Four of the five large moons of Uranus may have water in the form of an oceanic layer between the cores and the outer icy crust. Scientists came to such a conclusion by double-analyzing data from NASA's Voyager space probe.
This is the first study to describe in detail the internal composition and structural evolution of all five large moons of Uranus (Ariel, Umbriel, Titania, Oberon and Miranda). In total, there are at least 27 moons orbiting Uranus. The largest of them is Titania, with a diameter of 1,580 km, and Ariel, with a diameter of 1,160 km, completes the four largest satellites. And on these four moons, according to scientists, there can be oceans, the depth of which can reach tens of miles.
Scientists have long assumed that Titania, given its large size, would likely be able to retain the internal heat generated by radioactive decay. All other moons were previously thought to be too small to retain their heat, which is necessary to keep the inner ocean from freezing.
Scientists have previously found evidence of oceans in some unlikely places, including dwarf planets such as Ceres and Pluto and Saturn's moon Mimas. In a new study, scientists are trying to understand how water can be preserved in such objects.
They reviewed results from Voyager 2 flybys of Uranus in the 1980s, then built computer models based on additional data from NASA's Galileo, Cassini, Dawn and New Horizons spacecraft. That data includes information on the chemical composition and geological structure of Saturn's moon Enceladus, Pluto and its moons Charon, and Ceres. All of these icy objects are about the same size as Uranus' moons.
The researchers used simulations to determine how dense the surfaces of Uranus' moons might be. It was found that their surface components are probably sufficiently insulated from each other and therefore unable to retain the internal heat necessary to save the ocean. Additionally, scientists have identified a potential heat source in the moon's rocky mantle, which releases hot liquid and helps the ocean maintain a warm environment; it can happen on Titania and Oberon. According to scientists, it is possible that the oceans on these moons are so hot that, theoretically, life can exist in them.
Interestingly, according to data from telescopes, at least Ariel contains material that flowed onto its surface relatively recently, possibly from ice volcanoes.
Uranus' fifth largest moon, Miranda, also has surface features that suggest it may have at one point provided enough heat to sustain an ocean on its surface. However, recent thermal modeling has shown that Miranda could hardly retain water for long.
However, the internal heat of a moon or planet is not the only factor affecting the subsurface ocean. According to the researchers, chlorides, as well as ammonia, are likely abundant in the oceans of the ice giant's largest moons, and ammonia is known to act as an antifreeze. In addition, modeling shows that salts in water can also have an antifreeze effect.