A moment of silence, please, to mark this particularly special day in the history of space exploration. 51 years ago today, Russia launched Sputnik II into space, with a special passenger onboard - Laika, the first living mammal to orbit the Earth... as well as the first mammal to die in space (She died, it was revealed in 2002, from stress during the first seven hours of the mission). Her remains disintegrated, along with the rest of Sputnik II upon re-entry into the Earth's atmosphere in April, 1958, but her brief flight changed the course of human history.