Several influential philosophers and environmentalist thinkers argue that terraforming Mars and other planets, making them suitable for humans and other Earth life, would be immoral. As we near a day when terraforming is actually possible, the arguments against it are worth reviewing and rebutting.
"Trying to change whole planets to suit our ends is arrogant vandalism," Monash University philosopher Robert Sparrow asserts in a 1999 essay, saying the desire to do so reflects "aesthetic insensitivity and hubris." Sparrow maintains that "we must show that we are capable of looking after our current home before we could claim to have any place on another."
In a special 2019 issue of the academic journal Futures, neuroscientist Lori Marino likewise claims that "our species is not capable of living on any planet sustainably." Another contributor to that issue of the journal, University of Texas anthropologist John Traphagan, agrees. "We are not capable of enacting a successful colonization of another planet," he writes. "The fact that we have destroyed our home planet is prima facie evidence of this assertion."
Saint Paul College philosopher Ian Stoner, who contributed a chapter to the 2021 book Terraforming Mars, argues that doing so would violate "a duty to conserve objects of special scientific value, a duty to preserve special wilderness areas, and a duty not to display vices characteristic of past colonial endeavors on Earth." He therefore concludes that "terraforming Mars is probably morally wrong."
What should we make of people who oppose terraforming? In his contribution to the Futures special issue, Clemson University philosopher Kelly Smith, a terraforming advocate, tartly notes that his opponents think humanity "deserves" to perish "until and unless humans can demonstrate an ability to live in harmony with our environment." He describes that position as "eco-nihilism."
Similarly, Santa Clara University applied ethicist Brian Green decries as "necrotic ideology" the argument that humanity is headed to well-merited extinction and therefore should refrain from colonizing other worlds. Green instead argues that "self-preservation should be humankind's first ethical priority," so "rapid space settlement is necessary."
Some of the risks we face, such as global nuclear war or pandemics of lethal biotech pathogens, are human-made. But others, such as asteroid strikes or the eruption of a supervolcano, are natural. Since there is no morality without human beings, Green says, the most fundamental human moral obligation is to avoid extinction. And because colonizing other worlds reduces that risk, it is morally necessary.
It is not only humans who risk annihilation by remaining stuck on Earth. An asteroid strike or a nuclear winter could destroy most, if not all, Earth life. "All life and the total ecosphere [have] an interest in avoiding catastrophic risk and pursuing a long-term future," notes Andrea Owe, an environmental philosopher at the Global Catastrophic Risk Institute, in a 2022 essay. "There is no human and nonhuman world; there is one ecosphere. Humans are part of ecosystems and the animal kingdom alike."
Establishing self-sustaining ecosystems on other worlds would protect human beings and other Earth life. Owe therefore concludes that humans, "as the only species currently capable of space expansion," have an obligation as the "morally responsible stewards of the total Earth story" to spread themselves and Earth life throughout the universe.
What if there is indigenous life on Mars? Any Martians would most likely be rare and microbial, given that various rovers have yet to definitely identify life on Mars. "If there is life on Mars," cosmologist Carl Sagan said back in 1985, "I believe we should do nothing with Mars. Mars then belongs to the Martians, even if the Martians are only microbes."
Smith calls such noninterventionism "Mariomania." He agrees that "the scientific value of Martian life clearly justifies a very strong principle of conservatism in our early interactions with [it]." But once researchers have answered most of the major scientific questions about it, do humans have a moral obligation to protect Martian microbes? In general, we do not accord terrestrial microbes any moral consideration. Still, saving samples of Martian life for later study is a prudent precaution before embarking on terraforming.
Owe's ecocentric arguments jibe with evolutionary biologist Lynn Margulis' case for "ecopoiesis." Greek for "making of a home," ecopoiesis is the artificial creation of a sustainable Earth life ecosystem on another planet. In the 1970s, Margulis and atmospheric chemist James Lovelock co-developed the controversial Gaia hypothesis. They suggested that our planet could be viewed as a complex, integrated entity that relies on feedbacks in the biosphere, atmosphere, oceans, and soil to maintain an optimal physical and chemical environment for life. Margulis and Lovelock both were advocates of reproducing that complex system on Mars. Terraforming Mars would be, according to Margulis, "exactly equivalent to 'the reproduction of Gaia by budding.'"
Terraforming Mars, or any other planet in our solar system, certainly will not be easy. In its natural state, Mars is quite inhospitable. The temperature averages minus 81 degrees Fahrenheit, ranging from minus 220 degrees at the poles in the winter to 70 degrees near the equator during the summer. The atmosphere is 95 percent carbon dioxide, and atmospheric pressure on the surface is less than 1 percent of the pressure at sea level on Earth, equivalent to being 28 miles above Earth's surface. That is well above the Armstrong limit, where atmospheric pressure is so low that the boiling point for water equals normal human body temperature. The thin atmosphere also means the surface is unprotected from harsh ultraviolet solar radiation, while the lack of a global magnetic field means Mars is constantly bombarded by cosmic rays.
There may be ways to surmount these obstacles. SpaceX founder Elon Musk has suggested nuking the Martian poles to release carbon dioxide to thicken and warm the atmosphere and flood the planet's basins with water. In a 2019 Archives of Microbiology article, two Irish biologists described how developments in synthetic biology could create organisms that would survive on Mars and begin transforming its surface and atmosphere. This year in Acta Astronautica, a team of space scientists outlined how material from the Martian moons could be used to create an artificial magnetosphere to protect the planet's surface from radiation.
"While humanity's greatest immediate challenge is to survive the next century or two," Owe argues, "our greatest achievement will be eventually greening the universe and bringing it to life." It would be immoral not to terraform it all.