Last Thursday, the Mars Climate Orbiter was lost as it attempted to slip into orbit around the Red Planet. To some, this might appear to be proof of folly; the failure of a $125 million scientific probe that, had it succeeded, might only have discovered an odd phenomenon or two. I saw it all rather differently: I believe that the orbiter's failure was just one of the inevitable casualties taken in the course of the scouting campaign that will set the stage for the opening of the solar system to humanity.

Why should we take such risks? We need only to look back to find the reason we should explore a new frontier. We humans are the descendants of explorers. Four hundred million years ago, our distant ancestors forsook the aquatic environment in which they had evolved to colonize the alien world above the shoreline. It is remarkable when you think of it--sacrificing the security of the waters for the hazards of the land.

In the eons since some fish left the ocean, their fellows who stayed behind have not changed much, but the descendants of the emigrants have evolved legs and wings, feathers and fur, farseeing eyes, nimble hands and clever brains.

Out of the oceans to the land. Out of Africa to the north. Out of Earth into space. That, it seems to me, is our natural destiny. The human desire to explore is one of our primary adaptations. We have a fundamental need to see what is on the other side of the hill, because our ancestors did, and we are alive because they did. Therefore, I am firmly convinced that humanity will become space settlers. We would be less than human if we didn't.

We have been prepared in the past to pay dearly to cross frontiers. When colonists emigrated to the Massachusetts Bay in the 1600s, they commonly paid their one-way passage with seven years of indentured labor, the equivalent of $300,000 today. The Oregon Trail was lined with graves. Our space missions will be expensive, and not all of them will be successful. For in charting the unknown, the possibilities for disaster abound. Progress is never without risk. It was unacceptable to our forebears not to migrate north from Africa, not to cross the Atlantic, not to reach Oregon. So, too, is failure to reach the stars.

Yet we seem to be failing. The world's space programs, begun so proudly in the eras of Sputnik and the Apollo moon launches, appear to be in a state of retreat verging on rout. The Russian program has collapsed. The American effort, which has been going in circles for the past 20 years, has lost much support and is set for a fall the next time something goes wrong with the shuttle or space station programs.

Consider the following: From 1961 to 1973, the United States launched more than 30 robotic lunar and planetary missions and 10 piloted Apollo lunar missions. From 1974 to 1986, we launched six robotic and no manned missions beyond Earth orbit, while from 1987 to the present an additional 10 robotic and no piloted exploration missions were flown. Russian missions show a similar trend. While the demise of the Soviet, and later Russian, programs in the 1990s might be explained by the deterioration of that nation's economy (an oversimplification, since the material conditions in the Soviet Union were much worse in the 1950s when its program was launched than they are now), in the United States the opposite was the case. The U.S. economy today is more than double the size of the 1960s economy, per capita income is higher and we face no major military threat. Politicians complain about the incapacity of the national budget to support space programs, but neither we nor anyone else have ever been so able to afford to initiate a great wave of new exploration.

Surprising though it may seem, the average NASA budget in 1998 dollars during the heroic age of 1961 to 1973 was about $16 billion per year, only 20 percent more than it is today. During that period, NASA not only launched the Mercury, Gemini, Apollo, Skylab, Ranger, Surveyor and Mariner missions, but did all the development for the Pioneer, Viking and Voyager missions. It also developed almost the entire bag of tricks (from spacesuits to space nuclear reactors and hydrogen/oxygen rocket engines) that enables space exploration missions today.

The U.S. space program of the 1960s was vastly more productive than that of today because it had drive, imparted to it by a focused goal that made its reach exceed its grasp--landing humans on the moon. There can be no progress without a goal, and, lacking one, NASA has foundered for the past two decades. If U.S. leaders want to increase the taxpayers' return on their space dollar, by far the most important and effective thing they could do would be to give the space agency a challenge worthy of it--committing the nation to establish humans on Mars within a decade.

