by Michio Kaku
It is estimated that, if the ice caps of Mars were completely melted, there would be enough liquid water to fill a planetary ocean fifteen to thirty feet deep.
REACHING THE TIPPING POINT
These proposals all endeavor to bring the Martian atmosphere to a tipping point where the warming would become self-sustaining. Raising the temperature by six degrees Celsius would be sufficient to instigate the melting process. The greenhouse gases emitted from the ice caps would heat the atmosphere. The carbon dioxide absorbed into the desert aeons ago would also be released and contribute to planetary warming, causing further melting. Thus, the heating of Mars would continue without further intervention from the outside. The warmer the planet, the more water vapor and greenhouse gases are released, which in turn warms the planet even more. This process could carry on almost indefinitely and would increase Mars’s atmospheric pressure.
Once liquid water starts to flow within the ancient riverbeds of Mars, settlers could begin large-scale agriculture. Plants love carbon dioxide, so the first outdoor crops might be raised, and their waste products could be used to generate a layer of topsoil. Another positive feedback loop would be initiated: more crops would produce more soil, which could be used to nurture additional crops. The native soil of Mars also contains valuable nutrients such as magnesium, sodium, potassium, and chlorine that would help plants succeed. As plants begin to proliferate, they will also generate oxygen, an essential ingredient for terraforming Mars.
Scientists have created greenhouses that simulate the harsh conditions on Mars to see if plants and bacteria can survive there. In 2014, NASA’s Institute for Advanced Concepts partnered with Techshot to construct biodomes with controlled environments in which to grow oxygen-producing cyanobacteria and algae. Preliminary tests indicate that certain life-forms can indeed flourish there. In 2012, scientists at the Mars Simulation Laboratory, maintained by the German Aerospace Center, found that lichen, which is similar to moss, could survive there for at least a month. In 2015, scientists at the University of Arkansas showed that four species of methanogens, microorganisms that produce methane, can survive in a habitat resembling the Martian ecology.
Even more ambitious is NASA’s Mars Ecopoiesis Test Bed, a project that aims to send hardy bacteria and plants, such as extremophile photosynthetic algae and cyanobacteria, to Mars aboard a rover. These life-forms would be placed in canisters that could be drilled down into the Martian soil. Water would be added to the canisters, and then instruments would look for the presence of oxygen, which would indicate active photosynthesis. If this experiment is successful, Mars may one day be covered with farms of this kind to generate oxygen and food.
By the beginning of the twenty-second century, the technologies of the fourth wave—nanotech, biotech, and AI—should be mature enough to have a profound impact on the terraforming of Mars.
Some biologists have posited that genetic engineering may result in a new species of alga that is designed to exist on Mars, perhaps in the particular chemical mix of its soil or in newly formed lakes. This alga would thrive in the cold, thin, carbon-dioxide-rich atmosphere and release copious quantities of oxygen as a waste product. It would be edible and could be bioengineered to mimic flavors found on Earth. In addition, it would be engineered to produce an ideal fertilizer.
In the movie Star Trek II: The Wrath of Khan, a fantastic new technology called the Genesis Device was introduced. It was capable of terraforming dead planets into lush, livable worlds almost instantly. It would explode like a bomb and release a spray of highly bioengineered DNA. As this super DNA spreads to all corners of the planet, the cells would take root and dense jungles would form until the whole planet was terraformed within a matter of days.
In 2016, Claudius Gros, a professor at Goethe University in Frankfurt, Germany, published a paper in the journal Astrophysics and Space Science detailing what a real-life Genesis Device might look like. He predicts that a primitive version will be possible in fifty to one hundred years. First, scientists on Earth would have to carefully analyze the ecology of the lifeless planet. The temperature, soil chemistry, and atmosphere would determine which types of DNA should be introduced. Then, fleets of robotic drones would be sent to the planet to deposit millions of nano-sized descent capsules carrying an array of DNA. When these capsules release their contents, the DNA, engineered precisely to thrive in the planet’s environmental conditions, would latch onto the soil and begin to germinate. The contents of these capsules are designed to reproduce by creating seeds and spores on the barren planet and use the minerals found there to create vegetation.
