Scientists have made a groundbreaking discovery in the field of chemistry, coaxing one of the universe’s most elusive elements into a new compound. The formation of this iron-helium compound under high pressure and temperature suggests that helium from the early solar system could be stored in the iron that makes up Earth’s core.
Scientists have made a groundbreaking discovery in the field of chemistry, coaxing one of the universe’s most elusive elements into a new compound. The formation of this iron–helium compound under high pressure and temperature suggests that helium from the early solar system could be stored in the iron that makes up Earth’s core.
Helium is a noble gas that is the second most abundant element in the universe by mass.
It has an atomic number of 2 and an atomic mass of 4.0026 u.
Helium is a colorless, odorless, tasteless, non-toxic, and inert gas.
At room temperature, helium is a liquid with a boiling point of -268.93°C and a melting point of -271.36°C.
It has a high specific heat capacity, making it useful for cooling superconducting materials.
The Elusive Nature of Helium
“One of the least reactive elements on the periodic table, making it challenging to form chemical compounds.”
However, under extremely high pressures, “helium can interact with a few other elements, including nitrogen and sodium – and now iron, research shows.” This rare occurrence has significant implications for our understanding of Earth’s composition.
Creating the New Compound
Physicist Kei Hirose and his team used a diamond anvil cell to subject iron and “helium to pressures greater than 50,000 Earth atmospheres and temperatures above 1,000 degrees Celsius.” This compression formed crystals containing both iron and helium. The resulting compound exhibits unique properties, with the volume of the crystal being larger than that of pure iron at the same pressure.
Understanding the Interplay between Helium and Iron
The researchers found that “helium ions packed into interstitial sites between iron atoms in the crystal, but they don’t bond directly to iron due to its unreactive nature.” This behavior is characteristic of “chemistry without chemical bonds,” allowing helium to participate in ordered, crystalline compounds.
Implications for Earth’s Core and Mantle
The new compound could help explain observations of “helium in Earth’s interior. Most of Earth’s helium atoms have two neutrons and form from the radioactive decay of elements like uranium.” However, some ocean volcanic eruptions release helium atoms with just one neutron, which are thought to be “primordial” – formed shortly after the Big Bang.
The discovery suggests that Earth’s iron-rich core could hold a reservoir of primordial helium. Additional experiments will be necessary to determine whether helium is more likely to reside in the core or higher in its mantle. If helium is more stable in iron than in silicates found in the mantle, it would suggest that the helium is more likely to reside in the core.
The Earth's core is composed of two layers: a solid inner core and a liquid outer core.
The inner core is made up of iron and nickel, with an estimated temperature of around 5,000 to 6,000 degrees Celsius (9,000 to 11,000 degrees Fahrenheit).
The outer core surrounds the inner core and is composed mostly of molten iron and nickel, with some other elements present.
A New Frontier for Noble Gas Chemistry
The findings not only expand our understanding of noble gas chemistry but also raise questions about the possibility of forming other “helium metal compounds with different transition metals.” This could lead to new areas of research and potentially uncover “chemistry that we never thought of.
- sciencenews.org | A new iron compound hints ‘primordial’ helium hides in Earth’s core
