The Most Worrying Asteroid Is Bennu, Which Is 250 Metres Across

We think we've got a complete catalogue of all of those that are, that size that might cross the Earth's orbit. The most worrying one is something called Bennu, which is 250 metres across. But as long as you don't have plans for the year 2178, we don't have to worry about the big things. We're building a telescope down in the Chilean Atacama Desert - it's as big as some of the biggest telescopes today. It will scan the whole sky every three nights, partly to look for moving things.