Dr. Gros believes that life on the newly seeded planet would have to develop the old-fashioned way, by evolution. He warns that “global-scale ecological disasters” might occur if we try to rush this process, especially if one type of life-form ends up proliferating so rapidly that it pushes out the others.
WILL TERRAFORMING LAST?
If we succeed in terraforming Mars, what is to prevent it from reverting back to its original barren state? Investigating this issue brings us back to a critical question that has been nagging at astronomers and geologists for decades: Why did Venus, Earth, and Mars evolve so differently?
When the solar system formed, the three planets were similar in many ways. They had volcanic activity, which released large quantities of carbon dioxide, water vapor, and other gases into their atmospheres. (This is why, even today, the atmospheres of Venus and Mars consist almost exclusively of carbon dioxide.) The water vapor condensed into clouds, and the rain helped to carve out the rivers and lakes. If they had been closer to the sun, their oceans would have boiled away; and if they were farther out, their oceans would have frozen. But all three were within or very close to the “Goldilocks zone,” the band around a star that allows water to remain in liquid form. Liquid water is the “universal solvent” out of which the first organic chemicals materialized.
Venus and the Earth are almost identical in size. They are celestial twins, and by rights, they should have followed the same evolutionary history. Science fiction writers once envisioned Venus as a verdant world that would make a perfect vacation spot for weary astronauts. In the 1930s, Edgar Rice Burroughs introduced another interplanetary swashbuckler, Carson Napier, in Pirates of Venus, which described the planet as a jungle-like wonderland, full of adventure and danger. But today, scientists realize that Venus and Mars do not resemble the Earth at all. Something happened billions of years ago that sent these three planets on very distinct paths.
In 1961, when the romantic notion of a Venusian utopia still dominated the public imagination, Carl Sagan made the controversial conjecture that Venus suffered from a runaway greenhouse effect and was devilishly hot. His novel and disturbing theory was that carbon dioxide acts as a one-way street for sunlight. Light can readily enter through the carbon dioxide in Venus’s atmosphere because the gas is transparent. But once the light bounces off the ground, it turns into heat or infrared radiation, which cannot easily escape the atmosphere. The radiation becomes trapped, in a process similar to the way a greenhouse captures sunlight during winter or the way cars heat up in the summer sun. This process happens on the Earth, but it is vastly accelerated on Venus because it is much closer to the sun, and a runaway greenhouse effect was the result.
Sagan was proven correct the next year when the Mariner 2 probe flew past Venus and revealed something truly shocking: the temperature was a blistering nine hundred degrees Fahrenheit, hot enough to melt tin, lead, and zinc. Instead of being a tropical paradise, Venus was a hellhole resembling a blast furnace. Subsequent space shots confirmed the bad news. And there was no relief when it rained, because the rains consist of caustic sulfuric acid. Considering that Venus is linked to the Greek goddess of love and beauty, it is ironic that this sulfuric acid, which is highly reflective, is the reason why Venus shines so brightly in the night sky.
In addition, the atmospheric pressure of Venus was found to be almost one hundred times that o
f the Earth. The greenhouse effect helps to explain why. Most of the carbon dioxide on the Earth is recycled, dissolving in the oceans and in rocks. But on Venus, the temperature became so high that the oceans boiled off. And instead of dissolving in rocks, the gas was baked out of them. The more carbon dioxide outgassed from the rocks, the hotter the planet got, setting off a feedback loop.
Due to the planet’s high atmospheric pressure, being on the surface of Venus is equivalent to being three thousand feet below the surface of Earth’s oceans. You would be crushed like an eggshell. But if you could find a way to overcome this and the searing temperatures, you would still be confronted with a scene from Dante’s Inferno. The air is so dense that, when walking on the surface, you would have the sensation of walking through molasses, and the ground under your feet would feel soft and squishy because it is made of molten metal. The acid rains would eat through the tiniest tear in your space suit, and one false move and you might sink into a vat of molten magma.
