Four satellites of Uranus may contain oceans within | sorae Portal site to space

The second farthest planet in the solar systemUranusSo far, 27 satellites have been discovered. Among them is the large sizeMiranda」「Ariel」「Umbrella」「Titania」「OberonIt is known as the largest of the five satellites of Uranus.

These moons are called icy moons because they are made primarily of ice. For Titania and Oberon, which are particularly large, if ammonia, which acts as an anti-icing agent (a substance that prevents water from freezing even at temperatures below 0 ° C), were dissolved in seawater, the inner sea would not be preserved yet , there was also an expectation that it would be so. In particular, Ariel is an interesting target to monitor, as we have obtained data that appear to be traces of recent volcanic activity. However, in recent years, this seawater has been found to be unstable as a substance, and at least the presence of antifreeze alone cannot sustain the inland sea.

On the other hand, recent activity of planetary probes has raised the possibility that there are much more inner oceans than previously thought. Examples include Saturn’s active moon Enceladus, the dwarf asteroid belt planet Ceres, and Pluto and its moon Charon. All of these are icy-bottomed objects that have been explored in recent years, and the five largest moons of Uranus are about the same size as these objects.

A research team led by Julie Castillo-Rogues of JPL (Jet Propulsion Laboratory) investigated the presence of inner oceans on the five largest moons of Uranus based on previous exploration data of celestial bodies whose main constituents are ice. The data considered included surface chemistry, geology, mechanical models, and geometry data.

The only close observation data of Uranus was obtained by NASA’s “Voyager 2” planetary probe (National Aeronautics and Space Administration) which conducted a flyby exploration in 1986, and covers about 40% of the surface of the five major satellites. There is only limited observational data, but by comparing it with data from other celestial bodies, it is possible to estimate the internal structure of celestial bodies and to study in detail the movement of heat within the celestial body, which is especially important.

As a result of the analysis, it was found that rocks near the surface of the five largest satellites are porous and have high thermal insulation properties that keep heat inside. It was also found that the decay of short-lived radioactive substances generates heat for several hundred years immediately after the birth of the satellite, and that residual heat is the main source of heat that melts the ice inside.

On the other hand, it was also revealed that the tidal force (the force with which an object is pulled due to the interaction of gravity with other celestial bodies), which is considered for other icy bodies, is almost non-existent for the five main moons. Previous studies showed that tidal forces barely affect the five major satellites, but in this study, tidal forces only arose when the orbits were unstable immediately after the birth of the satellites.

Frictional heat is generated in celestial bodies where tidal forces act, and a phenomenon called tidal heating may occur, which leads to heating of the interior. However, among the five largest moons of Uranus, even Miranda and Ariel, which are most affected by tidal forces, were found to have an internal heating much lower than the heat of decay of radioactive material. It is also found that if the tidal force is too strong, the surface rock loses its porosity and has the negative effect of losing its residual heat retention insulating performance.

[▲ شكل 2: الهياكل الداخلية للأقمار الصناعية الخمسة الرئيسية المقدرة في هذه الدراسة. تشير التقديرات إلى أن محيطات أرييل وأومبرييل تحت السطحية يقل عمقها عن 25 كيلومترًا ، وأن محيطات تيتانيا وأوبرون بها محيطات جوفية أقل من 50 كيلومترًا ، بينما يُقدر أن ميراندا متجمدة تمامًا (Credit: NASA). / JPL-Caltech / تمت إضافة الترجمة بواسطة المؤلف)]

Consider theseAriel, Umbriel, Titania, and Oberon are large enough to sustain the inner oceans even today.It turns out. On the other hand, it is the smallest of the five large moons and loses its internal heat the fastest.Miranda’s inner ocean likely froze within a billion years after his birthestimated to be

In the case of an inland ocean on the four satellites, the average inland sea temperature is estimated to be between -5°C and -30°C, with chloride acting as an anti-icing agent in addition to ammonia. Volume of the inland seaLess than 50 km in Titania and Oberon、Depths of up to 25 km in Ariel and Imperialsupposed to be

As another consequence, Miranda has no clear core, Ariel and Umbriel have a water rock core, and Titania and Oberon have a water rock core and a dry inner rocky core. It also assumes that there is no metallic core in any target.

However, it is unclear whether the Inland Sea has actually remained unfrozen until now. Although the inner circumference of 50 km for Titania and Oberon is the best estimate, it is much smaller for the inner circumference of an ice body. In addition, model calculations this time indicate the possibility of rocks containing liquid water filling the voids rather than an ocean of liquid water.

By measuring the magnetic field of each satellite, we may be able to determine whether there is an inner ocean, and if so, what it is like. On the other hand, if the seawater contains a lot of ammonia and chlorides, the seawater will produce almost no magnetic field, so this can be difficult to prove through observation.

Every ten years, NASA and the NSF (United States National Science Foundation) publish a plan called the Planetary Science Decadal Survey, which explores mysteries and challenges in planetary science at the time. It covers exploration and monitoring plans recommended for resolution. 2023 is the time when the third plan will start, and the highest priority among them is the Uranus orbital exploration plan. Of course, the plan also includes observations of the five largest moons, so in the future, we may be able to learn more about the presence or absence of the inner oceans of the five largest moons through Uranus exploration missions.

[تصحيح]Corrected some codes. Dwarf planet Ceres incorrectly described as a quasi-satellite (22:50 on May 26, 2023)

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Text: Rare Aya