Uranus is a crooked side, the only planet turning on its side. Scientists now believe that they know how it came about: it was pushed by a rock at least twice the size of the earth.
Detailed computer simulations show that a massive rock fell from the sun into the seventh planet, said Durham University astronomy researcher Jacob Kegerreis, who presented his analysis this month at a major Earth and Space science conference.
Uranus is unique to the solar system. The mighty planet, like its five largest moons, leans about 90 degrees on its side. His magnetic field is also one-sided and does not look like ours, says NASA chief scientist Jim Green. It is also the only planet whose inner heat can not escape from the nucleus. It has rings like Saturn, though weak ones.
"It's very strange," said Carnegie Institutional Scientist Scott Sheppard, who did not participate in the research.
The computer simulations show that Uranus collides and transforms "Maybe the whole stone that he hit enveloped ̵
It's also possible that the large object that overturned Uranus is still lurking in the Solar System for us to see, Green said. He would explain some of the planet's orbits and fit the theory that a missing Planet X orbits the Sun far beyond Pluto, he said.
Green said it is possible that many smaller space rocks – the size of Pluto – rock – has precipitated Uranus, but Kegerreis & Research and Sheppard point to a single unknown suspect. Green said a single impact was "right thinking".
The collision occurred 3 to 4 billion years ago, probably before the larger moons of Uranus had formed. Instead, there was a disk with things that merged into moons. And when this happened, Uranus's unusual inclination behaved like a gravitational tidal force pushing those five great moons to the same slope, Kegerreis said.
It would also have created an icy shell that kept Uranus' inner heat trapped, Kegerreis said. (The surface of Uranus is minus 357 degrees or minus 216 degrees Celsius.)
Ice is the key to Uranus and its neighbor Neptune. Just over a decade ago, NASA classified these two planets as "ice giants," which they no longer associate with the other major planets of the solar system, the gas giants Saturn and Jupiter. Pluto, a little further from the sun and not even officially a planet anymore, was explored more than Uranus and Neptune. They received only brief fly-bys from Voyager 2, the spacecraft that had entered interstellar space last month.
Uranus and Neptune "are definitely the least understood planets," said Sheppard.
But that can change. A robotic probe for one or both of these planets has topped the last wish-list of leading planetary researchers, and is likely to be at the top of the list.
Uranus was named after the Greek god of the sky. Her name often creates youthful humor when mispronounced like a body part. (It is rightly pronounced YUR-uh-nus.)
"Nobody laughs when I say Uranus," Green told NASA. "You must say it wrong to get the giggle."
The "cataclysmic" collision shaped the development of Uranus