Martian Rainbow

by Robert L. Forward

  "Anything is better than the near-vacuum we have to work in now," Gus said. "What are your proposals?"

  "I've done some thinking about this before," Chris said, "being in atmospheric studies and all ... We already know that many plants can grow at low pressures and temperatures. Not Mars surface pressure and temperature, but if we can get the pressure up above one hundred millibars—ten percent of an Earth atmosphere—and the temperature above the freezing point of water for part of the day during growing season, then many plants not only can grow, but can fix nitrogen from the three percent there is in the present Mars atmosphere."

  "But people can't survive in one hundred millibars," Red Storm said from the back. "At least not for long. Air bubbles start to form under the skin and then the pain gets so bad you wish you were dead. You have to have at least two hundred millibars, and most of that has to be oxygen. I know—I once had to spend three weeks at that pressure to conserve air until I finally found the leak in my tug. A quarter atmosphere is better—that's what most belters use in their work suits."

  "Somewhere between a quarter and a third of an atmosphere, 250 to 350 millibars, is what I've been thinking," Chris said. "The top of Mount Everest is at 350 millibars, and there have been some crazies who have actually climbed the mountain without using oxygen masks. A half atmosphere would be nice—but I'm afraid that will be tougher to come by."

  "How are we going to get two hundred millibars, when all we have now is six?" Jay asked. "Not to mention that there isn't any oxygen in it."

  "You gave me one idea, yourself, Jay," Chris replied. "We just go to the middle of Hellas Basin and dig a hole forty kilometers deep. The Martian atmosphere rushes in, and bingo, down in the bottom of the hole we have half an atmosphere. All we need to do is divert a large asteroid from the asteroid belt and drop it in. We might even get some volatiles that way."

  "You're beginning to sound like the Great God Alexander!" Jay protested. "To get a hole forty kilometers deep, you'd need a seventy-kilometer diameter asteroid, roughly twice as big as the hole you want. That would raise a huge cloud of dust, crack the crust with earthquakes, and reactivate all the volcanoes."

  "Reactivating the volcanoes wouldn't be so bad," Chris said. "We'd get some of those subsurface volatiles put back into the air. The dust cloud would absorb more sunlight, generally heating the atmosphere, which is good, although if it were real thick it would get temporarily cooler near the surface. Besides, Mars has plenty of experience with planet-wide dust storms. Remember the really bad one we had last fall? It only took ten weeks to clear up."

  "It would take a good deal of time and effort to find and move the asteroid," Gus continued. "But it would be worth it if it gave us enough pressure that we could work without suits, even if we would have to have oxygen masks."

  "I don't think you eggheads know what you are talking about," Red blurted from the back. "A measly little asteroid a hundred meters in diameter weighs a million tons. Just how the hell are you going to move that seventy-kilometer sucker you're so glibly talking about? What sort of delta vee are you going to have to give it to get it moving toward Mars—and what rocket ship are you going to do it with? My tug sure ain't up to it."

  "Hmmmm ..." Chris said, pulling out his vidofax and setting it in compute mode. "Getting an asteroid from the belt would mean a lot of delta vee. Maybe, if we are lucky, we can find a Trojan asteroid or a distant outer moon of Jupiter or Saturn that we can kick into escape with just a delta vee of one kilometer per second."

  "I doubt it," Red said. "But so what if you did? Stick it in your computer and get ready to be appalled."

  "I'll assume a density of rock," Chris said, punching the number icons on the face of the vidofax. "Ouch ... Red is right ... Almost ten to twenty-three joules. Wonder what that means in real terms." He punched some more, then looked up.

  "Assuming fifty percent conversion efficiency, we would need twenty thousand one-megaton bombs ... or a ton of antimatter."

  "All the Earth's antimatter factories together produce only about a hundred kilograms a year," Gus said. "And we don't have all the Earth's antimatter factories. We'd have to spend a couple of centuries doing nothing but building antimatter factories, and we'd still be left in a hole."

