Occam’s Razor: Faced with multiple possible explanations, don’t go for the splashiest; choose the simplest – the one that requires the least number of coincidences – the one that is least astonishing. If the simplest explanation doesn’t pan out, move on to the next simplest (which is also a bit more astonishing). The leader of the team running an instrument aboard Mars Express – a European Space Agency spacecraft orbiting Mars – believes his data imply something truly astonishing: Martians.