Can We Colonize Other Planets?

"Interstellar" the Movie—and the Scientific Realities

The notion that humans might someday colonize other planets has been a recurring theme in the literature of science fiction. For much of the 20^th century, the desire to colonize other planets was portrayed as a modern  expression of the pioneering spirit that moved the Europeans to emigrate to the far corners of the earth and the pioneers to settle the American West. But in the 21^st century, the concept of extraterrestrial colonization has been increasingly portrayed as a solution to the looming crisis of overpopulation and environmental destruction.

This more contemporary notion is central to Christopher Nolan’s movie “Interstellar,” set in the near future, when the earth is depicted as being in the throes of rapid environmental collapse. A secret NASA project is underway to find another planet, somewhere else in the universe, that will be suitable for human colonization. The goal of this project is to protect the human species from the certain extinction that awaits it on a dying Earth.

“Interstellar” is advertised as being based on “real scientific concepts” such as black holes, distortions in the passage of time, and “wormholes” in space-time that could allow objects (such as spaceships) to pass instantly from one part of the universe to another. But a wormhole is not an actual phenomenon. It is merely a hypothetical construct predicted by the theory of relativity. No one has ever observed a wormhole, and no scientist has ever proposed a process by which a wormhole could actually be formed naturally in space.

While “Interstellar” is a very entertaining work of fiction, any real-world attempt to colonize another planet would require actual travel across the mind-numbing vastness of space. It would also require the construction of an artificial environment that would provide humans with an endless supply of food, water, and breathable air—a feat which modern science has thus far never been able to accomplish.

In my recent book, UNBOUND: How Eight Technologies Made Us Human, Transformed Society, and Brought Our World to the Brink (New York: Arcade Publishing, 2015), I explain why the passengers on a spaceship capable of travelling fast enough to reach the moon in 30 minutes would have to survive for nearly 24,000 years in an artificial environment before they could reach the nearest earth-like planet. 

The notion that humans might someday colonize other planets is a modern myth that does not square with the known scientific facts. While it may be an entertaining fantasy, it should never be regarded as an alternative to the urgent task of protecting the earth's unique and irreplaceable biosphere—the totality of living ecosystems that gave birth to our species and upon which we depend for our continued existence.

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The following passage is excerpted from Chapter 10 of UNBOUND:

 “Our World at the Brink: Is Humanity Drifting Toward a Planetary Catastrophe?”

On July 21, 1969, the American astronauts Neil Armstrong and Buzz Aldrin became the first human beings—indeed, the first terrestrial organisms—to set foot on the moon. They were followed over the next three and one-half years by ten others. And of all the unique sights and experiences that the moon landings provided, perhaps the most powerful, in its effect on the astronauts themselves, was the sight of the earth from the depths of space.

Frank Borman, the commander of the Apollo Mission, recalled the experience of seeing the earth, in all its multicolored glory, floating in space nearly a quarter of a million miles away. “I happened to glance out of one of the still-clear windows,” he wrote, ”just at the moment the earth appeared over the lunar horizon. It was the most beautiful, heart-catching sight of my life, one that sent a torrent of nostalgia, of sheer home-sickness, surging through me.” And James Lovell, the pilot of the command module, once remarked, “The most impressive sight I saw was not the moon, not the far side that we never see, or the craters.  It was Earth . . .”

Earthrise from the Moon

Yet the future of our unique, irreplaceable planet is now seriously threatened as never before by the very technologies that made us human. The human scourges of war, pollution, deforestation, species extinction, and climate change—all of which have flowed from our technological prowess—have put the living world at risk. But before we review each of these threats in detail, we must consider a fundamental question of our age. Can we escape the ills we have created for ourselves by leaving the earth behind and starting over? Can we build a better life for humanity on the virgin soil of another planet?

Can We Colonize Other Planets?

There is an idea that has become popular in recent years, in which it is imagined that future generations of humans will escape the earth’s problems by using advanced technologies to colonize other planets. But even if we ignore the sheer logistical problem of launching hundreds of thousands of tons of supplies and equipment into space—and we consider only the environmental conditions that we know to exist on other planets—the goal of colonizing other heavenly bodies appears to be, for all practical purposes, literally unattainable.

Our moon is a silent, airless world of lifeless rock and dust. A single day on the moon lasts for 28 earth days, and temperatures on the surface of the moon during these lunar “days” are hot enough to boil water, while surface temperatures during the lunar “nights” can plunge to nearly three hundred degrees below zero Fahrenheit.

The planet Mercury is an airless ball of iron and rock rotating so slowly that a single day on Mercury lasts almost as long as two months on Earth. For this reason, surface temperatures on Mercury rise to 650 degrees Fahrenheit during Mercury’s “day” and drop to 274 degrees below zero Fahrenheit during Mercury’s “night.”