  "I didn't say it would be easy—or quick," Chris said. "There's another way to terraform Mars. It's more conventional, but it will take time. What we need to do is heat up the polar ice caps. It's long been known that there is plenty of carbon dioxide and a small amount of ammonia frozen along with the water ice in the permanent polar caps and the dust-covered layered terrain around the poles. If we can heat those areas, then enough carbon dioxide will be released to raise the air pressure at Mars sea level to almost 200 millibars—250 millibars in Hellas Basin.

  "Once the carbon dioxide pressure reaches that level, the greenhouse effect will start and raise the temperature, melting the water ice all over the planet and releasing even more volatiles trapped in the water and on dust grains. The small amount of ammonia will complement the carbon dioxide since it absorbs in the infrared region between eight and twelve microns, where carbon dioxide doesn't. According to some old papers by Sagan, even one hundred parts per million of ammonia would be very effective."

  "Hmmm," Gus said. "We could start by illuminating the poles using those reflective battlefield illumination mirrors that Alex left in orbit. We would want to build more, of course, which would mean that Red and the belters would have to look for asteroids with aluminum in them."

  "Tin, copper, silver, even lead, aren't bad reflectors in space where they don't oxidize," Red said. "Maybe I'll find a solid silver asteroid next ..."

  "Dust from Phobos and Deimos dropped on the poles would darken surface of ice and increase absorption of sunlight," Boris suggested.

  "We will want to help out the process by making a few thousand tons a year of other greenhouse gases like the various fluorocarbons and the simpler hydrocarbons like methane, ethane, propane, and butane," Chris said. "The hydrocarbons will also help keep out the ultraviolet. If we are going to work outside, we'll need the protection. We should stop with butane, though. I understand that the next hydrocarbon, neo-pentane, smells like a mixture of yak shit and rotten fish."

  "It's going to be bad enough with ammonia and methane in the atmosphere," Gus said. "But I suppose we'll get used to it."

  "Our long-term objective will be to convert the carbon dioxide and water into oxygen and hydrocarbons," Chris continued. "That's what plants do, of course, and we'll want to start as many forests as we can, as fast as we can. It's still going to be a long time before we can do without oxygen masks."

  "We don't need to carry tanks of oxygen as long as there is some oxygen in the atmosphere," piped up Martha Turner, one of the chief techs at the institute. "It would be simple to design a battery-driven turbocharger with the right kind of filters to separate out the nitrogen and oxygen for use with a breathing mask."

  "Great," Chris said. "Work up a design and I'll give you a patent."

  "Now comes the cruncher," Gus said. "The last terraforming idea turned out to require tons of antimatter. What do the numbers say for this idea? I would say that there may not be enough solar energy hitting Mars to heat up the ice caps in a reasonable period of time."

  "I've already calculated that," Chris said. "To heat up the whole surface of Mars, not just the ice caps, to above freezing temperature, and to vaporize all the carbon dioxide from ice to gas, takes about two million joules of absorbed energy per square centimeter of planet surface."

  "Ouch!" Gus said. "Well, I guess that takes care of that idea. No way are we going to get two million joules of energy for each square centimeter of Mars. I'd hate to calculate the equivalent amount of antimatter."

  "No!" Chris protested. "That's not bad at all. Don't forget that in this case we can use plain sunlight as our energy source. And although only sixty milliwatts of sunlight falls on each square centimeter of the sunlit portion of Mars, just one Eart
h year's worth of sunlight is enough to heat Mars above the freezing point if all of it could somehow be absorbed in the planet. If we dust the ice caps and trigger the greenhouse effect, then one percent improvement in the absorption of sunlight means one hundred years before it gets warm. Two percent—fifty years; four percent—twenty-five years."

  "That's beginning to sound interesting," Gus said. "How long before the carbon dioxide has been converted into oxygen and hydrocarbons, so we can go out without even requiring Turner's turbocharged breathing masks?"

  "It's going to take a long time," Chris said. "Plants aren't very efficient at using sunlight to crack apart carbon dioxide molecules and rearranging them into something humans tolerate."

  "How long?" Gus asked.

