Colonization of Uranus
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Many planets within the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
have been considered for
colonization Colonization, or colonisation, constitutes large-scale population movements wherein migrants maintain strong links with their, or their ancestors', former country – by such links, gain advantage over other inhabitants of the territory. When ...
and
terraforming Terraforming or terraformation ("Earth-shaping") is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body to be similar to the environment of Earth to make ...
. The main candidates for colonization in the inner Solar System are
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
and
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
. Other possible candidates for colonization include the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
and even
Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...
. Many parts of the outer
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
have been considered for possible future colonization. Most of the larger moons of the outer planets contain
water ice Water ice could refer to: *Ice formed by water (as opposed to other substances) *The alternate term for various similar frozen fruit-flavoured desserts: **Italian ice primarily in Philadelphia and the Delaware Valley **Sorbet Sorbet (), also c ...
,
liquid water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a s ...
, and organic compounds that might be useful for sustaining human life.G.J. Consalmagno, ''Ice-rich moons and the physical properties of ice'', Journal of Physical Chemistry, vol. 87, no. 21, 1983, p. 4204-4208.Ralph Lorenz and
Jacqueline Mitton Jacqueline Mitton (née Pardoe, born 1948) is a British astronomer, writer, and media consultant who lives and works in Cambridge, UK. She studied at Somerville College, Oxford and Murray Edwards College, Cambridge. She has served as Public Rela ...
, ''Lifting Titan's veil: exploring the giant moon of Saturn'', Cambridge University Press, 2002
There have also been proposals to place robotic
aerostat An aerostat (, via French) is a lighter-than-air aircraft that gains its lift through the use of a buoyant gas. Aerostats include unpowered balloons and powered airships. A balloon may be free-flying or tethered. The average density of the cra ...
s in the upper atmospheres of the Solar System's
gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...
planets for exploration and possibly mining of
helium-3 Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (the most common isotope, helium-4, having two protons and two neutrons in contrast). Other than protium (ordinary hydrogen), helium-3 is the ...
, which could have a very high value per unit mass as a thermonuclear fuel.Robert Zubrin, ''Entering Space: Creating a Spacefaring Civilization'', section: Settling the Outer Solar System: The Sources of Power, pp. 158-160, Tarcher/Putnam, 1999, 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


Candidate locations


Moon

A number of government space agencies such as
Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
(2014),
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
(2012) and the US have periodically floated lunar plans for constructing the first lunar outpost. The
European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...
(ESA) head Jan Woerner has proposed cooperation among countries and companies on lunar capabilities, a concept referred to as ''
Moon Village A moonbase is a facility on the surface of the Moon, enabling human activity on the Moon. As such, it is different from a lunar space station in orbit around the Moon, like the planned Lunar Gateway of the Artemis program. Moonbases can be for ...
''. In a December 2017 directive, the
Trump Administration Donald Trump's tenure as the List of presidents of the United States, 45th president of the United States began with Inauguration of Donald Trump, his inauguration on January 20, 2017, and ended on January 20, 2021. Trump, a Republican Party ...
steered
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
to include a lunar mission on the pathway to other
beyond Earth orbit Summary A simple list of just the common orbit abbreviations. List of abbreviations of common Earth orbits List of abbreviations of other orbits Classifications The following is a list of types of orbits: Centric classifications * Gal ...
(BEO) destinations."Text of Remarks at Signing of Trump Space Policy Directive 1 and List of Attendees"
Marcia Smith, ''Space Policy Online'', 11 December 2017, accessed 21 August 2018.
In a May 2018 interview,
Blue Origin Blue Origin, LLC is an American private spaceflight, privately funded aerospace manufacturer and sub-orbital spaceflight services company headquartered in Kent, Washington. Founded in 2000 by Jeff Bezos, the founder and executive chairman of Am ...
CEO
Jeff Bezos Jeffrey Preston Bezos ( ;; and Robinson (2010), p. 7. ''né'' Jorgensen; born January 12, 1964) is an American entrepreneur, media proprietor, investor, and commercial astronaut. He is the founder, executive chairman, and former preside ...
indicated Blue Origin would build and
fly Flies are insects of the Order (biology), order Diptera, the name being derived from the Ancient Greek, Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwing ...
the '' Blue Moon lunar lander'' on its own, with private funding, but that they would build it a lot faster, and accomplish more, if it were done in a partnership with existing government space agencies. Bezos specifically mentioned the December 2017 NASA direction and the ESA ''Moon Village'' concepts.


