Posted on behalf of Chloe McIvor

Radioactive decay is responsible for about half of the heat coming from the bowels of the Earth, suggesting that the remaining 50% is the primordial heat left over from when the Earth first formed.

Most of the heat given off by our planet – estimated to be about 174 petawatts (10^15 W) – first came from the Sun. But about 44 terawatts (10^12 W) of that is geothermal energy (pdf).

Researchers at the KamLAND collaboration have now tracked the antineutrino particles released during radioactive decay to pin down how much it contributes to the Earth’s geothermal energy.

KamLAND is better known as the Kamioka Liquid-Scintillator Antineutrino Detector, based on the island of Honshu in Japan. It was designed to measure antineutrinos generated in nuclear reactors, in order to study neutrino oscillations – a change in their character that can help researchers work out how much mass these elusive particles have.

But KamLAND also has a nice sideline in detecting geoneutrinos produced by the decay of radioactive uranium-238 and thorium-232, which ultimately leads to the estimate of how much heat this radioactive decay generates, published today in Nature Geoscience.

Tracking geoneutrinos could also help to probe the Earth’s composition. “The physical properties of the Earth are well established by seismic wave analyses, but the chemical properties are rather uncertain because of the lack of knowledge of the rock composition in the deep mantle,” explains Itaru Shimzu, a key player in the KamLAND collaboration

Shimzu says that further measurements of geoneutrinos with detectors at other locations will help constrain the model of mantle convection, the process that drives plate tectonics. “If data from multisite measurements becomes available, the crustal contribution can be evaluated because geoneutrino flux strongly depends on the distance from thick continental crusts,” says Shimzu.