Claims have re-emerged that the US space agency (Nasa) did find signs of life on Mars during the historic Viking landings of 1976. Dr Gil Levin, a former mission scientist, says he now has the evidence to prove it, just days before the US and Europe send new expeditions to the Red Planet. The United States and Russia have spent billions since the 1960s on a handful of space craft designed to land on Mars. Only three have succeeded so far: the two Viking probes in the 1970s and Mars Pathfinder in 1997.