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What Are Asteroids?

Asteroids are rocky objects that orbit the Sun, and there are millions of them whizzing around in our solar system. They vary greatly in size, from large pebbles to huge chunks of rock, several kilometres across. Most are located hundreds of millions of kilometres away, in an area between Mars and Jupiter called the asteroid belt. Some, however, move around the Sun in a way that can occasionally bring them closer to Earth – much, much closer, in the case of asteroid 2017 AG13.

It was first spotted on January 7th by the telescopes of the Catalina Sky Survey – a project based at the University of Arizona, USA, that is constantly on the lookout for any asteroids or other space objects headed in Earth’s direction. An asteroid with an orbit that will bring it close to our planet is known as a Near Earth Object, or NEO.

Hundreds of new NEOs are discovered every year, and once identified, scientists can keep a close eye on them. What’s unusual in this case, however, is how close the asteroid got before anyone noticed. Just two days later, the asteroid shot past our planet at a speed of around 16 kilometres a second, coming closer than the distance that separates us from the Moon. That makes this a very near miss indeed!

Experts have compared 2017 AG13’s shape to a stretched-out rubber band, and estimate it was between 15 and 33 metres long. That’s a similar size to the asteroid that exploded over the city of Chelyabinsk in Russia, back in 2013. The Chelyabinsk asteroid burned up high in the atmosphere, around 25 kilometres above ground level, but the explosion was still powerful enough to damage buildings and cause injuries. Luckily, events like this are rare, and the risk of another dangerous impact is very low. Most of the time, the asteroids either miss us by tens of millions of kilometres, or are so small they burn up harmlessly in the atmosphere. When this happens, they’re known as shooting stars!

NASA and other space agencies are also working on new technology that could potentially be used to move dangerous asteroids out of the way in future. In the meantime, they’ll continue using telescopes to find as many Near Earth Objects as possible, trying to ensure that next time one passes by, it doesn’t take everyone by surprise!

Watch What are asteroids? to learn more about near-Earth objects.