Mars

The hypothetical colonization of Mars has received interest from public space agencies and private corporations and has received extensive treatment in science fiction writing, film, and art. The most recent commitments to researching permanent settlement include those by public space agencies—
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
,
ESA , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...
,
Roscosmos The State Space Corporation "Roscosmos" (russian: Государственная корпорация по космической деятельности «Роскосмос»), commonly known simply as Roscosmos (russian: Роскосмос) ...
,
ISRO The Indian Space Research Organisation (ISRO; ) is the national space agency of India, headquartered in Bengaluru. It operates under the Department of Space (DOS) which is directly overseen by the Prime Minister of India, while the Chairman ...
, and the
CNSA China National Space Administration (CNSA; ) is the government agency of the People's Republic of China that is responsible for civil space administration and international space cooperation, including organizing or leading foreign exchanges ...
—and private organizations—
SpaceX Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
,
Lockheed Martin The Lockheed Martin Corporation is an American aerospace, arms, defense, information security, and technology corporation with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It ...
, and
Boeing The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and product ...
.


Venus

The colonization of Venus has been a subject of many works of
science fiction Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel unive ...
since before the dawn of
spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in or ...
and is still discussed from both a fictional and a scientific standpoint. Proposals for Venus are focused on colonies floating in the upper-middle atmosphere and on
terraforming Terraforming or terraformation ("Earth-shaping") is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body to be similar to the environment of Earth to make ...
. In addition to the
aerostats An aerostat (, via French) is a lighter-than-air aircraft that gains its lift through the use of a buoyant gas. Aerostats include unpowered balloons and powered airships. A balloon may be free-flying or tethered. The average density of the cra ...
that can be used on Earth, of all known planets and moons in the Solar system, only the Venusian atmosphere has a Lana Coefficient that allows for the use of vacuum airships made of some composites (that will work up to an altitude of 15 km) and graphene (up to an altitude of 40 km). This could mean that Venus is safer to colonize than Mars. With discoveries as of 2020 traces of possibly indigenous life in the
atmosphere of Venus The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of supercritical carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740  K (467 °C, 872 ° ...
, attempts of any humanization of Venus have become an increased issue of
planetary protection Planetary protection is a guiding principle in the design of an interplanetary mission, aiming to prevent biological contamination of both the target celestial body and the Earth in the case of sample-return missions. Planetary protection refle ...
, since uncontrolled effects of human presence might endanger such life.


Mercury

Once thought to be a volatile depleted body like the Moon, Mercury is now known to be richer in minerals than any other terrestrial body in the inner solar system. The planet also receives almost seven times the solar flux as the Earth/Moon system and also has a magnetosphere, the safest for colonisation are Mars and Venus. Mercury is an ideal place (according to Geologist Stephen Gillett, who suggested in 1996) to build and launch
solar sail Solar sails (also known as light sails and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been p ...
spacecraft, which could theoretically launch as folded up, by a
mass driver A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to Acceleration, accelerate and catapult Payload (air and space craft), payloads up to high speeds. Existing and contemplated ...
from Mercury's surface. This could also make Mercury an ideal place to acquire materials useful in building hardware to send to (and terraform) Venus. As Mercury has essentially no axial tilt, crater floors near its poles lie in eternal darkness, never seeing the Sun. They function as cold traps, trapping volatiles for geological periods. It is estimated that the poles of Mercury contain 1014–1015 kg of water, likely covered by about 5.65×109 m3 of hydrocarbons. This would make agriculture possible. It has been suggested that plant varieties could be developed to take advantage of the high light intensity and the long day of Mercury. The poles do not experience the significant day-night variations the rest of Mercury does, making them the best place on the planet to begin a colony.


Asteroids

Asteroids, including those in the asteroid belt, have been suggested as a possible site of human colonization. Some of the driving forces behind this effort to colonize asteroids include the survival of humanity, as well as economic incentives associated with asteroid mining.


