Colonizing another planet is a reality and it is a good solution for many of the worldwide problems we are currently facing. Having a “second Earth” can solve issues such as overpopulation and can open new doors such as interplanetary commerce. Although colonization would be a costly task, the time is right and the right use of science and technology can drastically simplify the process.

      There are two main options for establishing a human population on an alien planet. First off we can build space stations or live underground and import materials from earth. The settings inside these stations would be identical to those of earth and we would have to wear spacesuits when venturing onto the surface. The other idea is to terraform an uninhabitable planet. Terraforming means to make something like Earth and its ultimate goal is to make a planet similar enough to earth so that humans and animals can live on it just as if it were Earth. Since we want another planet to live on and not just study, terraforming is by far our best choice in the long run. While the lengthy process will not benefit current or near future generations, it isn’t as complicated as most would think because nature does a great deal of terraforming with the right human actions.

      The planets we have studied the most and have the best chance of terraforming are Venus, Mars, and Earth’s moon. Further inspection of these three planets shows that Mars is the most biocompatible with Earth and therefore the most viable option for terraforming.

      The moon lacks any sort of atmosphere which would protect inhabitants from damaging solar radiation, and the extremely low gravity on the moon leads to bone detriments. Additionally, the moon’s day-night cycle lasts 28 days which would make plant life impossible and human life very uncomfortable. The moon’s lack of frozen water is also a concern. Venus on the other hand is a hellish fireball with a surface temperature of 400ºC and an atmospheric pressure of 90 atm. Ninety times the pressure on the surface of the Earth is what you would feel if you were 100 m below sea level. Along with these issues, Venus also has an unacceptable day-night cycle and its atmosphere consists of dense sulfuric acid clouds many km in height. Venus’s runaway greenhouse effect creates an environment ruled by volcanoes and flowing lava where liquid water cannot exist. But Mars shows much more terraforming potential than either Venus or the moon. Mars has a northern icecap containing tremendous amounts of frozen H₂O and a southern icecap containing massive amounts of solid CO₂. It also has a decent atmosphere, an Earth-like day-night cycle, and enough gravity to accommodate healthy life forms.

      Perhaps the biggest obstacle to terraforming is the lack of O, N, H₂O, and CO₂ on the planet. Fortunately, researchers believe Mars more than fulfils these requirements. One perceivable problem to colonizing Mars though is the issue of landing people on the planet. Among the three planets we just considered, Mars is the most distant from Earth at 80 million km away. Developing a spaceship and stocking it with enough supplies and fuel to travel from Earth to Mars and back would cost an infeasible amount of money. NASA’s answer for this is called “Mars direct” and it basically involves sending an unmanned craft to Mars using Venus’s gravity as propellant 2 years before astronauts arrive. This spaceship would essentially make loads of fuel for the return trip through natural reactions involving the Martian atmosphere and a stockpile of C, O, and H.

      Having eliminated Venus and the moon from terraforming considerations, let's closely examine the differences and similarities between Mars and Earth.  Keep in mind that the majority of the differences between the planets is caused by Mars's lack atmosphere and atmospheric pressure.  The lower gravity on Mars is due to its lower mass and its lower escape velocity is due to its weak atmosphere and weaker gravity.

      Robert Zubrin president of Pioneer Astronautics and Chris McKay of NASA Ames research center are the two biggest proponents of terraforming Mars and have done the majority of the research. According to Zubrin and McKay the key to warming Mars is the use of CO₂ as a greenhouse gas. As I mentioned earlier, Mars’s southern icecap is a good source of solid CO₂ and the release of this gas would have a dramatic effect on the planet’s surface temperature and atmospheric pressure. Zubrin and McKay calculate that a temperature change of 4-10 K at the southern icecap would sublimate enough CO₂ into gaseous CO₂ that the surface temperature of Mars would increase until the entire southern icecap is melted, since CO₂ would then sublimate at an even faster rate as temperature increases.

      Mars also is lacking in free oxygen and has many toxic peroxides in its upper soil. But both of these problems can be solved once the surface temperature rises. The northern icecap has an abundance of frozen oxygen as well as frozen water, and peroxides break up and give off oxygen when heated. Also, once the entire southern icecap is converted into CO₂ gas, the planet’s surface should be warm enough to support primitive plant life. Photosynthesis from these plants would help release more O₂ from CO₂ with the use of sunlight. Furthermore, planetary warming would allow adaptive algae or biologically engineered bacteria to begin living on Mars’s surface. These organisms would release nitrogen from the soil and produce methane and ammonia which are also greenhouse gases.

      Along with oxygen and nitrogen, water is also vital to terraforming Mars to support plant and animal life. Even with the frozen water in the northern icecap, 3% of the Martian soil, called regolith, is made of frozen H2O. In addition, there are believed to be many pockets of hot water trapped in an upper surface layer called permafrost and there is a layer of liquid water under the permafrost. Drilling 800 m to reach the trapped water liquid would also release large amounts of water vapor which is also a greenhouse gas.

      The general plan for terraforming Mars outlined by McKay and Zubrin consists of releasing gaseous CO₂ to warm the planet enough to then release free oxygen, nitrogen, and liquid water. The release of these gases would also contribute to thickening Mars’s current thin atmosphere of 6-10 mbars. Large amounts of free oxygen along with abundant gaseous CO₂ then promotes ozone formation and ultimately Mars’s atmosphere can be thick and protect inhabitants from ultraviolet radiation.

      How can we induce this change of 4-10 K at the southern icecap to sublimate enough CO₂ to cause dramatic climate change? The option under greatest consideration is the idea of having solar reflective mirrors on solar powered satellites. According to Zubrin and McKay only one large mirror focused on the southern icecap is needed. To raise the icecap’s temperature by 5 K, a mirror 125 K in diameter would be needed. To keep this mirror satellite in stationary orbit it would have to be distanced 214,000 km away from Mars’s surface, so that the Sun and Mars’s gravity won’t disturb it.

      Alternative methods for raising the surface temperature of Mars include building large factories which primarily produce man-made greenhouse gases and drilling for greenhouse gases. The realization of these CFC producing factories would take a great deal of money, manpower, and energy. To do the job we are looking at supplying enough energy to power a city like Chicago. The artificial greenhouse gases made through chemical and electrolytic means must be long lasting in the atmosphere but not harmful to future ozone development. This means that Cl cannot be apart of any produced compounds since it is notorious for ozone destruction. Fortunately, CF₄ is a good replacement for Cl based CFC’s. CF₄ lasts 10,000 years in the atmosphere and doesn’t adversely affect ozone. If terraforming is efficient, meaning that factories, mirrors, drilling, algae, and simple plants all work effectively then the entire process of terraforming should take about 1,500 years to 2,500 according to Zubrin and McKay. However, human populations on Mars can begin in 500 years and humans can begin to live on the surface with only a breathing device. At this time humans living on Mars can begin the final step of terraforming, filling the air with oxygen through growing plants.