Terraforming the Moon is itself a misnomer, as true terraformation would require increasing the lunar mass to be equal to the Earth’s, something that would be detrimental to life on Earth, and would likely destabilize our twin planetary system. The correct terms would be caeliforming, and ecogenisis; the creation of a terrestrial atmosphere, followed by the introduction of terrestrial life. However, although inaccurate, terraforming the term most people know and associate with the process, and therefore will be used in this article.
Terraforming the Moon presents similar problems to the terraformation of Mars and Venus; like Mars, the moon would need the substantial increase of atmosphere, and like Venus, it does not have a terrestrial day-night cycle. However, terraforming the moon, sans the mass/gravity issue, is possible on the same timescale as Mars and Venus; likely taking longer than Mars, and less time than Venus, to become habitable. There is no evidence that the Moon has ever had a significant atmosphere, hydrosphere, or biosphere; if any trace of indigenous life is found there, it will cause far more surprise than life on either Mars of Venus.
The Moon’s temperature is an issue. Due to both the moon’s slow rotation and the lack of a substantial atmosphere, the Moon has a tremendous variance in temperature; during the lunar day, the surface temperature averages 107°C, and during the lunar night, it averages -153°C. For reference the highest recorded temperature on the Earth was 58°C in Al’Aziziyah, Libya, 1922, and the coldest was -89.6°C at Vostok Station, Antarctica, 1983.
The main reason for the difference is the Moon’s lack of an atmosphere; the Earth’s atmosphere protects life by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night, by moving heat around the planet via the jet streams. Therefore, the creation of a terrestrial atmosphere on Luna would likely solve the bulk of the temperature issue; however, the 27.3 earth day long day-night cycle will continue to cause a significantly higher temperature variation than found on the Earth during an average 24 hour day-night cycle. Fortunately as the Moon is significantly smaller than the Earth, and that it has a lower comparative gravitational acceleration, a terrestrial atmosphere could move heat around the planet far more efficiently than on the Earth. Ultimately, unless a method is found to safely accelerate the Moon’s rotation, the lunar surface is likely to always have higher temperature variations than the Earth, and will resultantly have more consistently extreme weather than found on the Earth.
The current lunar atmosphere is less than one trillionth the density of the Earth's atmosphere at sea level. One source of the lunar atmosphere is outgassing: the release of gases such as radon that originate from radioactive decay within the crust and mantle. Another important source is the bombardment of the lunar surface by micrometeorites, the solar wind, and sunlight, in a process known as sputtering. Clearly an atmosphere would be an early requirement in any attempt to terraform the Moon.
The gaseous requirements of a terrestrial-type lunar atmosphere would be approximately 45% of the Earth’s gaseous mass, in similar proportions; approximately 2.29 exagrams of gas, primarily: 1.79 exagrams of nitrogen, 0.48 exagrams of oxygen, and 0.02 exagrams of argon. Other gasses would be needed to replicate the Earth’s atmosphere, however in smaller qualities: 878 teragrams of carbon dioxide, 42 teragrams of neon, 12 teragrams of helium, 4 teragrams of methane, 3 teragrams of krypton, and 1 teragram of hydrogen. The bulk of this gas could be obtained from Venus’ upper atmosphere, while some may need to be mined on asteroids, or in the Jovian system. Maintaining the atmosphere over long periods of time would require replenishing of lighter gasses as solar wind would blow hydrogen and helium from upper atmosphere due to the weak lunar gravitational field.
In addition to the moon’s lack of an atmosphere, the moon has no known appreciable surface water. Water is known to exist within the lunar soil and rocks, and is believed to exist underground; however, extracting large enough quantities in situ to support a lunar biosphere seems impractical. The most logical source of unused water is Ceres, or another large asteroid. The only problem with importing water from Ceres to create a Lunar ocean, from a terraformer’s point of view, is the fact that Ceres ice is not salty. The closest source of salt-water, other than the Earth, is Ganymede, orbiting within Jupiter’s radiation belt, and inaccessible to humans for the foreseeable future. Importing salt-water from Ganymede would allow terraformers to replicate terrestrial salt-water oceans; however, there is a strong possibility that Ganymede may support its own life forms, which would be mixed with terrestrial (and possibly Martian) life during the terraforming process. Ultimately the creation of freshwater oceans would still be progress from a terraformers point of view, however, there would be a limited amount of aquatic life that could be transplanted into such an ocean; mammals, reptiles, and some forms of fish, eels, and lamprey could likely adapt, however, most aquatic animals do not have appropriately developed gills or kidneys, and could not survive such a transition. Plant life would likely have an easier time adapting to a fresh water ocean, as Earth has many large lakes (Superior, Victoria, Tanganyika, Baikal, etc.) and rivers (Amazon, Congo, Nile, Mississippi, Ob, etc), that support a wide variety of fresh water plants.
The moon does not have a strong geomagnetic field like the Earth’s, and this is a potential long term problem as far as terraforming is concerned. The Earth’s geomagnetic field, protects the planet from solar radiation, and high energy particles; in the process minimizing the Earth’s loss of low mass gasses, such as hydrogen and helium. A with Mars and Venus, the lack of a stable geomagnetic field is a problem, as over millennia, the planet’s will likely loose their lighter gases, and in the process, loose water. In fact without a protective radiation shield, or the ongoing importation of lighter gasses, any attempt to terraform Mars Venus, and the Moon, will ultimately result in run-away greenhouse planets like Venus already is. This process would take millions of years, as the solar radiation and winds, break down water into hydrogen and oxygen, and blow away the hydrogen, leaving only the oxygen. Eventually any planet with terrestrial life would die without suffice water, and would leave a dry carbon rich corpse. Once the atmospheric oxygen level surpasses the nitrogen level, the atmosphere would be susceptible to atmospheric burning, whereby any meteor impact or even a lightning stick could ignite the oxygen rich atmosphere, and cause a global burn, converting the atmospheric oxygen to carbon dioxide, which would then lead to the run away greenhouse effect observed on Venus. Hopefully any human colonists would have the intelligence and capabilities to replenish the light gasses, as the outer solar system is rich in these gasses, and importing them should not pose a problem for a civilization capable of terraforming the moon in the first place.
