When the unmanned space probe Pioneer 10 took off from Cape Canaveral in March 1972, it had on board a remarkable diagram. The Pioneer Plaque was designed to communicate fundamental facts about Earth and its inhabitants to life on other planets. In carefully engraved graphic images and mathematical symbols, the plaque would reveal the Earth's location in the solar system and show extra-terrestrial intelligent life what human beings looked like.But how could one single diagram do all that - what do you put in and what do you leave out? With its naked human figures, the plaque sparked arguments amongst feminists and conservatives.So was it, in the end, a great intellectual game or was it the most enterprising, artistic and scientific diagram of all time, perhaps even the ultimate diagram?