Locations




Location is a frequent point of contention between space colonization advocates. The location of colonization can be on a physical body planet, dwarf planet, natural satellite, or asteroid or orbiting one. For colonies not on a body see also space habitat.

Near-Earth spaceedit

The Moonedit

Due to its proximity and familiarity, Earth's Moon is discussed as a target for colonization. It has the benefits of proximity to Earth and lower escape velocity, allowing for easier exchange of goods and services. A drawback of the Moon is its low abundance of volatiles necessary for life such as hydrogen, nitrogen, and carbon. Water-ice deposits that exist in some polar craters could serve as a source for these elements. An alternative solution is to bring hydrogen from near-Earth asteroids and combine it with oxygen extracted from lunar rock.

The Moon's low surface gravity is also a concern, as it is unknown whether 1/6g is enough to maintain human health for long periods.

The Moon's lack of atmosphere provides no protection from space radiation or meteoroids. The early Moon colonies may shelter in ancient Lunar lava tubes to gain protection. The two-week day/night cycle makes use of solar power more difficult.

Lagrange pointsedit

Another near-Earth possibility are the five Earth–Moon Lagrange points. Although they would generally also take a few days to reach with current technology, many of these points would have near-continuous solar power because their distance from Earth would result in only brief and infrequent eclipses of light from the Sun. However, the fact that the Earth–Moon Lagrange points L4 and L5 tend to collect dust and debris, whereas L1-L3 require active station-keeping measures to maintain a stable position, make them somewhat less suitable places for habitation than was originally believed. Additionally, the orbit of L2–L5 takes them out of the protection of the Earth's magnetosphere for approximately two-thirds of the time, exposing them to the health threat from cosmic rays.

The five Earth–Sun Lagrange points would totally eliminate eclipses, but only L1 and L2 would be reachable in a few days' time. The other three Earth–Sun points would require months to reach.

The inner planetsedit

Mercuryedit

Colonizing Mercury would involve similar challenges as the Moon as there are few volatile elements, no atmosphere and the surface gravity is lower than Earth's. However, the planet also receives almost seven times the solar flux as the Earth/Moon system.citation needed

Geologist Stephen Gillett suggested in 1996 that this could make Mercury an ideal place to build and launch solar sail spacecraft, which could launch as folded up "chunks" by mass driver from Mercury's surface. Once in space the solar sails would deploy. Since Mercury's solar constant is 6.5 times higher than Earth's, energy for the mass driver should be easy to come by, and solar sails near Mercury would have 6.5 times the thrust they do near Earth. This could make Mercury an ideal place to acquire materials useful in building hardware to send to (and terraform) Venus. Vast solar collectors could also be built on or near Mercury to produce power for large scale engineering activities such as laser-pushed lightsails to nearby star systems.

Venusedit

Marsedit

Asteroid beltedit

Colonization of asteroids would require space habitats. The asteroid belt has significant overall material available, the largest object being Ceres, although it is thinly distributed as it covers a vast region of space. Uncrewed supply craft should be practical with little technological advance, even crossing 500 million kilometers of space. The colonists would have a strong interest in assuring their asteroid did not hit Earth or any other body of significant mass, but would have extreme difficulty in moving an asteroidcitation needed of any size. The orbits of the Earth and most asteroids are very distant from each other in terms of delta-v and the asteroidal bodies have enormous momentum. Rockets or mass drivers can perhaps be installed on asteroids to direct their path into a safe course.

Moons of outer planetsedit

Jovian moons – Europa, Callisto and Ganymedeedit

The Artemis Project designed a plan to colonize Europa, one of Jupiter's moons. Scientists were to inhabit igloos and drill down into the Europan ice crust, exploring any sub-surface ocean. This plan discusses possible use of "air pockets" for human habitation. Europa is considered one of the more habitable bodies in the Solar System and so merits investigation as a possible abode for life.

NASA performed a study called HOPE (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System. The target chosen was Callisto due to its distance from Jupiter, and thus the planet's harmful radiation. It could be possible to build a surface base that would produce fuel for further exploration of the Solar System.

Three of the Galilean moons (Europa, Ganymede, Callisto) have an abundance of volatiles that may support colonization efforts.

Moons of Saturn – Titan, Enceladus, and othersedit

Titan is suggested as a target for colonization, because it is the only moon in the Solar System to have a dense atmosphere and is rich in carbon-bearing compounds. Titan has water ice and large methane oceans. Robert Zubrin identified Titan as possessing an abundance of all the elements necessary to support lifewhere?, 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".

