December 10, 2012 - A giant asteroid
is set to buzz Earth
next week, and astronomers are already keeping their eyes on the skiesâ€”but not because 4179 Toutatis
poses any danger.
Toutatis, at 2.7 miles (4.46 kilometers) long and 1.5 miles (2.4 kilometers) wide, is one of the largest asteroids that comes anywhere near Earth. But only an astronomer would consider its closest approach to be "near." When the peanut-shaped rock is at its closest to the Earth
on December 12, it'll be more than 4.3 million miles (6.9 million kilometers) away, or more than 18 times the distance from the Earth
to the moon.
So why are astronomers eagerly awaiting Toutatis? By figuring out what the asteroid is made of, they'll have a better picture of the early days of the solar system. And by refining a model of the asteroid's rotation, they'll get a better idea of its composition.
Michael Busch, a fellow at the National Radio Astronomy Observatory, studied radar images of Toutatis' previous passesâ€”the asteroid approaches Earth
every four yearsâ€”to try to figure out how it was moving through space. "It's tumbling," Busch
said. "It's spinning around its long axis, while that in turn is precessing around in a circle, like a gyroscope." Busch and his colleagues were hoping to use radar images taken in 2000, 2004, and 2008 to update a 1996 model of Toutatis' spin state. "[But] this became more complicated when we understood that [gravitational] tides were changing the spin," he said.
Every time Toutatis came close to the sun or the Earth, gravity would tug slightly on the asteroid, changing its spin by a tiny fraction. But over the years, those tugs added up. Once Busch and his collaborators were able to account for these changes, they had a much better model of its spin. And that told them how the asteroid's mass was distributed.
Toutatis is shaped sort of like a lumpy peanut, or from some angles, like a poorly built snowman. It's long and narrow, with two distinct lobes, one smaller than the other.