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http://news.nationalgeographic.com/news/2004/09/0924_040924_asteroid_toutatis.html<http://news.nationalgeographic.com/news/2004/09/0924_040924_asteroid_toutatis.html>

Asteroid Close Encounter Coming Wednesday 

John Roach
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. 

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. 

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." 

Observing Toutatis 

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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