Uranus experienced ancient collision

Ancient impact is likely responsible for Uranus's unusual axial tilt, magnetic field, and temperature.
By Laurel Kornfeld | Nov 19, 2018
Uranus's unusual axial tilt and other unusual characteristics are the result of an ancient impact by a planet twice the size of Earth.

The ice giant has an axial tilt of 98 degrees to the plane of its orbit, meaning it practically spins on its side. Its other anomalies include an unusual magnetic field and temperatures much colder than they should be at the planet's distance from the Sun.

To test the collision theory, which is not new, a team of scientists led by Jacob Kegerreis of Durham University's Institute for Computational Cosmology in the UK, ran simulations of hypothetical collisions of massive objects with Uranus using a high-powered supercomputer.

These simulations confirmed that a massive object composed of rock and ice hit Uranus about four billion years ago, causing the planet's extreme axial tilt.

According to Kegerreis, an impact is "pretty much the only way" Uranus could have this type of orbital inclination.

"We ran more than 50 impact scenarios using a high-powered supercomputer to see if we could recreate the conditions that shaped the planet's evolution," he stated.

Collisions between planets and proto-planets were common in the early years of the solar system, while it was still forming.

"All the evidence points to giant impacts being frequent during planet formation, and with this kind of research, we are now gaining more insight into their effect on potentially habitable exoplanets," said Luis Teodoro of BAER/NASA Ames Research Center.

Based on the fact that Uranus did not lose its atmosphere as a result of the impact, the researchers believe the planet was grazed by the impactor rather than hit head on.

While the impact was powerful enough to knock the planet on its side, it was not strong enough to influence its atmosphere.

Data from the simulation indicates debris in the form of rock and ice produced by the impact could have altered the rotations of existing Uranian moons as well as coalesced to form additional moons.

Some impact debris may have formed a thin shell around the planet that traps heat coming from its core. This could be the reason Uranus's outer atmosphere has such cold temperatures.

Within the planet, the impact may have produced molten ice and rock that altered its magnetic field.

A paper on the study has been published in The Astrophysical Journal.

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