles flying through it. When a particle passes, it leaves a trail of charge and a flash of light. These trails combine into a three-dimensional picture of the event, as if the particle were drawing its path in a transparent cube.

Neutrinos are tiny particles that zip through Earth, barely noticing it. In the MicroBooNE experiment, they are caught in a tank of liquid argon. When a neutrino strikes an argon nucleus, it produces an electron and protons, like splashes from a stone thrown into water.

A chamber the size of a small truck is filled with liquid argon at minus 186 degrees Celsius. When a particle flies in, it knocks electrons off argon atoms, and those electrons drift toward the walls, tracing a three-dimensional picture of the event.

Earth is a closed book for those accustomed to leafing through pages with light. But to neutrinos, the invisible particles born in cosmic rays and barely remembering the prediction of Pauli, our planet is a braille script: each kilometer of depth presses its relief into their…

For almost a century, seismology has been the planet’s chief X-ray, probing the interior through elastic waves. But neutrinos, ghost particles predicted by Wolfgang Pauli, offer a different perspective.

Deep beneath the ice of the South Pole, nearly two and a half kilometers down, an unusual telescope is at work. It is not pointed at the sky but through the Earth. Its quarry: neutrinos, nearly elusive particles that pass through planets and stars without interacting with anything.