The National Aeronautical Space Agency (Nasa) has offered a $250,000 prize to any scientist who discovers a way of extracting breathable oxygen from moondust. The competition is the latest in Nasa's 'Centennial Challenges' series, which aims to stimulate the development of technologies useful to space exploration. To claim the MoonROx prize, scientists must develop and demonstrate hardware capable of extracting at least five kg of breathable oxygen from a simulated lunar soil made from volcanic ash in an eight-hour period.