Space colonization, or extraterrestrial colonization, is the establishment of human settlements or colonies in outer space and on astronomical bodies. The concept, in its broadest sense, has been applied to any permanent human presence in space, such as a space habitat or other extraterrestrial settlements. It may involve notions of territorial occupation, resource control for economic or military purposes, such as extraterrestrial mining, or military practice ground as shown in a space force. Making territorial claims in space is under prohibition by international space law (ISL), defining space as a common heritage. International space law has had the goal to prevent colonial claims and militarization of space, and has advocated the installation of international regimes to regulate access to and sharing of space, particularly for specific locations such as the limited space of geostationary orbit or the Moon. To date, no permanent space settlement other than temporary space habitats have been established, nor has any extraterrestrial territory or land been internationally claimed. Currently there are also no plans for building a space colony by any government. However, many proposals, speculations, and designs, particularly for extraterrestrial settlements have been made through the years, and a considerable number of space colonization advocates and groups are active. Currently, the dominant private launch provider SpaceX, has been the most prominent organization planning space colonization on Mars, though having not reached a development stage beyond launch and landing systems. Space colonization raises numerous socio-political questions. Many arguments for and against space settlement have been made. The two most common reasons in favor of colonization are the survival of humans and life independent of Earth, making humans a multiplanetary species, in the event of a planetary-scale disaster (natural or human-made), and the commercial use of space particularly for enabling a more sustainable expansion of human society through the availability of additional resources in space, reducing environmental damage on and exploitation of Earth. The most common objections include concerns that the commodification of the cosmos may be likely to continue pre-existing detrimental processes such as environmental degradation, economic inequality and wars, enhancing the interests of the already powerful, and at the cost of investing in solving existing major environmental and social issues. The mere construction of an extraterrestrial settlement, with the needed infrastructure, presents daunting technological, economic and social challenges. Space settlements are generally conceived as providing for nearly all (or all) the needs of larger numbers of humans. The environment in space is very hostile to human life and not readily accessible, particularly for maintenance and supply. It would involve much advancement of currently primitive technologies, such as controlled ecological life-support systems. With the high cost of orbital spaceflight (around $1400 per kg, or $640 per pound, to low Earth orbit by SpaceX Falcon Heavy), a space settlement would currently be massively expensive, but ongoing progress in reusable launch systems aim to change that (possibly reaching $20 per kg to orbit), and in creating automated manufacturing and construction techniques.
Definition Space colonization has been in a broad sense referred to as space settlement, space humanization or space habitation. Space colonization in a narrow sense refers to space settlements, as envisioned by Gerard K. O'Neill. It is characterized by elements such as: settlement and exploitation, as well as territorial claim. The concept in its broad sense has been applied to any permanent human presence, even robotic, particularly along with the term "settlement", being imprecisely applied to any human space habitat, from research stations to self-sustaining communities in space. The words colony and colonization are terms rooted in colonial history on Earth, making them human geographic as well as particularly political terms. This broad use for any permanent human activity and development in space has been criticized, particularly as colonialist and undifferentiated (see below Objections). In this sense, a colony is a settlement that claims territory and exploits it for the settlers or their metropole. Therefore, a human outpost, while possibly a space habitat or even a space settlement, does not automatically constitute a space colony. Some have argued the presence of certain mechanisms or institutions are symptoms of having achieved a "critical mass"; for instance, sci-fi author Neal Stephenson argued a small Martian colony would feel more like living on a U.S. Navy nuclear submarine than being part of a vibrant community while economists Karl T. Muth and Jodi N. Beggs argued that, to meet American cultural and judicial norms, a Martian colony would need a large enough population to offer a defendant a jury of twelve strangers. Therefore, any basing can be part of colonization, while colonization can be understood as a process that is open to more claims, beyond basing. The International Space Station, the longest-occupied extraterrestrial habitat thus far, does not claim territory and thus is not usually considered a colony. Moriba Jah has criticized existing approaches to orbital space as colonialist, such as for satellites, on the grounds that it involves claiming ownership instead of collaborative stewardship. Some advocates of peaceful human settlement of space have argued against use of the word "colony" and related terms, so as to avoid confusing their goals with colonialism on Earth.
