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On Monday, the Earth survived a close encounter with a very large asteroid. If you think that a massive rock hurtling through space close to Earth is terrifying, be comforted that in this case, close is still 1.2 million kilometres away.

At this distance the enormous asteroid seems rather lovely for a lump of rock, especially as it has its own tiny moon.

A close encounter

On Monday 26 January the asteroid, called 2004 BL86, was at its closest to Earth. You could even see it with a pair of good binoculars if you were in the right place at the right time.

As it sped by, researchers took images that revealed the asteroid is 325 meters across, making it larger than even the biggest stadiums, such as the Melbourne Cricket Ground. Its tiny moon is a mere 70 meters across.

Monday’s flyby was the closest approach the asteroid will make to Earth for at least 200 years. The next time another massive asteroid will come close to Earth won’t be until 2027, when an asteroid called 1999 AN10 flies past.

An asteroid with a moon

This flyby gave us a chance to learn more about asteroids. It turns out that it’s not so strange for an asteroid to have a moon. Around 16 per cent of near-Earth asteroids that are larger than 200 meters have one or two moons.

Don Yeomans from NASA’s Near Earth Object Program was particularly excited about the encounter. “Asteroids are something special. Not only did asteroids provide Earth with the building blocks of life, and much of its water, but in the future, they will become valuable resources for mineral ores and other vital natural resources,” says Don.

“They will also become the fuelling stops for humanity as we continue to explore our solar system. There is something about asteroids that makes me want to look up.”

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