VASHINGTON – Uranus is an endless oddity, the only planet that revolves on its side. Scientists now think they know how it came about: a stone that is at least twice as big as the Earth is pushed.
Detailed computer simulations show that a huge rock collapsed on the seventh planet from the sun, said Jacob Kegerreis, a researcher at the University of Durham astronomy university, who presented his analysis at a major scientific conference on earth and space this month.
Uranus is unique in the solar system. The massive planet is tilted by about 90 degrees on its side, as well as its five largest months. His magnetic field is also turned around and does not come out of the poles like ours, NASA chief scientist Jim Green says. It is the only planet with no heat from the inside. It has rings like Saturn, though weak.
"It's very weird," said planetary scientist Carnegie Institution Scott Sheppard, who was not part of the research.
Computer simulations show that the collision and the transformation of Uranus – which may have affected some or all of the rocks that hit it – took place in a few hours, said Kegerreis. He produced an animation that shows the violent fall and its consequences.
It is also possible that the large object that ruined Uranus is still in the solar system too far to see it, said Green. It would explain some orbits of the planet and fit into the theory that the missing planet Ks circles the Sun far beyond Pluto, he said.
Green said that it is possible that many smaller space rocks – the size of Pluto – have led to Uranus, but Kegerreis's research and Sheppard point to one huge unknown suspect. Green said that one effect is "right thinking."
The collision occurred 3 billion to 4 billion years ago, probably before the larger months of Uranus. Instead, there was a disc of things that would ultimately merge to create months. And when this happened, Uran's weird tilt behaved like a gravitational tidal force that pushed those five big months to the same slope, Kegerreis said.
It would also create an ice sheet that kept the inner heat of Uranus, Kegerreis said. (Uran's surface is minus 357 degrees, or minus 216 Celsius.)
Ice is key to Uranus and his neighbor Neptune. Just over a decade ago, NASA reclassified these two planets as "ice giants", without hitting them with other large solar system planets, gas giants Saturn and Jupiter.
Pluto, which is tiny, away from the Sun and is no longer an official planet, has been explored more than Uranus and Neptune. They only received short leaflets from Voiager 2, a space probe that entered the interstellar space last month.
Uranus and Neptune are "definitely the least understood of the planets," Shepard said.
But that can change. A robotic probe for one or both planets was high on the last list of desires by top planetary scientists and is likely to be at or near the top of the next list.
Uranus was named after the Greek god of heaven. His name often creates juvenile humor when it is utterly mistaken as a part of the body. (That's rightly pronounced by IUR? -Uh-nus.)
"Nobody laughs when I say Uranus," said NASA's Green. "They must say it wrong to laugh."
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This Associated Press series was created in partnership with the Department of Scientific Education Hovard Hughes Medical Institute. AP is solely responsible for all content.