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Earth—Why Leave

EarthWhy Leave?

Only humans have the ability to leave their home planet and explore, settle, and even alter other worlds, and many people want to do all of these things. What is the attraction of these distant worlds that tempts humans to leave the comforts of Earth for uncertain, and probably hazardous, journeys beyond?

The history of human exploration of Earth provides a basis for understanding our motivations for exploring new places. At the same time, humankind's brief experiences with human exploration of the Moon, and the extensive robotic exploration of the solar system, show how space exploration will be different from past voyages of discovery in terms of motivation and operation.

In current and near-term space missions, the search for scientific knowledge has been more prominent, sometimes exclusively so, than it was in historical voyages. Furthermore, unlike the European migrations to the New World, it is unlikely that significant fractions of the population can be transported from Earth because of the limitations and costs of rockets . Nonetheless, human and robotic exploration of the other worlds in the solar system might lead to the establishment of permanent human settlements on the Moon, Mars, and elsewhere and eventually to the reconstruction of a planetary-scale biosphere on Mars.

History and Biology Lessons

Since our ancestors ventured out of Africa, humans have explored Earth. Prehistoric peoples successfully filled every ecological niche available to them on the planet, spreading to every continent except Antarctica. Clearly, this attests to an effective and possibly biologically based drive for exploration and expansion. However, the structure and motivation of prehistoric migrations are lost in the depths of time. They probably did not reflect a conscious decision to explore and expand any more than such decisions were part of the spread of the African killer bee through the Americas after its introduction to Brazil in the 1980s. Furthermore, biology is not destiny: Even if there is a biologically based drive to explore and expand, it does not necessarily follow that humans should and will explore and settle other worlds.

The drive to explore in humans can be demonstrated, by counterexample, to be nonobligatory. There are well-known examples of civilizations poised on the edge of great epochs of exploration and expansion that turned inward and developed cultural blocks to exploration and contact with foreigners. In a frequently told tale there is a striking parallel between the expansion of the Portuguese in the fifteenth century and the abortive voyages of the Chinese under the Ming emperors just a few decades before that time. After an impressive series of sea voyages far greater in scope than anything Europe could achieve, the Chinese withdrew, destroyed their seagoing vessels, and left the age of exploration to the Europeans.

There is a clear lesson in this parallel to space exploration, which shows that initial voyages of discovery do not automatically lead to subsequent exploration and expansion. If there is a biological drive to explore, it is greatly influenced, if not dominated, by cultural traditions and myths. In this regard there is general agreement that Western culture has a historical tradition and a collection of myths that inspire and reward exploration.

To Expand Scientific Knowledge

Many space scientists have argued that the fundamental motivation for a space program is the scientific understanding that it generates. In this view, the performance criterion for any mission is the scientific return compared to the cost. Certainly space missions have contributed to an understanding of Earth through studies of greenhouse effects on Venus, Mars, and Titan; the photochemistry of the acid clouds on Venus; the dust storms on Mars; and impact hazard assessments and prevention. Impact by an asteroid is the single most devastating natural hazard known, as testified by the extinction of the dinosaurs 65 million years ago. Through the exploration of space for scientific understanding and the development of space technologies, an asteroid on a collision course with Earth could be detected in advance and methods could be devised for deflection of the asteroid to prevent impact.

Perhaps the most compelling scientific motivation for space exploration is the search for a second genesis of life that has independently begun on another planet. More than being a matter of simple scientific curiosity, the question "Are we alone?" is asked by every person. The search for life is best conducted in space, whether this involves missions to search for biologically produced compounds in the subsurface of Mars, Titan's organic haze, or Europa's frozen oceans or telescopes probing the atmospheric composition of extrasolar planets . Space exploration, specifically the human exploration of planets and planetoids that are hospitable to life, is key in the search for life in the solar system and, by extrapolation, the universe.

But common sense and recent history show that space exploration is not about science alone. If science was the only important motivation for space exploration, the world's space programs would be placed within the basic science agencies and would compete directly with programs involving disciplines such as oceanography, particle physics, and geology. Yet clearly this is not the case. Space programs enjoy a special status, usually within a separate agency. This reflects a broader motivation base for space than science alone.