If a lunar geomagnetic field could be manufactured, it would prevent the loss of the lighter gasses to a large degree, however, due to the lower lunar gravity, it might not be enough to prevent the loss entirely. Creating a lunar geomagnetic field would pose significant problems, as the moon does not have a significant solid inner core, which on the Earth causes the geomagnetic field. Attempting to initial a geodynamo within the Moon, would probably not work as the Lunar solid core is so small compared to the Earth’s. In order for the Lunar core to replicate the Earth’s geomagnetic field as strong as the Earth’s, the lunar core would have to be spinning much faster than the Earth’s core. An estimate of 90 revolutions per day Earth-day has been proposed, however without a full understanding of the Earth’s core, and the geodynamo itself, any attempt to calculate the exact rate is impossible. Nevertheless, if the 90 revolution per day estimate were accurate, the heat generated would likely melt the lunar mantle in a matter of a few centuries. Accelerating the core’s spin is possible due to the small mass of the core in comparison to the rest of the Moon, this would be energy expensive, and would require building a series of power plants around the Moon, and connecting them via underground plasma tubes. Electricity moving around the Moon in the plasma tubes could generate a magnetic field strong enough to manipulate the core, as it has less mass than the lunar mantle. The cheapest most immediate solution would be to build a series of satellites with interlocking magnetic fields, and place them in orbit around the moon. As the satellites could be solar powered, maintenance should not be an issue for decades at a time, however, would be require as long as the satellite network was in use.
The Moon’s long rotation of 27.3 earth days is a potential problem for terrestrial life. As for methods of shortening the lunar day, terraformers are somewhat limited with the foreseeable technology of the next few centuries.As with Venus, the Series of Asteroid Impacts theory is valid, however, directing asteroids into a potential Earth-impacting trajectory seems idiotic.Building a large moon around the moon would not work, as the moon is tidally locked with the earth’s gravitational field, and any moon large enough to impact the Earth-Luna gravitational pull, would destabilize the Earth-Moon system. Finally, the rotation of the surface of the Moon can not be sped up in comparison to the rotation of the core using electromagnetic fields, as the lunar core is less massive that the crust and massive mantle, both of which are solid.
A 27.3 Earth-day rotation means that lunar days and nights would be about 13.8 Earth-days long. While life on Earth is capable of surviving long days and nights, the number of species that have adapted to these extreme conditions is low. Areas north of the Arctic Circle or south of the Antarctic Circle, experience long day-night cycles, peaking at Amundsen-Scott South Pole Station, and at the North Pole, where days and nights are each 6 months long. This extreme variation is caused by the Earth’s axial tilt of 23.44°, which causes day and night to be extended at regions within 23.44° of the poles; as the Moon’s axial tilt off of the Earth’s elliptic (Earth’s orbit around the sun) is only 1.54°, the lunar arctic and antarctic regions will be virtually non-existent, as will the topical region as a band of only 3.08° around the equator. Within the antarctic and arctic regions, there are several mammal species that have adapted to the long days and nights, including walruses, blue whales, orcas, reindeer, muskoxen, hares, foxes, lemmings, seals, wolves, wolverines, ermines, squirrels, and bears; in addition, it is known that mammoths (elephants) once lived within the regions, and cats have adapted to the climate on several antarctic islands, after having been introduced by humans. Bird species are numerous in both the arctic and antarctic regions, including owls, penguins, petrels, and albatrosses. Salt-water fish and invertebrate species thrive in the region, including icefish (notothenioidei species), toothfish, squid, and krill, however, unless the lunar ocean is salted, none of these species could be transplanted. It is also known from paleological findings, that alligators and several dinosaur species, including the Chasmosaurus, Hypacrosaurus, Troodon, and Edmontosaurus, lived in the region during the Cretaceous period (145-65 Ma) when the region was substantially warmer, indicating that reptiles would likely adapt to the longer day-night cycle as well, provided the temperature didn’t drop too low.
Throughout both the arctic and antarctic regions, the vegetation is composed of plants such as dwarf shrubs, graminoids, herbs, lichens and mosses, which all grow relatively close to the ground, forming tundra. As one moves northward, the amount of warmth available for plant growth decreases considerably. In the northernmost areas, plants are at their metabolic limits, and small differences in the total amount of summer warmth make large differences in the amount of energy available for maintenance, growth and reproduction. Colder summer temperatures cause the size, abundance, productivity and variety of plants to decrease. In the warmest parts of the Arctic, shrubs are common and can reach 2m in height; sedges, mosses and lichens can form thick layers. While trees do not thrive in the arctic or antarctic regions, this is because of the temperature rather than the day-night cycle. Trees do grow north of the arctic circle in Norway (70°N), Russia (66°N), Alaska (68°N), and Canada (69°N – in the Northwest Territories), in areas where the summer climate is warm enough to sustain tree growth in the summer, and the climate is not too harsh for trees to survive in the winter. Maritime influences such as ocean currents also play a major role in determining how far from the equator trees can grow. Therefore, even with the long day-night cycle of the Moon, terrestrial life should be able to adapt.
