‘Cataclysmic collision’: Uranus hit mystery star twice the size of Earth 4bn yrs ago

The freezing atmosphere and warped axis of Uranus was likely formed when the ice giant was involved in a “cataclysmic collision” with a massive object twice the size of Earth.

The seventh planet from the sun, which spins bizarrely on its side, is the only celestial world in the Solar System with such a pronounced tilt. Largely made up of hydrogen and helium gas, the almost-rolling planet has no solid surface and temperatures within its atmosphere are as low as -216 degrees celsius.

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Scientists now believe it’s likely that a 4-billion-year-old smash between Uranus and a giant star or asteroid set in place the conditions for the planet’s striking features. It could be the reason for the swirling icy mantle which surrounds the planet, as well as the dust found in Uranus’ set of rings.  

Using a series of high-resolution computer simulations, astronomers at Durham University have come to the conclusion that only a collision with a massive object could have pushed Uranus’s axis so far on its side.

Jacob Kegerreis, lead author of the new study in the Astrophysical Journal, indicated that while all evidence suggests a collision, the exact circumstances remain a mystery that might not be fully solved.

“This was almost certainly caused by a giant impact, but we know very little about how this actually happened and how else such a violent event affected the planet,” he said.

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The international team of experts ran more than 50 different impact scenarios into a “supercomputer” to figure out if it could have formed the conditions that shaped Uranus’s evolution. It concluded that a glancing-but-violent strike could have provided the conditions currently witnessed on the planet without sending it hurtling into space.

“Our findings confirm that the most likely outcome was that the young Uranus was involved in a cataclysmic collision with an object twice the mass of Earth, if not larger, knocking it on its side and setting in process the events that helped create the planet we see today,” Kegerreis explained.

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