Four out of five Uranus moons likely to have ocean under crust

A preview of what Uranus Orbiter and Probe might find in the 2040s

NASA revealed on Thursday that four of the largest moons of ice giant Uranus likely contain a layer of water beneath their surface.

The discovery was made when space boffins reanalyzed 1980-era Voyager spacecraft data using new computer modelling techniques. The researchers examined the flyby and ground-based observation data to better understand the composition and structure of five large moons.

Between planetary satellites Miranda, Ariel, Umbriel, Titania and Oberon, Miranda was the only moon found unlikely to host liquid – unless it is later found that it experienced tidal heating millions of years ago.

The water is believed to be located between the core and icy crusts in oceans 30km deep for moons Ariel and Umbriel, and less than 50m for Titania and Oberon.

It's not uncommon to find water in dwarf planets and moons, according to JPL's Julie Castillo-Rogez.

For example, dwarf planets Ceres and Pluto, as well as Saturn's moon Mimas, have all shown evidence of liquid.

According to Castillo-Rogez, "there are mechanisms at play that we don't fully understand." Her study on the Voyager data investigated what those mechanisms could be and how they play out in celestial bodies rich in water with limited internal heat.

Absent the right amount of heat, the study suggested that chlorides like ammonia or salt are likely abundant in the moons and could act as an antifreeze, able to maintain the ocean layer.

Currently Voyager 2 is the only spacecraft to have visited Uranus. A proposed Uranus Orbiter and Probe (UOP) mission is now considered a top priority by NASA and would further test the moons for oceans, as well as the planet's own atmosphere and other characteristics.

The hunt for oceans on the moons could be conducted by measuring their magnetic fields – as long as they are hypersaline. However, if the ocean is primarily ammonia, low temperatures could make electrical conductivity too small to detect water.

UOP was originally slated to launch in 2031 but a shortage of plutonium has pushed that date back to the mid to late 2030s. The spacecraft will not arrive near Uranus until over a decade after launch. ®