  "A hundred thousand years," Chris admitted softly, then added, "We can speed that up a factor of ten by choosing the right types of plants."

  There was a long silence.

  "It'll have to do," Gus said. "Alex has left us with little other choice. Anyone have any better ideas?"

  The room was silent. Finally Jay spoke up. "I think Chris' greenhouse approach is the one we should start working on. Being able to work outside and raise crops outside without being limited by high-tech pressure suits and pressurized buildings is going to make a big difference in our survivability. If Martha Turner can come up with a low-tech, low-weight, high-reliability turbomask, then we will be essentially as free of technology on Mars as an Eskimo is on Earth. That goal is worth putting in twenty-five to fifty years of effort—and the time it takes to reach that goal is short enough that people can stay motivated to work on it. I might even walk around outside without a Marsuit myself someday—if I m lucky."

  "We'll start working on Chris' idea immediately," Gus said. "I'll want Chris and others to go through the numbers carefully and come up with a detailed plan as soon as possible. In the meantime, if any of you have any new ideas or possible modifications to Chris' basic plan, please let me know."

  "I'm going to model the formation of some smaller 'air hole' craters with my asteroid impact computer simulation," Jay said. "If we have fifty or a hundred millibars of atmosphere at sea level, which we might get after ten years of warming, then we would need a much smaller hole to get the pressure up. Also, if we lived in the hole with the plants, then we could keep the oxygen level higher than if the plants were trying to oxygenate all of Mars."

  "You're still talking about an awfully massive asteroid," Red warned. "Don't forget that the mass goes up as the cube of the diameter, and you said that you needed an asteroid with a diameter almost twice the size of the hole you wanted to dig."

  "Not necessarily," Boris said, raising his hand to interrupt. "I witnessed a penetrator rod from the antisatellite missiles strike Deimos. It dug a deep hole in crust. Very deep compared to either its diameter or length."

  "That's why rods are used in warheads," Jay said. "They penetrate extremely well, even through armor. The French knights at Agincourt found that out the hard way when they met the arrows from King Henry's English longbowmen. Do you have any rod-shaped asteroids, Red?"

  "I can find you lots of sweet potatoes, but no rods," Red replied.

  "Maybe a closely spaced string of small asteroids would be just as effective as a rod," Jay mused, getting up. "I'll have to run it through my simulation."

  "I never tried to deliver more than one asteroid at a time, especially to the surface of a gravitating body," Red said, also standing up. "I've got some calculating to do myself."

  Gus stood, too. "Let's everybody do some calculating and modeling, then get back together tomorrow."

  THE ROOM was shortly empty except for Gus and Chris. Maury, who had ducked out to the nearby Olye Olye Outs Inne bar toward the end of the meeting, wandered back in carrying a beer.

  "Unless you have some objection," he said, "I'm going to make the results of this meeting a major feature article in the next Mars Weekly."

  "No objection," Gus said. "The more people who are thinking about making Mars a better permanent home for mankind, fte better."

  "Say, Maury," Chris said. "This terraforming project is going to keep me awfully busy."

  "I don't doubt it," Maury said. "I'll do all I can to take care of governor business for you."

  "Thanks," Chris said. "But I was thinking of something else. Elections are coming up in eleven weeks. I've just decided I'm not going to run for reelection again. Three terms is enough. Why don't you run?"

  "Why not?" Maury said, thoughtfully pausing to sip his beer. "It would give me something useful to do and let you scientist types have more time to save the human race."

  "Good," Chris said, pulling out the violet-colored Globe Coin of Office from his shirt pocket and hanging it around Maury's neck on its frayed rainbow ribbon. "You can start being governor now. You take all the calls, you make all the decisions, and if something needs a signature, just shove it in front of me and I'll sign it. I'll take the blame if anything goes wrong, and the people of Mars can get a good look at how you operate before they elect you."

  "But ..." Maury protested, picking up the violet coin to look at it, but Chris was already on his way out of the room.

  "Say, Governor," Gus said, with a slight smile. "You have some delicate negotiating work ahead of you."

