Contrary to long-held theories of diamond rain or super-ionic water beneath the blue hydrogen-and-helium atmospheres of Uranus and Neptune, a new proposition by a planetary scientist suggests that these planets may possess a layered interior. This revelation could provide explanations for the unusual magnetic fields of these seemingly ordinary ice giants of our solar system.
Burkhard Militzer, a planetary scientist at the University of California, Berkeley, suggests that underneath the clouds of these planets lies a deep ocean of water, beneath which is a highly compressed fluid of carbon, nitrogen, and hydrogen. His research, published in the journal Proceedings of the National Academy of Sciences, indicates that the combination of water, methane, and ammonia under the extreme conditions of these planets’ interiors would naturally separate into two distinct layers.
This separation, Militzer argues, could account for the distinctive magnetic fields of Uranus and Neptune— a discovery made by the Voyager 2 mission in the late 1980s that defied previous understanding. He likens the separation to oil and water, with the denser layer sinking towards the core due to the expulsion of hydrogen.
Militzer’s theory also holds implications for exoplanets in other star systems. If other systems share similar compositions to ours, it is possible that ice giant planets around those stars would have comparable internal structures.
On Earth, our magnetic field is generated by convective movement of material in our planet’s outer liquid iron core. However, Voyager 2 found that neither Uranus nor Neptune possesses a similar dipole field, implying the absence of large-scale convection in their interiors.
Militzer’s computer simulations, enhanced by machine learning, finally solved this conundrum. He discovered that under extreme heat and pressure, atoms in the planets’ interiors naturally separate into water-rich and carbon-rich layers. The heavier carbon layer sinks, preventing convection, while the lighter water layer above it could be responsible for the disorganized magnetic fields of Uranus and Neptune.
According to Militzer, beneath Uranus’ thick atmosphere, there’s a water-rich layer approximately 5,000 miles thick and a similarly thick hydrocarbon-rich layer underneath. Neptune, although more massive than Uranus, follows a similar pattern.
The scientist hopes for further testing and research, including potential NASA missions, to confirm this groundbreaking theory. His next project will involve studying how these layered structures might affect planetary vibrations.
This research received support from the National Science Foundation as part of the Center for Matter at Atomic Pressures.