History In the first half of the 17th century John Wilkins suggested in A Discourse Concerning a New Planet that future adventurers like Francis Drake and Christopher Columbus might reach the Moon and allow people to live there. The first known work on space colonization was the 1869 novella The Brick Moon by Edward Everett Hale, about an inhabited artificial satellite. In 1897, Kurd Lasswitz also wrote about space colonies in his book Auf zwei Planeten (Two Planets). The Russian rocket science pioneer Konstantin Tsiolkovsky foresaw elements of the space community in his book Beyond Planet Earth written about 1900. Tsiolkovsky imagined his space travelers building greenhouses and raising crops in space. Tsiolkovsky believed that going into space would help perfect human beings, leading to immortality and peace. One of the first to speak about space colonization was Cecil Rhodes who in 1902 spoke about "these stars that you see overhead at night, these vast worlds which we can never reach", adding "I would annex the planets if I could; I often think of that. It makes me sad to see them so clear and yet so far". In the 1920s John Desmond Bernal, Hermann Oberth, Guido von Pirquet and Herman Noordung further developed the idea. Wernher von Braun contributed his ideas in a 1952 Colliers magazine article. In the 1950s and 1960s, Dandridge M. Cole published his ideas. When orbital spaceflight was achieved in the 1950s colonialism was still a strong international project, e.g. easing the United States to advance its space program and space in general as part of a "New Frontier". As the Space Age was developing, decolonization gained again in force, producing many newly independent countries. These newly independent countries confronted spacefaring countries, demanding an anti-colonial stance and regulation of space activity when space law was raised and negotiated internationally. Fears of confrontations because of land grabs and an arms race in space between the few countries with spaceflight capabilities grew and were ultimately shared by the spacefaring countries themselves. This produced the wording of the agreed on international space law, starting with the Outer Space Treaty of 1967, calling space a "province of all mankind" and securing provisions for international regulation and sharing of outer space. The advent of geostationary satellites raised the case of limited space in outer space. In the 1960s and with an initial focus on communications spectrum management, the international community agreed to regulate the assignment of slots in the geosynchronous (GEO) belt through the International Telecommunication Union (ITU). Today, any company or nation planning to launch a satellite to GEO must apply to the ITU for an orbital slot. A group of equatorial countries, all of which were countries that were once colonies of colonial empires, but without spaceflight capabilities, signed in 1976 the Bogota Declaration. These countries declared that geostationary orbit is a limited natural resource and belongs to the equatorial countries directly below, seeing it not as part of outer space, humanity's common. Through this, the declaration challenged the dominance of geostationary orbit by spacefaring countries through identifying their dominance as imperialistic. Writers continued to address space colonization concepts by publishing books in the mid-1970s such as The High Frontier: Human Colonies in Space by Gerard K. O'Neill and Colonies in Space by T. A. Heppenheimer. In 1975, the first international joint space mission occurred as a symbol of the policy of détente that the two superpowers were pursuing at the time. The U.S. Apollo and Soviet Soyuz spacecraft docked in earth orbit for almost two days. In 1977, the first sustained space habitat, the Salyut 6 station, was put into Earth's orbit. Eventually the first space stations were succeeded by the ISS, today's largest human outpost in space and closest to a space settlement. Built and operated under a multilateral regime, it has become a blueprint for future stations, such as around and possibly on the Moon. Additional discourse on living in space was generated by writers including Marianne J. Dyson who wrote Home on the Moon; Living on a Space Frontier in 2003; Peter Eckart wrote Lunar Base Handbook in 2006 and then Harrison Schmitt's Return to the Moon written in 2007. An international regime for lunar activity was demanded by the international Moon Treaty, but is currently developed multilaterally as with the Artemis Accords. Threats to existing treaties come in areas such as space debris because of the lack of regulation on disposition of assets by operators (and controlling sovereign power) once their mission is complete. The only habitation on a different celestial body so far have been the temporary habitats of the crewed lunar landers. Similar to the Artemis program, China is leading an effort to develop a lunar base called the International Lunar Research Station beginning in the 2030s.
