The Call of Mars
At the most general level, Mars exploration is about understanding Earth’s arguably most interesting neighbor. Mars is both like and unlike Earth. It is the one planet people on Earth can see in some detail. Its rich, red color was always a source of speculation prior to the space age. The ancient Romans named the planet Mars after their red god of war. The fourth planet from the Sun, it travels an elliptical orbit. At its closest approach to Earth, it is 48,700,000 miles (78,390,000 kilometers) away. Mars’s diameter is about 4,200 miles (6,790 kilometers), which is a little over half the diameter of Earth. Mars takes about 687 Earth days to go around the Sun. While the length of a Mars year is much longer than that of Earth, the Mars day is remarkably similar. Mars rotates on its axis once every 24 hours and 37 minutes. Mars also, like Earth, has seasons. During the Martian winter, observers see polar caps that are relatively large, and which then shrink during the Martian summers. Mars has an atmosphere, but the atmosphere is much thinner than that of Earth. It consists chiefly of carbon dioxide, with small amounts of nitrogen and other gases. The atmosphere of Earth, in contrast, is heavy on nitrogen and oxygen. Because of its distance from the sun, Mars is extremely cold. The temperature ranges from -iphF to -24°F (-i24°C to -3i°C). It has two moons, Phobos and Deimos.4
The similarities and differences are striking. They have contributed to the human desire to know more about Mars. Beyond these factors, there are at least three reasons that Mars has long been a special magnet for scientists and public alike. First, there is the question of life on Mars. For many years prior to NASA’s establishment, and even for some time afterward, there was a belief in many circles that there was life on the surface. When it became clear that such life would have difficulty surviving, various scientists suggested there were still possibilities in sheltered places on Mars, what they termed oases. Even scientists who today believe no life exists on the surface admit possibilities under the surface, in permafrost. No one expects that such life is highly developed. Most likely it is bacterial. But even if no life at all exists now, it may have once existed when Mars apparently had a very different climate and substantial water flowed. So the question of life on Mars, now or in the past, has always been a compelling driver for the Mars exploration program, in many ways the most significant one in terms of NASA history. For when optimism about life on Mars reigned, the program did well in obtaining resources. When pessimism took hold, the program languished.
There is a holy grail for the Mars robotics program: it is called Mars Sample Return (MSR), the retrieval of soil and rock from Mars. Samples would be brought back to Earth for examination in laboratories around the world to detect signs that will answer the big question of life. The challenge is to bring back “the right stuff,” and do so in a way protective of possible Martian life as well as human life from contamination. MSR is a monumental test, perhaps the single most complex and important mission for NASA since Apollo. It lies ahead and probably will require international collaboration owing to projected cost. But it has enormous value as a goal, on which there is widespread consensus. It gives direction and sequence to missions leading to it.
The second driver is the desire to send human life to Mars. The robotic program thus becomes a precursor to human missions, much as robotic Ranger and Surveyor missions were scouts for the Apollo voyage to the Moon. This makes the human spaceflight program a potential ally of the robotic program. NASA leaders can envision useful connections between robotic activity and human Mars journeys. When President George H. W. Bush proclaimed in 1989 that America should return humans to the Moon and then go on to Mars, his declaration also carried an understanding that robotic missions and human flight were partners in exploration. The same understanding applied to his son George W. Bush’s similar declaration in his 2004 “Vision for Space Exploration.” President Barack Obama in 2010 decided to bypass the Moon and emphasize Mars as the ultimate destination for humanity, sometime in the 2030s. An asteroid landing would be the interim step. Again, robotic flight would pave the way.
Robots may be partners with human spaceflight over the long haul, but in the short run they often compete for limited funds and represent different cultures. The robotic science program of NASA sees the human space effort as embodying an engineering and astronaut culture that wants to go to Mars “because it is there.” This is indeed a motivation, a “frontier” attitude, sometimes with manifest destiny overtones, to extend the human presence to outer space. “We go because we must.” “It is in our genes,” goes the refrain. There are those human spaceflight advocates who see Mars as not only a mountain to be climbed but a territory to be “terraformed” and settled. NASA’s “can do” engineers see exceptional technological challenge in human Mars exploration. Astronauts see romance and adventure. In contrast, robotic-oriented scientists seek basic understanding in comparative planetology, with emphasis on Martian life issues.
The field centers that report to the human spaceflight directorate in NASA’s Washington headquarters are different from those that report to the robotic science office. The human spaceflight program, as noted, has astronauts, and they are more than just another set of employees within NASA; they are in many ways the agency’s public face and source of inspiration to young people. Mars is the only planet where human missions are likely in the twenty-first century. The human spaceflight institutions and their cadre recognize the precursory importance to them of the robotics program. The interests of robotic science and human exploration potentially connect in the MSR mission. NASA needs to know what environmental hazards astronauts would face on Mars and also if they can convert the Red Planet’s physical resources into assets for long-term stays. Also, if NASA cannot bring rocks and soil back to Earth, it may not be able to bring human beings home. The technologies of MSR have direct relevance to human spaceflight. The short-term budget competition nevertheless can interfere with cooperation concerning Mars across NASA divisions.
The third driver is political. Space has always engendered rationales concerned with national leadership, prestige, pride, inspiration, and competition with other nations. It has been used by governmental officials to enhance cooperation also. Mars in the 1960s was a destination both the United States and the Soviet Union sought to reach first during the Cold War. It was a target of Cold War rivalry. During and after the Cold War, advocates of both human and robotic programs also called for using Mars as a political symbol for a joint enterprise uniting the rival superpowers. More recently, Mars has been seen as a vehicle for global cooperation. While much “Mars Together” rhetoric has been about human expeditions, it includes the robotic program in its collaborative embrace. NASA and the European Space Agency (ESA) have sought in particular to work together on robotic missions, but relations have been turbulent.
Finding life on Mars, sending life to Mars, and using Mars for political ends have been the key drivers behind Mars exploration for decades. At different points in history one or another of these rationales has dominated. Sometimes more than one has influenced Mars exploration. Which one has resonated has depended on innumerable factors, including the strategies of Mars advocates. The most consistent theme affecting the direction and pace, as well as ups and downs, of the robotic program has been the prospect of finding evidence of Martian life. The connection with life has made Mars special among planets in the solar system.