Antarctic Neutrinos Are Being Used to Weigh the Earth’s Core

The tiny particles can also be used to map and measure the cosmos, but now they’re being used to weigh and study the least understood region of our planet.

Nov 9 2018, 3:27pm

Although some people argue that our oceans are the least-understood regions of our planet, there may be a better contender for that title: the core of the earth. But that may be about to change.

Scientists from the University of València in Spain have figured out to use neutrino particle data—the smallest, most abundant particle in the universe—from Antarctica’s “IceCube” observatory at the South Pole in to order to calculate the mass of the Earth, the mass of the earth’s core, prove that the core is denser than the mantle, and determine earth’s moment of inertia (oppositional force during rotation). They published their results in Nature this week.

Jordi Salvadó Serra, one of the lead researchers on the study, told Motherboard in an email that while using neutrino interactions is an unorthodox way to measure the earth, to say the least. The excitement in their research comes from its potential to unearth (pun intended) an unprecedented level of information about the core of our planet.

“From a more practical side the study of the core and inner core is interesting and may tell us something about the source of the Earth magnetic fields that can give a complementary information to the more classical geophysics approaches,” Salvadó Serra said.

All of the knowledge that we currently have about the core of the earth comes from analyzing the speed of seismic waves, since the speed of the waves varies depending on whether it’s going through, say, a liquid or a solid. But Salvadó Serra said that the method is so limited that we don’t truly understand the innermost regions of the earth.

“The main problem there is the study of the most inner parts of the planet, the core and the specially the inner core, seismic waves can not penetrate,” he said. “In the internal regions neutrinos may play and interesting complementary role.”

In other words, neutrinos could be used to get a granular understanding of the core of the earth, which helps drive distribution of earth’s gravity. Having this information could help us make more accurate weather forecasts and plan air and ship travel more safely. Sea surface activity and air resistance, which impact weather and transportation, can both be measured by understanding the distribution of gravity.

Image: Nature.

So, why haven’t we been measuring the earth like this for years? Mainly, it’s because Although neutrinos are incredibly abundant, they’re also incredibly difficult to detect: they’re just a fraction of the size of an electron, they have no electric charge, and they have a mass so infinitesimally small that physicists won the Nobel Prize in 2015 for proving they had any mass at all.

Neutrinos are so small and light that they very rarely interact with other objects, which is why they’re difficult to detect. But sometimes, rarely, the neutrinos interact with Antarctic ice, and this interaction emits a small amount of light. The IceCube observatory’s job is to detect these tiny rays of light happening beneath the ice. Salvadó Serra said that out of the handful of neutrino observatories in the world, the IceCube observatory undoubtedly had the most reliable data for their experiment.

“IceCube is the only [neutrino observatory] right now that has enough atmospheric neutrino (neutrinos produced from cosmic rays hitting the atoms in the atmosphere) events at high enough energies that get attenuated in the earth,” he said.

Image: NOAA, Wikimedia Commons.

However, there are limits to this novel approach. Salvadó Serra told Motherboard that without robust knowledge of neutrino flux—or why and how neutrino distribution varies—there’s a limit to how scientists can use neutrino data to make complex conclusions about the core of the earth.

“This of course can be improve using other data and improved theoretical computations,” Salvadó Serra said.

Since 2006, neutrinos detected at the IceCube observatory have been used to try and map, measure, and understand the cosmos. Although the core of the earth is less exotic than, say, outer space, using neutrinos to understand it could make real, tangible changes in the way people live and move through the world.