Scientists have solved the mystery of the xenon gas 'missing' from the Earth's atmosphere and suggest that it is stuck in the planet's core.
Researchers found that the noble gas, which usually does not bond with other atoms, may chemically react with iron and nickel in Earth's core, where it is held.
Xenon is a noble gas, so, like other noble gases, such as helium and neon, it is mostly chemically inert. Scientists have long analysed xenon to study the evolution of Earth and its atmosphere, 'LiveScience' reported.
Strangely, atmospheric levels of xenon are more than 90 per cent less than scientists would have predicted based on levels of other noble gases such as argon and krypton.
"The missing xenon paradox is a long-standing question," said study author Yanming Ma, a computational physicist and chemist at Jilin University in Changchun, China.
Although some researchers have suggested that this "missing" xenon may have escaped from the atmosphere into space, the majority of scientists think it is hidden in the Earth's interior.
However, investigators have long failed to find a way in which Earth might incorporate this gas into chemically stable compounds.
In 1997, scientists reported experiments that suggested xenon would not react with iron.
"Through a careful analysis of their work, however, we found that the experiment was carried out only up to 150 gigapascals, a pressure far from the Earth's inner-core pressure of 360 gigapascals," Ma said.
This past research also theoretically extrapolated what might happen if xenon were trapped at the high pressures found in Earth's inner core, and concluded that xenon would not bond with iron.
However, those prior studies assumed xenon would form a so-called "hexagonal close-packed lattice" - essentially, a lattice of atoms resembling a solid whose bottom and top faces are hexagons and whose side faces are rectangles.
This assumption was made because iron atoms normally form this kind of structure with other iron atoms.
However, Ma and his colleagues reasoned that, if the structures of iron-xenon compounds are different, they could form a compound.
Their calculations now suggest that at the extreme temperatures and pressures found in Earth's core, xenon can bond with both iron and nickel.
The study is published in the journal Nature Chemistry.
