The Case for Mars (45 page)

TABLE 9.2.
Greenhousing Mars with CFCs

As an added benefit, ammonia and methane will shield the planet’s surface against solar ultraviolet radiation. In the process, though, the ammonia and methane will be continuously destroyed, with a typical molecule having an atmospheric lifetime of several decades. The bacteria will constantly replace them, however. Also, as the planet warms and carbon dioxide outgasses from the regolith, Mars’ ozone layer will thicken, providing extra UV shielding to both the surface and the ammonia-methane greenhouse gases in the atmosphere. (Carbon dioxide contributes to ozone formation. In fact, Mars currently has an ozone layer about 1/60th as thick as Earth’s, which is pretty good when you consider that its atmosphere is only 1/120th as thick.)

In a matter of several decades, using a combination of these approaches Mars could be transformed from its current dry and frozen state into a relatively warm and slightly moist planet capable of supporting life. Humans could not breathe the air of the transformed Mars, but they would no longer require space suits and instead could travel freely in the open wearing ordinary clothes and a simple SCUBA type breathing gear. In addition, because the outside atmospheric pressure will have been raised to human tolerable levels, it will be possible to have enormous habitable areas for humans under huge dome-like inflatable tents containing breathable air. (The domes could be of unlimited size because, unlike the pressurized domes employed during the base-building phase, there would be no pressure differential between their interior and the outside environment.) On the other hand, simple hardy plants could thrive in the carbon dioxide-rich outside environment and spread rapidly across the planet’s surface. In the course of centuries, these plants would introduce oxygen into Mars’ atmosphere in increasingly breathable quantities, opening up the surface to advanced plants and growing numbers of animal types. As this occurred, the carbon dioxide content of the atmosphere would be reduced, which would cause the planet to cool unless greenhouse gases were introduced capable of blocking off those sections of the infrared spectrum previously protected by carbon dioxide. Providing these matters are attended to, however, the day would eventually come when the domed tents would no longer be necessary.

ACTIVATING THE HYDROSPHERE

The first steps required in the terraforming of Mars, warming the planet and thickening its atmosphere, can be accomplished with surprisingly modest means using in-situ production of halocarbon gases supplemented by helpful bacteria. The oxygen and nitrogen levels in the atmosphere, however, would be too low for many plants, and, if left in this condition, the planet would remain relatively dry, as the warmer temperatures would take centuries to melt Mars’ ice and deeply buried permafrost. It is in this second phase of terraforming Mars when the hydrosphere is activated, the atmosphere is made breathable for advanced plants and primitive animals, and the temperature is increased further, that space-based manufacturing of large solar concentrators is likely to assume an increasingly important role.

The use of orbiting mirrors provides a potentially rapid method for hydrosphere activation. For example, if the 125-kilometer radius reflector discussed earlier for relain vaporizing the pole were to concentrate its power on a smaller region, 27 terrawatts would be available to melt lakes (one terrawatt, or TW, equals one million megawatts). This is enough to melt 2 trillion tonnes of water per year (a lake 200 kilometers on a side and 50 meters deep). A single such mirror could also drive vast amounts of water out of the permafrost and into the nascent Martian ecosystem very quickly. The more rapidly water gets into circulation, the more action of denitrifying bacteria in breaking down nitrate beds to increase the atmospheric nitrogen supply and the spread of plants to produce oxygen will be accelerated. Activating the hydrosphere will also serve to destroy the oxidizing chemicals in the Martian regolith (which
Viking
showed are unstable in the presence of water), thereby releasing some additional oxygen into the atmosphere in the process. Thus, while the engineering of such mirrors may be somewhat grandiose, the benefits to terraforming of being able to wield tens of terrawatts of power in a controllable way can hardly be overstated.

