Uranus was hit by a huge icy planet during its formation

Hyperaxion Apr 8, 2020

After studying the moons of the planet, Japanese astronomers created a hypothesis about Uranus, a planet with several peculiarities and considered as the “weirdo” of the Solar System.

At some point in the history of our Solar System, Uranus was hit by an icy planet with a mass between one and three times that of Earth. That was the conclusion of a study conducted by astronomers at the Tokyo Institute of Technology, Japan, and published in late March on Nature Astronomy.

Uranus was hit by a huge icy planet during its formation.
Uranus was hit by a huge icy planet during its formation. (Credit: NASA).

For those who don’t know, Uranus is a rather peculiar planet. Unlike the other planets in the Solar System, the poles of the ice giant are not oriented perpendicular to the plane on which the planets rotate, but at a 98º angle. As Uranus transits around the Sun, it keeps its poles facing fixed points in relation to its orbit and, from our perspective, this gives the impression that the planet is “tilted” and “swaying”.

Like Saturn, Uranus has a ring system, as well as 27 moons that orbit the planet around its equator – and they also appear to be “tilted” and “swaying”. It was trying to understand the reason for all these peculiarities that Japanese researchers decided to investigate the planet.

Inclination of Uranus in comparison to the Earth
Inclination of Uranus in comparison to the Earth. (Credit: Youtube / Gooogolplex)

For this, they built a computer simulation of the formation of moons around icy planets. Since most bodies in the Solar System have their own satellites of different sizes, orbits and compositions, scientists believe that these moons can help explain how the planets formed.

For example, there is strong evidence that our Moon formed when a rocky object the size of Mars hit Earth almost 4.5 billion years ago. Therefore, when applying what is known about Uranus in the simulator, the scientists discovered that it must have been hit by an icy object with a mass between one and three times that of our planet.

Uranus rotation compared to the other planets in the Solar System.
Uranus rotation compared to the other planets in the Solar System. (Credit: Youtube / Dr. James O’Donoghue).

However, the ice giant is considerably further away from the Sun than we are, which suggests that the objects that impacted the two planets billions of years ago were quite different. Because it formed in a warmer region and closer to the star, the Earth is composed mainly of non-volatile elements, that is, elements that do not form gases at regular pressures and temperatures on the planet’s surface.

The most distant planets from the Sun, on the other hand, are largely composed of volatile elements, such as water and ammonia, that freeze at lower temperatures. This makes the result of impacts on these objects very different from that on planets like Earth. Astronomers speculate that, as water ice forms at low temperatures, debris from Uranus’ impact would have evaporated during the collision. As a result, the planet was “warped”, which also resulted in a period of rapid rotation (Uranus’ day is about 17 hours).

Illustration of Uranus's orbit around the sun. In the image, the yellow arrow indicates the north pole of the planet
Illustration of Uranus’s orbit around the sun. In the image, the yellow arrow indicates the north pole of the planet. (Credit: ELSI / Tokyo Institute of Technology).

In addition, the material resulting from the collision remained gaseous for a longer time, “collecting” the debris, which led to the enormous size of Uranus compared to its moons, considered small for the planet. “This model is the first to explain the configuration of Uranus’ moon system, and it may help explain the configurations of other icy planets in our solar system such as Neptune,” said Shigeru Ida, who led the research, in a statement.

Ida also believes that the model proposed by him and his team will help in the study of exoplanets. “The observations suggest that many of the newly discovered planets known as super-Earths in exoplanetary systems may consist largely of water ice, and this model can also be applied to these planets,” said the astronomer.

Related topics:

Solar System Uranus

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