Five large moons of Uranus were formed as a result of condensation of water vapor in the ice in the circumplanetary disk, which arose from a collision with a large body, changed the inclination of the rotation axis of the planet. A theoretical model that explains this process, developed by a group of Japanese researchers, in their article published in Nature Astronomy.
Among the 27 currently known natural satellites of Uranus (which, incidentally, are named after characters from the works of Alexander Pope and William Shakespeare) it is customary to distinguish five large ones, which have a shape close to spherical is Miranda, Ariel, Umbriel, Titania and Oberon. All of them, except almost entirely of ice Miranda, consist of roughly equal proportions of ice and rocks.
There are two possible scenarios for the formation of these satellites — the evolution of circumplanetary subdisk or accretion of matter that was ejected in the collision of a Uranium with a massive body. However, the first scenario does not explain the fact that the system the satellites rotate in the same direction as Uranus and has the same inclination to the axis of rotation — the plane of the equator of Uranus is inclined to the plane of the orbit nearly 98 degrees, it’s like he’s lying on his side. Because subdisk is formed in the orbital plane of the planet, pulling the hydrogen and helium from the disk surrounding the star.
The second scenario is the formation of satellites from a disk that was formed as a result of the collision of Uranus with another celestial body — much better explains the existing parameters of the orbits of the moons of this planet. This scenario also explains the significant inclination of the rotation axis of Uranus. However, the simulation process still worked circumplanetary disks, which are an order of magnitude smaller and two orders of magnitude more massive than the system of the five major satellites, and they are very poor rocks – in fact the substance from a small rocky core of Uranus is not so easy to release even under the condition of a collision with a massive object.
The authors of the study under the guidance of Shigeru IDA (Shigeru Ida) from Tokyo Institute of technology came to the conclusion that this is because the earlier simulation used the model of “giant impact” — as that in which the Earth formed the Moon. It does not take into account the peculiarities of the evolution of circumplanetary disk, which consists mainly of water vapour, and not from rocks, as was the case with the Earth.
Most likely, the body with which the Uranium encountered in the early period of its history, consisted mostly of ice — as, indeed, the Uranium. Since the evaporation temperature of water ice is small, the collision ejected into orbit of the planet the substance converts to a gaseous state and did not fly away into space and remained in orbit. Gradually the disc lost a significant mass of water vapor and distributed through the levels of the existing system of satellites until steam has cooled enough to start the condensation of ice on a solid, silicate fragments and the formation of ice grains larger bodies.
The models proposed by Japanese scientists, reproduces the orbits of the moons of Uranus and the approximate weight in accordance with the observed parameters. She offers the scenario of formation of satellites of the ice giants, depending on the mass and physical radius of the Central planet, which is different from the method of formation of satellites of the terrestrial planets and gas giants.
The authors believe that this model can be used for the inner part of the system of satellites of Neptune, by neglecting the presence of Triton, which could be captured by the planet. The scientists also hope that thus it will be possible to explain the possible presence of supertall icy satellites. Today observations point to the fact that many open in exoplanetary systems, super-earths can be rich in water ice, even at close to their stars orbit. Earlier we wrote about how the atmospheres of exoplanets discovered water vapor.
In addition to the 27 satellites, Uranus has an interesting ring system. N + 1 has already talked about how the moons interact with the rings and with each other.