Why does Earth's orbit tilt? Scientists finally think they know

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Jan 14, 2013, 1:38 PM EST

It's an enduring puzzle that's had astronomers and astrophysicists scratching their heads for years: Why does the Earth tilt? Our planet orbits with a slight (7-degree) angle relative to the sun, and we've never been able to figure out why, but now one scientist thinks he's got our planet's crooked spin solved.

When astronomers discovered a "hot Jupiter," a gas giant planet orbiting very close to its star, in 1995, they were baffled. Gas giants don't normally behave that way (or so they thought), so to explain this hot Jupiter's proximity to its star the theory of "disk migration" was developed. The theory goes that planets form farther away from their stars but then migrate inward until they reach the protoplanetary disk of gases surrounding the star. Once inside the disk, the planet begins to match the star's orbit.

But that theory was called into question four years ago when astronomers began discovering more hot Jupiters that were just as close to their stars but orbiting in very different ways. These planets orbited at odd angles, and some even orbited backward relative to their stars. Clearly the disk migration theory wasn't making sense anymore.

Some astronomers explained these oddly tilted orbits as the result of other planets pushing the hot Jupiters toward their stars, but Konstantin Batygin of the Harvard-Smithsonian Center for Astrophysics has a different idea.

"Misaligned orbits are actually a natural outcome of disk migration--once you take into account the fact that planetary systems are usually born in multistellar environments," Batygin said.

If a planet is born in a system with two stars, the second star can cause it to spiral in and tilt. The second star might eventually migrate away, but the orbit of the planet stays the same. According to Batygin, that's what happened to Earth.

"I think somewhere in the Milky Way, there's a star that's responsible for tilting us," he said.

Batygin's theory seems sound, but it still has to be tested, and Batygin hopes to confirm it with measurements of a system that still has multiple stars: Alpha Centauri. By measuring the alignments of each of Alpha Centauri's three stars, Batygin hopes to confirm that neighboring stars can tilt each other's protoplanetary disks, which would in turn affect the orbits of any planets in the area.

There's a good chance that astronomers will find misalignment in the Alpha Centauri system," he said.

So, if Batygin is right, he's just solved yet another of Earth's cosmic mysteries.

(Via Huffington Post)

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