Uranus and Neptune, the two icy giants of the solar system, have long fascinated scientists because of their unique characteristics, including their strange magnetic fields. Researchers have recently proposed a new theory that could explain these peculiarities: immense oceans of water, located at unknown depths, would be responsible for certain unusual behaviors observed in the magnetic fields of these distant worlds.
Oceans under pressure
THE magnetic fields Uranus and Neptune have always raised many questions. Nearly forty years ago, during their exploration by the Voyager 2 probe, surprising data was collected, revealing magnetic fields chaotic and deviated far removed from the clear and orderly configuration observed on planets like Earth or Jupiter. Indeed, while the magnetic fields of the latter are centered around the north and south poles, those of Uranus and Neptune are much more disorganized, with orientations that seem random. Why do these two planets have such an anomaly?
To answer this question, a group of researchers led by Burkhard Militzer of the University of California, Berkeley, proposed a computer model simulating the internal structure of Uranus and Neptune. According to this new approach, the cause of atypical magnetic fields could lie in the oceans of water which hide under the atmosphere of these planets in conditions of extreme pressure and temperature.
These oceans would not be composed of liquid water like on Earth, but “superionic” watera form of water where molecules break down under pressure to form a hybrid state halfway between solid and liquid. This “water” would also be mixed with substances like methane and ammoniacreating a unique dynamic and potentially responsible for the disorganized orientation of magnetic fields.
No convection
In detail, Uranus and Neptune, although similar in size, would however present notable differences which probably influence their magnetic field. According to Militzer's model, Uranus would have a dense atmosphere with a rocky core the size of Mercury which would be surrounded by a thick layer of hydrocarbons, itself covered with water. In contrast, Neptune, which is slightly more massive, would have a larger core, the size of Mars, and a thinner atmosphere. These differences in their internal structure could explain why their magnetic fields are distinct, although the two planets are comparable in size.
Regarding the disorganization of these magnetic fields, the model suggests that due to the extreme pressures present at these depths, two layers form: a layer of hydrocarbons and ammonia, located beneath the water, and a layer of colder, denser water above. These layers would create a stable lamination, almost like a plastic polymer, which prevents convectionthe process by which heat circulates materials at depth, such as on Earth or Jupiter. The absence of convection could therefore be the key to the disruption of the magnetic fields of Uranus and Neptune.
This new theory could have important consequences for the future exploration of these two planets. If pressurized oceans play a crucial role in shaping magnetic fields, this could offer new insights into how these planets evolve and the internal processes that govern them. Future space missions, such as the Uranus Orbiter mission proposed by NASA, could validate or refine this theory and better understand these fascinating and mysterious worlds.
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