Scientists still know too little about the moons of Uranus. It is quite possible that there are oceans of liquid water hiding in their depths. Recently, researchers have created a program that is able to find them by deviations in the motion of these bodies.
Planned new missions to Uranus
When Voyager-1 flew past Uranus in 1986, it took grainy photos of the large ice-covered moons. Now, after almost 40 years, NASA plans to send another spacecraft to Uranus, this time equipped to find out if these icy moons hide oceans of liquid water.
The mission is still in the early planning stages. But researchers at the University of Texas Institute of Geophysics (UTIG) are preparing for it by creating a new computer model that can be used to detect oceans under ice using only spacecraft cameras.
This study is important because scientists don’t know what method of detecting oceans would work best on Uranus. Scientists want to know if liquid water is there, as it is a key ingredient for life.
Moon oscillations and ocean detection
The new computer model works by analyzing small oscillations – or oscillations in the way the Moon orbits its parent planet. Hence, it can calculate how much water, ice, and rocks are contained within. Smaller oscillations mean that the Moon is predominantly solid, while greater oscillations mean that the icy surface is floating in an ocean of liquid water. Combined with gravity data, the model calculates the depth of the ocean as well as the thickness of the ice covering it.
Uranus, along with Neptune, belongs to a class of planets called ice giants. Astronomers have discovered more ice giant bodies outside our Solar System than any other type of exoplanet. If Uranus’ moons turn out to have internal oceans, it could mean that there are a huge number of potentially habitable worlds throughout the galaxy, says UTIG planetary scientist Doug Hemingway, who developed the model.
The UTIG study, published in the journal Geophysical Research Letters, will help mission scientists and engineers improve the chances of detecting oceans. UTIG is a research unit of the Jackson School of Geosciences at the University of Texas at Austin.
All the major moons of the Solar System, including Uranus, are tidally locked. This means that gravity has adjusted their spin so that they are always turned toward the parent planet on the same side while orbiting. However, this doesn’t mean that their spin is completely fixed, and all tidal moons oscillate back and forth as they orbit. Determining the extent of these oscillations will be key to understanding whether Uranus’ moons have oceans, and if so, how large they might be.
Moons with a liquid water ocean splashing around inside will wobble more than those that are solid all the way through. However, even the largest oceans cause only minor wobbles — the moon’s rotation can only deviate by a few hundred feet as it moves through its orbit.
That’s still enough to be detected by passing spacecraft. By the way, this method was previously used to confirm that Saturn’s moon Enceladus has an internal global ocean.
How will the spacecraft detect the ocean on the moon?
To determine whether this method would work on Uranus, Hemingway performed theoretical calculations for five of its moons and proposed a number of reasonable scenarios. For example, if Uranus’ moon Ariel wobbles 300 feet, it probably has an ocean 100 miles deep surrounded by a 20-mile-thick ice shell.
Detecting smaller oceans would mean the spacecraft would have to fly closer or be equipped with more powerful cameras. But the model gives mission developers a slide rule to know what will work, says UTIG associate professor Krista Soderlund.
The next step, according to Hemingway, will be to expand the model to include measurements from other instruments to see how they improve the picture of the moon’s interiors. The journal article was co-authored by Francis Nimmo of the University of California, Santa Cruz.
Provided by phys.org
