A massive asteroid that whizzed past the Earth last month belongs to an entirely new category of space rock, latest radar images have shown.

Asteroid 1998 QE2 and its moon sailed within 5.8 million kilometres of Earth on May 31, making their closest approach to our planet for at least the next 200 years.

Researchers say new radar images captured by the Arecibo Observatory in Puerto Rico are revealing just how unique this binary asteroid is, SPACE.com reported.

“Asteroid QE2 is dark, red, and primitive -- that is, it hasn’t been heated or melted as much as other asteroids,” Arecibo’s Ellen Howell said in a statement.

“QE2 is nothing like any asteroid we’ve visited with a spacecraft, or plan to, or that we have meteorites from. It’s an entirely new beast in the menagerie of asteroids near Earth,” Howell said.

The 305 meters Arecibo dish and NASA’s 70 metre Deep Space Network antenna in Goldstone, California, tracked 1998 QE2 as it approached Earth, then kept following the near-Earth asteroid as it receded into the depths of space.

The resulting images helped researchers take 1998 QE2’s measure. The dark, cratered main asteroid is 3 km wide, and it has a 750 metre moon that orbits it once every 32 hours.

“QE2’s moon is roughly one-quarter the size of the main asteroid,” Patrick Taylor, also of Arecibo, said in a statement.

Researchers said studying the moon of the asteroid and its orbit should help scientists determine the mass of the main asteroid, which in turn will shed light on the composition of the rock.

Scientists said although there was no danger of 1998 QE2 hitting Earth during last month’s flyby, however, if it had hit us, the damage would have been severe.

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