Why the Red Planet? One hundred times farther from Earth than the moon, Mars offers a much greater prize. It has the resources needed to support not only life but the development of a technological civilization. In contrast to the comparative desert of the Earth's moon, Mars possesses oceans of water frozen in its soil as permafrost, as well as carbon, nitrogen, hydrogen and oxygen. Virtually every element of significant interest to industry exists on the Red Planet. With its 24-hour day-night cycle and an atmosphere thick enough to shield its surface against solar flares, Mars is the only extraterrestrial planet that will readily accommodate large-scale greenhouses lit by natural sunlight.

But how to motivate such a program? It is clear that an essential element that gave urgency to the space programs of the 1960s was the Cold War competition between the United States and the Soviet Union. That challenge we have lost and would not wish to retrieve. But today a new challenge has come into view--one offered by the space frontier itself.

This challenge has come in the form of a series of remarkable discoveries and innovations over the past decade that have changed the relationship between the human future and the rest of the universe. They began in 1987 with the discovery by Paul Ching-Wu Chu, now director of the Texas Center for Superconductivity, of high-temperature superconductivity--which offers the potential of breakthrough technology in the area of magnetic sails (devices that propel spacecraft by deflecting the solar wind) and magnetic confinement fusion and, ultimately, low-cost interstellar flight. Then, in the 1990s, astronomers began to detect planets orbiting other stars. As a result, it is now clear that planetary systems--potential homes for life--are the rule in the universe rather than the exception. Also during the 1990s, evidence piled up to demonstrate that the impact of asteroids on Earth has been responsible not just for the extinction of the dinosaurs but for other mass extinctions as well. Earth, it seems clear, is part of a larger cosmic system that we ignore at our peril.

In the early '90s, the Strategic Defense Initiative Organization demonstrated a prototype reuseable launch vehicle, suggesting that space travel could become as cheap and commonplace as air travel. In 1996, NASA scientists revealed strong, though much-disputed, evidence for the presence of relics of microbial life in ancient Martian rocks. In 1997, this evidence was augmented by the arrival of NASA's Pathfinder craft on the surface of Mars, which, by landing in an ancient flood plain, proved the existence of aqueous environments that could have supported the evolution and development of microbial life on Mars in the distant past. Add to that the fact that, in 1998, NASA's Mars Global Surveyor probe produced topographic data that indicate the existence of a former northern ocean--and potential homes for bacterial life across large regions of the planet. As humble as such Martian microbes might be, the implications drawn from their existence are spectacular. The implication is that a very large number of stars possess planets that have given rise to life.

The history of life on Earth is one of continual development from simple forms to more complex ones, with the more advanced forms manifesting ever-increasing degrees of activity, intelligence and capability to evolve into even more advanced forms at an accelerated rate. If life is a general phenomenon in the cosmos, then so is intelligence. If the evidence of bacterial fossils presented in Martian meteorite ALH 84001 holds up--and, in my view, it's holding up quite well--the implication is clear: We are not alone.

Collectively, these discoveries make apparent what humanity is forsaking if we abandon space. We are no longer lords of the only relevant piece of cosmic real estate; the evidence suggests that we live in a system that contains billions of habitable and inhabited worlds. We also know that extraterrestrial objects--asteroids--have had a decisive impact on survival and evolution on the Earth, and therefore that we should face the fact that our future may only be secure if we gain control of the solar system's flight traffic. A few years ago, the costs suggested that spacefaring civilization was a chimera. Now we know that technologies can be brought into existence that can make this wider universe accessible to us--a universe that, in all probability, is already being accessed by others.

So we stand on a threshold, wondering whether to step back or forward. Perhaps a look back is just what we need in order to move forward. The human race first became technological when it left Africa to take on the challenge of the north. Later, as humans became seagoing, it was the stars--with poetic truth, the North Star--that gave us the guidance we needed to become a truly global species.

Today the stars beckon again, this time not to new continents, but new solar systems. Multitudes of worlds yet unknown wait to be filled, with menaces to be faced, challenges to be overcome, wonders to be discovered and history to be made.

Robert Zubrin, a former senior engineer at Lockheed Martin, is president of the Mars Society and founder of Pioneer Astronautics, a space exploration and development firm. He is the author of the recently published "Entering Space: Creating a Spacefaring Civilization" (Tarcher/Putnam).