Justification
Survival of human civilization
A primary argument calling for space colonization is the long-term survival of human civilization and terrestrial life. By developing alternative locations off Earth, the planet's species, including humans, could live on in the event of natural or human-made disasters on Earth. On two occasions, theoretical physicist and cosmologist Stephen Hawking argued for space colonization as a means of saving humanity. In 2001, Hawking predicted that the human race would become extinct within the next thousand years unless colonies could be established in space. In 2010, he stated that humanity faces two options: either we colonize space within the next two hundred years, or we will face the long-term prospect of extinction. In 2005, then NASA Administrator Michael Griffin identified space colonization as the ultimate goal of current spaceflight programs, saying:
... the goal isn't just scientific exploration ... it's also about extending the range of human habitat out from Earth into the solar system as we go forward in time ... In the long run, a single-planet species will not survive ... If we humans want to survive for hundreds of thousands of millions of years, we must ultimately populate other planets. Now, today the technology is such that this is barely conceivable. We're in the infancy of it. ... I'm talking about that one day, I don't know when that day is, but there will be more human beings who live off the Earth than on it. We may well have people living on the Moon. We may have people living on the moons of Jupiter and other planets. We may have people making habitats on asteroids ... I know that humans will colonize the solar system and one day go beyond. Louis J. Halle Jr., formerly of the United States Department of State, wrote in Foreign Affairs (Summer 1980) that the colonization of space will protect humanity in the event of global nuclear warfare. The physicist Paul Davies also supports the view that if a planetary catastrophe threatens the survival of the human species on Earth, a self-sufficient colony could "reverse-colonize" Earth and restore human civilization. The author and journalist William E. Burrows and the biochemist Robert Shapiro proposed a private project, the Alliance to Rescue Civilization, with the goal of establishing an off-Earth "backup" of human civilization. Based on his Copernican principle, J. Richard Gott has estimated that the human race could survive for another 7.8 million years, but it is not likely to ever colonize other planets. However, he expressed a hope to be proven wrong, because "colonizing other worlds is our best chance to hedge our bets and improve the survival prospects of our species". In a theoretical study from 2019, a group of researchers have pondered the long-term trajectory of human civilization. It is argued that due to Earth's finitude as well as the limited duration of the Solar System, mankind's survival into the far future will very likely require extensive space colonization. This 'astronomical trajectory' of mankind, as it is termed, could come about in four steps: First step, space colonies could be established at various habitable locations — be it in outer space or on celestial bodies away from Earth – and allowed to remain temporarily dependent on support from Earth. In the second step, these colonies could gradually become self-sufficient, enabling them to survive if or when the mother civilization on Earth fails or dies. Third step, the colonies could develop and expand their habitation by themselves on their space stations or celestial bodies, for example via terraforming. In the fourth step, the colonies could self-replicate and establish new colonies further into space, a process that could then repeat itself and continue at an exponential rate throughout the cosmos. However, this astronomical trajectory may not be a lasting one, as it will most likely be interrupted and eventually decline due to resource depletion or straining competition between various human factions, bringing about some 'star wars' scenario.
Vast resources in space
Resources in space, both in materials and energy, are enormous. The Solar System has enough material and energy to support anywhere from several thousand to over a billion times the current Earth-based human population, mostly from the Sun itself. Asteroid mining will likely be a key player in space colonization. Water and materials to make structures and shielding can be easily found in asteroids. Instead of resupplying on Earth, mining and fuel stations need to be established on asteroids to facilitate better space travel. Optical mining is the term NASA uses to describe extracting materials from asteroids. NASA believes by using propellant derived from asteroids for exploration to the moon, Mars, and beyond will save $100 billion. If funding and technology come sooner than estimated, asteroid mining might be possible within a decade. Although some items of the infrastructure requirements above can already be easily produced on Earth and would therefore not be very valuable as trade items (oxygen, water, base metal ores, silicates, etc.), other high-value items are more abundant, more easily produced, of higher quality, or can only be produced in space. These could provide (over the long-term) a high return on the initial investment in space infrastructure. Some of these high-value trade goods include precious metals, gemstones, power, solar cells, ball bearings, semi-conductors, and pharmaceuticals. The mining and extraction of metals from a small asteroid the size of 3554 Amun or (6178) 1986 DA, both small near-Earth asteroids, may yield 30 times as much metal as humans have mined throughout history. A metal asteroid this size would be worth approximately US$20 trillion at 2001 market prices. The main impediments to commercial exploitation of these resources are the very high cost of initial investment, the very long period required for the expected return on those investments (The Eros Project plans a 50-year development), and the fact that the venture has never been carried out before—the high-risk nature of the investment.
