REPUBLIKA.CO.ID, JAKARTA— Size of planetary rings Uranus controlled by its five main moons, which are capable of ejecting large amounts of dust out of the system’s seventh planet from the sun. This is according to new simulations designed to find out where the rings might come from.
Reported SpaceTuesday (31/10/2023), Uranus is famous for its tilt of 98 degrees, a legacy of past giant impacts in the planet’s history.
“One of my motivations was to find out what Uranus rings is an artifact of the original impact that knocked Uranus onto its side,” said Stephen Kane, professor of planetary astrophysics at the University of California, Riverside (UCR), in a telephone interview with Space.com. “The answer, it turns out, is probably not, because the ring material won’t last long.”
Kane and fellow UCR planetary scientist Zhexing Li are the authors of a new paper that describes simulated interactions between Uranus’ five major moons, namely Umbriel, Titania, Oberon, Miranda and Ariel, and their rings. In particular, interactions are at their peak when the moons are in “mean motion resonance” with the rings.
Mean motion resonance between two orbiting bodies occurs when the orbital period of the outer body is greater than the orbital period of the inner body. For example, if the moon makes one orbit for every two orbits completed by a ring particle at a certain distance from Uranus, then the particle will fall into gravitational resonance.
This resonance can eject ring material from the system and cut the size of Uranus’ ring system. It is the resonance with Uranus’ two innermost large moons, namely Miranda which is 480 km wide and Ariel which is 1,160 km wide, that has the greatest influence, cutting the rings drastically at a distance of 4.3 planetary radii. The radius of Uranus is 25,362 km, so 4.3 planet radius is 109,000 km.
Uranus’ rings may have been bigger and brighter when they first formed, but have now shrunk due to the scouring effect of the moon. The fact that Uranus still has rings suggests that they are being replenished by various dust sources in the Uranus system. One of the main sources is impacts, large and small, on the moon.
Kane said it is still relatively unknown what the level of impact will be on Uranus. “But [keberadaan cincin-cincin tersebut meskipun ada kehilangan massa] suggests that the size may be higher than previously thought,” he said.
In addition to impacts, gas releases can also contribute to the supply of particulate matter in the system. When icy moons enter resonance, gravitational waves from other moons and Uranus itself can flex their interiors, triggering cryovolcanism that causes material to be ejected from the moons.
Kane and Li found that after introducing dusty particles into the Uranus system via one of the above methods, the moon was able to eject 35 percent of the material within 40 planetary radii (about 1 million km) of Uranus in just half a million years. The rate of mass loss then slows and reaches 40 percent after tens of millions of years.
Kane was surprised by the high rate of mass loss. It is the interactions between the moons that cause this loss of mass.
To make things even more complicated, the orbits of Uranus’ moons have changed over time. “There is a lot of evidence that they have moved over time to different resonance locations,” Kane said. Given that there are more opportunities for resonant orbits closer to Uranus, “ring shearing would have been more severe in the past as the inner moons moved in and out of resonance.”
Simulations also show that there is a chance for the ring to have a stable orbit among the orbits of the large moons. “It’s interesting to think about what it would look like, with the moons embedded in the rings and the moons carving out these gaps,” Kane said.
Uranus is not the only planetary system with this characteristic. In 2022, Kane conducted similar research on Jupiter, which has very faint and thin rings, so it does not know the planet’s enormous mass. In the study, Kane found that Jupiter’s four large Galilean moons were responsible for ejecting most of the dusty material that might otherwise have found its way into the rings.
Jupiter’s four large Galilean moons are Io, Europa, Ganymede, and Callisto. Currently, the scenarios on Jupiter and Uranus only exist in theoretical modeling.
2023-10-31 01:13:47
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