A recent discovery changes our understanding of helium, a gas considered inert, by revealing its ability to bond with iron under extreme pressures. This breakthrough opens new perspectives on the composition of Earth's core and its geological history.
Image: Argonne National Laboratory / Flickr / CC 2.0
Helium, known for its chemical inertness, has long been considered incapable of forming stable compounds. However, Japanese and Taiwanese researchers have demonstrated that it can integrate into the crystalline structure of iron under extreme conditions of pressure and temperature. This discovery, made using a laser-heated diamond anvil cell, challenges decades of scientific knowledge.
Helium and iron: an unexpected alliance
By subjecting iron and helium to pressures of up to 55 gigapascals and temperatures close to 3,000 kelvins, the researchers observed the formation of compounds designated FeHex. These compounds show a significant expansion of the crystalline structure of iron, indicating substantial retention of helium.
This reaction, although surprising, had been predicted by theoretical models. However, this is the first time it has been confirmed experimentally.
The measured helium concentrations reach 3.3%, which is 5,000 times more than in previous studies. This discovery suggests that Earth's core could harbor vast reserves of helium, particularly helium-3, a rare and primordial isotope.
A new perspective on Earth's formation
The presence of helium in Earth's core could rewrite the history of our planet's formation. It indicates that the young Earth may have captured gases from the solar nebula, a cloud of hydrogen and helium surrounding the nascent solar system.
This hypothesis contradicts traditional models, which assume that these gases were largely lost during the planet's formation. It also suggests that other volatile elements, such as hydrogen, could be stored similarly, offering a new explanation for the origin of Earth's water.
These results open up prospects for research in geology and materials science. They could also shed light on the composition of exoplanets and the formation of stellar systems.
To go further: What is helium-3?
Helium-3 is a rare isotope of helium, composed of two protons and a single neutron. Unlike helium-4, produced by radioactive decay, helium-3 is primordial, meaning it dates back to the formation of the solar system. Its presence in volcanic rocks, such as those in Hawaii, suggests that it originates from deep within the Earth.
This isotope is particularly valuable to scientists, as it provides clues about the conditions that prevailed during the formation of Earth and the solar system. It is often considered a "fingerprint" of the gases present in the solar nebula, the cloud of gas and dust that gave rise to our planetary system.
Helium-3 is also used in cutting-edge fields, such as nuclear fusion, where it is studied for its potential to produce energy without radioactive waste. On Earth, it is extremely rare, but significant quantities are found on the Moon, making it a potential resource for future space missions.
Finally, the recent discovery of its possible presence in Earth's core opens new perspectives. If helium-3 is indeed stored in large quantities in the core, it could explain the high ratios observed in volcanic eruptions and provide information on deep geochemical processes.
Article author: Cédric DEPOND