"When it comes to smaller celestial bodies like dwarf planets and moons, planetary scientists have previously found evidence of oceans in unexpected locations, such as the dwarf planets Ceres and Pluto, and Saturn's moon Mimas," said study lead author Julie Castillo-Rogez of NASA's Jet Propulsion Laboratory in Southern California. "This indicates that there are underlying mechanisms we have yet to fully comprehend."
The study combines Voyager 2 data from the 1980s with information on other icy moons, including Pluto's Charon and Saturn's Enceladus, gathered from more recent NASA missions like Galileo, Cassini, Dawn, and New Horizons. Although Uranus boasts 27 moons, the researchers concentrated on the five largest – Ariel, Umbriel, Titania, Oberon, and Miranda. Ariel, the smallest, measures 720 miles (1,160 kilometers) in diameter, while Titania, the largest, spans 980 miles (1,580 km) across.
Initially, only Titania was thought to generate internal heat through radioactive decay, a process where unstable atoms release energy via radiation. Scientists believed the other moons were too small to create internal heat. However, new models suggest that all moons except Miranda are sufficiently insulated to retain heat produced by radioactive decay. Moreover, researchers found that potential oceans beneath these icy crusts would contain chlorides, ammonia, and salts, which lower the water's freezing point. This combination of low freezing points and adequate internal heat could indicate that Ariel, Umbriel, Titania, and Oberon possess deep oceans within their interiors.
In 2020, scientists discovered evidence of recent geological activity on Ariel, hinting at the possible movement of an inner ocean. While Miranda also displays relatively fresh surface features, the researchers' models suggest that any liquid ocean it once had is likely frozen now.
To confirm the existence of these hidden oceans, scientists must employ innovative methods. Spectrometers capable of detecting light wavelengths reflected by ammonia and chlorides could help verify the presence of these chemicals beneath the crusts. Additionally, instruments that can sense electrical currents carried by liquid water might be used to explore beneath the moons' surfaces. New modeling studies on the formation of these moons may also assist researchers in determining the necessary future observations, adds Castillo-Rogez.
Four of Uranus' largest moons may have hidden, underground oceans, new research suggests. (Image credit: NASA, ESA, CSA, STScI. Image processing: J. DePasquale (STScI))
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