Mars will be terraformed into a new home for Earth life.
The next step in the colonization of the galaxy is the settling of Mars. The Elysian fields were the Greek idyllic paradise and provide a suitable mythic realm for Mars. In fact, the geography of Mars is already replete with landmarks named for the pantheon of Ancient Greece: Olympus Mons, Hellas Planitia, and even the Elysium Plains themselves.
Here is the population of the solar system at the time we reach this step, assuming a sustained growth rate of 2% from 6 billion in 2000 AD:
| TERRA Water-based (in the style of Aquarius) |
10 billion |
| Land-based | 10 billion |
| LUNA (in the style of Avallon) | 20 billion |
| FREE SPACE (in the syle of Asgard) | 60 billion |
| 100 billion |
Figure 1 shows a photograph of Phobos.
The first step toward colonizing Mars is to occupy its inner moon Phobos. To understand the convenience of this base of operations, we must realize that travel in space is not measured only by distance moved, but by energy spent, a function of 'change of velocity' (Dv). In terms of distance, outer space is close to where you're sitting right now - 100 km away. In terms of energy, though, space is very far away. The change in velocity (Dv) required to escape the Earth's gravitational pull is 11.2 kilometers per second (kps). After escaping the Earth, it requires only an additional Dv of 2.4 kps to fly to and land on Luna. Flying from Earth orbit to the Martian moons requires a Dv of only 3.2 kps.
Phobos forms a natural space-station with an escape velocity only a tiny fraction of that needed to escape Earth. Escape velocity is only ten meters per second (22 mph). With aerobraking available in the Martian atmosphere, and Phobos' low escape velocity, the Martian surface is literally only a stone's throw away. You could actually throw a rock off Phobos and hit Mars.
Phobos is more like an orbiting island than a moon. It is only about 27 km long and 20 km across. It is perfectly situated for our purposes. Phobos orbits directly above the Martian equator at an altitude of just 6000 km. Phobos makes one complete orbit in less than eight hours, putting it over every point on the Martian equator three times a day. It is oriented so its long axis points toward Mars, and it spins at exactly the same rate that it orbits. Therefore, it always keeps the same end pointed toward the planet. This facilitates ground observations and radio communications.
There is a large crater on the Mars end of Phobos called Stickney (after the wife of Phobos' discoverer). This crater provides a good site for our base of operations. The crater is more than large enough - ten km across - to accommodate a major base. Fully developed, Stickney will have a domed area of over 75 square kilometers. Inside this ecosphere, life will be an interesting hybrid. Conditions will be a cross between zero-gravity habitats like Asgard and low-gravity ones like Avallon. A person who weighs 75 kg (165 lbs.) on Earth will weight just 50 grams (17 oz.) on Phobos - barely more than a loaf of bread.
The outpost on Phobos will be well illuminated, even though it always faces Mars. When Phobos is on Mars' dark side, the sun is overhead. When Phobos is on the planet's light side, Mars, which fills a quarter of the sky, is lit up. Mars will shine down on Phobos a brightly as 6000 full moons on Earth. Because of this double light source, Mars on one side and the sun on the other, the ecosphere in Stickney will be in the dark only about 10% of the time. Darkness falls only when Mars eclipses the sun and Phobos is on the dark side of the planet, a relatively rare circumstance.
Before we even begin to terraform Mars, it will be vital to set up mining outposts on Phobos and Deimos. There is only enough water in the Apollo Amor asteroids to supply a population of a couple of billion people. There will be 80 billion people living in areas other than the Earth as shown in Table I. The cosmography of the solar system actually favors the export of materials from Mars to the Earth-Moon system. To send a kilogram of material from the Earth to the Moon requires a total change in velocity (Dv) of 13.6 kilometers per second (kps). By contrast, moving a kilogram from Mars to the Moon requires a Dv of only 9.4 kps.