Enceladus is a small, icy moon orbiting close to Saturn, notable for its extremely bright surface and the geyser-like plumes of ice and water vapor that erupt from its southern polar region. If Enceladus has liquid water, it joins Mars and Jupiter's moon Europa as one of the prime places in the Solar System to look for extraterrestrial life and possible future settlements.

Other large satellites: Rhea, Iapetus, Dione, Tethys, and Mimas, all have large quantities of volatiles, which can be used to support settlements.

Trans-Neptunian regionedit

The Kuiper belt is estimated to have 70,000 bodies of 100 km or larger.

Freeman Dyson has suggested that within a few centuries human civilization will have relocated to the Kuiper belt.

The Oort cloud is estimated to have up to a trillion comets.

Outside the Solar Systemedit

Looking beyond the Solar System, there are up to several hundred billion potential stars with possible colonization targets. The main difficulty is the vast distances to other stars: roughly a hundred thousand times farther away than the planets in the Solar System. This means that some combination of very high speed (some more-than-fractional percentage of the speed of light), or travel times lasting centuries or millennia, would be required. These speeds are far beyond what current spacecraft propulsion systems can provide.

Space colonization technology could in principle allow human expansion at high, but sub-relativistic speeds, substantially less than the speed of light, c.  An interstellar colony ship would be similar to a space habitat, with the addition of major propulsion capabilities and independent energy generation.

Hypothetical starship concepts proposed both by scientists and in hard science fiction include:

  • A generation ship would travel much slower than light, with consequent interstellar trip times of many decades or centuries. The crew would go through generations before the journey is complete, so that none of the initial crew would be expected to survive to arrive at the destination, assuming current human lifespans.
  • A sleeper ship, in which most or all of the crew spend the journey in some form of hibernation or suspended animation, allowing some or all who undertake the journey to survive to the end.
  • An embryo-carrying interstellar starship (EIS), much smaller than a generation ship or sleeper ship, transporting human embryos or DNA in a frozen or dormant state to the destination. (Obvious biological and psychological problems in birthing, raising, and educating such voyagers, neglected here, may not be fundamental.)
  • A nuclear fusion or fission powered ship (e.g. ion drive) of some kind, achieving velocities of up to perhaps 10% c  permitting one-way trips to nearby stars with durations comparable to a human lifetime.
  • A Project Orion-ship, a nuclear-powered concept proposed by Freeman Dyson which would use nuclear explosions to propel a starship. A special case of the preceding nuclear rocket concepts, with similar potential velocity capability, but possibly easier technology.
  • Laser propulsion concepts, using some form of beaming of power from the Solar System might allow a light-sail or other ship to reach high speeds, comparable to those theoretically attainable by the fusion-powered electric rocket, above. These methods would need some means, such as supplementary nuclear propulsion, to stop at the destination, but a hybrid (light-sail for acceleration, fusion-electric for deceleration) system might be possible.
  • Uploaded human minds or artificial intelligence may be transmitted via radio or laser at light speed to interstellar destinations where self-replicating spacecraft have travelled subluminally and set up infrastructure and possibly also brought some minds. Extraterrestrial intelligence might be another viable destination.

The above concepts which appear limited to high, but still sub-relativistic speeds, due to fundamental energy and reaction mass considerations, and all would entail trip times which might be enabled by space colonization technology, permitting self-contained habitats with lifetimes of decades to centuries. Yet human interstellar expansion at average speeds of even 0.1% of c  would permit settlement of the entire Galaxy in less than one half of the Sun's galactic orbital period of ~240,000,000 years, which is comparable to the timescale of other galactic processes. Thus, even if interstellar travel at near relativistic speeds is never feasible (which cannot be clearly determined at this time), the development of space colonization could allow human expansion beyond the Solar System without requiring technological advances that cannot yet be reasonably foreseen. This could greatly improve the chances for the survival of intelligent life over cosmic timescales, given the many natural and human-related hazards that have been widely noted.

If humanity does gain access to a large amount of energy, on the order of the mass-energy of entire planets, it may eventually become feasible to construct Alcubierre drives. These are one of the few methods of superluminal travel which may be possible under current physics. However it is probable that such a device could never exist, due to the fundamental challenges posed. For more on this see Difficulties of making and using an Alcubierre Drive.

Intergalactic traveledit

Looking beyond the Milky Way, there are at least 2 trillion other galaxies in the observable universe. The distances between galaxies are on the order of a million times farther than those between the stars. Because of the speed of light limit on how fast any material objects can travel in space, intergalactic travel would either have to involve voyages lasting millions of years, or a possible faster than light propulsion method based on speculative physics, such as the Alcubierre drive. There are, however, no scientific reasons for stating that intergalactic travel is impossible in principle.

Uploaded human minds or AI may be transmitted to other galaxies in the hope some intelligence there would receive and activate them.

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