[▲ Figure 1: Contrary to its appearance, Uranus has a characteristic that other planets do not have: the axis of rotation is almost sideways. (Credit: NASA/JPL-Caltech)]
Among the planets in the solar system,Uranus” is characterized by the inclination of the rotation axis.UranianThe rotation axis is tilted at 98 degrees from the orbit, almost to the side.. Considering that the inclination of the rotation axis is within 30 degrees for other planets in the solar system, this is a unique value.
For a long time, there has been a debate as to why Uranus’s axis of rotation turned sideways.Giant collision theory‘ has been suggested as a cause. Evidence has been found on other planets, making giant impacts a not uncommon phenomenon, and no other factor could have been found to tilt a planet’s axis to such an extent. is. It has also been suggested that rather than one large object colliding, multiple smaller objects collided.
However, in the case of the giant impact theory, there was no evidence to support the collision, and it was difficult to verify. Also, Neptune, whose rotation axis is tilted by only about 28 degrees, would not have had a giant impact. This contradicts the fact that the internal structures and atmospheric phenomena of Uranus and Neptune are very similar. This is because the existence or non-existence of giant impacts can be the cause of the diversity of terrestrial planets, each of which has different characteristics.
Furthermore, in recent years, a theory has been proposed that the tilts of the rotation axes of Jupiter and Saturn, which are not so tilted today, may have changed frequently on a billion-year timescale. The cause is thought to be the tidal forces of the giant satellites of Jupiter and Saturn. It seems worth testing this theory on Uranus as well.
A research team such as Melaine Saillenfest of the University of Paris Cians & Lettres used simulations to verify the tilt of the rotation axis by the satellite. The team hypothesized the existence of moons of varying masses and distances, and examined the interactions between Uranus and its moons over more than four billion years.
as a result,0.044% of Uranus (0.64% of Earth, 52% of Earth’s Moon) If there is a satellite with a mass ofon a short time scale of millions of years, the rotation axis of Uranus isEasily tilts more than 80 degreeswas shown. However, since its mass is four times that of the satellites currently revolving around Uranus, such satellites do not exist today.
It was also shown that changes in the satellite’s orbit and the tilt of Uranus’ axis of rotation become unstable when the tilt of the axis of rotation reaches this degree. This disordered stateUltimately ends with a giant moon colliding with UranusI understand. The loss of the interacting giant satellite will semi-permanently fix the tilt of the rotation axis of Uranus in a sideways position, and it can also explain why this satellite does not exist today. If a giant satellite has this mass and the orbital radius varies by more than 10 times the radius of Uranus, then this scenario has a probability of more than 80%.
In this theory, you may think that it is impossible to test like the giant impact theory because the moon will eventually collide with Uranus and be lost. However, satellites still in existence may provide clues. In the scenario proposed this time, it was shown through simulations that satellites other than giant satellites are also affected. Not all affected satellites are deorbited and expelled from the Uranian system, and orbital synchronization occurs for some.For this reason, existing satellitesNarrowing down the influence range of ancient satellites from orbital synchronizationcan potentially refine this scenario.
connection:Can Saturn’s tilted axis and ring formation be explained by missing satellites?
Source
- Melaine Saillenfest, et.al. “Tilting Uranus via the migration of an ancient satellite”. (arXiv)
- Bob Yirka. “A possible explanation for Uranus’s odd tilt angle and opposite spin”. (Phys.org)
- NASA/JPL-Caltech. “PIA18182: Uranus as seen by NASA’s Voyager 2” (Jet Propulsion Laboratory)
Text: Riri Ayae