Expansion with fewer negative consequences
Expansion of humans and technological progress has usually resulted in some form of environmental devastation, and destruction of ecosystems and their accompanying wildlife. In the past, expansion has often come at the expense of displacing many indigenous peoples, the resulting treatment of these peoples ranging anywhere from encroachment to genocide. Because space has no known life, this need not be a consequence, as some space settlement advocates have pointed out. However, on some bodies of the Solar System, there is the potential for extant native lifeforms and so the negative consequences of space colonization cannot be dismissed. Counterarguments state that changing only the location but not the logic of exploitation will not create a more sustainable future.
Alleviating overpopulation and resource demand An argument for space colonization is to mitigate proposed impacts of overpopulation of Earth, such as resource depletion. If the resources of space were opened to use and viable life-supporting habitats were built, Earth would no longer define the limitations of growth. Although many of Earth's resources are non-renewable, off-planet colonies could satisfy the majority of the planet's resource requirements. With the availability of extraterrestrial resources, demand on terrestrial ones would decline. Proponents of this idea include Stephen Hawking and Gerard K. O'Neill. Others including cosmologist Carl Sagan and science fiction writers Arthur C. Clarke, and Isaac Asimov, have argued that shipping any excess population into space is not a viable solution to human overpopulation. According to Clarke, "the population battle must be fought or won here on Earth". The problem for these authors is not the lack of resources in space (as shown in books such as Mining the Sky), but the physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth.
Other arguments Advocates for space colonization cite a presumed innate human drive to explore and discover, and call it a quality at the core of progress and thriving civilizations. Nick Bostrom has argued that from a utilitarian perspective, space colonization should be a chief goal as it would enable a very large population to live for a very long time (possibly billions of years), which would produce an enormous amount of utility (or happiness). He claims that it is more important to reduce existential risks to increase the probability of eventual colonization than to accelerate technological development so that space colonization could happen sooner. In his paper, he assumes that the created lives will have positive ethical value despite the problem of suffering. In a 2001 interview with Freeman Dyson, J. Richard Gott and Sid Goldstein, they were asked for reasons why some humans should live in space. Their answers were:
Spread life and beauty throughout the universe Ensure the survival of our species Make money through new forms of space commercialization such as solar-power satellites, asteroid mining, and space manufacturing Save the environment of Earth by moving people and industry into space Biotic ethics is a branch of ethics that values life itself. For biotic ethics, and their extension to space as panbiotic ethics, it is a human purpose to secure and propagate life and to use space to maximize life. A 2026 Ipsos opinion poll found 59% of Americans find establishing a long-term presence on the Moon important.
Opposition Space colonization has been seen as a relief to the problem of human overpopulation as early as 1758, and listed as one of Stephen Hawking's reasons for pursuing space exploration. Critics note, however, that a slowdown in population growth rates since the 1980s has alleviated the risk of overpopulation. Critics also argue that the costs of commercial activity in space are too high to be profitable against Earth-based industries, and hence that it is unlikely to see significant exploitation of space resources in the foreseeable future. Other objections include concerns that the forthcoming colonization and commodification of the cosmos is likely to enhance the interests of the already powerful, including major economic and military institutions e.g. the large financial institutions, the major aerospace companies and the military–industrial complex, to lead to new wars, and to exacerbate pre-existing exploitation of workers and resources, economic inequality, poverty, social division and marginalization, environmental degradation, and other detrimental processes or institutions. Additional concerns include creating a culture in which humans are no longer seen as human, but rather as material assets. The issues of human dignity, morality, philosophy, culture, bioethics, and the threat of megalomaniac leaders in these new "societies" would all have to be addressed in order for space colonization to meet the psychological and social needs of people living in isolated colonies. As an alternative or addendum for the future of the human race, many science fiction writers have focused on the realm of the 'inner-space', that is the computer-aided exploration of the human mind and human consciousness—possibly en route developmentally to a Matrioshka Brain. Robotic spacecraft are proposed as an alternative to gain many of the same scientific advantages without the limited mission duration and high cost of life support and return transportation involved in human missions. A corollary to the Fermi paradox—"nobody else is doing it"—is the argument that, because no evidence of alien colonization technology exists, it is statistically unlikely to even be possible to use that same level of technology ourselves.