The Jovian System

The
Jovian Jovian is the adjectival form of Jupiter and may refer to: * Jovian (emperor) (Flavius Iovianus Augustus), Roman emperor (363–364 AD) * Jovians and Herculians, Roman imperial guard corps * Jovian (lemur), a Coquerel's sifaka known for ''Zoboomafo ...
system in general has particular disadvantages for colonization, including its severe radiation environmentR. Walker Fillius, Carl E. McIlwain, and Antonio Mogro-Campero, ''Radiation Belts of Jupiter: A Second Look'', Science, Vol. 188. no. 4187, pp. 465–467, 2 May 1975 and its particularly deep
gravity well The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sp ...
. Its radiation would deliver about 36 Sv per day to unshielded colonists on Io and about 5.40 Sv per day to unshielded colonists on
Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Cliff ...
. Exposure to about 0.75 Sv over a few days is enough to cause radiation poisoning, and about 5 Sv over a few days is fatal.Robert Zubrin, ''Entering Space: Creating a Spacefaring Civilization'', section: Colonizing the Jovian System, pp. 166-170, Tarcher/Putnam, 1999, Jupiter itself, like the other gas giants, is not generally considered a good candidate for colonization. There is no accessible surface on which to land, and the light hydrogen atmosphere would not provide good buoyancy for some kind of aerial habitat as has been proposed for Venus.


Io

Io is not ideal for colonization, due to its hostile environment. The moon is under influence of high tidal forces, causing high volcanic activity. Jupiter's strong radiation belt overshadows Io, delivering 36 Sv a day to the moon. The moon is also extremely dry. Io is the least ideal place for the colonization of the four Galilean moons. Despite this, its volcanoes could be energy resources for the other moons, which are better suited to colonization.


Europa

The
Artemis Project The Artemis Project was a private spaceflight venture to establish a permanent, self-supporting base on the Moon by 2002. It was named after Artemis, the goddess of the hunt, in some myths the moon, and twin sister of Apollo (a reference to the ...
proposed a plan to colonize
Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Cliff ...
. Scientists would inhabit igloos and drill down into the Europan ice crust, exploring any subsurface ocean. The report also discusses the use of air pockets for human habitation.


Ganymede

Ganymede is the largest moon in the Solar System. Ganymede is the only moon with a
magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
, albeit overshadowed by Jupiter's magnetic field. Because of this magnetic field, Ganymede is one of only two Jovian moons where surface settlements would be feasible because it receives about 0.08 Sv of radiation per day. Ganymede could be terraformed.


Callisto

Due to its distance from Jupiter's powerful radiation belt,
Callisto Callisto most commonly refers to: *Callisto (mythology), a nymph *Callisto (moon), a moon of Jupiter Callisto may also refer to: Art and entertainment *''Callisto series'', a sequence of novels by Lin Carter *''Callisto'', a novel by Torsten Kro ...
is subject to only 0.0001 Sv a day. When
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
carried out a study called ''HOPE'' (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System, the target chosen was Callisto. It might be possible to build a surface base that would produce fuel for further exploration of the Solar System.


Jupiter trojans

The
Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when comp ...
announced in 2006 that the binary
Jupiter trojan The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange poin ...
617 Patroclus 617 Patroclus ( ) is a large binary Jupiter trojan asteroid. It is a dark D-type asteroid and a slow rotator, due to the 103-hour orbital period of its two components. It is one of five Jovian asteroids targeted by the ''Lucy'' space probe, and ...
, and possibly many other Jupiter trojans, are likely composed of water ice, with a layer of dust. This 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 The Interplanetary Transport Network (ITN) is a collection of gravitationally determined pathways through the Solar System that require very little energy for an object to follow. The ITN makes particular use of Lagrange points as locations whe ...
, may be feasible in the not-so-distant future. This could make
colonization of the Moon Colonization of the Moon or Lunar settlement is a process, or concept employed by some proposals, for claiming robotic or human exploitation and settlement on the Moon. Laying claim to the Moon has been declared illegal through international ...
,
Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...
and main-belt
asteroids An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
more practical.


