Prize offered to tag an asteroid

A $50,000 (£25,000) competition has been launched to find the best way to tag a 400m-wide asteroid.
The Apophis space rock is set to make a close pass of Earth in 2029 and scientists would like to confirm that it poses no danger to our world.
The Planetary Society will give a prize to the designers of a mission that would allow the huge asteroid's orbit to be tracked with the most precision.
The competition has support from the US and European space agencies.

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