[Homestead] Wednesday - look out for it :
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Mon Sep 27 18:05:48 EDT 2004
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Asteroid Close Encounter Coming Wednesday
for National Geographic News
September 24, 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 on Wednesday.
"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.
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.
So is there any chance that Toutatis may hit Earth in the future?
"The answer is obviously, yes," Ostro said. "There's a good chance [of Earth impact] in the next several tens of millions of years. But you could make that statement about any one of the near-Earth asteroids."
Despite NASA's assurances that Toutatis poses no immediate threat of impacting Earth on Wednesday, doomsday predictions spreading via chain e-mail earlier this year put the chances of impact at 63 percent.
Alan MacRobert, senior editor for Sky and Telescope magazine, noted in a recent article for the magazine that while such doomsday predictions are false, Toutatis does whiz close enough to Earth to make a "fine observing challenge for telescope users."
The best opportunity for Northern Hemisphere viewers using at least a four-inch (ten-centimeter) telescope will be a few days prior to the asteroid's closest approach, when Toutatis will cross the southern portion of the constellation Capricornus.
MacRobert writes that on the night of its closest approach, the asteroid will be visible from the Southern Hemisphere, where it will pass within one degree of the star Alpha Centauri.
Early next month Ostro and his colleagues will make additional radar observations of Toutatis using the Arecibo telescope in Puerto Rico. Their main goal is to determine the asteroid's mass using an experiment based on the Yarkovsky effect.
The Yarkovsky effect is a force produced by the manner in which an asteroid absorbs energy from the sun and reradiates it into space as heat. "If we can model the force adequately, then we can [determine Toutatis's] mass by analyzing very precise radar measurements," Ostro said.
Measuring the asteroid's Yarkovsky effect will also help astronomers to better refine their predictions of the asteroid's orbit. With that information, scientists can calculate if, and/or when, Toutatis poses a real risk of impacting Earth.
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