SPACE.com -- Moon-like Asteroid to Make Close Earth Approach

Earths New Travelling Companion: Quasi-Satellite Discovered

Moon Holds Earth's Ancient Secrets

Tally of Asteroids Harboring Moons Grows Beyond 30

New Study Downplays Risk of Killer Asteroids Hitting Earth


	Moon-like Asteroid to Make Close Earth Approach By SPACE.com Staff posted: 07:00 am ET 03 January 2003

Headline:

An asteroid that behaves something like a second Moon to Earth will make its closest approach to our planet next week before shuttling back into deep space for nearly a century.

The space rock is about 200 feet (60 meters) across and never gets as close as the real Moon. Scientists say there is no chance it will hit Earth anytime in the foreseeable future.

First reported in October and named 2002 AA29, the asteroid moves in a horseshoe-like pattern around Earth, inhabiting the same region of space through which the planet travels. It is under the gravitational influence of both Earth and the Sun, sometimes leading Earth around the Sun and sometimes lagging behind during Earth's annual trek.

"In some ways, the Earth and this asteroid are like two racecars on a circular track," said Paul Chodas, a researcher at NASA's Propulsion Laboratory, in a statement released today by NASA. "Right now the asteroid is on a slightly slower track just outside Earth's, and our planet is catching up."

On Wednesday, Jan. 8, the rock will be about 3.7 million miles (5.9 million kilometers) from Earth. The Moon, Earth's only true natural satellite, is a mere 238,900 miles (384,402 kilometers) away.

"Unlike racecars, the two bodies will not pass when they approach each other," Chodas said. "Instead, the combined gravitational effects of the Earth and Sun will nudge the asteroid onto a slightly faster track just inside Earth's, and it will begin to pull ahead."

In 95 years, the asteroid will have advanced all the way around to where it is catching up to the Earth from behind. A similar interaction will then push the asteroid back onto a slower outside track, and the pattern will repeat.

In about 600 years, the asteroid may begin looping around Earth like a tiny, distant quasi-moon.

"The asteroid will appear to orbit the Earth at that time, but in fact it will be too far away to be considered a true satellite of our planet," Chodas said. "Our calculations indicate the space rock will circle the Earth as a quasi-satellite for about 40 years before resuming its horseshoe orbital pattern."

Earth's gravity keeps the asteroid at bay, said Don Yeomans, JPL manager of NASA's Near Earth Objects Program Office. "The asteroid and Earth take turns sneaking up on each other, but they never get too close," Yeomans said.