Scientists Predict ‘Very Weird’ Helium Compounds Inside Gas Giants
"The role of such phenomena inside planets needs to be explored.”
Giant planets like Jupiter and Saturn are majestic to behold up close, as evidenced by the gorgeous imagery recently returned by NASA's Juno and Cassini orbiters, respectively. But while exterior snapshots of these worlds deliver valuable information and planetary eye candy, the chemical processes roiling beneath their surfaces remain a persistent puzzle for scientists.
Among the many outstanding mysteries of gas giants is the behavior of one of their main ingredients: Helium (He), the second-most plentiful element in the universe after hydrogen.
As a noble gas, helium is notoriously inert, meaning that it likes to hang out by itself rather than join forces with other elements to make chemical compounds. (Elements like carbon and silicone, by comparison, are team players open to forming all kind of bonds with other substances.)
But research published on Monday in Nature Chemistry suggests that the immense pressures inside gas giants and stars can convince helium to put its loner status aside and form stable bonds with sodium (Na) atoms. An international team of authors predicted two such new compounds, NaHe and NaHe O, with the help of the USPEX code, an algorithm designed to identify possible crystal structures. These compounds could only be produced at pressures 1.1 million times that of Earth's atmosphere, conditions that exist inside planets and stars.
"Our work shows that helium is not as inert as previously thought, and can form stable compounds under pressure," said study co-author Artem Oganov, head of the Computational Materials Discovery Laboratory at the Moscow Institute of Physics and Technology and a professor Stony Brook University in New York, in an email interview with Motherboard.
"If helium were completely inert, and formed no stable compounds, it would be completely removed from planetary interiors. Now, the case seems to be much more complicated."
"It shows." he said, "that very weird chemical phenomena and compounds can emerge at extreme conditions, and the role of such phenomena inside planets needs to be explored."
Perhaps Juno and Cassini will yield further insights into these reactions when the spacecraft fatally end their missions by diving into their host planets. (Cassini will self-immolate in Saturn in September of this year, while Juno is on track to throw itself into Jupiter in 2018.)
Until then, scientists will rely on computational tools like USPEX to model the interior of these worlds, and understand the chemical processes ongoing within them. "We have several [USPEX] works in progress related to Earth's core and to giant gas planets Uranus and Neptune," Oganov told me. "But these are still in progress."
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