When the US Mars rover Spirit weakened last month – sending unintelligible data – Opportunity knocked for NASA, as its second rover landed safely on the Red Planet. But when Europe’s lander, Beagle 2, failed to bark and disappeared, there was no backup vehicle for consolation. The recent dramas on Mars offer a graphic illustration of the challenges facing European space scientists as they battle to keep up with their American counterparts exploring our solar system. Sometimes rivals, sometimes partners of their US colleagues, torn between competition and cooperation, the Europeans face one overriding reality: Their budgets are only one-sixth that of the US.