Weird celestial mechanics.

There are several mysteries about the solar system, but one of the biggest was how Neptune and Uranus formed. Where’d they get so much material, way out there at the furthest reaches of the solar system?

Four billion years ago, Uranus and Neptune switched places during a gentle ride out to their current orbits.

That’s the conclusion of Steve Desch, an astrophysicist at Arizona State University, who thinks that all of the gas giant planets took shape twice as close to the sun as they are at present. His work could cut out much of the mystery of how our “impossible” solar system formed.

The solar system is 4.6 billion years old. The formation of rocky planets, from collisions between ever-larger objects, is a fairly rock-solid theory. But how the outer giants developed remains an open question.

Desch, an astrophysicist at Arizona State University, thinks he knows.

To make our solar system work, Desch elaborated on the “Nice” model of planet formation that debuted in 2005. That theory suggests gassy planets formed about twice as close to the sun as they are now — which means our dusty solar nebula would have been four to 10 times denser than most models predict.

“My colleagues seem pretty shocked by my paper, but they’ve found nothing wrong with it,” Desch said. “Basically, I’m saying we have it all backwards: Planet-forming material had to have drifted outward, not in towards the sun.”

What are the scientific ramifications? [italics]”For Desch’s orbital math to jibe, however, Neptune had to have overtaken Uranus about 650 million years into the solar system’s evolution.”[/italics] Cool! Uranus and Neptune must have swapped orbits!

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