Here's How Much the Earth Weighs in 'Ghostly' Neutrinos

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Despite being stuck on this rock tumbling through space all the time, we don't really know exactly how heavy that rock is, or how its mass is distributed.

Of course, researchers have some pretty good estimates. Our planet weighs about 13.17 septillion (or 13.17 with 24 zeroes after it) lbs. (5.974 septillion kilograms) in an Earth-like gravity field, according to Caltech. But that number comes from an indirect calculation based on Earth's gravity. Similarly, scientists have tried to measure how Earth's mass is distributed based on how seismic waves move through it, but those results aren't very precise. [The Large Numbers That Define the Universe]

So a team of researchers at the Instituto de Física Corpuscular (IFIC) in Spain came up with an alternative method for studying the heavy stuff inside the planet, using a detector designed to hunt ultralight particles from outer space known as neutrinos.

In a paper published Monday (Nov. 5) in the journal Nature Physics, the researchers used data from Antarctica's massive IceCube Neutrino Observatory to estimate the mass and density distribution of the Earth. IceCube can sense these ghostly neutrinos arriving from all directions, including from inside Earth.

Neutrinos are extremely weakly interacting particles, so they pass through most matter without being detected. But when passing through a massive, dense object like Earth, some of them will eventually collide with other matter and disappear. In particular, high-energy neutrinos, which more often collide with other objects, rarely make it through Earth.

Using data from IceCube on neutrinos that pass through Earth, the researchers were able to work backward to figure out how many neutrinos never made it out of Earth to hit IceCube. From there, they arrived at a pretty good estimate of how much mass was blocking those neutrinos and where it was. In effect, they figured out Earth's mass by studying its neutrino shadow.

And the method worked reasonably well. The scientists came to a similar estimate of Earth's mass: about 13 septillion lbs. (6 septillion kg). They also measured Earth's core mass at 6 septillion lbs. (2.72 septillion kg). That's 45 percent of the planet's total mass, and significantly higher than the results from seismic measurements, which estimate the core makes up 33 percent of Earth's total mass.

In an accompanying News & Views article in Nature Physics, Véronique Van Elewyck, an astrophysicist at the Laboratoire Astroparticule et Cosmologie at Paris Diderot University in France, called the paper are good "proof of concept." Van Elewyck, who was not involved in the research, suggested that in another 10 to 15 years, researchers would likely use this kind of calculation to probe the interior of the Earth. However, this paper tells scientists more about whether this method can work than anything specific about the inside of Earth, she wrote.

To get to the point of useful calculations, she wrote, scientists need a lot more data from IceCube and other detectors still under construction.

Originally published on Live Science.

Rafi Letzter
Staff Writer
Rafi joined Live Science in 2017. He has a bachelor's degree in journalism from Northwestern University’s Medill School of journalism. You can find his past science reporting at Inverse, Business Insider and Popular Science, and his past photojournalism on the Flash90 wire service and in the pages of The Courier Post of southern New Jersey.