Colonialism
Space colonization has been discussed as a postcolonial continuation of imperialism and colonialism, with some calling for decolonization instead of colonization. Critics argue that the present politico-legal regimes and their philosophic grounding, advantage imperialist development of space, that key decisionmakers in space colonization are often wealthy elites affiliated with private corporations, and that space colonization would primarily appeal to their peers rather than ordinary citizens. Furthermore, it is argued that there is a need for inclusive and democratic participation and implementation of any space exploration, infrastructure or habitation. According to space law expert Michael Dodge, existing space law, such as the Outer Space Treaty, guarantees access to space, but does not enforce social inclusiveness or regulate non-state actors. Particularly the narrative of the "New Frontier" has been criticized as unreflected continuation of settler colonialism and manifest destiny, continuing the narrative of exploration as fundamental to the assumed human nature. Joon Yun considers space colonization as a solution to human survival and global problems like pollution to be imperialist; others have identified space as a new sacrifice zone of colonialism. Furthermore, the understanding of space as empty and separate is considered a continuation of terra nullius. More specifically the advocacy for territorial colonization of Mars has been called surfacism, in contrast to habitation in the atmospheric space of Venus, a concept similar to Thomas Golds surface chauvinism. More generally space infrastructure such as the Maunakea Observatories have also been criticized and protested against as being colonialist. Guiana Space Centre has also been the site of anti-colonial protests, connecting colonization as an issue on Earth and in space. In regard to the scenario of extraterrestrial first contact, it has been argued that the employment of colonial language would endanger such first impressions and encounters. Furthermore, spaceflight as a whole and space law more particularly has been criticized as a postcolonial project by being built on a colonial legacy and by not facilitating the sharing of access to space and its benefits, too often allowing spaceflight to be used to sustain colonialism and imperialism, most of all on Earth instead.
Planetary protection and risk of contamination
Agencies conducting interplanetary missions are guided by COSPAR's planetary protection policies, to have at most 300,000 spores on the exterior of the craft—and more thoroughly sterilized if they contact "special regions" containing water, or it could contaminate life-detection experiments or the planet itself. It is impossible to sterilize human missions to this level, as humans are host to typically a hundred trillion microorganisms of thousands of species of the human microbiome, and these cannot be removed while preserving the life of the human. Containment seems the only option, but it is a major challenge in the event of a hard landing (i.e. crash). There have been several planetary workshops on this issue, but with no final guidelines yet for a way forward. Human explorers could also inadvertently contaminate Earth if they return to the planet while carrying extraterrestrial microorganisms.
Challenges Colonization beyond the Earth involves overcoming a number of difficult challenges.
Distance from Earth 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. Even communication with Earth would be slow, with delays of 4 – 24 minutes for a message to Mars, and 35 – 52 minutes to Jupiter and its moons.
Extreme environments Extreme cold – due to the distance to the sun, temperatures are near absolute zero in many parts of the outer Solar System.
Sustainable power sources Power – Solar power 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 would be necessary. Use of geothermal systems to generate power may be practical on some of the planets and moons of the solar system.
Physical and mental health risks to colonists
The health of the humans who may participate in a colonization venture would be subject to increased physical, mental and emotional risks.
