Above: The chemistry of the elements of life, carbon, hydrogen, nitrogen and oxygen, is largely unexplored at the densities found inside large planets. First principles, quantum mechanical, searches have revealed many novel compounds. (Image credit: Lewis Conway)
The outer planets in our solar system, and likely many of the exoplanets beyond it, are largely made up of the lighter elements – hydrogen, carbon, nitrogen and oxygen. How they react with each other, deep within the planets, is a mystery. Using first-principles structure searching methods, based on quantum mechanics, Chris Pickard, with colleagues Andreas Hermann, and Lewis Conway at the University of Edinburgh, have computationally searched through the possible compounds.
At lower pressures, the elements (which are the basis for life on Earth) form a variety of complex ices, including water, ammonia and methane. At much higher pressures, such as those found deep within Uranus, it is discovered that they combine to form a true quaternary compound, which is isoelectronic with diamond, and has the simple chemical formula HCNO. This study paves the way for the computational investigation of complex mineralogy in these hidden, compressed, places.
The research has been published in the Proceedings of the National Academy of Sciences, and also features as a Paper of the Month in the Department of Materials Science and Metallurgy, University of Cambridge.
Rules of formation of H-C-N-O compounds at high pressure and the fates of planetary ices
Lewis J. Conway, Chris J. Pickard, and Andreas Hermann
Proceedings of the National Academy of Sciences118 (19), e2026360118 (2021)