Scientists have proposed that Uranus and Neptune may harbor vast oceans of water beneath their atmospheres. Observations from NASA's Voyager 2 spacecraft in 1986 revealed that Uranus's magnetic field is significantly distorted, deviating from the planet's center.
Three years later, a similar anomaly was detected in Neptune's magnetic field. The magnetic field generated in Earth's outer core aligns nearly perfectly with its rotational axis, creating distinct poles.
Astronomer Heidi Hammel noted that it seems as if there is a giant bar magnet within the planets. This phenomenon is also observed in Earth, Saturn, Jupiter, and some of Jupiter's moons.
For years, researchers have sought to understand why the magnetic fields of Uranus and Neptune are tilted. A study published this month suggests that a solar storm occurred during Voyager 2's visit may have caused disruptions in Uranus's magnetic field, leading scientists to speculate about the existence of oceans on the planet.
On November 25, a new study in the journal PNAS argues that hypothetical oceans on both planets might contribute to the unusual characteristics of their magnetic fields. Dr. Burkhard Militzer, a planetary scientist from the University of California, Berkeley, created a computer model to investigate this anomaly.
The model indicates that there is a water mass approximately 8,000 kilometers thick beneath the planets' atmospheres, separated from their cores by a hydrocarbon-rich layer. Dr. Militzer believes that the extreme pressure—60,000 times that of Earth's surface—prevents mixing between these layers.
According to the research, Uranus possesses a core about the size of Mercury, while Neptune's core is slightly larger, comparable to Mars. The study posits that the hydrocarbon layer inhibits convection, leading to the magnetic field distortions observed.
Previously, scientists thought the two planets had more homogeneous structures. Dr. Militzer explains that normally, the water layer beneath a hydrogen envelope would disperse. However, the ice giants, being farther from the Sun, may have formed with less hydrogen, which could clarify the differences between the two ice giants and Jupiter and Saturn.
Dr. Militzer concluded that they now have a strong theory explaining why Uranus and Neptune have distinct magnetic fields that are very different from those of Earth, Jupiter, and Saturn. He remarked, 'We did not know this before. It resembles oil and water; the only difference is that the oil sinks because hydrogen is lost.'