It is 2.7 kilometres long. Its surface is covered in a sticky black substance similar to the gunk at the bottom of a barbecue. If it hit Earth it would probably result in global extinction. Good thing it is just making a flyby. Asteroid 1998 QE2 will make its closest pass to Earth at 4.59 am Hong Kong time on June 1. Scientists are not sure where this unusually large space rock, which was discovered 15 years ago, originated. But the mysterious sooty substance on its surface could indicate it may be a result of a comet that flew too close to the sun, said Amy Mainzer, who tracks near-Earth objects at Jet Propulsion Laboratory in La Canada Flintridge, California. It might also have leaked out of the asteroid belt between the orbits of Mars and Jupiter, she said. We will know more after the asteroid zips closer to Earth and scientists using the Deep Space Network antenna in Goldstone, California, and the Arecibo Observatory in Puerto Rico can get a better look at it. At its closest approach the asteroid will still be 5.8 million km from our planet (about 15 times the distance between the Earth and the moon), but it will be close enough for these powerful radar antennas to see features as small as 12 feet across. "With radar we can transform an object from a point of light into a small world with its own characteristics," Lance Benner, JPL's principal investigator for Goldstone radar observations, said. There is no chance that asteroid 1998 QE2 could collide with Earth this go-around. Its next close approach will be in 2119.