Gas giants can be difficult to understand. What lies beneath the thick, opaque clouds of planets like Uranus and Neptune? Is it more gas, or perhaps a solid core? Do these planets have a definite boundary, or are there just a series of different layers?
Deep oceans. A recent study published in Proceedings of the National Academy of Sciences suggests that Uranus and Neptune might have oceans hidden behind their clouds of hydrogen and helium. Relying on computer simulations, researchers believe that the ice giants could have multiple layers, some composed of hydrocarbons and others of water.
These layers behave like oil and water, remaining separate under the dense atmospheres of Uranus and Neptune. The presence of these water bodies may relate to the unusual magnetic fields exhibited by the two planets.
Different magnetic fields. NASA’s Voyager 2 was the first and only probe to approach Uranus and Neptune closely. During its journey, it gathered valuable data about the planets, including their peculiar magnetic fields.
Earth’s magnetic field is dipolar and results from convective movements of molten iron in its core. In contrast, the magnetic fields of Uranus and Neptune are disorganized. Voyager 2’s observations indicated that the ice giants don’t possess a typical dipolar magnetic field.
As a result, scientists started to hypothesize that Uranus and Neptune may have interiors made up of distinct layers of compounds that don’t mix. This would prevent large-scale convection as seen in Earth’s interior. The challenge that followed was to determine the nature of these compounds.
Simulating the interior. The new study relied on computer simulations to explore the conditions and compounds that could explain the unusual characteristics of Uranus and Neptune. These simulations revealed distinct layers of water, methane, and ammonia, which are separated from each other. The escape of hydrogen atoms from the methane and ammonia layers facilitates this separation due to pressure changes. Calculations based on these simulations suggest that the ice giants may have a water layer around 5,000 miles thick.
“We now have, I would say, a good theory why Uranus and Neptune have really different [magnetic] fields, and it’s very different from Earth, Jupiter and Saturn,” author Burkhard Militzer says. “We didn’t know this before. It’s like oil and water, except the oil goes below because hydrogen is lost.”
A mission to the ice giants. Another paper published in Geophysical Research Letters recently speculated that the gravitational interactions between Uranus and its moons could aid future missions in discovering hidden oceans on the satellites.
Astronomers are interested in Uranus and Neptune because they’re among the most popular exoplanets in our galaxy. Unsurprisingly, a 2023 study found widespread consensus among experts that a mission to Uranus must be planned within the next decade.
This hypothetical mission would involve launching a probe in the early 2030s to take advantage of favorable orbital dynamics, allowing the spacecraft to reach the ice giant in just over a decade. The probe could conduct detailed examinations of not only the planet itself but also its moons and investigate the potential presence of liquid water oceans on them.
Image | NASA/JPL-Caltech
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