Three years after hundreds of webcams captured a 19m-wide space rock exploding over a Russian city, damaging hundreds of buildings and injuring nearly 1500 people, scientists are no nearer to figuring out just where it came from.

At the time, on February 15, 2013, scientists were busy monitoring the approach of another, bigger asteroid, when suddenly a fireball meteor brighter than the sun entered the atmosphere above Chelyabinsk, causing a huge shockwave and an explosive spectacle. Since then, more than 200 research papers have been published - 50 in the past year - but finding the parent rock that it broke off has been a tough job.

The key appears to be calculating its precise speed as it touched the top of the atmosphere, which would help determine the orbit of whatever launched it.

The meteor appears to have come from the Apollo group of nearly 7000 near-Earth asteroids. But which one launched it is a mystery.

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