OXYGENATING THE PLANET

The most technologically challenging aspect of terraforming Mars will be the creation of sufficient oxygen in the planet’
s atmosphere to support animal life. While bacteria and primitive plants can survive in an atmosphere without oxygen, advanced plants require at least 1 mbar and humans need 120 mbar. While Mars may have super-oxides in its regolith or nitrates that can be heated to release oxygen and nitrogen gas, the process would require enormous amounts of energy, about 2,200 TW-years for every millibar produced. Similar amounts of energy are required for plants to release oxygen from carbon dioxide. Plants, however, offer the advantage that once established they can propagate themselves. The production of an oxygen atmosphere on Mars thus breaks down into two phases. In the first phase, brute-force engineering techniques supplemented by pioneering cyanobacteria and primitive plants are employed to produce sufficient oxygen (about 1 millibar) to allow advanced plants to propagate across Mars. Assuming three 125-kilometer radius space mirrors active in supporting such a program and sufficient supplies of suitable target material on the ground, such a goal could be achieved in about twenty-five years. Alternatively, a 1 millibar oxygen content could be added to the atmosphere in about a century through the action of photosynthetic bacteria. Either way, once an initial supply of oxygen is available, and with a temperate climate, a thickened carbon dioxide atmosphere to supply pressure and greatly reduce the space radiation dose, and a good deal of water in circulation, plants that have been genetically engineered to tolerate Martian regoliths and to perform photosynthesis at high efficiency could be released together with their bacterial symbiotes. Assuming that global coverage could be achieved in a few decades and that such plants could be engineered to be 1 percent efficient (rather high, but not unheard of among terrestrial plants) then they would represent an equivalent oxygen-producing power source of about 200 TW. By combining the efforts of such biological systems with perhaps 90 TW of space-based reflectors and 10 TW of installed power on the surface (terrestrial civilization today uses about 13 TW) the required 120 millibars of oxygen needed to support humans and other advanced animals in the open could be produced in about nine hundred years. If more powerful artificial energy sources or still more efficient plants (or perhaps truly artificial self-replicating photo
synthetic machines) were engineered, then this schedule could be accelerated accordingly, a fact that may well prove a driver in bringing such technologies into being. It may be noted that thermonuclear fusion power on the scale required for the acceleration of terraforming also represents the key technology for enabling piloted interstellar flight. If terraforming Mars were to produce such a spinoff, then the ultimate result of the project will be to confer upon humanity not only one new world for habitation, but myriads.

A GIFT TO THE FUTURE

Witness this new-made World, another Heav’n

From Heaven Gate not farr, founded in view

On the clear Hyaline, the Glassie Sea;

Of amplitude almost immense, with Starr’s

Numerous, and every Starr perhaps a World

Of destined habitation ...

—John Milton,
Paradise Lost

The theoretical calculations are quite clear in their verdict: The Red Planet can be terraformed. But only human explorers operating on Mars can learn enough about the planet and the methods of utilizing its resources to transform such a dream into reality. Yet the game certainly is worth the candle, for what is at stake is an entire world.

In a sense, the discussion of humanity’s potential to terraform Mars brings us full circle. Are we first-class citizens of the cosmos, or are we beings of lesser order? Kepler proved that the laws of the heavens were
understandable
by the human mind. The first astronauts to reach Mars will prove that the worlds of the heavens are
accessible
to human life. But if we can terraform Mars, it will show that the worlds of the heavens themselves are
subject to
the human intelligent will.

Mars could become a second home for life, all life; not only for humans, nor even just “the fish of the sea . . . the fowl of the air, and every living thing that moveth upon the Earth,” but for a plenitude of species yet unborn. New worlds invite new forms, and in the novel habitats that a terraformed Mars would provide life brought from Earth could go forth and multiply into realms of diversity yet unknown.

This is the wondrous heritage that we can begin for future generations—not only a new world for life and civilization, but an example of what men and women of intelligence, daring, and vision can accomplish when acting upon their highest ideals. Gods we’ll never be. But the humanity that terraforms Mars will have shown that humans are more than just animals, that we are in fact creatures who carry a unique spark that is worthy of respect. No one will be able to look at the new Mars without feeling prouder to be human. No one will be able to hear its story without being inspired to rise to the tasks that will lie ahead among the stars.

EQUATIONS FOR MODELING THE MARTIAN SYSTEM

We can estimate the average temperature on Mars as a function of the CO
₂
atmospheric pressure and the solar constant using the following equation:

where T
_mean
is the mean planetary temperature in Kelvins, S is the amount of solar output where that of the present-day Sun equals 1, and P is the atmospheric pressure at Mars’ mean surface elevation, given in bars. (One bar is what flat-landers believe is normal atmospheric pressure, 14.7 pounds per square inch. Since people living in the fetid swamps near such major capitals as Washington, London, and Paris are influential in such things, this odd unit has become a standard.)

Since the atmosphere is an effective means of heat transport from the equator to the pole, Chris McKay and I estimated:

It is also reasonable to assume, based upon a rough approximation to observed data, that: