Analysis Of The Tilting Uranus Hypothesis Variations

Uranus is the seventh planet from the sun in our solar system. The planet has been named after the Greek god of the sky. It is similar in composition to Neptune. It is also known as an ice giant. Its atmosphere is similar to those of gas giants’, composed of hydrogen and helium. Unlike the gas giants’ atmosphere, Uranus’ atmosphere contains more ices such as water, ammonia, and methane, along with traces of other hydrocarbons. It is the coldest planet in the solar system. Like the other giant planets, Uranus has a ring, a magnetosphere, and numerous moons. It has an axial tilt of 97.77 degrees. Wait, what? 97.77 degrees! Doesn’t that sound weird? You might be wondering why.

While most of the planets in our solar system spin in the anti-clockwise direction, Uranus whirls in the clockwise direction when viewed from the top. The leading hypothesis for this mystifying occurrence is that a body of exorbitant size might have smacked into Uranus a long time back, knocking it off from its original axial tilt.

Although this sounds convincing, there are significant holes in this model. However, astronomers at the University of Maryland have come up with a hypothesis that neatly overcomes these loopholes. As per this hypothesis, Uranus could have been tilted by its giant ring system. No doubt, you might be thinking whether Uranus has a giant ring system. It doesn’t have a giant ring system now; however, it might have had a giant ring system a long time back. Presently, its rings are faint when compared with Saturn’s rings.

Recent evidence from Cassini found that rings are temporary systems, so it is plausible to take into consideration the existence of an extensive ring system sometime in the 4.5-billion-year history of Uranus. The problem with the smacked upside model is that the spin period of Uranus is similar to that of the Neptune, which implies that the two planets were born together. The probability of similar spin periods becomes much lower if we factor in one or more impacts large enough to tip Uranus sideways. Additionally, the impact would have disrupted and destabilized Uranus’ satellite system. As per the present scenario, we, however, don’t see this at all. The satellite system of Uranus is similar to the Galilean moons.

Moreover, Uranus’ moons are icy. If a large impact would have taken place in the past, the impact would have generated enough heat to vaporize ice on these moons, but that is not the case again. However, all of these problems are solved if we incorporate a giant ring system capable of causing it to wobble on its axis like a spinning top, according to the astronomers Zeeve Rogoszinski and Douglas Hamilton of the University of Maryland. This phenomenon is known as precession. If this precession aligns with the planet’s orbital precession, a phenomenon in which the planet’s orbit slowly shifts its position around the sun, a large axial tilt is generated. This alignment between the planet’s precession and the orbit’s precession is known as secular spin-orbital resonance.

It's thought that resonance of this type could have introduced an axial tilt in Saturn greater than that of Jupiter, for example. This phenomenon has been explored with Uranus too; however, in the presence of a hypothetical ninth planet, which was discarded as extremely unlikely. Rogoszinski and Hamilton propose that a large disc could be able to solve this problem. They simulated both Uranus and Neptune with large disks to see how they interact with the planets. What they found out was that a large disc of material accreting onto the planet, which is a part of a giant planet’s formation process, was the best fit. Although this model was the best of all the others, it still couldn’t satisfy the reason behind the axial tilt. Over a million years, it only produced a 70-degree tilt, which means there's life in the big boom theory yet.

However, impacting rocks required to push Uranus the rest of the way over would be much smaller, therefore more likely. “Although we can generate tilts greater than 70 degrees only rarely and cannot drive tilts beyond 90 degrees, a subsequent collision with an object about half the mass of Earth could tilt Uranus from 70 to 98 degrees,' the researchers wrote in their paper. As of now, these are just hypotheses. The reason behind the axial tilt of Uranus is still uncertain. Whatever would have had happened might have been wild.