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 and there has been no opportunity to test the effects of such low gravitational accelerations on the human body. It is speculated (but not confirmed) that the low gravity environments might have very similar effects to long-term exposure in weightlessness. Such effects might be avoided by rotating spacecraft creating artificial gravity. Dust – breathing risks associated with fine dust from rocky surface objects, for similar reasons as harmful effects of lunar dust. NASA learned that – without gravity – bones lose minerals, causing osteoporosis. Bone density may decrease by 1% per month, which may lead to a greater risk of osteoporosis-related fractures later in life. Fluid shifts towards the head may cause vision problems. NASA found that isolation in closed environments aboard the International Space Station led to depression, sleep disorders, and diminished personal interactions, likely due to confined spaces and the monotony and boredom of long space flight. Circadian rhythm may also be susceptible to the effects of space life due to the effects on sleep of disrupted timing of sunset and sunrise. This can lead to exhaustion, as well as other sleep problems such as insomnia, which can reduce their productivity and lead to mental health disorders. High-energy radiation is a health risk that colonists would face, as radiation in deep space is deadlier than what astronauts face now in low Earth orbit. Metal shielding on space vehicles protects against only 25–30% of space radiation, possibly leaving colonists exposed to the other 70% of radiation and its short and long-term health complications.
Locations Space colonization has been envisioned at many different locations inside and outside the Solar System, but most commonly at Mars and the Moon.
Near-Earth space
Earth orbit
Geostationary orbit was an early issue of discussion about space colonization, with equatorial countries arguing for special rights to the orbit (see Bogota Declaration). Space debris, particularly in low Earth orbit, has been characterized as a product of colonization by occupying space and hindering access to space through excessive pollution with debris, with drastic increases in the course of military activity and without a lack of management.
Most of the delta-v budget, and thus propellant, of a launch is used bringing a spacecraft to low Earth orbit. This is the main reason why Jerry Pournelle said "If you can get your ship into orbit, you're halfway to anywhere". Therefore, the main advantages to constructing a space settlement in Earth orbit are accessibility to the Earth and already-existing economic motives such as space hotels and space manufacturing. However, a big disadvantage is that orbit does not host any materials that is available for exploitation. Space colonization altogether might eventually demand lifting vast amounts of payload into orbit, making thousands of daily launches potentially unsustainable. Various theoretical concepts, such as orbital rings and skyhooks, have been proposed to reduce the cost of accessing space.
Moon
The Moon is discussed as a target for colonization, due to its proximity to Earth and lower escape velocity. The Moon is reachable from Earth in three days, has a near-instant communication to Earth, with minable minerals, no atmosphere, and low gravity, making it extremely easy to ship materials and products to orbit. Abundant ice is trapped in permanently shadowed craters near the poles, which could provide support for the water needs of a lunar colony, though indications that mercury is also similarly trapped there may pose health concerns. Native precious metals, such as gold, silver, and probably platinum, are also concentrated at the lunar poles by electrostatic dust transport. There are only a few materials on the Moon which have been identified to make economic sense to ship directly back to the Earth, which are helium-3 (for fusion power) and rare-earth minerals (for electronics). Instead, it makes more sense for these materials to be used in-space or being turned into valuable products for export. However, the Moon's lack of atmosphere provides no protection from space radiation or meteoroids, so lunar lava tubes have been proposed sites to gain protection. 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. Since the Moon has extreme temperature swings and toxic lunar regolith, it is argued by some that the Moon will not become a place of habitation, but instead attract polluting extraction and manufacturing industries. Furthermore, it has been argued that moving these industries to the Moon could help protect the Earth's environment and allow poorer countries to be released from the shackles of neocolonialism by wealthier countries. In the space colonization framework, the Moon will be transformed into an industrial hub of the Solar System. Interest in establishing a moonbase has increased in the 21st century as an intermediate to Mars colonization. The European Space Agency (ESA) head Jan Woerner at the International Astronautical Congress in Bremen, Germany, in October, 2018 proposed cooperation among countries and companies on lunar capabilities, a concept referred to as Moon Village. In a December 2017 directive, the first Trump administration steered NASA to include a lunar mission on the pathway to other beyond Earth orbit (BEO) destinations. In 2023, the U.S. Defense Department started a study of the necessary infrastructure and capabilities required to develop a moon-based economy over the following ten years. As of 2024, on one side, China, along with other partner countries, has announced its intention to establish the International Lunar Research Station. On the other side, the United States, in collaboration with international partners, is advancing its Artemis program, which includes plans to build moonbases near the lunar poles, close to permanently shadowed craters, in the 2030s. The Chinese Lunar Exploration Program is seen as a means to bolster China's political influence and support its aspirations for superpower status, while the United States aims to maintain its position as the leading space power.
