Primordial Helium-3 May Be Locked in Earth’s Core, Study Finds

Helium-3, a rare isotope formed during the early solar system, may be locked within Earth’s solid core, as indicated by recent research. This discovery could provide insights into how quickly the planet was formed. Unlike helium-4, which is commonly produced through radioactive decay, helium-3 originates from the primordial gas cloud that shaped the solar system. While traces of this isotope have been detected in volcanic hotspots and mid-ocean ridges, the mechanism behind its retention for billions of years remains uncertain. Given helium’s volatile nature, most of it was expected to escape Earth’s mantle due to tectonic activity or the giant impact that led to the formation of the Moon.

Helium and Iron Interaction at Core Conditions

According to the study published in Physical Review Letters, researchers at the University of Tokyo led by Kei Hirose examined whether helium could mix with iron under conditions mimicking Earth’s core. Using a diamond-tipped anvil, the team subjected iron and helium to extreme pressures ranging from 50,000 to 550,000 times the atmospheric pressure at Earth’s surface. As per reports, the samples were heated to temperatures between 727 and 2,727 degrees Celsius before being depressurised and analysed at cryogenic temperatures to prevent helium escape. Findings indicated that solid iron could incorporate up to 3.3 percent helium, suggesting the isotope may remain trapped in the core over long periods.

Potential Impact on Earth’s Formation Timeline

Peter Olson, a geophysicist at the University of New Mexico, told that these results confirm helium’s compatibility with Earth’s solid core. However, he noted that only 4 percent of the core is solid, with the majority existing in a liquid state. Further research is needed to determine whether helium-3 could be similarly retained in the liquid portion. Olson also highlighted the significance of this discovery in dating Earth’s formation. If helium-3 was incorporated into the core, it suggests the planet formed rapidly within a few million years. A slower formation process spanning 100 million years would likely have resulted in minimal helium retention.