Capa Canaveral (Florida): Nine months ago, Nasa's Phoenix probe blasted off for Mars with an unprecedented mission to sample water on another world. Before that can happen, however, the space agency faces a formidable challenge: landing. The odds are not great. Historically, 55% of all attempts to land on Mars have failed and the method being used for the touchdown of the Phoenix spacecraft on May 25 hasn't been attempted in 32 years.