Old satellites don't die, they just crash into things, sometimes intentionally. NASA plans to knock its highly successful Lunar Prospector out of its orbit around the moon and smack it into the surface on July 31st. The object is to generate enough energy to liberate water vapour that may be detectable from ground- and space-based observatories. This would prove the presence of water ice on the moon. The satellite has been collecting data since soon after its launch in January 1998, and is approaching the end of its expected 18-month life-span. NASA plans to steer it towards the Mawson crater at the southern lunar pole, thought likely to contain water ice, and watch the result, although it gives itself only a 10 per cent probability of success.