The planet Venus is smothered in rolling clouds of sulphuric acid, and its atmosphere is so dense that atmospheric pressure on the planet’s surface is a crushing 1,350 lbs. per square inch. This is 92 times greater than the 14.7 lbs. per square inch on Earth at sea level and is, in fact, equivalent to the pressure that a diver would feel by descending half a mile into the sea. Due to the “runaway greenhouse effect” of its carbon dioxide atmosphere, surface temperatures on Venus remain uniformly above eight hundred degrees Fahrenheit. This is hot enough to melt most soft metals, including lead and zinc.

The planet Mars is a frozen wasteland of rocks and dust that are red from their high concentration of iron oxide. Surface temperatures on Mars average eighty degrees below zero Fahrenheit. The Martian atmosphere is one hundred times thinner than the atmosphere of Earth and 95% of this atmosphere consists of carbon dioxide, with only a trace of oxygen. In addition to its inhospitable temperatures and unbreathable atmosphere, Mars is regularly pounded by gigantic dust storms which can last for months at a time and often grow large enough to envelop the entire planet.

Jupiter, Saturn, Neptune, and Uranus—the “gas giants” of our solar system—are composed of cores of ice and rock larger than Earth that are covered with thick atmospheres of hydrogen and helium and buried under immense oceans of liquefied hydrogen and helium thousands of miles deep. None of these planets have any real “surfaces” in the normal sense of the word—only mushy regions where gases become compressed into liquids and where liquids become compressed into solids, all of which are hidden in total and perpetual darkness.

Considering the hostility of their environments to all known forms of life, none of the other planets in our solar system are reasonable candidates for human colonization. Certainly, it would be vastly more practical to colonize the earth’s great uninhabited deserts or the frozen wastelands of the polar regions. These lands are not only endowed with more temperate climates than any other of our sister planets but they are also blessed with Earth’s eminently breathable, oxygen-rich atmosphere.

But what about the “earth-like planets” that astronomers have been discovering in other, nearby solar systems? Could one of them provide a second home for the surplus hominid populations that—given the current rate of human population increase—may soon be overrunning the earth?

While astronomers generally agree that the universe contains many other earth-like planets, all of these worlds are so distant that we know very little about their climates or surface characteristics. The earth-like planet nearest to our solar system is believed to orbit the star Tau Ceti, located twelve light-years from Earth, but the planet believed most likely to have an earth-like climate is called Gliese 832 c, located at a distance of sixteen light-years from Earth. (I am using the word "believed" for good reason. Due to their small size and immense distance from Earth, no planet outside of our own solar system has actually been observed directly. Instead, their existence is inferred from “wobbles” in the stars themselves, caused by the gravitational pull of the planets revolving around them.)

Gliese 832 c has been estimated to be five times the size of the earth. Thus, a person who weighed 160 lbs. on Earth would weigh 800 lbs. on the surface of Gliese 832 c. This would prevent a normal human being from either standing or walking. But let us suppose for the sake of argument that the gravity problem could be solved somehow—for example, by strapping on metal braces to help support the body under these crushing loads. Even so, the daunting problem of how a group of humans would survive the long journey from our solar system to these “neighboring” solar systems would still have to be solved.

The typical space rocket escapes the earth’s gravitational pull by achieving a launch speed of approximately 18,000 miles per hour. NASA’s “New Horizons” mission—designed to explore the region outside of our own solar system—achieved a launch velocity of 36,000 miles per hour which, combined with the speed of the earth’s orbit around the sun, boosted the spacecraft to a velocity of 100,000 miles per hour. Although this was fast enough to escape the sun’s gravity, New Horizons had slowed to 31,000 miles per hour by the time it actually left the solar system.

In 2018, a planned mission by NASA called the “Solar Probe Plus” is projected to use the “slingshot effect” of the sun’s gravity to reach a staggering 450,000 miles per hour while orbiting the sun. This is fast enough to travel from the earth to the moon in thirty minutes. But even if a spacecraft capable of carrying live humans plus all their cargo and equipment could somehow—even while fighting the sun’s gravity—attain a speed of 450,000 miles per hour on its way out of the solar system, it would have to travel through space for nearly twenty-four thousand years before arriving in the vicinity of Gliese 832 c. (Since light travels at the speed of 670,616,629 miles per hour, this equals 16,094,799,096 miles per day. Multiplied by 365 days in a year, this is 5,874,601,670,040 miles per year. Sixteen light-years is thus 93,993,626,720,640 miles. At 450,000 miles per hour, it would require 208,874,726 hours, which equals 8,703,114 days or 23,844 years to cover the distance from the earth to Gliese 832 c.)

It is difficult to imagine how a handful of human beings could survive inside the confines of a spaceship for roughly five times longer than the entire history of human civilization. It is even more difficult to imagine what the tiny population of such a spaceship would look like after more than seven hundred generations of inbreeding.

