A simulation study published in Natural Communication showed that the old, boring elements like hydrogen and carbon must form unusual, helical structures under the intense pressures and temperatures of giant ice centers like Neptune and Uranus.
Besides showing a brand new structure of matter that is only found under extreme conditions, the simulations also found that these structures should behave in unusual ways—so unusual, in fact, that they could help explain some of the most mysterious aspects of planetary science.
It’s been more than 40 years since Voyager made a successful flyby of Uranus, producing the first detailed readings of that planet’s magnetic field. Its findings formed a theory about the inner structure of the planet that would last for decades.
In this figure, carbon is highlighted in yellow, and hydrogen is in blue.
Credit: Cong Liu
Now, however, a new study is muddying the field by directly calling into question some of the undisputed facts about ice giants that have filled the astronomy literature for generations.
The core of the ice giant can have pressures reaching thousands of gigapascals and, “ice” aside, temperatures reaching thousands of degrees. This study posits that these conditions must force simple objects into new forms.
In particular, they predict a duo of intertwined helices, one of hydrogen atoms and the other of carbon atoms. It’s not as neat as the double helix of DNA, but it’s close.
They call it a quasi-1D superionic state. The quasi-1D component means that these structures behave well probably as a 1D material in the graphene phase, but not quite. The superionic component means that while one element (carbon, in this case) is confined in the solid state, the other in the mixture (hydrogen) can still flow as a liquid.
When combined, these two factors seem to lead to unusual behavior. In particular, this structure must form different types of lattices under different temperatures and pressures, each with different compositional properties. The most interesting of these is “anisotropic” energy conduction, where electrons flow more efficiently in one direction than the other.
Illustration of Uranus’ magnetic field.
Credit: NASA
Flows within the planet’s core are one of the causes of the magnetic field; usually, that is the physical movement of molten material, but it can also refer to the flow of energy within stationary materials, such as high-energy materials. This can refer to electrons, or self-heating.
If this study’s hypothesis is correct, such natural directionality in the flow of energy within the planet could help explain the strange forces observed in the magnetic fields of giant ice sheets. This causes the spectacular aurora seen around Uranus, among other things.
These are only simulations, however, based on machine learning and quantum simulations of atomic interactions. It will have to be confirmed by direct observation, and given NASA’s current priorities, it may be a long time before we send another probe to orbit any planet other than Earth or Mars.
