Yet another reminder of the dangers to which the Earth is subjected every day has been brought to our attention by the Arecibo Radio Observatory and the Massachusetts Institute of Technology's LINEAR search program which discovered earlier this year an asteroid expected to make a fly-by around Earth sometime today. 2008 BT18 is a binary asteroid about 600 and 200 meters across respectively and will come as close to Earth as 2 million kilometers, six times the distance between the Moon and our planet.

As you might have probably realized by now, the newly found pair poses no danger to our planet for now, although since the orbit of the two hasn't been established yet they could end up heading our way somewhere in the future. Not only do the newly found asteroids add up to the already long list of big rocks that could one day crash into Earth, but the deflection of a binary asteroid is even more troublesome than in the case of single objects.

"Observations clearly show two objects," said Lance Benner of NASA's Jet Propulsion Laboratory regarding the radar images taken on July 6 and 7 by the Arecibo Observatory. Although not much is known about the density, shapes and orbit of the pair, researchers have been able to establish that the bigger asteroid rotates about its axis in roughly 3 hours.

Binary asteroids are quite common in the solar system, mostly because asteroids are often composed of multiple chunks of rock held loosely together. Researchers have recently created a model through which they explained how binary asteroids may be formed under the influence of sunlight alone, which determines them to spin and break up due to centrifugal forces.

About 15 percent of all asteroids ejected from the asteroid belt and passing through the vicinity of Earth are in binary systems, although not many come so close to our planet as 2008 BT18 will.

Because its orbit hasn't been predicted yet, NASA classified it as "potentially hazardous" until further observations are available. Meanwhile, asteroid Apophis, considered in 2004 as the biggest threat to our planet, is expected to pass by Earth in 2029, during which time its orbit will be significantly altered. Nevertheless, the next encounter in 2036 could still end up in disaster, although the chances of this happening are minor.