Colonization of the outer solar system

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Some of the moons of the outer planets of the solar system are large enough to be suitable places for colonization. Many of the larger moons contain water ice, liquid water, and organic compounds that might be useful for rocket fuel production among other things. Colonies in the outer solar system could also serve as centres for long term investigation of the planet and the other moons. In particular, robotic devices could be controlled by humans without the very long time delays needed to communicate with Earth. There have also been proposals to place robotic aerostats in the upper atmospheres of the gas giant planets for exploration and possibly mining of helium-3, which could have a very high value per unit mass as a thermonuclear fuel.[1][2]


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[edit] The Jupiter system

The Jupiter system in general poses particular disadvantages for colonizing because of its severe radiation environment and its particularly deep gravity well. Its radiation would deliver about 3,600 rems per day to unshielded colonists at Io and about 540 rems per day to unshielded colonists at Europa, while somewhere around 75 rems within only a few days is generally enough to cause radiation poisoning, and somewhere around 500 rems within only a few days is fatal.[3]

The radiation and gravity well issues are likely to make Jupiter persistently infeasible relative to the more distant gas giants as a source for mining helium-3. However, its gravity is a considerable advantage in providing a spacecraft with a gravitational boost to shorten its trip time to those outer gas giants. The advantage of its gravitational boost could make it economical to operate a way station, with Callisto the likeliest spot, and allow spacecraft that have had maintenance or re-supply on a Callisto station to take off for one of the outer gas giants, with the gravity boost more than making up for the delta-V lost in stopping in the Jovian system. Provided that short-term radiation shielding is provided for electronics and any crew on board a spacecraft, expending six km/s of delta-V - feasible with today's chemical rockets - while skimming 7,150 km above the cloud surface, can be leveraged into a departure speed of 24 km/s, i.e. 5 AU/year.[3]

Jupiter has an atmospheric depth with the same pressure as Earth at sea level, where there is also a blue sky, though it is colder than on Earth; further down, Jupiter has an atmospheric depth that is the same average temperature as the surface of the Earth, where the pressure is about five bars. However, even here, airborne colonies such as floating cities would be unlikely, because Jupiter has a gravitational acceleration of around 2.4 g near the surface of its atmosphere. Also, because the atmosphere is dominated by hydrogen, any leak of an oxygen atmosphere or a liquid oxygen bipropellant would present a significant risk of catastrophic explosion.

[edit] Europa

Main article: Colonization of Europa

The Artemis Project designed a plan to colonize Europa.[4][5] Scientists are to inhabit igloos and drill down into the Europan ice crust, exploring any sub-surface ocean. It also discusses use of air pockets for human inhabitation.

[edit] Ganymede

Ganymede is the largest moon in the Solar System, making it a possible target for colonization. Ganymede is also the only moon with a magnetosphere. Ganymede is far enough away from Jupiter that it only receives around 8 rems per day of radiation from Jupiter's radiation belts, well within the range to be managed with shielding; while Ganymede is also close enough to Jupiter that models indicate it likely experiences significant tidal stresses from Jupiter, which should make geothermal energy and liquid water available underground. Ganymede also possesses water ice, carbonaceous material, metals, and silicates. Ganymede is still fairly deep within Jupiter's gravity well, however, making travel to and from Ganymede relatively energy-intensive and therefore expensive.[3]

[edit] Callisto

NASA performed a study called HOPE (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the solar system.[6] The target chosen was Callisto. It could be possible to build a surface base that would produce fuel for further exploration of the solar system. Since it is outside of Jupiter's radiation belt and also geologically very stable, it could prove to be a suitable place for a base. This base would also be a centre for exploration of the Jupiter system, for example remote exploration of Europa. It would also be the ideal location for a Jovian system way station that could service spacecraft headed farther into the outer Solar System, using a gravity assist from a close fly-by of Jupiter after departing Callisto.[3]

[edit] Trojan asteroids

The 2006 announcement by the Keck Observatory that the binary Trojan asteroid 617 Patroclus, and possibly large numbers of other Trojan objects in Jupiter's orbit, are likely composed of water ice, with a layer of dust, suggests that mining water and other volatiles in this region and transporting them elsewhere in the Solar system, perhaps via the proposed Interplanetary Transport Network, may be feasible in the not-so-distant future. This could make colonization of the Moon, Mercury and main-belt asteroids more practical.

[edit] The Saturn system

Robert Zubrin identified Saturn, Uranus and Neptune as "the Persian Gulf of the solar system", as the largest sources of deuterium and helium-3 to drive the pending fusion economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and excellent system of moons.[7]

[edit] Titan

Main article: Colonization of Titan

Robert Zubrin identified Titan as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization, and saying "In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonization."[8] The surface of Titan is very young and active, and contains large amounts of water ice and perhaps oceans and canals of liquid organic compounds. It should be able to support a base, but more information regarding Titan's surface and the activities on it is necessary. The thick atmosphere and the weather are also factors to consider.

