Object twice size of Earth hit Uranus and caused it to tilt

The planet Uranus was given its tilt after being hit in a "cataclysmic collision" by a massive object roughly twice the size of Earth, new research has suggested.

A study by researchers at Durham University believe that a collision in the planet's history left it rotating on a tilt - potentially explaining its freezing temperatures.

Uranus is unique among the solar system's planets for rotating on an axis set almost 90 degrees off of the sun's orbital plane, meaning its poles experience 42 years of continuous sunlight and darkness over the course of its orbit.

Running high-resolution computer simulations of different collisions with the ice giant, the team attempted to establish how the planet evolved.

Their work, published in The Astrophysical Journal, confirms a previous study which stated that its tilted position was most likley caused by a collision with a massive proto-planet made of rock and ice.

The collision is believed to have taken place during the formation of the solar system about four billion years ago.

According to the simulation, debris from the proto-planet probably forms a thin shell near the edge of the ice layer on the outside of Uranus - trapping the heat at its core.

The trapping of this internal heat might explain the extremely cold temperature of Uranus's outer atmosphere of -216 C (-357 F), according to the researchers.

The paper's lead author, Mr Jacob Kegerreis, a PhD researcher, said: "Uranus spins on its side, with its axis pointing almost at right angles to those of all the other planets in the solar system.

"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.

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

"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 to its side and setting in process the events that helped create the planet we see today."

Scientists have been puzzled as to how Uranus managed to retain any atmosphere at all after the violent collision, but the simulations have suggested an anwer.

A glancing glow, rather than a direct hit, would have been strong enough to create the planet's tilt, but Uranus would have retained the majority of its atmosphere.