Uranus’ moons may hold deep oceans, NASA study finds

New computer modeling and a re-examination of data from NASA’s Voyager spacecraft have led scientists at NASA to conclude that four of Uranus’ largest moons may contain oceans between their icy crusts and cores, possibly reaching depths of dozens of miles. This study is the first to provide a detailed account of the interior makeup and structure of all five large moons orbiting Uranus. While the largest moon, Titania, was previously thought to be the most likely to retain internal heat, causing radioactive decay, the other moons were believed to be too small to prevent internal oceans from freezing.

With at least 27 moons orbiting Uranus, scientists are focusing on the ice giant to increase their understanding of the mysterious Uranus system in preparation for future missions. The National Academies’ 2023 Planetary Science and Astrobiology Decadal Survey has prioritized exploring Uranus. This new research, published in the Journal of Geophysical Research: Planets, could aid in the investigation of the moons during such missions. Furthermore, it could have implications beyond Uranus, as evidence of oceans has been found in unexpected locations, such as dwarf planets Ceres and Pluto and Saturn’s moon Mimas. As a result, the research investigates mechanisms that could be at play in bodies with limited internal heat that could be rich in water.

A recent NASA Hubble Space Telescope view reveals Uranus surrounded by its four major rings and by 10 of its 17 known satellites. Credit: NASA/JPL/STScI

To conduct the study, the researchers analyzed data from NASA’s Voyager 2 flybys of Uranus in the 1980s, as well as data from ground-based observations. They created computer models and incorporated data from other NASA missions, including Galileo, Cassini, Dawn, and New Horizons, which have discovered other ocean worlds. This included information on the geology and chemistry of icy bodies such as Saturn’s moon Enceladus, Pluto and its moon Charon, and Ceres, which are similar in size to Uranus’ moons. These additional findings helped the researchers gain a deeper understanding of the potential makeup of the Uranian moons and the possibility of oceans within them.

What lies above and beneath

The team of researchers utilized their computer modeling to determine the porosity of the surfaces of Uranus’ moons, which led them to conclude that the moons’ interiors are insulated enough to retain the necessary internal heat required for hosting an ocean. The team also identified a potential heat source in the rocky mantles of the moons, which could release hot liquid and aid in maintaining a warm environment. The moons Titania and Oberon appear to be particularly conducive to sustaining warm oceans, potentially supporting habitability.

By studying the composition of the oceans, planetary scientists can gain insight into the materials that may be present on the icy surfaces of the moons. Evidence suggests that Ariel has had material flow onto its surface, potentially from icy volcanoes, relatively recently. Meanwhile, the fifth-largest moon, Miranda, has surface features indicating recent activity, but it is unlikely to have maintained water for long.

The research also suggests that chlorides and ammonia are abundant in the oceans of the Uranian moons, with ammonia serving as an antifreeze to help maintain the internal oceans. Salts present in the water are also believed to act as antifreeze, further contributing to the moons’ ability to sustain internal oceans.

Although this study sheds new light on the potential ocean worlds of Uranus’ moons, there are still many unknowns. According to Castillo-Rogez, more models are needed to better understand the origin of these moons and guide future observations.

Furthermore, the newfound understanding of the composition and potential habitability of these moons can inform the development of specialized instruments to probe their deep interiors. For example, knowledge of the presence of ammonia and chlorides can guide the selection of wavelength ranges for spectrometers. However, the cold water of the interior oceans could also present a challenge for detecting electrical currents and understanding what lies beneath the surface.

Overall, while this study provides important insights into the potential for oceans on Uranus’ moons, there is still much more work to be done to fully understand these enigmatic worlds.

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