Scientists may finally unravel a major mystery behind the thick atmospheres of the Solar System’s icy giants, Uranus and Neptune. A new study suggests that giant water oceans lurk inside these planets, which explains their unusual magnetic fields.
“Previously, we knew little about the internal structure of these planets,” notes Adam Masters of Imperial College London. A new theory proposed by Burkhard Militzer of the University of California, Berkeley, changes that. His study, published in the journal Proceedings of the National Academy of Sciences, suggests the existence of a water layer about 8,000 kilometers thick beneath the atmospheres of Uranus and Neptune.
Unusual magnetic fields
On Earth, the magnetic field is generated in the core, creating a dipole with well-defined north and south poles. This structure is characteristic of Jupiter, Saturn and some moons. But data obtained by the Voyager 2 spacecraft showed that the magnetic fields of Uranus and Neptune are significantly tilted and offset from the planets’ centers.
At first, it was thought that the deviation could have been caused by a giant impact that tipped Uranus on its side. However, similar properties of Neptune’s magnetic field hint at a very different explanation.
Deepest oceans
According to Dr. Militzer’s modeling, water on these planets exists in a supercritical state – a mixture of liquid and gas – because of the high pressure, which is 60,000 times greater than on the surface of Earth. This water does not mix with the carbon-rich layer that separates it from the planets’ cores. The core of Uranus is similar in size to Mercury, and the core of Neptune is similar to Mars.
This layer of water, rather than the core, is probably responsible for the chaotic structure of the magnetic fields. Uranus and Neptune have significantly less hydrogen than Jupiter and Saturn due to their greater distance from the Sun, which may have affected their unique internal structure.
Return to Uranus
This theory could be the basis for a new NASA mission to Uranus planned for the 2030s. The orbiter will be able to measure the planet’s magnetic field and internal structure to confirm the existence of a water layer.
“This is another good reason to return to Uranus,” notes Fran Bagenal, a member of the Voyager science team.
We previously reported on how astronomers were wrong about the composition of Uranus and Neptune.
Provided by Space
