Colonization of Titan
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Surface and atmospheric composition
According to Cassini data from 2008, Titan has hundreds of times more liquid hydrocarbons than all the known oil and natural gas reserves on Earth. These hydrocarbons rain from the sky and collect in vast deposits that form lakes and dunes. "Titan is just covered in carbon-bearing material—it’s a giant factory of organic chemicals," said Ralph Lorenz, who leads the study of Titan based on radar data from Cassini. “This vast carbon inventory is an important window into the geology and climate history of Titan.” Several hundred lakes and seas have been observed, with several dozen estimated to contain more hydrocarbon liquid than Earth's oil and gas reserves. The dark dunes that run along the equator contain a volume of organics several hundred times larger than Earth's coal reserves. 
Radar images obtained on July 21, 2006 appear to show lakes of liquid hydrocarbon (such as methane and ethane) in Titan's northern latitudes. This is the first discovery of currently existing lakes beyond Earth. The lakes range in size from about a kilometer in width to one hundred kilometers across.
On March 13, 2007, JPL announced that it found strong evidence of seas of methane and ethane in the northern hemisphere. At least one of these is larger than any of the Great Lakes in North America.
The American aerospace engineer and author Robert Zubrin identified Saturn as the most important and valuable of the four gas giants in the solar system, because of its relative proximity, low radiation, and excellent system of moons. He also named Titan as the most important moon on which to establish a base to develop the resources of the Saturn system. 
Robert Zubrin has pointed out that Titan possesses an abundance of all the elements necessary to support life, saying "In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonization."  The atmosphere contains plentiful nitrogen and methane, and strong evidence indicates that liquid methane is on the surface and, liquid water, and ammonia are present under the surface and are often delivered to the surface by volcanic activity. Water can easily be used to generate breathable oxygen. Nitrogen is ideal to add buffer gas partial pressure to breathable air; indeed, nitrogen forms about 78% of Earth's atmosphere. Nitrogen, methane and ammonia can all be used to produce fertilizer for growing food.
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Additionally, Titan has an atmospheric pressure one and a half times that of Earth. This means that the interior air pressure of landing craft and habitats could be set equal or close to the exterior pressure, reducing the difficulty and complexity of structural engineering for landing craft and habitats compared with low or zero pressure environments such as on the Moon, Mars, or the asteroids. The thick atmosphere would also make radiation a non-issue, unlike on the Moon, Mars, or the asteroids. While Titan's atmosphere does contain trace amounts of hydrogen cyanide, in the event that an astronaut's respiration system is breached, the concentration would not inflict more than a slight headache. A greater danger is that the gases of the atmosphere can generate an explosive mixture with oxygen, which requires special measures in the event that a leak occurs in a habitable module or a spacesuit.
Titan has a surface gravity of 0.14 g, slightly less than that of the Moon. Managing long-term effects of low gravity on human health would therefore be a significant issue for long-term occupation of Titan, more so than on Mars. These effects are still an active field of study. They can include symptoms such as loss of bone density, loss of muscle density, and a weakened immune system. Astronauts in Earth orbit have remained in microgravity for up to a year or more at a time. Effective countermeasures for the negative effects of low gravity are well-established, particularly an aggressive regime of daily physical exercise or weighted clothing. The variation in the negative effects of low gravity as a function of different levels of low gravity are not known, since all research in this area is restricted to humans in zero gravity. The same goes for the potential effects of low gravity on fetal and pediatric development. It has been hypothesized that children born and raised in low gravity such as on Titan would not be well adapted for life under the higher gravity of Earth.
The temperature on Titan is about 94 K (−179 °C, or −290.2 °F), so insulation and heat generation and management would be significant concerns. Although the air pressure at Titan's surface is about 1.5 times that of Earth at sea level, because of the colder temperature the density of the air is closer to 4.5 times that of Earth sea level. At this density, temperature shifts over time and between one locale and another would be far smaller than comparable types of temperature changes present on Earth. The corresponding narrow range of temperature variation reduces the difficulties in structural engineering.
Relative thickness of the atmosphere combined with extreme cold makes additional troubles for human habitation. Unlike in a vacuum, the high atmospheric density makes thermoinsulation a significant engineering problem.
The very high ratio of atmospheric density to surface gravity also greatly reduces the wingspan needed for an aircraft to maintain lift, so much so that a human would be able to strap on wings and easily fly through the atmosphere. However, due to Titan's extremely low temperatures, heating of a flight-bound vehicle becomes a key obstacle.
- Findings from the study led by Ralph Lorenz, Cassini radar team member from the Johns Hopkins University Applied Physics Laboratory, USA, are reported in the 29 January 2008 issue of the Geophysical Research Letters.
- Titan’s surface organics surpass oil reserves on Earth. 13 February 2008 http://www.esa.int/esaSC/SEMCSUUHJCF_index_0.html
- Cassini-Huygens: News
- Cassini-Huygens: News
- Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: The Persian Gulf of the solar system, pp. 161-163, Tarcher/Putnam, 1999, ISBN 978-1-58542-036-0
- Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Titan, pp. 163-166, Tarcher/Putnam, 1999, ISBN 978-1-58542-036-0
- Robert Zubrin, The Case for Mars: The Plan to Settle the Red Planet and Why We Must, p. 146, Simon & Schuster/Touchstone, 1996, ISBN 978-0-684-83550-1
- Robert Zubrin, "Colonizing the Outer Solar System", in Islands in the Sky: Bold New Ideas for Colonizing Space, pp. 85-94, Stanley Schmidt and Robert Zubrin, eds., Wiley, 1996, ISBN 978-0-471-13561-6
- Randall Munroe (2013). "Interplanetary Cessna" (in English). Retrieved 2013-01-29.
- Stephen L. Gillett, "Titan as the Abode of Life," Analog, Vol. CXII No. 13, pp. 40–55 (1992)
- Julian Nott - Titan: A Distant But Enticing Destination for Human Visitors (White Paper for National Academy of Sciences]