But let us suppose for the sake of argument that some future civilization, having developed a technology unknown to us, will defy the known laws of physics and succeed in constructing a functioning space vehicle capable of travelling at nearly the speed of light. Would such a technology open up the universe to interstellar colonization by hominids?

Even in the case of this highly improbable scenario, such interstellar colonists would still be required to survive for many years in space without life support from their home planet before they arrived at the vicinity of the nearest earth-like planet. These colonists would therefore need a technological infrastructure capable of providing them with a reliable supply of food, warmth, and breathable air while they traveled for years through the blackness of space. And thus far even the best efforts of modern technology have utterly failed to provide human beings with a means of surviving indefinitely once all physical contact with the "biosphere"—the sum total of all life forms and ecological systems that cover the surface of Earth—has been severed.

Life Without the Biosphere

Any attempt to colonize other worlds would require the creation of an artificial ecosystem capable of supporting human life without being connected to the earth’s biosphere, and an attempt to do exactly that was made in 1991—not on another planet but in the relatively benign terrestrial environment of the Southwestern United States. At a cost of $200 million, a three-acre enclosure called “Biosphere 2” was constructed in the Sonoran Desert near Tucson, Arizona to serve as the model for a self-sustaining environment that could be replicated in an extraterrestrial colony. It was to be inhabited by a group of eight people who called themselves “the Biospherians.”

Biosphere 2 in 1991

The four men and four women who volunteered for this mission intended to live inside this enclosure for two years, sustaining themselves without any supply of air, food, or water from the outside. Biosphere 2 was stocked with soil, water, plants, and animals, and it included a small sea, a savanna environment, a mangrove swamp, a rain forest, a desert, and a farm. The idea was that these various environments and their atmospheres would interact to form a totally independent life-support system within which humans could live indefinitely.

In September of 1991, the Biospherians passed through the airlocks of Biosphere 2 and began their two-year mission. But in spite of the availability of massive technological and financial support from outside the enclosure, the Biosphere 2 experiment demonstrated how quickly an ecosystem can collapse when its connection with the natural biosphere has been severed.

Throughout the entire first year of the mission, the farm that had been established inside Biosphere 2 failed to provide sufficient food for the crew. During the first twelve months, the Biospherians experienced continual hunger, were obsessed about the scarcity of food, and lost a significant amount of weight. By the end of the first year, the eight Biospherians had split into two opposing factions that were barely on speaking terms with each other.

In spite of a profusion of green plants, oxygen levels inside the enclosure steadily declined, ultimately falling to the level normally found at an elevation of 17,500 feet. Meanwhile, carbon dioxide levels skyrocketed, fluctuating wildly from one day to the next. Fearing for the health of the crew, project administrators were forced to pump oxygen into the enclosure repeatedly, beginning seventeen months into the experiment.

Over time, the atmosphere inside Biosphere 2 also became permeated with nitrous oxide, ultimately reaching levels that threatened the crew with permanent brain damage. In addition, the stillness of the air inside the enclosure caused the trunks and branches of the trees—normally strengthened by the action of the wind—to grow weak and brittle, and they became prone to what scientists later reported as “catastrophic dangerous collapses.” At the same time, morning glory vines grew wildly, smothering the other plants and trees and requiring constant weeding.

All the species of pollinating insects that had been brought into the Biosphere died out, preventing most of the agricultural plants from reproducing and ensuring that they would not survive beyond their normal life spans. Most of the other insects also died, ultimately leaving Biosphere 2 completely overrun by vast swarms of cockroaches and “longhorn crazy ants” running wildly in all directions. (Paratrechina longicornus, the “longhorn crazy ant” is one of the most common species of ants and is found in human habitations throughout the world. Its name is derived from its long antennae and its habit of running erratically at high speeds in all directions.)

Areas that had been intended as deserts turned into chaparral and grasslands, and the water system became so loaded with chemical nutrients that it was necessary to circulate all of the water over thick mats of algae that had to be periodically harvested, dried, and stored inside the enclosure. Finally, of the twenty-five species of birds, mammals, fish, and reptiles originally introduced into Biosphere 2, all the animals except for six species had died by the time the experiment ended twenty-four months later.

In a sobering report on the lessons of Biosphere 2 published in 1996, biologist Joel E. Cohen and ecologist G. David Tilman concluded, “At present there is no demonstrated alternative to maintaining the viability of Earth. No one knows yet how to engineer systems that provide humans with the life-supporting services that natural ecosystems produce for free.”

There is only one world we know of that can sustain human life, and it is our blue-green planet that so thrilled and delighted the astronauts during their visits to the moon. We have no other home; we can breathe no other air; no other planet can feed us. The earth is quite literally the only life support system available to the human species. We have no alternative to keeping the earth’s biosphere healthy and alive so that we ourselves can remain healthy and alive. 

At this point in our species' history, all else is science fiction and fantasy.