Gigantic helium deposits may be hidden inside of the Earth’s core

For decades, noble gases like helium have been considered chemically inert, refusing to form stable bonds under normal conditions. But new research challenges this assumption, revealing that helium can bond with iron when subjected to extreme pressures and temperatures.

This surprising discovery has profound implications for understanding Earth's deep interior and its formation history.

Scientists from Japan and Taiwan recently demonstrated that helium, the second-lightest element, can integrate into iron's crystal structure under intense conditions.

Using a laser-heated diamond anvil cell, they exposed iron and helium to pressures between 5 and 55 gigapascals—50,000 to 550,000 times atmospheric pressure—and temperatures ranging from 1,000 to nearly 3,000 kelvins.

The results were striking. Instead of helium remaining separate, as expected, it became incorporated into iron’s atomic lattice, forming compounds designated as FeHex (where x represents the helium content). The presence of helium expanded the iron’s crystal structure, suggesting significant helium retention.

These findings align with theoretical predictions that hinted at possible helium insertion into metals at extreme pressures, but experimental confirmation had remained elusive—until now.

Professor Kei Hirose, a researcher at the University of Tokyo’s Department of Earth and Planetary Science, described the discovery, “I have spent many years studying geological and chemical processes inside Earth. Given the intense temperatures and pressures, we must replicate these conditions to understand them. So, we often turn to a laser-heated diamond anvil cell to apply extreme pressures to samples and see the result. In this case, we crushed iron and helium together, revealing an entirely new behavior.”

The discovery of helium bonding with iron provides new insights into Earth’s deep interior. Scientists have long theorized that primordial helium—helium-3, an isotope formed before Earth’s creation—exists in the planet’s core.

Evidence for this comes from volcanic eruptions, particularly in places like Hawaii, where unusually high helium-3 to helium-4 ratios have been found in lava.

Until now, researchers believed that helium was stored in the mantle, trapped in ancient rock formations. But the new findings suggest a different possibility: helium could be locked away within the iron core itself. If helium is present at these depths, it could serve as a major reservoir of primordial gas, altering our understanding of Earth's internal composition and the mechanisms driving volcanic activity.

Previous studies detected only minuscule traces of helium in iron, around seven parts per million. However, the new experiment revealed helium concentrations as high as 3.3%—about 5,000 times higher than previously observed.

The key to this breakthrough was the experimental approach: while the materials were synthesized at high temperatures, chemical analyses were performed at cryogenic temperatures to prevent helium from escaping.

“Helium tends to escape at ambient conditions very easily; everyone has seen an inflatable balloon wither and sink,” Hirose explained. “So, we needed a way to avoid this when taking our measurements. By keeping samples at extremely cold temperatures during analysis, we could detect helium in iron without losing it.”

Beyond reshaping ideas about the core, this research also provides new clues about Earth's early development. If helium is present in the core, it suggests that young Earth captured significant amounts of gas from the solar nebula—a cloud of hydrogen and helium that surrounded the early solar system. This challenges conventional models, which assume that most of this primordial gas was lost as Earth formed.

Helium’s presence in the core could also mean that other volatile elements, such as hydrogen, were captured in the same way. If so, some of Earth’s water may have originated from these early gas interactions rather than from asteroid impacts, as traditionally believed. This could provide a missing link in explaining how the planet accumulated and retained its atmosphere and oceans over billions of years.

The discovery of FeHex compounds opens up new avenues for research. Scientists now aim to explore whether similar bonding occurs with other noble gases and whether helium remains stable within iron over geologic time.

Future experiments will push pressures even higher to determine if helium-iron compounds exist deeper in planetary interiors or in the extreme environments of exoplanets.

Additionally, this research could impact fields beyond geology. Understanding how helium interacts with metals at extreme conditions could inform the development of new materials with unique properties, such as improved superconductors or radiation-resistant alloys.

By challenging long-standing assumptions about helium’s reactivity, this study reshapes the way scientists view both the deep Earth and the broader universe. It turns out, even the most inert elements can behave unexpectedly under the right conditions.

The research findings were published in the journal Physical Review Letters.

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