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By Ken Croswell
Published in New Scientist (September 1, 2010)
Somersaulting stars could explain why some planets orbit backward.
Planets tend to form in a disk that surrounds their star's equator, and orbit the star in the same direction as its spin. But recently, astronomers have found about ten stars that host planets in tilted orbits--some so extreme that the planets travel backward. Some researchers suspected that gravitational encounters with other planets or a distant star were to blame.
Now Dong Lai at Cornell University in Ithaca, New York, and his colleagues say there is no need to invoke such violence. The researchers calculate that a newborn star's magnetic field interacts with its planet-forming disk, which is electrically conducting, causing the star to tilt and in some cases flip over.
It is not clear how common the process might be, or how many of the unusual orbits it could explain. But it "might have happened in our solar system", says Lai. Earth's orbit is at an angle of 7.2 degrees to the solar equator, suggesting that the young Sun may have tipped a bit.
Ken Croswell is an astronomer and the author of Magnificent Universe and The Lives of Stars.
"Magnificent Universe by Ken Croswell is elegant and eloquent."--Washington Post. See all reviews of Magnificent Universe here.
"A stellar picture of what we know or guess about those distant lights."--Kirkus. See all reviews of The Lives of Stars here.
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