Asteroid that flew past Earth has its own mini moon

The first radar images of a huge asteroid that safely flew past Earth show that the space rock has its own small moon, NASA scientists say.

The asteroid 2004 BL86 made its closest approach on January 26 at a distance of about 1.2 million kilometres, or three times the distance from Earth to the Moon.

Scientists working with NASA's 70-metre Deep Space Network antenna at Goldstone, California have released 20 images of the asteroid.

The images show the primary body is approximately 325 metres across and has a small moon approximately 70 metres across.

In the near-Earth population, about 16 per cent of asteroids that are about 200 metres or larger are a binary (the primary asteroid with a smaller asteroid moon orbiting it) or even triple systems (two moons).

The trajectory of asteroid 2004 BL86 is well understood, researchers said. The flyby was the closest approach the asteroid will make to Earth for at least the next two centuries.

It is also the closest a known asteroid this size will come to Earth until asteroid 1999 AN10 flies past our planet in 2027.

Asteroid 2004 BL86 was discovered on January 30, 2004, by the Lincoln Near-Earth Asteroid Research survey in White Sands, New Mexico.

Image: Pictures of asteroid 2004 BL86 were captured by NASA's Deep Space Network antenna at Goldstone, California. Photograph: NASA