Hydrogen could be sent from Mars to be recombined with plentiful lunar oxygen to form water on the Moon. Only one tenth of the mass of water is hydrogen. Therefore, the transport cost for water on the Moon if produced with Martian hydrogen, would be 4.4 megajoules per kilogram - about 6 cents per liter. Transporting enough hydrogen from Mars to produce 60 tons of water for each Lunar colonist would involve an energy cost of around $3600 per person.
By some stroke of cosmic good fortune, Phobos and Deimos (Mars' other moon) are both carbonaceous chondrites. The presence of two such treasure troves in orbit around Mars is unbelievable good luck (if luck it is). Phobos alone will provide us with 16 trillion tons of invaluable supplies, including over 3 trillion tons of water.
Phobos will be an interplanetary gas station. We can extract water from the Martian moon's carbonaceous ore body, and then break the water down into hydrogen and oxygen. With these elements, we can produce LHOX (liquid hydrogen oxygen) fuel on site. Space craft arriving in orbit around Mars can refuel at Phobos for their descent to the Martian surface. More significantly, passenger and cargo ships coming up from Mars will not need to carry fuel with them. The ships can land on Phobos or Deimos and take on all the fuel they need for flights back to the Earth-Moon system.
There will be three ways to transport miners, settlers, and material to Mars. Traveling to Mars in one of the transfer habitats will take five to eight months. Traveling between planets on one of the Apollo Amor asteroid colonies will take years. A fast fusion clipper service taking only a few weeks will be available for urgent missions.
The first method requires relatively little energy, but it takes a long time. A minimum energy trajectory to Mars takes eight months (such flight paths are called "Hohmann Orbits"). All cargo and most travelers will take the slow boat to Mars. It is relatively easy to accelerate payloads to Mars. The change in velocity from Earth orbit to the transfer orbit is less than three kps. The harder task is to provide life support and radiation shielding during the eight-month trip.
Eventually, we will establish a chain of small ecospheres in transfer orbits between the two planets. The transfer habitats will take an average of 26 months to cycle between Earth and Mars. With a couple of dozen such cycling habitats in place, waiting times between outbound and inbound ships could be as little as 30 days. Figure 2 shows a drawing of potential habitat orbits.
The second method will be to use the numerous Apollo Amor asteroid colonies that will already be established at this time. The AA's orbits periodically take them close to both planets. AA asteroids sometimes approach within a million kilometers of the Earth. A shuttle pod catapulted off the lunar mass driver at 10 or 15 kps could reach such an asteroid in less than 24 hours. Figure 3 shows a few of the Apollo Amor asteroid orbits.
A given asteroid colony might only have a favorable conjunction with both Earth and Mrs once in a decade, but when it did it would carry passengers. With a hundred asteroid colonies cycling between Earth and Mars there will usually be one or two with favorable orbital windows. The AA asteroid colonies will together act like a continuous conveyor belt, moving people out to Mars, through celestial osmosis.
The third method will use fusion-powered rockets. The preferred fusion reaction combines deuterium and helium3. This reaction is the easiest to initiate, produces the greatest amount of energy, and creates no dangerous flux of neutrons as a byproduct. Helium3 is virtually nonexistant on Earth, but the lunar soil is a rich source. The presence of helium3 on the Moon is a boon to space colonization, and its extraction will be a major Lunar industry.
The products of fusion between deuterium and helium3 are helium4 atoms and protons. Both types of particle carry a charge, so the fusion reaction takes place within a magnetic field. Thrust is produced by expelling these superheated ions through a magnetic rocket nozzle. Single stage fusion rockets will be able to achieve velocities of 30,000 kps and more. At 64 kps, the straight line route to Mars takes between 20 days and 144 days, depending on the relative positions of the Earth and Mars in the solar system. This requires accelerating and decelerating for one hour each at 1 g. Because this method is more expensive, it will be used as a fast clipper service only for urgent missions.
