U.S. astronomers reported on Thursday that they have for the first time acquired detailed images of a binary asteroid system, where two asteroids orbit around one another like Earth and Moon.

Presenting their findings at a meeting of the American Astronomical Society in Pasadena, California, the researchers said understanding the motion of the bizarre asteroid named 1999 KW4 would be important for the security of Earth.

The asteroid had been classified as a "potentially hazardous asteroid" because of the proximity of its orbit to Earth's orbit, but new observations excluded any chance of such collision within at least the next 1,000 years, the researchers said.

Two papers describing these findings also appeared in the Oct.12 online advance edition of the journal Science.

"The KW4 results have profound consequences for ideas about mitigation of the asteroid collision hazard," said Daniel Scheeres, lead author of one paper and an associated professor at the University of Michigan.

The radar images of asteroid 1999 KW4 were obtained in May 2001, when the asteroid passed 4.8 million kilometers from Earth, the researchers said. They mapped both its components by bouncing radar waves off their surfaces, and measuring the strength and lag time of the returning signal.

The main asteroid component, Alpha, is unconsolidated rubble and spins on its axis every 2.8 hours, and the smaller companion, Beta, is elongated and denser than Alpha, the researchers found.

The images also showed that Alpha is spinning in its orbit so fast that it has been flattened into a kind of flying saucer shape. Because of this, the mountainous region along the center of the asteroid actually forms the lowest part on the asteroid.

In fact, the asteroid is spinning so fast that the equatorial ridge is very close to lifting off the surface and spinning into space.

The binary asteroid may have originated from the disruption of a rubble-pile precursor asteroid, and was sent into a spin when it came particularly close to the Sun or Earth, the researchers suggested.

Of the 840 large near-Earth asteroids that have been discovered, 28 are binaries. Binary systems in general are common in space, including binary stars and planet-moon pairs.

Source: Xinhua