Some truths take a lifetime to learn; some you know when you're 5 years old. At that age, I knew that human beings were meant to explore space. It was 1961, and the space age had barely begun. I didn't know about President Kennedy's challenge to send people to the moon within the decade, but I knew that humans would go there - after all, my picture books almost always included astronauts exploring alien vistas.
Today, decades after the final Apollo mission, we still haven't sent a human back to the moon - or beyond it. We explore the solar system with robots, like the Spirit and Opportunity rovers, which have been roaming the deserts of Mars for close to a year. These rovers are magnificent examples of human ingenuity. They drill into rocks to analyze chemical composition. Their microscopic imagers zero in on tiny details, while a pair of cameras capture widescreen, Imax-quality panoramas. The rovers can even dig trenches to reveal what's beneath the surface.
It's tempting to think that wonderful machines like these could replace human explorers. But Spirit and Opportunity can do only what they're told. They can detect only what they have been designed to detect. The data they can collect in a month on Mars could be gathered in a matter of hours by a lone human field geologist. Even the mission's scientists and engineers agree that to realize the full potential of scientific discovery on other planets, we'll need to put human minds and hands to work. The question is not whether to send people, but when.
Of course, the costs and risks of sending humans to the moon, Mars, or nearby asteroids will outweigh the benefits for at least the next decade. Until that balance is tilted by the development of new spacecraft and protective measures that reduce danger and expense, we'll have to live by the watchword of engineer Gentry Lee, a 30-year veteran of NASA's Mars missions: "Never send a human to do a robot's job."
But the balance will tilt, and when it does, humans will follow in the footsteps of our robotic creations. That doesn't mean machines will act only as a kind of advance team for people; even after astronauts have begun exploring alien worlds, they will need robotic assistants to handle repetitive or especially dangerous tasks. But only human explorers can raise the pace of discovery a quantum leap. And only they will tell us what it is like to be there.
This is the precious gift we got from the Apollo astronauts who visited the moon between 1968 and 1972. One recalled his amazement at exploring the lunar landscape, a wilderness that was more ancient than he could comprehend and more beautiful than he had imagined. Another described orbiting the moon alone, in darkness, gazing out at a sky filled with unblinking stars, and wondering who might be staring back. All spoke of their awe at seeing Earth, lovely and distant, rising beyond the moon's lifeless horizon - and of the sobering realization of how far from home they really were.
These stories, postcards from the edge of human experience, are just a taste of what we will gain when humans once again journey to other worlds. The future of space exploration is for robots and people. But don't take my word for it. Ask a 5-year-old - the one inside you, who longs to be an explorer.
Andrew Chaikin (www.andrewchaikin.com) is the author of A Man on the Moon, the basis for the HBO miniseries, From the Earth to the Moon.
