What's Inside Uranus and Neptune? A New Way to Find Out
Artist exploded view of an ice giant planet similar to Uranus and Neptune. Credit: @iammoteh/Quanta magazine
In our search for exoplanets, we’ve found that many of them fall into certain types or categories, such as Hot Jupiters, Super-Earths, and Ice Giants. While we don’t have any examples of the first two in our solar system, we do have two Ice Giants: Uranus and Neptune. They are mid-size gas planets formed in the cold outer regions of the solar system. Because of this, they are rich in water and other volatile compounds, and they are very different from large gas giants such as Jupiter. We still have a great deal to learn about these worlds, but what we’ve discovered so far has been surprising, such as the nature of their magnetic fields.
The Mystery of their Magnetic Fields
When the Voyager 2 spacecraft flew past Uranus and Neptune in the 1980s, it found that neither world had a strong dipolar magnetic field like Earth’s. Instead, each had a weaker and more chaotic magnetic field, similar to that of Mars. This was surprising given what we understand about planet formation.
Models for the interior structures of the ice-giant planets Uranus and Neptune. Credit: Burkhard Militzer, UC Berkeley
Several theories have emerged to explain this phenomenon, but the details remain unknown. We can’t create the tremendously high-density, high-pressure conditions of a gas giant’s core in the lab, which limits our ability to test various models. Compounding the problem is the lack of recent observational data from either planet, as we haven’t sent another probe since Voyager 2.
Research Developments: Computer Simulations
To tackle the mysteries surrounding Uranus and Neptune, researchers have turned to sophisticated computer simulations. A recent study has simulated the bulk properties of over 500 molecules, which is enough to calculate how an ice giant’s layers form and interact.
The simulations indicate that water, methane, and ammonia in the middle region of Uranus and Neptune separate into two unmixable layers. This primarily occurs because hydrogen is squeezed out of the deep interior, limiting the amount of mixing. Without a convection zone in these layers, the planets cannot form a strong dipolar magnetic field. Notably, it is speculated that Uranus contains a rocky core about the size of Mercury, while Neptune likely has a rocky core around the size of Mars.
Future Directions: Laboratory Experiments and Missions
Future laboratory experiments could further confirm the identified bulk properties of these ice giants and refine our understanding of their interior structure. Additionally, there are proposals for new missions to Uranus and Neptune, which could provide fresh data to validate or challenge the current models.
Conclusion: Expanding Our Knowledge of Ice Giants
Our understanding of Uranus and Neptune continues to evolve, shedding light on the unique characteristics that differentiate them from gas giants like Jupiter and Saturn. By utilizing advanced simulation techniques and advocating for renewed exploratory missions, scientists hope to unravel the complex mysteries of these elusive worlds.
Reference: Militzer, Burkhard. “Phase separation of planetary ices explains nondipolar magnetic fields of Uranus and Neptune.” Proceedings of the National Academy of Sciences 121.49 (2024): e2403981121.
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CategoriesPlanetary FormationTagsNeptune, Uranus
