Uranus hit by huge object that tilted it to the side, scientists find

The violent impact might also explain why the planet is so cold

Uranus's strange climate and unusual tilt could be explained by an impact with a huge object, according to new research.

Scientists have long been puzzled over why the planet is shunted slightly over to its side. The new research could finally offer an answer, in a major collision with another object.

As well as explaining the planet's jaunty angle, the vast collision might also be the reason why Uranus came to have such freezing temperatures. And it could help us understand the mysterious exoplanets that are dotted throughout the universe and give hope for finding alien life.

Computer simulations showed that debris from the impact could have made a thin shell around the ice layer on the planet. That could have trapped the internal heat and led to the freezing conditions in the outer atmosphere, according to the research.

Most likely, the important collision happened about 4 billion years ago. Uranus probably hit a young proto-planet made of rock and ice, the researchers said.

The impact was probably only a glancing blow, with the object striking the Uranus's side and moving on into space. That would explain how the impact was enough to tip the planet, but not enough to destroy its atmosphere.

"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," said Lead author Jacob Kegerreis, a researcher in Durham University's Institute for Computational Cosmology.

"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."

The discovery could also help us understand exoplanets outside our own solar system. Uranus is similar to the most common type of exoplanets that we find, and so researchers hope they can use the discovery to understand more about how those other worlds evolved and what they might be made of.

“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 co-author Dr Luis Teodoro, of the BAERI/NASA Ames Research Center.