In an attempt to settle the question of whether ice exists on the moon, NASA plans to launch the Lunar Reconnaissance Orbiter (LRO) in 2008. Travelling in a polar orbit only 50 kilometres above the moon’s surface, the probe will focus a high-resolution neutron sensor on the suspected ice deposits to determine their precise locations. But because the ice is probably buried and mixed with lunar dirt, NASA will also need to land a probe to dig up and analyze soil samples. This mission, scheduled for 2011, is a challenging one because instruments operating in shadowed areas cannot use solar power. The craft could land at a sunlit site and send a battery-powered vehicle into a dark crater, but the batteries would quickly die. A radioisotope thermal generator could provide electricity using heat from plutonium decay, but NASA is leaning against this option because it is expensive and controversial. Another idea under consideration is sending a probe that could hop from place to place on the lunar surface by restarting its landing rockets, lifting the craft to 100 metres above its original landing site and moving it to another spot in the crater basin to hunt for ice. Investigating more than one site is crucial because the ice may be unevenly distributed. Yet another alternative would be to fire ground- penetrating instruments at several places in the shadowed basin, either from a lander at the crater’s rim or from an orbiting craft.