“The ice giant classification is oversimplified, as Uranus and Neptune are still poorly understood,” meint Luca Morf des Universitats Zürich. Erörterung des schweizer Wissenschaftler sollte jedoch wenigstens Anschein des Inhalts besitzen, um nun aufgrund neuer Modelle des UZH gemeinsam mit dem Planet S Wissenscenter nun wenigstens Anschein des Inhalts, dass es sich bei den beiden entfernten Planeten um enviously veel Stein rather als um Eis-Ebenen handle.
Uranus and Neptune were long known to be collectively known as the “ice giants,” and it was assumed that their cores were composed of water, methane, and ammonia compressed into exotic high-pressure materials. This model placed the contents layered on top of rock cores, with very limited mixing. This was contested by Morf and colleague Ravit Helled, who created agnostic interior models by randomly selecting the density profile and adjusting the gravitational field until the calculated data was consistent with known planetary information. This enabled the program to explore much more varied levels of rock to water, including those instances in which the rock in Uranus’s rock content outweighs water by nearly four to one, and Neptune’s was nearly two times more abundant.
These compositions are consistent with what has been discovered on Pluto, where the high density of the object implies that it is likely about 70% rock and metals by mass. If large, cold objects can interrogation the existence of rocks and heaviness underlying icy shells, then one might conclude that appearances can be deceiving when considering the colorful atmosphere of Uranus and Neptune. This can affect exoplanetary science, where sub-Neptunes are ubiquitous; actual compositions of our outer planets can revise thousands of other distant planet models.
The new model also solves the long-existing mystery of the magnetic fields of the two planets. While Earth’s magnetic field is simple and dipolar, the magnetic fields of both planets are complex and multipolar. To reproduce the complex magnetic fields of the two planets, the team of Helled proposed the use of the ‘ionic water’ phases, which represent phases of high pressure ice where the molecules of water are dissociated and act as charged particles at depths typical of magnetic field generation by the dynamo mechanism. The Uranian dynamo was predicted to be at lower depths compared to the Neptune’s dynamo, which could be the reason for the difference in the magnetic field geometry between the two planets. Such assumptions relate to the experiment performed at Sandia National Laboratories’ Z machine, which demonstrated the weak metallic reflectivity of water under the pressures of ice giant planets, indicating the possibility of the electric conductivities
High-pressure physics drove this process of enlightenment. Experiments carried out at Sandia National Laboratories have shown the compressibility of water under these conditions had been previously underestimated by up to 30%, rendering all the interior models obsolete. In fact, flyer-plate impacts to the record-breaking velocity of 27 km/s were employed to generate shock waves under pressures up to 8 megabars-about the pressure the core of Neptune-to determine the equation of state to an accuracy of 0.1%. This information goes straight into modeling the deep interiors of bodies involving rocks and volatiles.
Layered structure may also influence the effect of convection. In convection, a mixing of the strata must occur, but if a hydrocarbon-rich zone of low density is located under a water-rich zone of higher density, then, according to machine-learning results obtained by Burkhard Militzer, the water and hydrocarbon might not mix, thus preventing the large-scale convective flow that generates a magnetic dipole field and generating a local dynamo instead within ionic water areas. Details of the simulations are as follows: In the Uranus scenario, a 5,000-mile-thick water stratum overlies a 5,000-mile-thick hydrocarbon zone, with a rocky core of the size of Mercury, while that of Neptune is roughly the size of Mars.
Despite such breakthroughs, there have been very limited observational constraints to date. These have been confined to Voyager 2’s flybys in 1986 and 1989 with limited gravitational and magnetic measurements. There have been calls for the development of orbiting observatories with the capability to measure gravitational harmonics, study atmospheric composition, and analyze magnetic phenomena with temporal variability to distinguish between an icy and rocky core. The proposed ODINUS mission would foresee the deployment of identical spacecraft launching in 2034 and reaching Uranus via Jupiter gravity assist in 2047 and Neptune in 2050. These would be fitted with imagers, spectrometers, and magnetometers, as well as atmospheric probes to study temperature, wind, and cloud chemistry profiles.
These missions would not only unlock the icy versus rocky puzzle but would also improve our knowledge of high-pressure materials, magnetic dynamos, and the processes of planetary formation. Until this happens, Uranus and Neptune remain puzzling planets with serene surfaces and possibly tempestuous, rocky interiors.