  "Me?" Maury protested. "Negotiating? What? With whom?"

  "If we're going to terraform Mars so it is more suitable for humans, don't you think we should inform the original inhabitants of the planet what we're up to?"

  "But I thought the Lineups weren't talking to us."

  "We at least ought to try and let them know," Gus persisted. "We'll go visit their North Pole enclave as soon as Chris, Jay, and the others have firmed up the detailed plan."

  A FEW days later the lecture hall at the Sagan Institute was full again. They had moved the walls so that more of the cafeteria was included, but still there were people standing in the back. Nearly everyone on Mars was working on some portion or other of the terraforming problem.

  Jay reported that a string of small one-kilometer-diameter asteroids would indeed be better than one large asteroid at digging an "air hole" in Hellas.

  "When you drop a big asteroid on a planet it makes a big hole," Jay said. "But it also shakes up the ground so much that the dirt loses all its strength and it starts to flow like water. It flows in and fills up the hole. That's why you don't find any really deep impact craters on Earth or Mars.

  "A string of small asteroids will dig a hole roughly equal to the length of the string, but the total energy deposited is down by many orders of magnitude, so the ground-shaking is less. Hopefully this means less fill-in afterward. We won't really know until after we try."

  "How many asteroids will be needed?" Gus asked.

  "Eighteen one-kilometer-diameter dense asteroids as close together as Red can get them," Jay said. "They'll dig a hole twenty-four kilometers deep, and I'm hoping it will only fill back halfway—leaving us twelve kilometers."

  "But you are still talking about kilometer-sized asteroids—and eighteen of them, at that," Red protested. "We can get a net around them, but the typical sail will take hundreds of years to move that amount of tonnage."

  "Depends upon the gravity well they are in and whether you can use gravity assist," Jay said. "Have you found any bodies that size near Jupiter and Saturn—but not too near?"

  "I'm still collecting that data," Red said. "Been trying to get some of the astronomer-types out in 'Giant Land' to look for stones instead of stars."

  "If worse comes to worst, we'll just have to wait a hundred years," Jay said.

  "I'll let you know," Red said. "But it'll take a week or so to collect the data."

  "I'm sort of held up, too," Chris said. "The gang on Phobos have gone out in an orbiter to look at the battlefield-illumination mirrors still floating around. But it will be awhile before they can check to see how many are operational. I'll need that solar influx data before I can do any more detailed calculatio
ns."

  "Then perhaps it's a good time to go tell the Lineups what we are planning," Gus said.

  "If they'll listen," Chris said. "I never felt so insulted in all my life as when that character 'Biddeliboop' told us to shove off and not only locked the door in our face, but sealed it shut."

  "We still should try," Gus said. "I'll take along a laser communicator and try sending the beam through the door and up the tunnel. If that doesn't work, I'll break into their cable one more time and try contacting them that way."

  "That sure brought them out last time," Red said. "By the way—we don't have to go to the North Pole to talk with them. They have at least five enclaves at various places all around the globe. Last winter I looked up maintenance reports on crawlers for 'optical fiber tangles' and found a number that couldn't have been caused by missile fibers. It didn't take long to go to the scene, find the fiber end, and track it down to their enclave. All of the enclaves are widely separated and buried deep underground. They almost never come out except to fix a broken fiber. They must use them to keep in touch."

  "I wonder why they're underground, and so limited in distribution?" Max MacFadden asked.

  "According to some of the biology-types I talked to, they don't understand it either," Red said. "The Lineups seem to have made little oases and are just trying to hold on, rather than trying to expand their population. Not the normal response."

  "They also aren't normal in that they haven't evolved in two billion years," Gus said.

  "The buried enclaves distributed over the whole globe make perfect sense," Jay said. "If you're trying to maintain status quo in a few oases over billions of years of time, then your real danger is asteroid strikes. You want deep cover so the small ones don't get you unless it's a direct hit, and you want wide distribution so you survive even a big one."

  "They also avoid the volcanic regions," Red said. "The known enclaves are at each pole and near the impact craters Copernicus, Maunder, and Kunowsky."