Mars awaits us; a living world in kit form. it has the right orbit, the right seasons, the right day; it has a ready-made atmonsphere; it even has hidden oceans. Its orbit - 228 million kilometers from the sun - is only half again as far out as Earth's. This puts Mars well within the sun's 'ecosphere' - the region around the sun where liquid water, and so Life, can persist on a planet's surface. A titlted axis endows a planet with dynamism that may be essential to a diverse biospehere. The annual succession of seasons is the driving engine, both atmospheric and oceanic. A living planet needs a tilted axis, but like Goldilocks' porridge it must be just right. It is more than a little surprising then to find tha the axial tilt of Mars almost exactly matches the Earth's: 24.5 degrees on Mars vs. 23.5 degrees on Earth.
The strangest 'coincidence' of all is the length of Mars' day - 24 hours and 37 minutes. Earth's day is 1444 minutes long, Mars' is 1477. Mars is barely half Earth's diameter and a mere one-tenth Earth's mass; it spins at half the speed of the Earth , yet Mars' day is the same length. The Earth flies in tandem with a moon so large it is virtually a companion planet. Mars' moons put together are not bigger than the island of Maui. Why should such different planets have such similar days?
To render the Martian surface hospitable to Terran life, we need to raise the air pressure to 500-600 millibars, half the pressure that prevails on Earth at sea level. There is enough carbon dioxide in the dry ice glaciers of Mars' poles - 3000 trillion tons - to do just that. To liberate carbon dioxide from dry ice requires raising its temperature to only sixty degrees below zero.
How do we provide this increase in temperature? The champion green-house gas is water vapor. Adding enough water vapor to Mars' atmosphere to produce a water vapor pressure of 6.1 millibars will raise the red planet's mean temperature above freezing. It will require adding 24 trillion tons of water vapor, doubling the mass of the atmosphere.
We can get the water we need from a single comet of surprisingly small size. Comets are 60% water by weight. Just one comet with a raduis of 21 kilometers, could provide all the water needed to reconstitute Mars. Most comets are less than 15 km in diameter, with an average diameter of three to four kilometers.
On average, six comets a year cross the orbit of Mars in the plane of the ecliptic. All we need to do is arrange a rendezvous between some of these comets and the surface of Mars. A very small impulse delivered to a comet at perihelion can put it on a radically different orbital path. We might adjust the orbit of a five year comet several times before finally locking it on target for its cataclysmic meeting with Mars.
We can deliver these navigational impulses by any number of means. The simplest approach will be to detonate several hydrogen bombs in the right spot on or near the comet. It will probably be desirable to rig the comet with explosive charges so it breaks up into many chunks just before reentry. Otherwise, the intact comet will blast a crater miles deep in the Martian crust.
On impact, all the ice in the cometary chunks will instantly vaporize. At the same moment, a large amount of ice held as permafrost deep in the Martian soil will flash into steam. In fact, the comet will vaporize an amount of permafrost equal to hundreds to thousands of times the mass of the comet itself. Comets will therefore be directed to impact in higher latitudes, where permafrost is concentrated.
Once all the carbon dioxide has been liberated from the polar caps and the permafrost, Mars will have an atmosphere thicker than the Earth's and a balmy mean surface temperature of 15 degrees Celsius (60 degrees Fahrenheit). Humans who are not genetically engineered will probably always require oxygen masks to breathe comforably on Mars, but it will be a shirt-sleeve environment.
Geologic evidence suggests that Martian water has been liberated, perhaps many times, in the past. As Mars cooled ground water must have been frozen and been permanently trapped. A tenth to a third of the total water released by Mars' great volcanoes must remain in the soil as permafrost. Oceans will fill in the basins and impact craters, producing a Mars that looks something like Figure 4.
In a replay of the early processes of life on Earth, the plants will pioneer the planetary ecosphere. Ultimately, the plants will crate conditions hospitable for animal life. At first, plant life will be confined to aquatic and marine species - primarily algae. Eventually, we will introduce genetically engineered plant species, designed for a high tolerance to carbon dioxide. The classic progression of species will spread over the terrain, clothing the naked red soil in a verdant blanket.
When we have completed the metamorphosis of Mars, the universe will be a different place. Around mighty Sol, will circle now two exquisite gem planets.