Some scientists believed on 13 January that a 30m object, later designated 2004 AS1, had a one-in-four chance of hitting the planet within 36 hours. It could have caused local devastation and the researchers contemplated a call to President Bush before new data finally showed there was no danger. The procedures for raising the alarm in such circumstances are now being revised. At the time, the president's team would have been putting the final touches to a speech he was due to make the following day at the headquarters of Nasa, the US space agency. In it he planned to...