Every year, thousands of decent-sized chunks of rock hurtle past — and often into — the Earth. Of the ones that do hit, most burn up leaving a pretty trail. Occasionally, a bigger one explodes with a boom that shatters windows. More rarely, a big one wipes leaves a large smoking crater and widespread local destruction. Then there was that huge one that devestated the planet, wiping out the dinosaurs. Wouldn't want one of those again/ Fortunately, loads of astronomers are watching the skies to spot any asteroids getting too close for comfort. But what if they find one — what do we do about it? This month, a small spacecraft called DART began its mission to crash into a distant asteroid, to see if maybe we can shift it's orbit a little. It's a test, for sometime in the future, when we might need to do that for real, to save the planel.