4 of Uranus's icy moons could have liquid water oceans

When it comes to exploring planets in our solar system, most of the attention gets placed on those nearest to Earth which are easier to visit, and with powerful telescopes, we often observe the gas giants Jupiter and Saturn too. The more distant planets like Uranus and Neptune, however, are often overlooked and there’s growing support among planetary scientists for sending a mission there. Now, new evidence gives even more impetus for a mission to Uranus, with a recent study showing that four of the planet’s moons could host water.

Researchers from NASA’s Jet Propulsion Laboratory reanalyzed data from the Voyager 2 mission which passed Uranus in the 1980s to look at the five largest of its 27 moons: Ariel, Umbriel, Titania, Oberon, and Miranda. Using computer modeling of how porous the surfaces are, they found that four of these moons likely have liquid water oceans beneath icy crusts.

Uranus is surrounded by its four major rings and 10 of its 27 known moons in this color-added view that uses data taken by the Hubble Space Telescope in 1998. A study featuring new modeling shows that four of Uranus’ large moons likely contain internal oceans. NASA/JPL/STScI

The diagram below shows what the interiors of the five largest moons are thought to be composed of, with layers of ice, rock, and water. Even though Uranus and its moons are very far from the sun and therefore have very cold surface temperatures, there could be salty oceans present because they are insulated by a thick layer of ice and seem to have ammonia in them, which acts like an antifreeze. And in some cases, the moons could be warmed by internal heat mechanisms from their rocky mantles.

New modeling shows that there likely is an ocean layer in four of Uranus’ major moons: Ariel, Umbriel, Titania, and Oberon. Salty – or briny – oceans lie under the ice and atop layers of water-rich rock and dry rock. Miranda is too small to retain enough heat for an ocean layer. NASA/JPL-Caltech

The insulating effect is similar to what is seen at the icy moons around Jupiter and Saturn, which are also thought to host oceans and are targets for studying habitability. There seem to be a wide range of places that could host water oceans, even if they are outside the habitable zone.

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“When it comes to small bodies – dwarf planets and moons – planetary scientists previously have found evidence of oceans in several unlikely places, including the dwarf planets Ceres and Pluto, and Saturn’s moon Mimas,” said lead author Julie Castillo-Rogez of NASA’s Jet Propulsion Laboratory in a statement. “So there are mechanisms at play that we don’t fully understand. This paper investigates what those could be and how they are relevant to the many bodies in the solar system that could be rich in water but have limited internal heat.”

The research is published in the Journal of Geophysical Research.