The Saturnian System

Robert Zubrin Robert Zubrin (; born April 9, 1952) is an American aerospace engineer, author, and advocate for human exploration of Mars. He and his colleague at Martin Marietta, David Baker, were the driving force behind Mars Direct, a proposal in a 1990 res ...
identified
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
,
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
and
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
as "the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
of the Solar System", as the largest sources of
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...
and helium-3 to drive a
fusion Fusion, or synthesis, is the process of combining two or more distinct entities into a new whole. Fusion may also refer to: Science and technology Physics *Nuclear fusion, multiple atomic nuclei combining to form one or more different atomic nucl ...
economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and large system of moons.Robert Zubrin, ''Entering Space: Creating a Spacefaring Civilization'', section: The Persian Gulf of the Solar System, pp. 161-163, Tarcher/Putnam, 1999, On the other hand, planetary scientist
John Lewis John Robert Lewis (February 21, 1940 – July 17, 2020) was an American politician and civil rights activist who served in the United States House of Representatives for from 1987 until his death in 2020. He participated in the 1960 Nashville ...
in his 1997 book ''
Mining the Sky ''Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets'', is a 1997 book by University of Arizona Planetary Sciences professor emeritus John S. Lewis that describes possible routes for accessing extraterrestrial resources, either ...
'', insists that Uranus is the likeliest place to mine helium-3 because of its significantly shallower gravity well, which makes it easier for a laden tanker spacecraft to thrust itself out. Furthermore, Uranus is an
Ice giant An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System: Uranus and Neptune. In astrophysics and planetary science t ...
, which would likely make it easier to separate the helium out of the atmosphere.


Titan

Zubrin identified
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
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. He said, "In certain ways, Titan is the most hospitable extraterrestrial world within the Solar System for human colonization."Robert Zubrin, ''Entering Space: Creating a Spacefaring Civilization'', section: Titan, pp. 163-166, Tarcher/Putnam, 1999, A widely published expert on
terraforming Terraforming or terraformation ("Earth-shaping") is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body to be similar to the environment of Earth to make ...
,
Christopher McKay Dr Christopher P. McKay (born 1954) is an American planetary scientist at NASA Ames Research Center, studying planetary atmospheres, astrobiology, and terraforming. McKay majored in physics at Florida Atlantic University, where he also studied m ...
, is also a co-investigator on the ''Huygens'' probe that landed on Titan in January 2005. 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.


Enceladus

On 9 March 2006,
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
's '' Cassini'' space probe found possible evidence of liquid water on
Enceladus Enceladus is the sixth-largest moon of Saturn (19th largest in the Solar System). It is about in diameter, about a tenth of that of Saturn's largest moon, Titan. Enceladus is mostly covered by fresh, clean ice, making it one of the most refl ...
. According to that article, "pockets of liquid water may be no more than tens of meters below the surface." These findings were confirmed in 2014 by NASA. This means liquid water could be collected much more easily and safely on Enceladus than, for instance, on Europa (see above). Discovery of water, especially liquid water, generally makes a celestial body a much more likely candidate for colonization. An alternative model of Enceladus's activity is the decomposition of methane/water
clathrate A clathrate is a chemical substance consisting of a lattice that traps or contains molecules. The word ''clathrate'' is derived from the Latin (), meaning ‘with bars, latticed’. Most clathrate compounds are polymeric and completely envelop t ...
s – a process requiring lower temperatures than liquid water eruptions. The higher density of Enceladus indicates a larger than Saturnian average silicate core that could provide materials for base operations.


Uranus

Because
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
has the lowest
escape velocity In celestial mechanics, escape velocity or escape speed is the minimum speed needed for a free, non- propelled object to escape from the gravitational influence of a primary body, thus reaching an infinite distance from it. It is typically ...
of the four gas giants, it has been proposed as a mining site for
helium-3 Helium-3 (3He see also helion) is a light, stable isotope of helium with two protons and one neutron (the most common isotope, helium-4, having two protons and two neutrons in contrast). Other than protium (ordinary hydrogen), helium-3 is the ...
. If human supervision of the robotic activity proved necessary, one of Uranus's natural satellites might serve as a base.


Neptune

It is hypothesized that one of
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
's satellites could be used for colonization.
Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus' ...
's surface shows signs of extensive geological activity that implies a subsurface ocean, perhaps composed of ammonia/water. If technology advanced to the point that tapping such geothermal energy was possible, it could make colonizing a cryogenic world like Triton feasible, supplemented by
nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manifest ...
power.