Beyond Science

Clearly there are significant nonscientific issues of a national and international nature that drive the current space programs of the world. At the highest levels these issues deal with national self-image, international political competition, economic competition, and national technological development. On a more direct level national space programs are perceived as having tangible benefits in terms of the level of education and the overall perception of technology as a positive force in society. For all these reasons there seems to be a consensus that a vigorous space program is in the national and international best interests.

Economics has been suggested as a possible motivation for the exploration and utilization of space. Communication satellites, the mining of helium-3 on the lunar surface and metals on asteroids, and oxygen production on the Moon have received the most attention. Microgravity manufacturing and space tourism also reflect economic incentives for space missions. From this list the only two that have proven profitable so far have been telecommunications satellites and space tourism. Space tourism has only three examples in its support: the flights of a Japanese reporter, a wealthy American businessman, and a South African Internet tycoon, all on Russian missions. From this humble beginning could come luxury hotels in orbit and on the Moon and possibly eco-tourism to Mars.

Reasons for Not Exploring Space

Many past migrations of human populations were driven by acute local problems such as dire economic conditions, famine, warfare, overpopulation, and environmental degradation. It is sometimes suggested that other worlds may provide similar relief when Earth becomes overpopulated or uninhabitable as a result of human actions. However, the limitation of space transport makes these motivations for settling other worlds irrelevant in the near-term. Space exploration and settlement may help solve problems on Earth by providing useful knowledge but is unlikely to provide an escape valve for mismanagement of this planet.

From Exploration to Settlement

The exploration of environments, such as the surface of Mars, that are instantly lethal to humans naturally leads to the question: Does exploration lead to settlement? Historically it has, but the historical record is based upon the exploration of the surface of Earth and, in particular, of environments in which premodern peoples with a rudimentary technology base could thrive. The only example of exploration not based on this model was the exploration of Antarctica. Although permanent scientific research bases have been established in Antarctica and some nations have made legalistic gestures toward inhabitation, there is no effective human settlement in Antarctica. Similarly, but less telling in light of the limited time spent on undersea exploration, there are no human settlements below the water. Human activity on the Moon could be expected to follow the Antarctic model, with the establishment of long-lived research stations and observatories but without a permanent population. Commuting to the Moon from Earth is not out of the question, but travel to Mars is likely to be a different case for two reasons. First, the long trip time and the intermittent nature of Earth-Mars transfer would favor more permanent, self-sufficient settlements than those on the Moon. Second, Mars may allow for the creation of a habitable environment through terraforming efforts.

From Settlement to Terraforming

The presence of humans on another planet will inevitably alter that world's environment, but this can also be done in a purposeful fashion, resulting in a planet that is capable of supporting a rich biospherea process called terraforming. The ultimate motivation for terraforming and for space exploration itself is enhancing the abundance and diversity of life in the universe and enriching the lives of humans. These are goals worthy of an advanced civilization.

see also Communities in Space (volume 4); Environmental Changes (volume 4); Human Missions to Mars (volume 3); Impacts (volume 4); Living on Other Worlds (volume 4); Lunar Bases (volume 4); Lunar Outposts (volume 4); Mars Bases (volume 4); Mars Missions (volume 4); Scientific Research (volume 4); Settlements (volume 4); Social Ethics (volume 4); Space Industries (volume 4); Space Tourism, Evolution of (volume 4); Terraforming (volume 4); Tourism (volume 1).

Christopher P. McKay and Margarita M. Marinova


Clarke, Arthur C. The Snows of Olympus: A Garden on Mars. New York: Norton, 1995.

McKay, Christopher P. "Let's Put Martian Life First."Planetary Report 21 (July/August 2001):4-5.

. "Flowers for Mars."The Planetary Report 20 (September/October 2000):4-5.

. "Does Mars Have Rights? An Approach to the Environmental Ethics of Planetary Engineering." In Moral Expertise, ed. Donald MacNiven. New York: Routledge, 1990. Pp. 184-197.

McKay, Christopher P., and Margarita Marinova. "The Physics, Biology, and Environmental Ethics of Making Mars Habitable."Astrobiology 1, no. 1 (2001):89-109.

Zubrin, Robert, with Richard Wagner. The Case for Mars: The Plan to Settle the Red Planet and Why We Must. New York: Free Press, 1996.

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