Asteroid Close Encounter Today

John Roach
for National Geographic News
Updated September 29, 2004

Tumbling through space like a fumbled football, a peanut-shaped asteroid named 4179 Toutatis is expected to pass within a million miles (1.6 million kilometers) of Earth today.

"The September 29 … approach is the closest in this century of any known asteroid at least as big as Toutatis," said Steven Ostro, who studies asteroids at NASA's Jet Propulsion Laboratory in Pasadena, California.

Radar images of the three-mile-long (4.6-kilometer-long) asteroid suggest it could be composed of two or three space rocks held together by gravity. But to know for sure would require drilling through the object, Ostro said.

Toutatis makes an elliptical four-year trek around the sun that takes it from just inside Earth's orbital path to the asteroid belt between Mars and Jupiter.

Scientists say the asteroid also has one of the strangest rotation states yet observed in the solar system. Instead of spinning on a single axis—as do most asteroids and the planets, including our own—Toutatis wobbles around two.

The asteroid rotates around one axis once every 5.4 Earth days and, in turn, rotates around the other axis once every 7.3 Earth days. As such, "the orientation of the asteroid never repeats exactly," Ostro said.

Impact Risk?

French astronomer Christian Pollas discovered Toutatis in 1989 as he was examining photographic plates of Jupiter's faint satellites.

Pollas named the asteroid after a Celtic god whose name is invoked in the hugely popular French comic book series Asterix. (Toutatis is the protector of Asterix and his companions, who fear nothing except that the sky may someday fall on their heads.)

Ostro and his colleagues have studied the orbit of Toutatis more closely than any other known near-Earth object its size. The scientists say with confidence that the asteroid poses no risk of impacting Earth at least through 2562, when Toutatis will pass within 250,000 miles (400,000 kilometers) of Earth.

"We can't see the future beyond that close approach, and we must know exactly how close it will be to [project] the orbit out further [in time]," Ostro said.

Continued on Next Page >>


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