Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100

terra-formed. Perhaps the simplest way would be to inject methane gas or other greenhouse gases into the atmosphere. Since methane gas is an even more potent greenhouse gas than carbon dioxide, the methane gas might be able to trap sunlight, raising the surface temperature of Mars to above the melting point of ice. In addition to methane, other greenhouse gases have been analyzed for possible terraforming experiments, such as ammonia and chlorofluorocarbons.
    Once the temperature starts to rise, the underground permafrost may begin to thaw out, for the first time in billions of years. As the permafrost melts, riverbeds would begin to fill up with water. Eventually, lakes and even oceans might form again on Mars as the atmosphere thickens. This would release more carbon dioxide, setting off a positive feedback loop.
    In 2009 it was discovered that methane gas naturally escapes from the Martian surface. The source of this gas is still a mystery. On earth, most of the methane gas is due to the decay of organic materials. But on Mars, the methane gas may be a by-product of geologic processes. If one can locate the source of this methane gas, then it might be possible to increase its output and hence alter the atmosphere.
    Another possibility is to deflect a comet into the Martian atmosphere. If one can intercept a comet far enough away, then even a small nudge by a rocket engine, an impact with a probe, or even the tug of the gravity of a spaceship might be enough to deflect it. Comets are made mainly of water ice and periodically race through our solar system. (Halley’s comet, for example, consists of a core—resembling a peanut—that is roughly twenty miles across, made mainly of ice and rock.) As the comet gradually gets closer to the surface of Mars, it would encounter friction from the atmosphere, causing the comet to slowly disintegrate, releasing water into the atmosphere in the form of steam.
    If comets are not available, it could also be possible to deflect one of the ice moons of Jupiter or perhaps an asteroid that contains ice, such as Ceres, which is believed to be 20 percent water. (These moons and asteroids would be harder to deflect, since they are usually in stable orbits.) Instead of having the comet, moon, or asteroid slowly decay in its orbit around Mars, releasing water vapor, another choice would be to maneuver them into a controlled impact on the Martian ice caps. The polar regions of Mars are made of frozen carbon dioxide, which disappears during the summer months, and ice, which makes up the permanent part of the ice caps. If the comet, moon, or asteroid hits the ice caps, they can release a tremendous amount of heat and vaporize the dry ice. Since carbon dioxide is a greenhouse gas, this would thicken the atmosphere and help to accelerate global warming on Mars. It might also create a positive feedback loop. The more carbon dioxide is released from the ice caps, the warmer the planet becomes, which in turn releases even more carbon dioxide.
    Another suggestion is to detonate nuclear bombs directly on the ice caps. The drawback is that the resulting liquid water might contain radioactive fallout. Or we could try to create a fusion reactor that can melt the polar ice caps. Fusion plants use water as a basic fuel, and there is plenty of frozen water on Mars.
    Once the temperature of Mars rises to the melting point of ice, pools of water may form, and certain forms of algae that thrive on earth in the Antarctic may be introduced to Mars. They might actually thrive in the atmosphere of Mars, which is 95 percent carbon dioxide. They could also be genetically modified to maximize their growth on Mars. These algae pools could accelerate terraforming in several ways. First, they could convert carbon dioxide into oxygen. Second, they would darken the surface color of Mars, so that it absorbs more heat from the sun. Third, since they grow by themselves without any prompting from the outside, it would be a relatively cheap way to change the environment of the planet. Fourth, the algae can be harvested for food. Eventually these algae lakes would create soil and nutrients that may be suitable for plants, which in turn would accelerate the production of oxygen.
    Scientists have also looked into the possibility of building solar satellites surrounding the planet, reflecting sunlight onto Mars. Solar satellites by themselves might be able to heat the Martian surface above freezing. Once this happens and the