Washington, United States

Uranus — the seventh planet from Sun — has not just one, two or three moons, but a total of 27 moons. New research suggests that four of its moons may be hiding oceans beneath their icy exteriors. 

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These four moons, namely Miranda, Ariel, Umbriel, and Titania, are over 1500 km in diameter and have been studied extensively by scientists. 

However, a fresh look at 40-year-old data sent to Earth by NASA's Voyager 2 spacecraft indicates that the four moons may have oceans buried kilometres deep under their surface.

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Of these, Titania and Oberon, which orbit the farthest from Uranus, may have oceans buried some 50 kilometres (30 metres) deep. Oceans on Ariel and Umbriel, on the other hand, may be closer to the surface at 30 kilometres (19 miles) deep.

These astonishing findings were shared in a new study published in the Journal of Geophysical Research in December 2022.

Talking to Space.com, Julie Castillo-Rogez, a planetary scientist at NASA's Jet Propulsion Laboratory in California and the lead author of this study said: "Finding oceans in the Uranian moons would increase the prospect that [...] ocean worlds are frequent in our solar system, and maybe — by extension — in other solar systems."

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The new research can help explain how even in the frigid outer reaches of the solar system, persistent internal heat and a few chemicals can make the Uranian moons watery worlds.

As per the researchers, early in their histories, Uranus' five largest moons — namely Titania, Oberon, Ariel, Umbriel and Miranda — had substantial oceans that ran deep, ranging from 100 km to 150 km (62 miles to 90 miles).

Also read | Saturn’s mesmerising rings vanishing, further aggravate its cosmic identity crisis

"If the moons had benefited from long-term heating from their planet, then they could have maintained a thick ocean," said Castillo-Rogez.

Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, both have significant subsurface oceans. The gravitational pull of their respective host planets causes these moons to experience deformation in their interiors and icy crusts, a phenomenon known as tidal flexing. 

This process generates heat, which as per scientists, may be responsible for maintaining the subsurface water on these moons in a liquid, potentially life-supporting state.

However, Uranus has weaker tidal forces than Jupiter or Saturn, which means that the oceans on its four largest moons are "mostly frozen by now," according to Castillo-Rogez.

To gain a better understanding of the evolution of Uranus's largest moons, her team created a model using data collected from NASA missions that investigated other celestial bodies with subsurface oceans. The team examined findings from the Cassini mission, which studied Saturn's moon Enceladus, the Dawn mission, which explored the dwarf planet Ceres, and the New Horizons mission, which flew by Pluto and its largest moon Charon in 2015. 

By analysing data from these missions, the team was able to construct a model of how the moons of Uranus may have formed and evolved over time.

The model created by the team reveals that the Uranian moons likely hold "thin oceans with high salt concentrations". This is likely due to limited internal heat left over from their births and considerable ammonia. The chemical is antifreeze in nature which helps keep water in its liquid form even in very low temperatures.

The researchers also suggest that the subsurface oceans could be habitable environments for microbial life that are adapted to living in extreme environments. They estimate that oceans would contain around 150 grams of salt per litre. Earth's Great Salt Lake in Utah has twice the salt volume but still boasts of life in and around it.

(With inputs from agencies)

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