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Potentially Hazardous Potato?
PHA (Potentially Hazardous Asteroid) 4179Imagine a potato 5km long and 2km wide hurling though space like a badly thrown football. Now imagine that spud crashing into your backyard and decimating the planet with the combined energy of millions of atomic bombs. Such a collision would destroy most of life on Earth. Any surviving cockroaches would be mighty pleased, however.

The space spud is PHA (Potentially Hazardous Asteroid) 4179. French scientists discovered the asteriod in 1989 and named it Toutatis after the Gaulish god of Thunder and Destruction. Toutatis' peculiar shape, wobbly rotation and wacky orbit make it unique among the near-Earth asteroids whizzing around our blue planet. Scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., study these space rocks with radar.

Radar astronomy is not passive measurement of reflected light or radiation, but a transmitted signal aimed at a targeted object by a scientist. By comparing the echo to the transmission, astronomers generate radar images that reveal the asteroid's topology, orbit and rotation. This element of human control, from designing the time/frequency of the radar to hitting the target millions of miles away, makes radar astronomy unlike nearly every other astronomical technique; it's an experiment. Radar images like this one of Toutatis are the result of combined and modeled data from two distinct elements of the echoed transmission: time delay (range) and Doppler frequency (line-of-sight velocity).

So what has radar astronomy told scientists about PHA 4179? Scientists aren't sure how Toutatis got its funny shape. Part of the asteroid may have been chipped away by impacts with other asteroids, or it might actually be that a would-be sculptor asteroid collided with Toutatis and stayed put. The asteroid's peculiar rotation comes from its spinning around two axes: one for a period of 5.4 Earth-days and the other for 7.3 days. The result is an asteroid that travels through space tumbling like a wobbly pass.

Orbit-altering experiences with planets Earth, Mars, Venus and Jupiter, as well as the Sun, make Toutatis consistently inconsistent, passing closer or farther to larger bodies as gravity wills. On its most recent visit, October 31, 2000, Toutatis passed within less than 29 lunar distances of earth (a lunar distance is the average distance from Earth to Moon: 384,400 km). When Toutatis is next in the neighborhood (galactically speaking), on Sept. 29, 2004, it will pass just 4 lunar distances from Earth. The asteroid will be the brightest it's ever been and easy to see through binoculars.

Mpeg movie courtesy Scott Hudson. View the mpeg movie now at NASA.

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