An international team of planetary researchers from the University of Edinburgh, UK, and Jilin University, China, has used computer simulations to attempt to solve the mystery of what lies beneath the surfaces of Uranus, Neptune, and extrasolar ‘ice giants.’
Artist’s impression of an extrasolar ‘ice giant.’
Inside our Solar System, we have two ice giants: Uranus and Neptune.
Extremely low temperatures on these planets mean that chemicals exist there in a frozen state.
Frozen mixtures of water, ammonia and methane make up a thick layer between the planets’ atmosphere and core — known as the mantle. However, the form in which these chemicals are stored is poorly understood.
Using lab experiments to study these conditions is difficult, as it is very hard to recreate the extreme pressures and temperatures found on ice giants.
Instead, Dr. Andreas Hermann, a reader in the School of Physics and Astronomy at the University of Edinburgh and a member of the University’s Centre for Science at Extreme Conditions, and his colleagues ran large-scale computer simulations of conditions in the mantle.
By looking at how the chemicals there react with each other at very high pressures and low temperatures, the team was able to predict which compounds are formed in the mantle.
“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,” Dr. Hermann said.
The researchers found that frozen mixtures of water and ammonia inside an ice giant likely form a compound called ammonia hemihydrate.
“This compound is stable in a sequence of ionic phases up to 500 GPa, pressures found deep within ice giants,” the researchers said.
The findings will influence how ice giants are studied in future and could help astronomers classify newly discovered exoplanets as they look deeper into space.
“This study helps us better predict what is inside icy planets like Neptune,” Dr. Hermann said.
“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.”
The study is published in the Proceedings of the National Academy of Sciences.
_____
Victor Naden Robinson et al. Stabilization of ammonia-rich hydrate inside icy planets. PNAS, published online August 7, 2017; doi: 10.1073/pnas.1706244114
