Running large-scale computer simulations of conditions of the thick layer between the Neptune's atmosphere and core, known as the mantle, researchers have helped solve the mystery of what lies beneath the most distant planet in our solar system.
Frozen mixtures of water, ammonia and methane make up the planet's mantle, but the form in which these chemicals are stored is poorly understood.
The study, published in the journal Proceedings of the National Academy of Sciences, showed that frozen mixtures of water and ammonia inside Neptune - and other ice giants, including Uranus - are likely to form a little-studied compound called ammonia hemihydrate.
"This study helps us better predict what is inside icy planets like Neptune. Our findings suggest that ammonia hemihydrate could be an important component of the mantle in ice giants, and will help improve our understanding of these frozen worlds," said Andreas Hermann from University of Edinburgh in Britain.
Extremely low temperatures on planets like Neptune - called ice giants - mean that chemicals on these distant worlds exist in a frozen state, the researchers said.
Using laboratory experiments to study these conditions is difficult, as it is very hard to recreate the extreme pressures and temperatures found on ice giants.
So the scientists ran large-scale computer simulations of conditions in the mantle and by looking at how the chemicals there react with each other at very high pressures and low temperatures, they were able to predict which compounds are formed in the mantle.
The work was carried out in collaboration with scientists at Jilin University, China.
"Computer models are a great tool to study these extreme places, and we are now building on this study to get an even more complete picture of what goes on there," Hermann said.