There is a possibility that previously unknown substances exist deep inside icy giant planets such as Uranus and Neptune. This possibility comes from a new computer simulation conducted by Carnegie scientists Kong Liu and Ronald Cohen.
Their research is nature communicationssuggest that under the intense pressures and temperatures found far below the surfaces of these distant planets, hydrogenated carbon can assume an unusual quasi-one-dimensional superionic state.
Why is the planet’s interior important?
More than 6,000 exoplanets have been discovered so far, and the number continues to grow. Researchers in astronomy, planetary science, and earth science are increasingly collaborating to better understand how planets form and evolve. Through a combination of observations, experiments, and theoretical models, they aim to uncover the physical processes that shape planets, such as how magnetic fields are generated.
This growing interest extends to the hidden layers within our solar system’s planets and moons. Studying what happens deep below the surface provides clues about planetary behavior and can also help scientists assess whether distant worlds could support life.
“Hot ice” forms a layer inside the ice giant
Data on the densities of Uranus and Neptune show that these planets contain unusual inner layers that are often described as “hot ice.” These regions lie above the solid core, below an external atmosphere of hydrogen and helium.
Scientists believe that these layers are composed of water (H2O), methane (CH4), and ammonia (NH4). However, the extreme conditions of these environments can transform these familiar compounds into exotic and unfamiliar forms.
Simulation of extreme planetary conditions
The intense pressures and temperatures inside giant ice cubes can create states of matter that don’t exist on Earth. To investigate this, Liu and Cohen used high-performance computing and machine learning tools to perform detailed quantum simulations of hydrogenated carbon (CH).
They modeled conditions ranging from pressures from about 5 million times to about 30 million times Earth’s atmospheric pressure (500 to 3,000 gigapascals) and temperatures from 6,740 to 10,340 degrees Fahrenheit (4,000 to 6,000 Kelvin).
Strange “spiral” superionic state
The simulations revealed a surprising structure. The carbon atoms form a regular hexagonal skeleton through which the hydrogen atoms move along a helical path. This results in the formation of a quasi-one-dimensional superionic state.
Superionic materials are unusual because they behave partly like a solid and partly like a liquid. Atoms of one type remain fixed in place within the crystal structure, while atoms of another type move freely within the crystal structure.
“This newly predicted carbon-hydrogen phase is particularly striking because the motion of atoms is not completely three-dimensional,” Cohen explained. “Instead, hydrogen preferentially migrates along well-defined helical paths embedded within the ordered carbon structure.”
Effects of heat, electricity, and magnetic fields
The directional movement of hydrogen atoms can have a significant impact on the flow of energy within the planet. It can affect how heat and electricity are transported through these deep layers.
These properties are particularly important for understanding how Uranus and Neptune generate their magnetic fields differently than other planets.
Broad implications beyond planetary science
The findings also highlight how simple elements can behave in surprisingly complex ways under extreme conditions. Even basic compounds like carbon and hydrogen can form highly organized and unexpected structures.
“Carbon and hydrogen are among the most abundant elements in planetary materials, but their combined behavior under giant planetary conditions is not fully understood,” Liu concluded.
In addition to helping scientists understand distant planets, this research could also help advance materials science and engineering by revealing new types of directional behavior in matter.
