NASA to Search for Subsurface Oceans within Uranian Moons

Several of the icy moons in the Jupiter and Saturn systems appear to possess internal liquid water oceans. Our knowledge of the Uranian moons is more limited but a future tour of the Uranus system has the potential to detect subsurface oceans. Planning for this requires an understanding of how the moons’ internal structures — with and without oceans — relate to observable quantities. New research from the University of Texas Institute for Geophysics and the University of California Santa Cruz shows that certain aspects of their rotational states could be diagnostic of the presence or absence of internal liquid water oceans within several of the Uranian moons — such as Miranda, Ariel, and Umbriel — and that combining this with measurements of the gravity field could provide comprehensive constraints on the internal structures and histories of the Uranian moons.

When NASA’s Voyager 2 flew by Uranus in 1986, it captured grainy photographs of large ice-covered moons.

Now, NASA plans to send another spacecraft to Uranus, this time equipped to see if those icy moons are hiding liquid water oceans.

The mission is still in an early planning stage, but planetary researchers are preparing for it by building a new computer model that could be used to detect oceans beneath the ice using just the spacecraft’s cameras.

Their computer model works by analyzing small oscillations — or wobbles — in the way a moon spins as it orbits its parent planet.

From there it can calculate how much water, ice and rock there is inside. Less wobble means a moon is mostly solid, while a large wobble means the icy surface is floating on a liquid water ocean.

When combined with gravity data, the model computes the ocean’s depth as well as the thickness of the overlying ice.

“If Uranus’ moons are found to have interior oceans, that could mean there are vast numbers of potentially life-harboring worlds throughout our Galaxy,” said Dr. Doug Hemingway, a planetary scientist at the University of Texas Institute for Geophysics.

“Discovering liquid water oceans inside the moons of Uranus would transform our thinking about the range of possibilities for where life could exist.”

All large moons in the Solar System, including the Uranian moons, are tidally locked.

This means that gravity has matched their spin so that the same side always faces their parent planet while they orbit.

This doesn’t mean their spin is completely fixed, however, and all tidally locked moons oscillate back and forth as they orbit.

Determining the extent of the wobbles will be key to knowing if Uranus’ moons contain oceans, and if so, how large they might be.

Moons with a liquid water ocean sloshing about on the inside will wobble more than those that are solid all the way through. However, even the largest oceans will generate only a slight wobble: A moon’s rotation might deviate only a few hundred feet as it travels through its orbit.

That’s still enough for passing spacecraft to detect. In fact, the technique was previously used to confirm that Saturn’s moon Enceladus has an interior global ocean.

To find out if the same technique would work at Uranus, Dr. Hemingway and his colleague, Dr. Francis Nimmo from the University of California, Santa Cruz, made theoretical calculations for five of its moons and came up with a range of plausible scenarios.

Detecting smaller oceans will mean a spacecraft will have to get closer or pack extra powerful cameras.

“The next step is to extend the model to include measurements by other instruments to see how they improve the picture of the moons’ interiors,” Dr. Hemingway said.

The team’s work was published in the journal Geophysical Research Letters.

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D.J. Hemingway & F. Nimmo. 2024. Looking for Subsurface Oceans within the Moons of Uranus Using Librations and Gravity. Geophysical Research Letters 51 (18): e2024GL110409; doi: 10.1029/2024GL110409

This article is a version of a press-release provided by the University of Texas.