Physicists named the main source of underground heat

Physicists named the main source of underground heat
Physicists named the main source of underground heat

The bowels of our planet emit 47 terawatts of heat. Judging by the content of radioactive elements in the earth's crust, their decay provides from 7 to 10 terawatts. Where does the rest come from?

The controversy about this does not subside. Some experts say that our Earth was born hot, and at least half of the current heat flow from its depths is the energy stored at the time of formation. Others believe that the planet was formed as cold, and it is heated mainly by friction from immersion to the center of the Earth of heavy rocks and floating to the surface of the lungs.

Do not forget that radioactive substances are probably found not only in the crust, but also in the mantle (in the core of the planet, according to geophysicists, they are negligible). But how many are there? The mantle, unlike the crust, cannot be reached with a drill. Therefore, it remains unclear how much of the underground heat is generated by radioactive decay. Estimates vary from 15% to 50%.

The answer to this burning question is given by a scientific article published in the journal Physical Review D by an international group, which also includes Russian scientists.

Physicists have measured the flux of neutrinos emanating from the interior of the earth. Neutrinos are very light particles that are formed, among other things, during the radioactive decay of uranium-238 and thorium-232. Knowing the intensity of the neutrino flux, it is possible to determine how many of these elements decay every second in the depths of the Earth.

The researchers worked with the Borexino detector launched in 2007. They processed the data accumulated from December 2007 to April 2019. It should be noted that scientists from the Research Institute of Nuclear Physics of Moscow State University, the National Research Center "Kurchatov Institute" and the Joint Institute for Nuclear Research have made a great contribution to the creation of this tool and obtaining these data.

During this time, the detector recorded 53 particles. Do not be fooled: every second every square centimeter of the earth's surface is penetrated by millions of neutrinos born in the bowels of the planet. But this capricious particle almost never interacts with matter, including the substance of the detector.

By the number of detected neutrinos, the authors calculated their total flux and recalculated it in the number of uranium and thorium nuclei decaying in the depths of the Earth.

Based on the known radioactivity of the earth's crust, physicists calculated the contribution of the mantle. In doing so, they took into account that 18% of the radiogenic heat comes from the decay of potassium-40, while uranium and thorium provide the remaining 82%.

According to the calculations of the researchers, the radioactive substances of the mantle provide from 14 to 36 terawatts of underground heat. The most likely value is 25 terawatts. That is, in total, the radioactive substances of the crust and mantle give about 70% of all underground heat.

More definite numbers can be named when the neutrino flux from the mantle will be measured more accurately.

"A serious challenge for physicists today remains a more accurate measurement of the flow of geoneutrinos from the mantle. For this, it is likely that several detectors located in different parts of the Earth will be used. There is a project to create a geoneutrino detector in Russia, at the Baksan Neutrino Observatory. Another project is the JUNO detector., currently under construction in China, which will be 70 times larger than Borexino in mass, which will allow achieving greater measurement accuracy in a shorter time frame, "summarizes Alexander Chepurnov, senior researcher at the Research Institute of Nuclear Physics at Moscow State University.

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