Lagrange points
Another near-Earth possibility are the stable Earth–Moon Lagrange points L4 and L5, at which point a space colony can float indefinitely. The L5 Society was founded to promote settlement by building space stations at these points. Gerard K. O'Neill suggested in 1974 that the stable region around L5 could fit several thousand floating colonies, and would allow easy travel to and from the colonies due to the shallow effective potential at this point.
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. While there have been many plans for a human Mars mission, including affordable ones such as Mars Direct, none has been realized as of 2025. Both the United States and China have plans to send humans to Mars sometime in the 2040s, but these plans are not backed with hardware and funding. However, SpaceX is currently developing Starship, a super-heavy-lift reusable launch vehicle, with a vision of sending humans to Mars. As of November 2024, the company plans to send five uncrewed Starships to Mars in either 2026 or 2028–2029 launch windows and SpaceX's CEO Elon Musk has repeatedly stated his support for the Mars efforts, both financially and politically. Mars is more suitable for habitation than the Moon, with a stronger gravity, rich amount of materials needed for life, day/night cycle nearly identical to Earth, and a thin atmosphere to protect from micrometeroids. The main disadvantage of Mars compared to the Moon is the six-to-nine-month transit time and the lengthy launch window, which occurs approximately every two years. Without in situ resource utilization, Mars colonization would be nearly impossible as it would require bringing thousands of tons of payload to sustain a handful of astronauts. If Martian materials can be used to make propellant (such as methane with the Sabatier process) and supplies (such as oxygen for crews), the amount of supplies needed to bring to Mars can be greatly reduced. Even then, Mars colonies will not be economically viable in the near term; thus, reasons for colonizing Mars will be mostly ideological and prestige-based, such as a desire for freedom.
Other inner Solar System bodies
Mercury Mercury is rich in metals and volatiles, as well as solar energy. However, Mercury is the most energy-consuming body on the Solar System to land for spacecraft launching from Earth, and astronauts there must contend with the extreme temperature differential and radiation.
Once thought to be a volatile-depleted body like the Moon, Mercury is now known to be volatile-rich, surprisingly richer in volatiles than any other terrestrial body in the inner Solar System. The planet also receives six and a half times the solar flux as the Earth/Moon system, making solar energy an effective energy source; it could be harnessed through orbital solar arrays and beamed to the surface or exported to other planets. 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 "chunks" by a mass driver from Mercury's surface. Once in space, the solar sails would deploy. Solar energy for the mass driver should be easy to produce, 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 light sails to nearby star systems. 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 km3 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 do, making them the best place on the planet to begin a colony. Another option is to live underground, where day-night variations would be damped enough that temperatures would stay roughly constant. There are indications that Mercury contains lava tubes, like the Moon and Mars, which would be suitable for this purpose. Underground temperatures in a ring around Mercury's poles can reach room temperature on Earth, 22±1 °C; and this is achieved at depths starting from about 0.7 m. This presence of volatiles and abundance of energy has led Alexander Bolonkin and James Shifflett to consider Mercury preferable to Mars for colonization. Yet a third option could be to continually move to stay on the night side, as Mercury's 176-day-long day-night cycle means that the terminator travels very slowly. Because Mercury is very dense, its surface gravity is 0.38g like Mars, even though it is a smaller planet. This would be easier to adjust to than lunar gravity (0.16g), and presents advantages regarding lower escape velocity from Mercury than from Earth. Mercury's proximity gives it advantages over the asteroids and outer planets, and its low synodic period means that launch windows from Earth to Mercury are more frequent than those from Earth to Venus or Mars. On the downside, a Mercury colony would require significant shielding from radiation and solar flares, and since Mercury is airless, decompression and temperature extremes would be constant risks.
Venus
Though the surface of Venus is extremely hostile, habitats high above the surface are fairly habitable, with temperatures ranging from 30 °C to 70 °C (86 to 158 °F) and a pressure similar to the Earth's sea level at an altitude of 50 kilometers (30 miles). However, beside tourism opportunities, the economic benefit of a Venusian col