Given these constraints, terraforming Venus seems out of the question.
WHAT HAPPENED TO MARS’S OCEAN?
If our twin, Venus, turned out differently because it was closer to the sun, how do we explain the evolution of Mars?
The key is that Mars is not only farther from the sun, but it is also much smaller and therefore cooled off faster than the Earth. Its core is no longer molten. Planetary magnetic fields are generated by the motion of metal within a liquid core, creating electrical currents. Since the core of Mars is made of solid rock, it cannot create an appreciable magnetic field. In addition, it is believed that heavy meteor bombardment three or so billion years ago triggered so much chaos that the original magnetic field was disrupted. This may explain why Mars lost its atmosphere and water. Without a magnetic field to protect it against harmful solar rays and flares, the atmosphere was gradually blown into outer space by the solar wind. As the atmospheric pressure dropped, the oceans boiled away.
Another process accelerated the loss of its atmosphere. Much of the original carbon dioxide on Mars dissolved into the oceans and turned into carbon compounds, which subsequently were deposited on the ocean floor. Tectonic activity on the Earth periodically recycles the continents and enables carbon dioxide to rise to the surface again. But because the core of Mars is probably solid, it has no significant tectonic activity, and its carbon dioxide was locked into the ground permanently. As carbon dioxide levels began to drop, a reverse greenhouse effect took place and the planet went into a deep freeze.
The dramatic contrasts between Mars and Venus can help us appreciate the Earth’s geologic history. The core of the Earth could have cooled down billions of years ago. But it is still molten, because unlike the Martian core, it contains highly radioactive minerals like uranium and thorium with half-lives of billions of years. Whenever we are faced with the awesome power of a volcanic explosion, or the devastation caused by a massive earthquake, we are encountering a demonstration of how the energy of the Earth’s radioactive core drives events on the surface and helps sustain life.
The heat generated by radioactivity deep inside the Earth causes the iron core to churn and produce a magnetic field. This field protects the atmosphere from the solar wind and deflects deadly radiation from space. (We see this in the form of the Northern Lights, which are created when the sun’s radiation hits the Earth’s magnetic field. The field around the Earth is like a gigantic funnel, channeling radiation from outer space toward the poles, so that most of the radiation is either deflected or absorbed by the atmosphere.) The Earth is larger than Mars, so it did not cool down as quickly. The Earth also did not suffer a collapse of its magnetic field caused by giant meteor impacts.
We can now revisit our earlier question about how to keep Mars from returning to its prior state after it has been terraformed. One ambitious method is to artificially generate a magnetic field around Mars. To do this, we would have to place huge superconducting coils around the Martian equator. Using the laws of electromagnetism, we can calculate the amount of energy and materials necessary to produce this band of superconductors. But such a tremendous undertaking is beyond our capabilities in this century.
Settlers on Mars, however, would not necessarily regard this threat as an urgent problem. The terraformed atmosphere could remain relatively stable for a century or even longer, so adjustments may be made slowly over the centuries. The upkeep might be a nuisance but would be a small price to pay for humanity’s new outpost in space.
Terraforming Mars is a primary goal for the twenty-second century. But scientists are looking beyond Mars as well. The most exciting prospects may be the moons of the gas giants, including Europa, a moon of Jupiter, and Titan, a moon of Saturn. The moons of gas giants were once thought to be barren hunks of rock that were all alike, but they are now seen as unique wonderlands, each with its own array of geysers, oceans, canyons, and atmospheric lights. These moons are now being eyed as future habitats for human life.
How bright and beautiful a comet is as it flies past our planet—provided it does fly past it.
—ISAAC ASIMOV
6 GAS GIANTS, COMETS, AND BEYOND
One fateful week in January 1610, Galileo made a discovery that would shake the very foundations of the church, alter our conception of the universe, and unleash a revolution.
