As the robot Curiosity touched down on Mars, the event was accessed via Internet by millions worldwide, witnessed by tens of thousands at live events, and highlighted in the media for days. I hope that politicians and bureaucrats got the message: Space exploration is not just valuable to scientists; it is also popular with the public who pays taxes. And why not? The exploration of Mars is not only a search for signs of alien life. It is an exploration of the human future.
Mars is the only world accessible to us beyond Earth that was once and again may be habitable. It is the laboratory in which the evolution of the human species will be tested and ultimately determined. In its atmosphere, on its surface, and through its water, we seek answers and insights about the nature, origin and evolution of life, particularly of ourselves. Contemplating Mars, we wonder: Are we alone in the universe? Where will our future lie?
In the current space program, however, it is chic to consider Mars as only one of many destinations. After all, there are six other planets, many moons and even more asteroids in our solar system, and some people dream of travel to other stars, and their planets and moons. We have been exploring robotically and remotely investigating as many other worlds as possible, and we want to continue. But for humans, we've only touched down briefly on the moon, and Mars is the only place we might repeat that triumph. Traveling to other worlds — for example, to hellishly hot Venus, or the far, cold and radiation-battered environs of Jupiter — is beyond our ability, at least for now, and I argue, forever!
Mars is not just the next or most accessible human destination, it is the ultimate one. Science-fiction literature abounds with human voyages through and beyond the solar system. But the ideas for such voyages have changed little over the past 50 years. They imagine exotic, unobtainable propulsion systems, or undefined warp drives, freezing people to wake them up in tens of thousands of years, or spaceships with anti-gravity drives supporting generations of travelers among the stars. Those ideas haven't improved or become any more realistic. Neither has real, obtainable human spaceflight technology. The life-support systems we will use for human flight over the next few decades are remarkably the same as those we used in the Mercury, Gemini and Apollo era, and they will make use of capsules and heavy rockets much like those of the 1960s.
Contrast that with how far robotic spacecraft have evolved, and how information technologies have simply transformed. Any cellphone has more computing power than the earliest planetary probes or the Apollo spacecraft. Electronics and sensors keep getting smaller, while information processing and communications capabilities get greater. Small spacecraft have evolved from micro-spacecraft (10-100 kg), to nano-spacecraft (1-10kg), to pico-spacecraft (under 1 kg), and the limits are not yet known. Except for the speed of light, we don't yet know the limits for communication data rates and for information processing speed and capacity. The combined exponential reduction of electronics size and increases in information processing capabilities give us a "Moore's Law" for increasing robotics technology capability, whereas the technology predictions for transporting human spaceflight actually seem to give us an inverse Moore's Law, describing a rate of decreasing capability and longer time-scales.
Extrapolating from current robotic developments, we will have super-fast, ultra-light spacecraft propelled by lightsails that will enable interstellar travel with the human brain, but not the body. The human brain will be integrated with that of the spacecraft, utilizing advances even more profound than those in the physical and electronic technologies. Combining genetic, biological and nano-technologies in future payloads with advances in information processing, we will extend human presence into worlds much farther and faster than we now imagine. This is how humans will explore beyond Mars.
By the time human spaceflight technology is theoretically capable of journeys beyond Mars, humans in modern space systems will be virtual explorers interacting with the environments of distant worlds, but without the baggage of physical transportation or presence. This is already happening on Earth. More astronomy is now done by astronomers sitting in their offices and homes than by trooping to mountaintops to sit at a telescope. Data reach the virtual observer just milliseconds later than it would if he or she were on the mountain. An even starker example: Modern warfare, conducted more and more by telerobotics, is leaving the human warriors safe at home, as with U.S. drones in Asia and Africa.
If humans will explore the vastness of space beyond Mars virtually, why won't it be that way with Mars? Why won't humans give up exploring beyond Earth altogether? There are two simple reasons: Humankind will not leave all its eggs in one basket, where they are susceptible to extinction by asteroid impact, disease, war or environmental catastrophe. And Mars is accessible — less than one year's travel time — and with a relative abundance of water, oxygen and useful minerals within reach of humans. There's nothing else like it within billions and billions of miles.
Human travel to Mars is inevitable. Human journeys beyond Mars will be virtual. This makes Mars the ultimate destination for humans, in body at least. Once we realize that, the context of robotic missions like Spirit, Opportunity and, now, Curiosity changes. President Obama may actually understand this; he is the first president to announce that human expeditions to Mars (he said by the mid-2030s) is the goal of America's space program. The president may understand it, but his administration doesn't. It has cut out most future Mars plans in NASA. That disconnect needs fixing.