The universe is a big, big place. But how big? And how do we know?
Throughout history, humans have used a variety of techniques and methods to help them answer the questions 'How far?' and 'How big?' Generations of explorers have looked deeper and deeper into the vast expanse of the universe. And the journey continues today, as new methods are used, and new discoveries are made.
Is life a fluke unique to Earth or is it teeming across our galaxy? We may have the answer within a few decades. Nasa's Curiosity for example, the rover now on Mars, may find evidence for creatures that lived early in Martian history; firm evidence for even the most primitive bugs would have huge import. There could be life in the ice-covered oceans of Jupiter's moon Europa. But what really fuels popular imagination is the prospect of advanced life – the "aliens" familiar from science fiction – and nobody expects a complex biosphere in those locations.