The study builds on new simulations and explores how oceans could exist in unlikely places in our solar system. New computer simulations and reanalysis of Voyager data suggest that Uranus’ four largest moons likely have oceanic layers between their cores and icy crusts. While the insulation and potential sources of heat in the moons’ mantles may contribute to trapping ocean heat, their oceans likely have an abundance of nonfreezing materials such as chlorides, ammonia, and salts.

Re-analysis of data from NASA’s Voyager spacecraft and new computer simulations led NASA scientists to conclude that the four largest moons of Uranus likely contain an oceanic layer between their cores and icy shells. Their work is the first to describe in detail the evolution of the internal composition and structure of all five major moons: Ariel, Umbriel, Titania, Oberon, and Miranda. Researchers suggest that the four moons contain oceans tens of miles deep.

In total, at least 27 moons orbit Uranus; The four largest range from Ariel, which is 720 miles (1,160 kilometers) in diameter, to Titania, which is 980 miles (1,580 kilometers) in diameter. Scientists have long believed that Titania most likely retained internal heat caused by radioactive decay, given its size. Other moons were previously thought to be too small to hold the heat needed to keep the inner ocean from freezing, especially since the heating created by the gravity of Uranus is only a small source of heat.

The 2023 National Academy of Planetary Sciences and Astrobiology Decadal Survey prioritized Uranus studies. In preparation for such a mission, planetary scientists focus on the ice giant to bolster their knowledge of the mysterious Uranus system. New study published in Journal of Geophysical Research: Planets“It may offer insight into how a future mission might discover moons, but the paper also has implications beyond Uranus,” said lead author Julie Castillo-Roguez of NASA’s Jet Propulsion Laboratory in Southern California.

“When it comes to small bodies — dwarf planets and moons — planetary scientists have previously found evidence of oceans in many unlikely places, including the dwarf planets Ceres and Pluto and Saturn’s moon Mimas,” he said. “So there are mechanisms at work that we don’t fully understand. This article explores what these might be and how to apply them to the many bodies in the Solar System that are rich in water but may have limited internal heat.”

The study reviewed findings and ground-based observations from NASA’s Voyager 2 flights of Uranus in the 1980s. The authors created computer models supported by additional findings from NASA’s Galileo, Cassini, Dawn and New Horizons (each of which explored oceanic worlds), including understanding the chemistry and geology of Saturn’s moon Enceladus, Pluto and its moons Charon and Ceres. – all icy bodies are approximately the same size as the moons of Uranus.

What lies above and below

The researchers used simulations to estimate how porous the surfaces of the moons of Uranus are, and found that they are insulated enough to possibly retain the internal heat needed to host an ocean. Additionally, they discovered that there could be a potential source of heat in the moons’ rocky mantles, which secrete warm fluid and help the ocean maintain a warm environment – ​​a possible scenario for Titania and Oberon, where the oceans in particular are. even potentially hot enough to sustain life.

By studying the composition of the oceans, scientists can learn about materials that can also be found on the icy surfaces of the moons, depending on whether the materials are being pushed up from below by geological activity. The telescopes suggest that at least one of the moons, Ariel, had material flowing to its surface relatively recently, possibly from icy volcanoes.

In fact, Miranda, the innermost and fifth largest moon, also has surface features that appear to have formed recently, suggesting it may have retained enough heat to support an ocean at one point. Recent thermal simulations have shown that Miranda is unlikely to retain water for long: it loses heat very quickly and has probably frozen by now.

But internal heat won’t be the only factor affecting the ocean below the lunar surface. A key finding of the study is the abundance of chlorides as well as ammonia in the oceans of the ice giant’s largest moons. It has long been known that ammonia acts as an antifreeze. Additionally, the simulations suggest that salts likely to be found in the water could be another source of antifreeze that protects the bodies’ inner oceans.

Of course, there are still many questions about the large moons of Uranus, Castillo-Roges said.

Discovering what lies beneath and on the surface of these satellites will help scientists and engineers choose the best scientific instruments for their exploration. For example, determining that ammonia and chlorides may be present means that spectrometers that detect compounds by reflected light must use a wavelength range that covers both types of compounds.

Additionally, they can use this knowledge to develop instruments that can go deep into the liquid. Looking for electrical currents that contribute to the moon’s magnetic field, as the Galileo mission scientists did to Jupiter’s moon Europa, is often the best way to find the deep ocean. However, the cold water in the inner oceans of moons like Ariel and Umbriel causes the oceans to be less able to carry these electrical currents, presenting a new challenge for scientists trying to understand what’s underneath.