Colonization of the outer solar system

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Space colonization

Mercury Venus Earth Moon Mars Asteroids Ceres Outer solar system Jupiter Europa Saturn Titan Pluto Kuiper Belt and Oort Cloud

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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]

Contents 1 The Jovian system 1.1 Europa 1.2 Ganymede 1.3 Callisto 1.4 Trojan asteroids 2 The Saturnian system 2.1 Titan 2.2 Enceladus 3 Uranus 4 Neptune 5 Kuiper Belt and Oort Cloud 6 Challenges 7 See also 8 References

[edit] The Jovian system

The Jovian 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 surface gravity 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 Jovian 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 Saturnian 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 mostly uncratered and thus inferred to be very young and active, and probably composed of mostly water ice, and lakes of liquid hydrocarbons (methane/ethane) in its polar regions. While the temperature is cryogenic (95 K) 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, such as potential flash floods, 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. An alternative model of Enceladus' activity is the decomposition of methane/water clathrates - a process requiring lower temperatures than liquid water eruptions. The relatively higher density of Enceladus indicates a larger than Saturnian average silicate core that should provide materials for base operations.

[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. Triton's surface shows signs of extensive geological activity implying a sub-surface ocean, perhaps of ammonia/water^[10]. Such geothermal energy would make colonising a cryogenic world like Triton feasible.

[edit] Kuiper Belt and Oort Cloud

See also Colonization of Pluto

See also Colonization of the Kuiper Belt and Oort Cloud

The noted physicist Freeman Dyson identified comets, rather than planets, as the major potential habitat of life in space.^[11]

[edit] Challenges

There are various difficulties in colonizing the outer solar system. They include:

• Distance from Earth: The outer planets are much further from Earth than inner planets, and are therefore harder to reach and it takes longer to get there.
• Planetary conditions: The outer planets have no surface to land on, so any habitation would have to use floating colonies, increasing complexity and decreasing reliability. The moons/comets do not have this problem, although some have specific problems (like Europa is in Jupiter's intense radiation bands).
• Power: Solar power is generally considered unsuitable because of the large distance from the sun. Nuclear power is believed to be the only suitable power source for the colonies.

For these reasons, colonization of the outer planets is only likely after large-scale colonization of the inner solar system.

[edit] See also

• Floating cities
• Solar System in fiction

[edit] References