It's often said that we know less about Earth's deep interior than we do about the surface of Mars (or maybe even Pluto). A new global map of subatomic particles called antineutrinos is helping to change that. It's showing scientists just how radioactive our little Blue Marble is.
The neutrino and its antimatter cousin — the antineutrino — are the smallest particles known to science. They're produced by the radioactive decay of elements that occurs everywhere, all the time — in stars, black holes, and our planet's interior. And they're absolutely everywhere: At any given moment, trillions of these tiny particles are zipping through our homes and our bodies. Most of us are none the wiser.
But scientists studying Earth's deep interior are very interested in these sneaky neutrinos. That's because radioactive decay produces a tremendous amount of heat within the Earth, heat that fuels tectonic activity and magnetism on the surface. Neutrinos and antineutrinos are a ghostly fingerprint of the energy-producing processes driving Earth's heat engine.
Being virtually massless and carrying no electric charge, neutrinos have proven extremely hard to detect. But one particular flavour of antineutrinos (electron antineutrinos) is a little easier to spot, through a process known as inverse beta decay.
The map shown above, published this week in Nature Scientific Reports, is the very first global picture of electron antineutrino emissions. It was created using antineutrino data collected at two huge detectors — one in Italy and one in Japan — housed a mile underground to avoid cosmic ray interference. The map also pulls data collected by the International Atomic Energy Agency (IAEA) on more than 400 operational nuclear reactors. Interestingly, these human-made sources of radiation only account for less than 1% of the total antineutrinos detected. If you don't like the idea of radiation in your environment, too bad: You're living on a radioactive world.
"Keeping tabs on nuclear reactors is important for international safety and security. But as a geologist, I'm particularly excited for the potential to learn more about Earth's interior," said University of Maryland geologist and study co-author William McDonough. "This project will allow us to access basic information about the planet's fuel budget across geologic time scales, and might yet reveal new and exciting details on the structure of the deep Earth."
In other news from the subatomic world, physicists recently confirmed the existence of cosmic neutrinos, high energy subatomic particles produced by supernovae explosions and black holes. Whether we're trying to peer into the far reaches of the cosmos or deep underground, tiny subatomic particles are leading the way.
First-ever global map of antineutrino fluxes, accounting for natural and human-made sources of antineutrinos. Picture: National Geospatial-Intelligence Agency/AGM2015