Kuiper belt and Oort cloud

The noted
physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate caus ...
Freeman Dyson Freeman John Dyson (15 December 1923 – 28 February 2020) was an English-American theoretical physicist and mathematician known for his works in quantum field theory, astrophysics, random matrices, mathematical formulation of quantum m ...
identified
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...
s, rather than
planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
s, as the major potential ''habitat'' of life in space.Freeman Dyson, "The World, the Flesh, and the Devil", Third J.D. Bernal Lecture, May 1972, reprinted in ''Communication with Extraterrestrial Intelligence'',
Carl Sagan Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator. His best known scientific contribution is research on ext ...
, ed., MIT Press, 1973,
Several hundred billion to trillion comet-like ice-rich bodies exist outside the orbit of Neptune, in the Kuiper belt and Inner and Outer Oort cloud. These may contain all the ingredients for life (water ice, ammonia, and carbon-rich compounds), including significant amounts of deuterium and helium-3. Since Dyson's proposal, the number of trans-Neptunian objects known has increased greatly. Colonists could live in the dwarf planet's icy crust or mantle, using fusion or geothermal heat itation neededand mining the soft-ice or liquid inner ocean for volatiles and minerals. Given the light gravity and resulting lower pressure in the ice mantle or inner ocean, colonizing the rocky core's outer surface might give colonists the largest number of mineral and volatile resources as well as insulating them from cold. itation neededSurface habitats or domes are another possibility, as background radiation levels are likely to be low. itation needed


Difficulties

There would be many problems in colonizing the outer Solar System. These include: *Distance from
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
: The outer planets are much farther from Earth than the inner planets, and would therefore be harder and more time-consuming to reach. In addition, return voyages may well be prohibitive considering the time and distance. *Extreme cold: temperatures are near
absolute zero Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin. The fundamental particles of nature have minimum vibration ...
in many parts of the outer Solar System. *Power:
Solar power Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic e ...
is many times less concentrated in the outer Solar System than in the inner Solar System. It is unclear as to whether it would be usable there, using some form of concentration mirrors, or whether
nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...
would be necessary. There have also been proposals to use the
gravitational potential energy Gravitational energy or gravitational potential energy is the potential energy a massive object has in relation to another massive object due to gravity. It is the potential energy associated with the gravitational field, which is released (conv ...
of planets or dwarf planets with moons. * Effects of low gravity on the human body: All moons of the gas giants and all outer dwarf planets have a very low gravity, the highest being Io's gravity (0.183 g) which is less than 1/5 of the Earth's gravity. Since the Apollo program all crewed spaceflight has been constrained to
Low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
and there has been no opportunity to test the effects of such low gravitational accelerations on the human body. It is speculated that the low gravity environments might have very similar effects to long-term exposure in
weightlessness Weightlessness is the complete or near-complete absence of the sensation of weight. It is also termed zero gravity, zero G-force, or zero-G. Weight is a measurement of the force on an object at rest in a relatively strong gravitational fi ...
. Such effects can be avoided by rotating spacecraft creating artificial gravity.


See also

*
O'Neill cylinder An O'Neill cylinder (also called an O'Neill colony) is a space settlement concept proposed by American physicist Gerard K. O'Neill in his 1976 book '' The High Frontier: Human Colonies in Space''. O'Neill proposed the colonization of space for th ...
*
Space colonization Space colonization (also called space settlement or extraterrestrial colonization) is the use of outer space or celestial bodies other than Earth for permanent habitation or as extraterrestrial territory. The inhabitation and territori ...
*
Asteroid mining Asteroid mining is the hypothetical exploitation of materials from asteroids and other minor planets, including near-Earth objects. Notable asteroid mining challenges include the high cost of spaceflight, unreliable identification of asteroids ...
*
Lagrange point colonization Lagrange point colonization is a proposed form of space colonization of the five equilibrium points in the orbit of a planet or its primary moon, called Lagrange points. The Lagrange points and are stable if the mass of the larger body is ...
*
Colonisation (biology) Colonisation or colonization is the process in biology by which a species spreads to new areas. Colonisation often refers to ''successful'' immigration where a population becomes integrated into an ecological community, having resisted initial ...


References

{{Use American English, date=January 2014 Space colonization Solar System