Everything about Curiosity's landing on Mars comes in superlatives. The sky crane by which it was lowered to the surface was the first of its kind, its success – after "seven minutes of terror" – an unprecedented achievement. Then there is the rover itself, the largest ever sent to Mars, bristling with the most sophisticated equipment. Now, for two years, possibly more, it will seek out details of the planet's geological history.
Not only is Curiosity another spectacular example of the spirit of inquiry that propelled the human race out of the caves. Its findings, plus those of proposed follow-up missions, may yet prove whether life has existed elsewhere.
Such evidence would, in an instant, change everything; the implications – practical, philosophical, scientific – are of an almost inconceivable magnitude. There is no bigger question. If it gets us a step closer to the answer, Curiosity is $2.5bn well spent.