It is a desert plain, caramel-smooth and windswept-empty. To its north rises a mountain taller than Mont Blanc, Mount Rainier or Fuji-san and though, because it is also wider, its sides are less steep and prospects less dramatic, it is still an impressive thing. A massive central shoulder, banded with rocks of different ages, juts out over the plain; to its side, the mountain’s forest-free flanks are cut with canyons. The summit—whittled away by the wind but a stranger to snow—sits farther back, hidden from view. Both plain and mountain are ringed by a wall four kilometres high and almost 500 kilometres long, the rim of a crater the size of Wales. Above the landscape is a washed-out, alien sky. At the right time of year, the Earth hangs over that horizon-rim at twilight, a blueish evening star.
This is Gale crater, a part of Mars with which some of the inhabitants of that evening star have made an appointment. As this page went to press in late November, a six-wheeled rover called Curiosity was due to be thrown there by a 500-tonne Atlas V rocket. If all goes well—a substantial if, as Mars missions often don’t; a Russian one failed to get beyond Earth’s orbit in early November—then next August a complex system of parachutes and retrorockets will lower the rover through the thin Martian atmosphere to its destination. It will trundle across the plain to the ancient rocks of the mountain’s base and start a slow ascent. It will sniff the air and take samples of rock and soil to analyse in its on-board laboratory. With the help of an orbiting intermediary, it will send back to Earth a torrent of pictures, from the panoramic to the microscopic.
Curiosity’s climb up that still unnamed mountain promises an extraordinary return in terms of science (and with a price tag of over $2 billion, so it should). It also opens up a new era of exploration—so new, in fact, that it may no longer be exploration at all.
The Mars Reconnaissance Orbiter, the well-named flagship of the small flotilla of satellites now orbiting the planet, boasts a camera on a par with those of Earth’s best spy satellites, able to pick out rocks the size of footballs on the surface below it. Since Gale made the shortlist of possible landing sites for Curiosity, that camera has devoted a lot of time and many megabytes to the crater. When I wrote a book called “Mapping Mars”, a decade ago, one of its centrepieces was the unveiling of a three-dimensional map of Mars better than anything ever seen before. The maps of Gale crater available today have more data in them than that state-of-the-art map used to model the whole world. Draped over the topography is data from other instruments that have studied Gale by day and by night in wavelengths both visible and invisible.
Unlike earlier spacecraft, then, Curiosity is not going into the unknown. It is going to somewhere mapped to the last metre. Its investigations of sediments that carry the mineralogical signatures of earlier, wetter periods in Mars’s history—sediments known to be there thanks to spectral analysis by instruments on the satellites orbiting above it, sediments that led to the choice of Gale rather than any of the thousands of other potential sites that Curiosity could reach—may prove remarkable. It is not beyond the bounds of possibility that they may reveal signs of long-gone life. But Curiosity will never round a corner and reveal a vista unexpected by the scientists monitoring its progress. Its data may surprise; its otherworldly surroundings will not. Every line of sight can be presimulated, every track will be the subject of computerised premonition hundreds of millions of kilometres away.
Space flight and science both draw on the imagery of the frontier, that limitless source of new possibility which America believed itself to have lost at the end of its expansionist 19th century, and has hearkened back to, one way or another, ever since. Mars, the only other planet in the solar system on which people might plausibly live, and one with landscapes reminiscent of a Brobdingnagian Arizona to boot, brings those strands of frontier imagery together in spectacular fashion. To think of it now as a place so well known that, while it can offer new knowledge, it promises no new vistas, feels a bit like the passing of an age. It makes the adventure more purely one of the intellect, shifting its emphasis to the unfathomable gulfs in time—Curiosity will scrape and zap rocks that are almost 4 billion years old—rather than the conquered vastness of space.
But if the planet next door is losing some idealised mystique, it is gaining something, too. Gale may be too well mapped to be surprising. But it can still be inhabited, if only virtually. Curiosity will make it a setting for travel and stories and setbacks—a real place, not just a vision or an idea of another world. The loss of strangeness, looked at another way, is an expansion of the shared human experience to another planet. Mars is not diminished by becoming ever better known. Earth is ennobled.