Europe's off to Mars. Again. We have sent robots to fly over Mars, crawl over Mars and soon to dig down into Mars - searching for signs that once, perhaps deep in the past, this planet may have been home to life. It might be an obvious choice, but still a puzzle, and one that we're only just beginning to piece together. And finding evidence of life will require the skill of the finest detectives.

This is a mystery that Europe's ExoMars mission is ready to solve. In 2016 it will have a satellite in orbit around Mars, designed to test for methane, and by 2018 this rover will be rolling around the Red Planet. The mission will be the first to set out with the direct intention of finding signs of life, now, and in the past.