Kuiper belt helps with terraforming Mars
The Kuiper belt is an asteroid belt in the
outer-solar system which extends beyond the orbits of Neptune and Pluto. This asteroid belt will play a crucial role in terraforming Mars. As discussed in the lesson on Terraforming and Colonizing Mars, these asteroids are rich in powerful greenhouse gasses such as ammonia and methane. By redirecting the paths of these worlds towards Mars, we could hurl them into Mars' atmosphere. Either we could maneuver these iceteroids into a stable orbit around Mars and allow Mars' atmosphere to heat them up until they disintegrate releasing gaseous ammonia and methane into the atmosphere, or we could hurl them directly towards Mars and as they made a direct impact with Mars' surface the heat generated by such collisions would be so stupendous that the iceteroids initially frozen ammonia and methane would get outgassed into the atmosphere. But these icy bodies also contain large amounts of frozen water. By the time our remote descendants have reached the Kuiper belt, humanities progress in terraforming Mars would have increased the planet's average temperature above the melting point of water. Thus, once these iceteroids impacted Mars'
A size comparison of the Kuiper belt and outer solar system to the Oort Cloud.
surface, the frozen water would vaporize and subsequently condense to form massive bodies of liquid water. The soletta (a system of three orbital mirrors in Mars' orbit which, in the article on Terraforming and Colonizing Mars, we assumed was constructed sometime during the 21st century) had beamed on the order of ten terrawatts of solar energy onto the Martian surface to carve extensive canal systems all across Mars' surface, similar to how this device was used in the novel Green Mars. And also, as robotic explorers have confirmed, Mars once had running streams and rivers of liquid water on its surface. After Mars somehow lost its magnetosphere and its atmosphere and liquid water oceans were stripped away by the Sun's solar winds, the relics of these ancient rivers where water once ran still remain. The water contained in these iceteroids would fill all of these canals and ancient water streams and cover Mars with vast oceans, lakes, and rivers of liquid water.
Artist's depiction of Fesenkov Crater on Mars filled with liquid water.
Reasons for going to the Kuiper belt and Oort Cloud
One might ask: since the inner-asteroid belt is right next to Mars and all of those asteroids also contain ammonia, methane and water, why not hurl some of those asteroids towards Mars instead? Since the asteroids within the inner-asteroid belt are so close to the Sun, they must travel at enormous speeds of tens of thousands of kilometers per second to remain in orbit around the Sun. In order to change their momentum (by an amount \(Δ\vec{p}\)) in a direction towards Mars, an enormous force \(\sum{\vec{F}}\) (and, hence, an enormous power output) must be exerted on these asteroids in order to move them to Mars. Since the iceteroids in the Kuiper belt are very far away from the Sun, they only need to move at a speed of \(300km/s\) to stay in orbit around the Sun. Thus, much less power and energy would be required to change their momentum in a direction towards Mars. But this isn't the only reason why it would be much easier to move an asteroid from the Kuiper belt towards Mars than from the inner-asteroid belt towards Mars instead. The second reason why we would use the iceteroids from the Kuiper belt to help us in the project of terraforming Mars is because of gravity assists. By sending these iceteroids on a path towards any one of the gas giants (Jupiter, Saturn, Uranus, or Neptune), one of those gas giants could "sling shot" the iceteroid with its gravity towards Mars.
Terraforming Mars isn't the only reason why our descendants would be interested in going to the Kuiper belt. As we discussed in the lesson, Colonizing the Asteroids and Comets of our Solar System, and as popularized by the legendary scientist Carl Sagan in his book, Pale Blue Dot, these asteroids could be used as homesteads and spaceships. This could be accomplished by hollowing out such an asteroid and using its materials to construct a rotating cylindrical habitat inside of the asteroid. This cylindrical habitat would rotate at just the right speed to produce centrifugal forces everywhere along the cylinder's interior which emulates Earth's gravity. Humans would live along the inner-surface of such a cylinder. In the aforementioned lesson that we covered previously, we discussed one way of using such an asteroid as a spaceship. Essentially, we could just spit out asteroidal materials at very high speeds giving the asteroid a thrust which would allow one to use the asteroid as a spacecraft. But we'll assume that by time humans have had ventured to the Kuiper belt, they will have had developed nuclear fusion. We believe that the iceteroids in the Kuiper belt will have deuterium for nuclear reactions. But for long interstellar voyages, humans would likely harvest the vast reservoirs of helium-3 (\(H_3\)) from Neptune's atmosphere (see top image below) or possibily from Uranus's atmosphere as well (see bottom image below) and then use that and the indigenous asteroidal deuterium to fuel their nuclear powered, rocky/icy spaceships.
After the Kuiper belt, humanities next likely destination would be the Oort Cloud. The Oort Cloud is a vast array of trillions of icy comets which form a great spherical swarm around the Sun. The Kuiper belt ends at about 10,000 astronomical units (AUs) away from the Sun—this is also where the realm of the Oort cloud begins. The outer limits of the Oort Cloud extends to a distance of about 100,000 AUs away from the Sun. This outer limit of the Oort Cloud is roughly half the distance to the nearest stars which is the Alpha Centuari star system. As the famous physicist Freeman Dyson once said, since the comets in the Oort Cloud contain all the ingredients necessary to support life, this comet cloud would be a good way point between the stars. According to the engineer Robert Zubrin and as long ago envisioned by Carl Sagan, we humans will eventually build settlements and homesteads in both the Kuiper Belt and the Oort cloud. And after colonizing the Oort Cloud, the next destination could possibly be a rocky Earth-like planet named Proxima B in the Alpha Centuari star system.
Another size comparison of the solar system to the Oort Cloud.
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References
1. Zubrin, Robert. Entering Space: Creating a Spacefaring Civilization. New York: Jeremy P. Tarcher/Putnam, 1999. Print.
2. Wikipedia contributors. "Atmosphere of Titan." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 6 Sep. 2017. Web.11 Oct. 2017