For generations, people gazing up at Mars could only mythologize the pink sparkle in the sky. Only in the seventeenth century did telescopes pointed at the planet reveal an orb, capped in white at the poles, with a mysterious dark splotch around its middle. Centuries on still, it took a barrage of spacecraft at the dawn of the space age to prise its secrets open: ice caps that contained not just water but frozen carbon dioxide, and Syrtis Major, a dark field of lava squeezed out by long-dead volcanoes, which seemed to be regularly scoured by wind. More recent orbiters, reaching their peak with the spy-camera resolution of the Mars Reconnaissance Orbiter, have caught Mars in action today — red-handed, if you like. Streaks on crater walls that come and go with the seasons are probably the signature of near-surface water. And little flashes of colour appear as if from nowhere as tiny asteroids penetrate and expose the blue ice below.

Mike Malin, a scientist and businessman in San Diego, California, has been a constant witness to this steady march of knowledge. Indeed, as the News Feature on page 460 makes clear, he made much of it happen, having had a hand in building the cameras on every NASA Mars orbiter that followed the 1975 Viking missions. But his cameras have not seen the surface before. Now finally, with the launch of the Mars Science Laboratory, or Curiosity, scheduled for as early as 25 November, Malin's cameras will, he hopes, at last view Mars in close-up. One of his camera systems sits at the end of the new rover's robotic arm, a microscopic imager with the power to see, for the first time, tiny grains of silt thought to exist on Mars — particles that would bear the history of billions of years of erosion from wind and water.

This is one benefit of a coordinated and sequenced NASA Mars programme. But at what cost? Getting to Mars has never been cheap. Just ask Russia, which spent US$163 million to launch on 8 November an attempt to retrieve a few cups of soil from one of Mars's moons. Now the stricken spacecraft is stuck in Earth orbit, laden with fuel: cheap as failed Mars missions go, but dearly expensive for a firework. NASA's Curiosity, at $2.5 billion, is at the luxury end of the spectrum. Part of this staggering cost is because of the checks and further checks that NASA hopes will guarantee the mission's success. But it also reflects the sophistication of the science payload, which will investigate whether ancient watery environments may have been suitable for life.

Still, NASA has largely danced around the question of whether it will pursue Martian life itself. Last week, before the US Congress, Mars exploration advocates were explaining their next steps — a joint plan with the European Space Agency — and how this question would finally be addressed. A planned orbiter in 2016 would sniff for trace amounts of methane, a potential biosignature. And then in 2018 a rover would land and drill to see if microorganisms have been living beneath the surface. This rover would also grab bits of rock and soil as the first stage in a three-pronged plan to bring samples back to Earth, a long-term priority for Mars scientists.

But sample return of any sort is expensive. One credible assessment from the National Academies' decadal survey review puts the costs of a three-stage Mars sample return at as much as $8.5 billion. That is why budget minders for the administration of President Barack Obama are rightly concerned about embarking down this road — $8.5 billion happens to be roughly the price tag for a similarly ambitious mission, the James Webb Space Telescope, a successor to the Hubble Space Telescope. But the Webb telescope at least buys diversity: the ability to investigate millions of galaxies and stars, and even to look for the atmospheric biosignatures of planets not too much larger than Earth. A Mars sample return buys you a few rocks from one specific place. After Viking, in the late 1970s and early 1980s, NASA — exploring space during a terrestrial economic slump and a time of post-Apollo drift — did not launch a Mars mission for almost a generation. And that is why Curiosity, for all its prowess, may also be the last in the current line of landed robotic Mars missions. Godspeed, Curiosity.