With the telescope that he had just crafted, he gazed at the planet Jupiter and was puzzled when he saw four luminous objects hovering near the planet. Carefully analyzing their motion over a week, he was convinced that they orbited around Jupiter. He had found a miniature “solar system” in outer space.
He quickly understood that this revelation had cosmological and theological implications. For centuries, the church, citing Aristotle, had taught that all the heavenly bodies, including the sun and the planets, circled the Earth. Yet here was a counterexample. The Earth was dethroned as the center of the universe. In one fell swoop, the beliefs that had girded church doctrine and two thousand years of astronomy were refuted.
Galileo’s discoveries sparked widespread excitement among the public. He did not need an army of spin doctors and PR advisers to convince the people of the truth of his observations. They could see with their own eyes that he was correct, and he received a hero’s welcome when he visited Rome the following year. The church, however, was not pleased. His books were banned, and he was put on trial by the Inquisition and threatened with torture unless he recanted his heretical ideas.
Personally, Galileo believed that science and religion could coexist. He wrote that the purpose of science is to determine how the heavens go, while the purpose of religion is to determine how to go to heaven. In other words, science is about natural law, while religion is about ethics, and there is no conflict between them as long as one keeps this distinction in mind. But when the two collided during his trial, Galileo was forced to recant his theories under pain of death. His accusers reminded him that Giordano Bruno, who had been a monk, had been burned alive for making statements about cosmology far less elaborate than his. Two centuries would pass before most of the ban on his books was finally lifted.
Today, four centuries later, these four moons of Jupiter—often referred to as Galilean moons—have again ignited a revolution. Some even believe that they, along with moons of Saturn, Uranus, and Neptune, may hold the key to life in the universe.
THE GAS GIANTS
When the Voyager 1 and 2 spacecraft flew by the gas giants from 1979 to 1989, they confirmed how similar these planets were. They are all made primarily of hydrogen and helium gas, roughly in the ratio of four to one, by weight. (This mix of hydrogen and helium is also the basic composition of the sun and, for that matter, most of the universe itself. It probably dates back almost 14 billion years, when about a quarter of the original hydrogen fused to become helium at the instant of the Big Bang.)
The gas giants likely share the same basic history. As discussed previously, it is theorized that 4.5 billion years ago, all the planets were small rocky co
res that condensed out of a disc of hydrogen and dust surrounding the sun. The inner ones became Mercury, Venus, Earth, and Mars. The cores of the planets farther from the sun contained ice, which was plentiful at that distance, as well as rock. Ice acts as a glue, so cores with ice could grow to be ten times larger than cores made only of rock. Their gravity became so strong that they could capture much of the hydrogen gas that remained in the early solar plane. The larger they grew, the more gas they attracted, until they exhausted all the hydrogen in their neighborhood.
It is believed that the gas giants have the same interior structure. If you could slice them in half like an onion, you would see a thick gaseous atmosphere on the outside. Below that, we would expect a supercold liquid hydrogen ocean. One conjecture is that, as a result of the enormous pressures, the very center would contain a small, dense core of solid hydrogen.
The gas giants all have colorful bands, which are caused by impurities in the atmosphere interacting with the spin of the planet. And they each have huge storms raging on the surface. Jupiter has the Great Red Spot, which seems to be a permanent feature and is so big that several Earths could easily fit inside it. Neptune, on the other hand, has an intermittent dark spot that sometimes disappears.
They differ, however, in size. The largest is Jupiter, named after the father of the gods in Roman mythology. It’s so massive that it outweighs all the other planets combined. It could comfortably encompass 1,300 Earths. Much of what we know of Jupiter comes from the Galileo spacecraft, which, after eight years of faithfully orbiting Jupiter, was allowed to end its storied life by plunging into the planet in 2003. It continued to broadcast radio messages as it descended into the atmosphere until it was crushed by the huge gravitational field. The wreckage of the spacecraft probably sank into the ocean of liquid hydrogen.