Does Mars have rights? What about Europa, Ganymede, and Titan—the moons of Jupiter and Saturn that may be home to rudimentary extraterrestrial life? The 1967 Outer Space Treaty requires spacefaring nations to conduct exploration of the moon and other celestial bodies "so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter." The goal of the treaty is to prevent both back contamination (the introduction of extraterrestrial life to Earth) and forward contamination (the introduction of Earth life to extraterrestrial environments).
The reason for avoiding back contamination is pretty clear. We want to prevent an Andromeda Strain scenario in which an unleashed alien life form harms life on Earth. Returning Apollo astronauts and their hauls of moon rocks were quarantined for a couple of weeks, just to make sure that no lunar microbes escaped to wreak havoc. Years of testing found no indication of life hidden in the moon rocks.
The main reason to guard against forward contamination is to prevent equipment designed to detect extraterrestrial life from getting confused. Consequently, NASA regularly sterilizes gear destined to land on other celestial bodies. So far no mission has detected life anywhere else in our solar system.
All this caution is reasonable, as long as we are just poking around and taking some readings. But what are our ethical obligations if, as some space exploration visionaries urge, humanity begins the process of making other worlds fit for human habitation? British planetary scientist Martyn Fogg explains, "The ultimate in terraforming would be to create an uncontained planetary biosphere emulating all the functions of the biosphere of the Earth—one that would be fully habitable for human beings."
Mars in its current condition is not a promising home for Earth life. The Red Planet's average temperature is -60°C, well below Earth's average of 15°C. The pressure of its carbon dioxide atmosphere is one-hundredth that of our planet's nitrogen-oxygen atmosphere, and it lacks an ozone layer, so its surface is blasted by DNA-destroying ultraviolet rays from the sun.
Can Mars be made more hospitable? The level of life-sustaining carbon dioxide could be raised by pumping potent man-made greenhouse gases like perfluorocarbons into the Martian atmosphere or by directing extra sunlight from a space mirror 250 kilometers in diameter at the Martian South Pole. Either solution would take an estimated 100 years to build up an atmosphere thick enough so that the new warmth would prove hospitable to colonizing anaerobic microbes that thrive in extreme environments on Earth.
Later, we could genetically engineer Earth plants so that they could begin to pump oxygen into Mars' atmosphere. It might take another 10,000 to 100,000 years for the terraformed Martian atmosphere to contain enough oxygen for people to breathe unassisted. But assuming that terraforming Mars would work, would doing so violate a moral obligation to leave Mars and other worlds alone?
Yes, argued Australian philosopher Robert Sparrow in a 1999 article, "The Ethics of Terraforming," in the journal Environmental Ethics. An effort to terraform Mars, Sparrow asserted, "demonstrates two serious defects of moral character: an aesthetic insensitivity and the sin of hubris. Trying to change whole planets to suit our ends is arrogant vandalism."
Developing what he called an agent-based virtue ethics, Sparrow argued that what makes actions right or wrong is the character of the moral agent. Terraforming Mars indicates an ethically significant aesthetic insensitivity reminiscent of a remote hiker wantonly whacking a transient but beautiful set of icicles on a wintry day. "What is significant is the blindness the hiker has displayed to beauty even though no one else may suffer from its loss," he wrote. The blindness is a vice. Filling Mars' Valles Marineris, the largest canyon in the solar system, with genetically modified redwoods would indicate that we do not properly appreciate its present desolate beauty.
The second moral defect demonstrated by terraforming, according to Sparrow, is hubris, which "occurs when humans willfully ignore their limits and seek to become like gods." Instead we should stay in our proper place. "A proper place is one in which one can flourish without too much of a struggle," Sparrow explained. So our proper place is Earth, and "we must show that we are capable of looking after our current home before we could claim to have any place on another."
Sparrow acknowledged that he did not offer an objective account of beauty, so the notion still resides in the eye of the beholder, as does desolate ugliness. And as awesome as the view down Valles Marineris might be right now, it would arguably be even more so if it were teeming with life. With regard to the hubris of terraforming, one initial response should be a hearty "so what?" Terraforming offers the promise of helping humanity toward practical moral improvement by increasing our understanding of just how precious terrestrial life is, aiding us in managing it toward greater integrity, stability, and beauty.
Mars may not be lifeless. Some researchers believe that Martian life may have retreated to warm underground refuges as the planet's oceans dried up and froze hundreds of millions of years ago. Do we have any moral obligations toward Martian microbes, should they exist?
"If life is present on another world, the introduction of terrestrial life forms could lead to an ecological holocaust, a moral and aesthetic tragedy, as well as an immense loss to science," argued University of Oregon sociologist Richard York in a 2005 article, "Toward a Martian Land Ethic," in Human Ecology Review.
Martian life might indeed constitute a "second genesis," that is, life that has arisen independent of Earth life. Or it might be the result of transpermia, in which organisms were spread via meteors between planets. Perhaps life originated on Mars and eventually reached Earth, where it thrived. If so, what we could learn from Martian life probably would be limited, and terraforming would not be ethically much different from colonizing terrestrial ecosystems uninhabited by humans.
NASA astrobiologist Christopher McKay, who first raised the question of whether Mars has rights in a 1990 essay in the book Moral Expertise: Studies in Practical and Professional Ethics, argues that if Martian life is a second genesis, "its enormous potential for practical benefit to humans in terms of knowledge" might "exceed the opportunity cost of not establishing human settlements on Mars." But finding a second genesis so close to Earth also would suggest that the emergence of life is a relatively common occurrence in the cosmos, reducing the moral force of arguments for preserving Martian microbes. Saving samples of Martian life for later study is a prudent precondition before embarking on terraformation.
Dead planets and moons are not intrinsically valuable. And as fascinating as they might be, Martian microbes are not moral agents, any more than are terrestrial microbes. They simply do not have an ethical point of view that we must consider. On that account, there is no good moral reason why humans should limit the expansion of terrestrial life, including themselves, throughout the solar system.
Science Correspondent Ronald Bailey is the author of Liberation Biology (Prometheus Books).