Incidentally, a widely published expert on terraforming, Christopher McKay, is also a co-investigator on the Huygens probe that landed on Titan in January 2005.

[edit] Enceladus

On March 9th, 2006, NASA's Cassini space probe found possible evidence of liquid water on Enceladus.[9] According to that article, "pockets of liquid water may be no more than tens of meters below the surface." If these findings are confirmed, it would mean liquid water could be collected much more easily on Enceladus than on, for instance, Europa (see above). Discovery of water, especially liquid water, generally improves a celestial body's consideration for colonization dramatically.

[edit] Uranus

Because Uranus has the lowest escape velocity of the four gas giants, it has been proposed as a mining site for helium-3.[2] If human supervision of the robotic activity proved necessary, one of Uranus' natural satellites might serve as a base. An alternative is to place floating cities in its atmosphere. By using balloons filled with hydrogen, large masses can be suspended [citation needed] underneath at roughly Earth gravity. Saturn and Neptune could be suitable as well, but Jupiter would likely not be, due to its high gravity, escape velocity, and radiation.

[edit] Neptune

Neptune and its satellites could also be used for colonization, but are farther away, and Neptune has a higher surface gravity than Uranus. Its satellites, especially Triton, could also be colonized.

[edit] Kuiper Belt and Oort Cloud

The noted physicist Freeman Dyson identified comets, rather than planets, as the major potential habitat of life in space.[10] It is thought that several trillion comets or iceteroids exist outside the orbit of Neptune. These may harbour all the ingredients for life (water ice and organic compounds) including significant amounts of deuterium, tritium, and helium-3. Estimates indicate the ratio of deuterium to standard hydrogen in the comets to be about 1 part per 10,000 to 100,000, which would provide around 50 to 100 kilotonnes of deuterium in an average comet, which may be used as fusion fuel to provide sufficient power to a comet colony for thousands of years.[11] Two astrophysicists have also proposed that an average comet may include enough aluminum to create a solar power collector with a radius in the thousands of kilometers, which could collect starlight from the brightest star even when the comet is deep into the Oort Cloud or interstellar space, to provide enough indefinitely sustainable power for a colonized comet with around 500 colonists.[12] Colonies sent to these far flung worldlets could build rotating habitats or live in dug-out spaces and light them with fusion reactors for thousands or millions of years before moving on. It is envisaged that over the eons humanity could migrate to neighbouring star systems, which may have similar clouds, without the need for large interstellar starships, by using comets as slow interstellar vessels with substantial natural resources; and that such interstellar comet colonies could also serve as way-stations for faster, smaller interstellar ships.[13]

[edit] See also

Space colonization edit


[edit] References

  1. ^ Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Settling the Outer Solar System: The Sources of Power, pp. 158-160, Tarcher/Putnam, 1999, ISBN 1-58542-036-0
  2. ^ a b Jeffrey Van Cleve (Cornell University) et al., "Helium-3 Mining Aerostats in the Atmosphere of Uranus", Abstract for Space Resources Roundtable, accessed May 10, 2006
  3. ^ a b c d Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Colonizing the Jovian System, pp. 166-170, Tarcher/Putnam, 1999, ISBN 1-58542-036-0
  4. ^ Artemis Society International official website
  5. ^ Peter Kokh et al., "Europa II Workshop Report", Moon Miner's Manifesto #110, Nov. 1997
  6. ^ Patrick A. Troutman (NASA Langley Research Center) et al., Revolutionary Concepts for Human Outer Planet Exploration (HOPE), accessed May 10, 2006 (.doc format)
  7. ^ Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: The Persian Gulf of the solar system, pp. 161-163, Tarcher/Putnam, 1999, ISBN 1-58542-036-0
  8. ^ Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Titan, pp. 163-166, Tarcher/Putnam, 1999, ISBN 1-58542-036-0
  9. ^ http://www.nasa.gov/mission_pages/cassini/media/cassini-20060309.html
  10. ^ Freeman Dyson, "The World, the Flesh, and the Devil", Third J.D. Bernal Lecture, May 1972, reprinted in Communication with Extraterrestrial Intelligence, Carl Sagan, ed., MIT Press, 1973, ISBN 0-262-69037-3
  11. ^ Richard P. Terra, "Islands in the Sky: Human Exploration and Settlement of the Oort Cloud", in Islands in the Sky: Bold New Ideas for Colonizing Space, Stanley Schmidt and Robert Zubrin, eds. Wiley, 1996, ISBN 0-471-13561-5
  12. ^ Ben R. Finney and Eric M. Jones, eds., Interstellar Migration and the Human Experience, University of California Press, 1986, ISBN 0-520-05898-4
  13. ^ David G. Stephenson, "Comets and Interstellar Travel", in Journal of the British Interplanetary Society, 36, 1983, pp. 210-214.
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