Radar plot of near-Earth asteroid Apophis. The tall spike shows the peak echo reflection from Apophis above background noise (low spikes). Initial calculations showed that there was a chance that it would strike Earth on its close approach on 13th April 2029. This radar study helped to show that it will miss Earth at that approach, but only by around 36,000 kilometres, the same distance at which geostationary satellites orbit Earth. The close approach may deflect it enough for it to collide with Earth at its next close approach in 2036. Apophis is 350 metres wide, too small for an impact to wipe out life on Earth, but it would devastate a wide area, releasing 65,000 times as much energy as the Hiroshima atom bomb. Data from the Arecibo radio telescope on 27th January 2005.