To vaporize the caps, we must heat them; perhaps we could dust them with a dark powder, heating them by absorbing more sunlight, the opposite of what we do to the Earth when we destroy forests and grasslands. But the surface area of the caps is very large. The necessary dust would require 1,200 Saturn 5 rocket boosters to be transported from Earth to Mars; even then, the winds might blow the dust off the polar caps. A better way would be to devise some dark material able to make copies of itself, a little dusky machine which we deliver to Mars and which then goes about reproducing itself from indigenous materials all over the polar caps. There is a category of such machines. We call them plants. Some are very hardy and resilient. We know that at least some terrestrial microbes can survive on. Mars. What is necessary is a program of artificial selection and genetic engineering of dark plants – perhaps lichens – that could survive the much more severe Martian environment. If such plants could be bred, we might imagine them being seeded on the vast expanse of the Martian polar ice caps, taking root, spreading, blackening the ice caps, absorbing sunlight, heating the ice, and releasing the ancient Martian atmosphere from its long captivity. We might even imagine a kind of Martian Johnny Appleseed, robot or human, roaming the frozen polar wastes in an endeavor that benefits only the generations of humans to come.
The general concept is called terraforming: the changing of an alien landscape into one more suitable for human beings. In thousands of years humans have managed to perturb the global temperature of the Earth by only about one degree through greenhouse and albedo changes, although at the present rate of burning fossil fuels and destroying forests and grasslands we can now change the global temperature by another degree in only a century or two. These and other considerations suggest that a time scale for a significant terraforming of Mars is probably hundreds to thousands of years. In a future time of greatly advanced technology we might wish not only to increase the total atmospheric pressure and make liquid water possible but also to carry liquid water from the melting polar caps to the warmer equatorial regions. There is, of course, a way to do it. We would build canals.
The melting surface and subsurface ice would be transported by a great canal network. But this is precisely what Percival Lowell, not a hundred years ago, mistakenly proposed was in fact happening on Mars. Lowell and Wallace both understood that the comparative inhospitability of Mars was due to the scarcity of water. If only a network of canals existed, the lack would be remedied, the habitability of Mars would become plausible. Lowell’s observations were made under extremely difficult seeing conditions. Others, like Schiaparelli, had already observed something like the canals; they were called canali before Lowell began his lifelong love affair with Mars. Human beings have a demonstrated talent for self-deception when their emotions are stirred, and there are few notions more stirring than the idea of a neighboring planet inhabited by intelligent beings.
The power of Lowell’s idea may, just possibly, make it a kind of premonition. His canal network was built by Martians. Even this may be an accurate prophecy: If the planet ever is terraformed, it will be done by human beings whose permanent residence and planetary affiliation is Mars. The Martians will be us.
CHAPTER VI
Travelers’ Tales
Do there exist many worlds, or is there but a single world? This is one of the most noble and exalted questions in the study of Nature.
– Albertus Magnus, thirteenth century
In the first ages of the world, the islanders either thought themselves to be the only dwellers upon the earth, or else if there were any other, yet they could not possibly conceive how they might have any commerce with them, being severed by the deep and broad sea, but the aftertimes found out the invention of ships . . . So, perhaps, there may be some other means invented for a conveyance to the Moone . . . We have not now any Drake or Columbus to undertake this voyage, or any Daedalus to invent a conveyance through the aire. However I doubt not but that time who is still the father of new truths, and hath revealed unto us many things which our ancestors were ignorant of, will also manifest to our posterity that which we now desire but cannot know.
– John Wilkins, The Discovery of a World in the Moone, 1638
We may mount from this dull Earth; and viewing it from on high, consider whether Nature has laid out all her cost and finery upon this small speck of Dirt. So, like Travellers into other distant countries, we shall be better able to judge of what’s done at home, know how to make a true estimate of, and set its own value upon every thing. We shall be less apt to admire what this World calls great, shall nobly despise those Trifles the generality of Men set their Affections on, when we know that there are a multitude of such Earths inhabited and adorn’d as well as our own.
– Christiaan Huygens, The Celestial Worlds Discovered, c. 1690
This is the time when humans have begun to sail the sea of space. The modern ships that ply the Keplerian trajectories to the planets are unmanned. They are beautifully constructed, semi-intelligent robots exploring unknown worlds. Voyages to the outer solar system are controlled from a single place on the planet Earth, the Jet Propulsion Laboratory (JPL) of the National Aeronautics and Space Administration in Pasadena, California.
On July 9, 1979, a spacecraft called Voyager 2 encountered the Jupiter system. It had been almost two years sailing through interplanetary space. The ship is made of millions of separate parts assembled redundantly, so that if some component fails, others will take over its responsibilities. The spacecraft weighs 0.9 tons and would fill a large living room. Its mission takes it so far from the Sun that it cannot be powered by solar energy, as other spacecraft are. Instead, Voyager relies on a small nuclear power plant, drawing hundreds of watts from the radioactive decay of a pellet of plutonium. Its three integrated computers and most of its housekeeping functions – for example, its temperature-control system – are localized in its middle. It receives commands from Earth and radios its findings back to Earth through a large antenna, 3.7 meters in diameter. Most of its scientific instruments are on a scan platform, which tracks Jupiter or one of its moons as the spacecraft hurtles past. There are many scientific instruments – ultraviolet and infrared spectrometers, devices to measure charged particles and magnetic fields and the radio emission from Jupiter – but the most productive have been the two television cameras, designed to take tens of thousands of pictures of the planetary islands in the outer solar system.
Jupiter is surrounded by a shell of invisible but extremely dangerous high-energy charged particles. The spacecraft must pass through the outer edge of this radiation belt to examine Jupiter and its moons close up, and to continue its mission to Saturn and beyond. But the charged particles can damage the delicate instruments and fry the electronics. Jupiter is also surrounded by a ring of solid debris, discovered four months earlier by Voyager 1, which Voyager 2 had to traverse. A collision with a small boulder could have sent the spacecraft tumbling wildly out of control, its antenna unable to lock on the Earth, its data lost forever. Just before Encounter, the mission controllers were restive. There were some alarms and emergencies, but the combined intelligence of the humans on Earth and the robot in space circumvented disaster.
Launched on August 20, 1977, it moved on an arcing trajectory past the orbit of Mars, through the asteroid belt, to approach the Jupiter system and thread its way past the planet and among its fourteen or so moons. Voyager’s passage by Jupiter accelerated it towards a close encounter with Saturn. Saturn’s gravity will propel it on to Uranus. After Uranus it will plunge on past Neptune, leaving the solar system, becoming an interstellar spacecraft, fated to roam forever the great ocean between the stars.
These voyages of exploration and discovery are the latest in a long series that have characterized and distinguished human history. In the fifteenth and sixteenth centuries you could travel from Spain to the Azores in a few days, the same time it takes us now to cross the channel from the Earth to the Moon. It took then a few months to traverse the Atlantic Ocean and reach what was called the New World, the Americas. Today it takes a few months to cross the ocean of the inner solar system and make planet-fall on Mars or Venus, which are truly and literally now worlds awaiting us. In the seventeenth and eighteenth centuries you could travel from Holland to China in a year or two, the time it has taken Voyager to travel from Earth to Jupiter.* The annual costs were, relatively, more then than now, but in both cases less than 1 percent of the appropriate Gross National Product. Our present spaceships, with their robot crews, are the harbingers, the vanguards of future human expeditions to the planets. We have traveled this way before.