A so-called "mystery" object heading for a close encounter with Earth has turned out to be not so mysterious after all: Astronomers say it is a plain old asteroid, about the size of a delivery truck, one of many that buzz past the planet every couple of days.
After the object was first spotted by telescope Nov. 6 by a University of Arizona scientist, astronomers speculated that it might be a piece of a 20-year-old Apollo moon rocket or a scrap from a cloak-and-dagger space launch.
But Diane Ainsworth, a spokeswoman for the Jet Propulsion Laboratory in Pasadena, Calif., said yesterday that astronomers concluded late Monday that the object, the smallest yet sighted approaching Earth, "was definitely not a piece of space junk." The orbit was not consistent with an Earth launch, she said.
"This is probably a tiny asteroid that's orbiting the sun in a period of just over one year," she said. "There are probably hundreds of thousands of these small objects at least 10 yards in size orbiting the sun and passing close to Earth."
The asteroid, named 1991VG, is about 10 yards in length, she said, and will pass within about 288,000 miles of Earth tomorrow at 4:45 a.m. At its closest point, it will be just outside the moon's orbit.
Ms. Ainsworth noted that some reports called it a "mystery" object. But she said, "This type of Earth approach is not an unusual event." As telescopes become more sophisticated, she said, astronomers are able to spot and track smaller and smaller bits of space debris.
Concerned about the possibility that a larger asteroid -- perhaps a mile wide -- might someday strike Earth, the National Aeronautics and Space Administration is studying plans to track and deflect them. The concern has grown out of scientific studies suggesting that the impact of large asteroids on Earth throughout its history has caused catastrophic changes, possibly including the extinction of the dinosaurs.