Earth is too big to fit into an X-ray or MRI scanner, so a group of physicists in Spain found a fascinating new way to peer inside – they used the subatomic particles that are constantly flowing through the planet.
The team scanned inside the ground using neutrinos – and even used them to make a whole new measurement of our planet's mass.
Neutrinos are odd little things. They are among the most abundant particles in the universe, yet it is difficult to detect. They resemble electrons, but they have no electrical charge and their mass is almost zero, so they interact very little with normal matter as they flow through the universe at close lightning speed.
Millions of neutrinor are sipping through your body right now. You can see why they are called "ghost particles".
While historically, our discovery effort has been poor, the IceCube neutrino detector all the way down in Antarctica has opened a brave new world of neutrino science.
With the help of a year's value of IceCube data, physicists at the Institute for Corpus Physics (IFIC) in Valencia, Spain, could also study the intestines of the earth.
It worked almost exactly like an X-ray. When you radiate, rays are sent through your body. They pass most through soft tissues like muscles and organs. Tighter material, like bone, absorbs the rays to a greater extent, but fewer x-rays turn the detector on the other side, giving a picture of your skeleton.
Instead of X-rays, however, the team used atmospheric neutrins, where showers are created when energetic particles from space collide with the Earth's atmosphere. These then zoom through the ground – but can be absorbed by the nuclei of the material they pass through.
The denser the material, the higher the absorption rate; which in turn allowed the research group to compile a study of the density of the planet.
"The use of atmospheric neutrins allows us to get neutrins from all directions, with a wide range of energy and a known flow with sufficient precision," explains IFIC physicist Sergio Palomares-Ruiz.
"The amount of absorption of atmospheric neutrin flow depends on how much material passes as well as the neutrin energy, so by studying the variation in the amount of absorption in different directions of neutrinos of different energy, we can determine the distribution of the density of the earth."
The different angles are a big factor here. Some neutrinos traveled all the way through the core of the earth, while others traveled at an oblique angle that completely crossed the nucleus.
Analyzing both the concentration and the angle gave the team the tools to calculate the density of the planet at different depths.
Traditionally, the density of the Earth is extrapolated from the way seismic waves produced by earthquakes spread. Seismic waves, however, can not penetrate the inner core.
"Neutrines on the other hand go through everything and offer valuable information about the unknown nucleus of the earth, where the planet's magnetism is generated," says IFIC physicist Andrea Donini.
The team did not learn anything new about our planet. The density map of the Earth's interior, the planet's mass and the moment of inertia were all calculated using neutrino data – and they were consistent with previous measurements in a different way and less detailed.
But the research was not learning anything new about the earth – it was learning something new about what we can learn from neutrinos. And at that point, the results are truly amazing.
"Our results show whether this approach is to study the earth's internal structure, which complements traditional geophysical methods," wrote the researchers in his newspaper.
However, at the moment, neutrino data is still relatively limited; The researchers hope their research will encourage the release of newer IceCube data, as well as more neutrino science in the coming years.
The paper has been published in nature Physics.