Charles Bolden, NASA’s administrator, asserted that the robotic vehicle Curiosity will “blaze a trail for human footprints on Mars.” He could be right. But there is a gulf between what’s technically feasible and what is actually achieved. Neil Armstrong made his “one small step” on the moon in 1969, only 12 years after Sputnik 1. Had the pace been sustained over the subsequent 40 years, there would be footprints on Mars already. But after the U.S. had beaten the Russians in the moon race, there was no motive to sustain such a huge expenditure.
Perhaps the Chinese will prioritize a “space spectacular.” If so, they will surely set their sights on Mars. After all, a return to the moon, 50 years behind the U.S., would not proclaim parity in the superpower stakes.
But would humans on Mars serve a purpose beyond mere prestige? There’s no denying that an observant geologist might make startling discoveries that Curiosity would overlook. But the current cost gap between manned and unmanned missions is huge. This is partly because public and political opinion imposes a demanding “safety culture” on NASA. The space shuttle failed twice in 135 launches. Astronauts or test pilots would willingly accept this risk level. But the shuttle had been promoted as a safe vehicle for civilians. So each failure caused a national trauma and was followed by a hiatus, while costly efforts were made (with very limited effect) to reduce the risk still further.
The future of manned spaceflight lies with privately funded adventurers. The SpaceX company, led by entrepreneur Elon Musk, has successfully docked a payload with the space station and returned to Earth. The involvement of Musk, and others in the high-tech community with credibility and resources, is surely a positive step. Maybe within a decade the really wealthy will be able to sign up for a weeklong trip around the far side of the moon—voyaging farther from Earth than anyone has been before (but avoiding the greater challenge of a moon landing and blastoff).
Still, the phrase “space tourism” should be avoided. It lulls people into believing that such ventures are routine and low risk. And if that’s the perception, the inevitable accidents will be as traumatic as those of the space shuttle.
Manned missions to Mars will be viable only if they are cut-price ventures with travelers accepting high risks—perhaps even “one-way tickets” for those who want to live out their days there. Remember that nowhere in our solar system offers an environment as clement, even, as the Antarctic or the top of Everest. It is foolish to claim, as some do, that mass emigration into space offers escape from the Earth’s problems.
But I believe and hope that some people now living will walk on Mars. Moreover, a century or two from now, small groups of intrepid adventurers may be living there, or perhaps on asteroids, quite independently from the Earth. And machines of human intelligence could spread still farther. But will these pioneers encounter life out there already? Curiosity may reveal evidence of creatures that lived early in Martian history, and there could be life in the ice-covered oceans of Jupiter’s moon Europa. But nobody expects a complex biosphere in such locations. To seriously seek the “aliens” familiar from science fiction we must look to the distant stars—far beyond the range of any spacecraft we can now conceive.
Astronomers have learned (but only since the 1990s) that other stars have planets circling around them, just as Earth, Mars, and Jupiter circle our own star, the sun. We’re especially interested in possible “twins” of our Earth—planets the size of ours, orbiting other sunlike stars. The Kepler spacecraft (another of NASA’s unmanned successes) has indirectly found hundreds of these—by detecting the slight dimming of a star that occurs when such a planet transits in front of it.
But do we expect life on these alien worlds? We know too little about how life began on Earth to lay confident odds. And even if simple life is common, it is of course a separate question whether it’s likely to evolve into anything we might recognize as intelligent. Maybe the cosmos teems with life, and we will one day find E.T. On the other hand, Earth’s intricate biosphere may be unique. That may be disappointing. But it would have its upside: it would entitle us to be less cosmically modest. Our tiny planet could indeed be special—perhaps even a seed from which life could spread through the galaxy.
We may learn this century whether biological evolution is unique to the “pale blue dot” that is our home or whether the wider universe is full of life—even with intelligence. As Curiosity trundles across Martian craters, we hope for some early clues.
Martin Rees is a cosmologist and the author of From Here to Infinity: A Vision for the Future of Science.