Water, water everywhere, including the icy moons of Uranus

Computer modelling suggests briny oceans may exist below the frigid crusts of Uranus’ four larger moons, sandwiched between an outer layer of ice and lower layers of water-rich rock and dry rock. The smaller moon Miranda is not large enough to retain the heat needed for a layer of liquid water. Image: NASA/JPL-Caltech

Oceans of water hidden beneath the frozen crusts of large moons orbiting Jupiter, Saturn and other icy bodies in the outer solar system are a hot topic in planetary astronomy, with NASA and the European Space Agency both sending probes to Jupiter to look for evidence of habitable sub-surface environments.

Now add Uranus to the mix.

Re-analysis of data collected by NASA’s Voyager 2 spacecraft, along with advanced computer modelling, suggests that four of Uranus’ largest moons – Ariel, Umbriel, Titania and Oberon – may harbour oceans dozens of miles below their frigid surfaces.

“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 Julie Castillo-Rogez, a Jet Propulsion Laboratory researcher and lead author of a paper in the Journal of Geophysical Research.

“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 study incorporates data collected by Voyager and computer models using data from the Galileo Jupiter orbiter, the Dawn asteroid mission and the New Horizons flyby of Pluto and its moon Charon, along with insights provided by the Cassini probe’s study of Saturn’s moon Enceladus.

The modelling helped researchers determine the porosity of the surfaces of Uranus’ moons, which indicates they are likely insulated enough to retain the heat needed for liquid oceans to exist beneath the surface.

That heat may be provided by radioactive decay, but the study also suggests chlorides, as well as ammonia, are likely to be abundant, serving as a sort of antifreeze. But many questions remain and more work is needed to hammer out the details.

“We need to develop new models for different assumptions on the origin of the moons in order to guide planning for future observations,” said Castillo-Rogez.