A superintelligence is a hypothetical agent that possesses intelligence surpassing that of the most giftedhuman minds. Philosopher Nick Bostrom defines superintelligence as "any intellect that greatly exceeds the cognitive performance of humans in virtually all domains of interest".
Technological researchers disagree about how likely present-day human intelligence is to be surpassed. Some argue that advances in artificial intelligence
(AI) will probably result in general reasoning systems that lack human
cognitive limitations. Others believe that humans will evolve or
directly modify their biology to achieve radically greater intelligence. Several future study scenarios combine elements from both of these possibilities, suggesting that humans are likely to interface with computers, or upload their minds to computers, in a way that enables substantial intelligence amplification. The hypothetical creation of the first superintelligence may or may not result from an intelligence explosion or a technological singularity.
Some researchers believe that superintelligence will likely follow shortly after the development of artificial general intelligence.
The first generally intelligent machines are likely to immediately hold
an enormous advantage in at least some forms of mental capability,
including the capacity of perfect recall, a vastly superior knowledge base, and the ability to multitask in ways not possible to biological entities.
Several scientists and forecasters have been arguing for prioritizing early research into the possible benefits and risks of human and machine cognitive enhancement, because of the potential social impact of such technologies.
Artificial superintelligence
Artificial intelligence, especially foundation models, has made rapid progress, surpassing human capabilities in various benchmarks.
Philosopher David Chalmers argues that artificial general intelligence is a very likely path to artificial superintelligence (ASI). Chalmers breaks this claim down into an argument that AI can achieve equivalence to human intelligence, that it can be extended to surpass human intelligence, and that it can be further amplified to completely dominate humans across arbitrary tasks.
Concerning human-level equivalence, Chalmers argues that the
human brain is a mechanical system, and therefore ought to be emulatable
by synthetic materials. He also notes that human intelligence was able to biologically evolve,
making it more likely that human engineers will be able to recapitulate
this invention. Evolutionary algorithms, in particular, should be able to produce human-level AI. Concerning intelligence extension and amplification, Chalmers argues
that new AI technologies can generally be improved on, and that this is
particularly likely when the invention can assist in designing new
technologies.
An AI system capable of self-improvement could enhance its own
intelligence, thereby becoming more efficient at improving itself. This
cycle of "recursive self-improvement" might cause an intelligence explosion, resulting in the creation of a superintelligence.
Computer components already greatly surpass human performance in
speed. Bostrom writes, "Biological neurons operate at a peak speed of
about 200 Hz, a full seven orders of magnitude slower than a modern
microprocessor (~2 GHz)." Moreover, neurons transmit spike signals across axons
at no greater than 120 m/s, "whereas existing electronic processing
cores can communicate optically at the speed of light". Thus, the
simplest example of a superintelligence may be an emulated human mind
running on much faster hardware than the brain. A human-like reasoner
who could think millions of times faster than current humans would have a
dominant advantage in most reasoning tasks, particularly ones that
require haste or long strings of actions.
Another advantage of computers is modularity, that is, their size
or computational capacity can be increased. A non-human (or modified
human) brain could become much larger than a present-day human brain,
like many supercomputers. Bostrom also raises the possibility of collective superintelligence:
a large enough number of separate reasoning systems, if they
communicated and coordinated well enough, could act in aggregate with
far greater capabilities than any sub-agent.
Humans outperform non-human animals in large part because of new
or enhanced reasoning capacities, such as long-term planning and language use. (See evolution of human intelligence and primate cognition.)
If there are other possible improvements to reasoning that would have a
similarly large impact, this makes it more likely that an agent can be
built that outperforms humans in the same fashion humans outperform
chimpanzees.
The above advantages hold for artificial superintelligence, but
it is not clear how many hold for biological superintelligence.
Physiological constraints limit the speed and size of biological brains
in many ways that are inapplicable to machine intelligence. As such,
writers on superintelligence have devoted much more attention to
superintelligent AI scenarios.
Projects
In 2024, Ilya Sutskever left OpenAI to cofound the startup Safe Superintelligence, which focuses solely on creating a superintelligence that is safe by design, while avoiding "distraction by management overhead or product cycles". Despite still offering no product, the startup became valued at $30 billion in February 2025.
In 2025, Meta created Meta Superintelligence Labs, a new AI division led by Alexandr Wang.
Biological superintelligence
Carl Sagan suggested that the advent of Caesarean sections and in vitro fertilization may permit humans to evolve larger heads, resulting in improvements via natural selection in the heritable component of human intelligence. By contrast, Gerald Crabtree has argued that decreased selection pressure is resulting in a slow, centuries-long reduction in human intelligence
and that this process instead is likely to continue. There is no
scientific consensus concerning either possibility and in both cases,
the biological change would be slow, especially relative to rates of
cultural change.
Selective breeding, nootropics, epigenetic modulation, and genetic engineering
could improve human intelligence more rapidly. Bostrom writes that if
we come to understand the genetic component of intelligence,
pre-implantation genetic diagnosis could be used to select for embryos
with as much as 4 points of IQ gain (if one embryo is selected out of
two), or with larger gains (e.g., up to 24.3 IQ points gained if one
embryo is selected out of 1000). If this process is iterated over many
generations, the gains could be an order of magnitude improvement.
Bostrom suggests that deriving new gametes from embryonic stem cells
could be used to iterate the selection process rapidly. A well-organized society of high-intelligence humans of this sort could potentially achieve collective superintelligence.
Alternatively, collective intelligence might be constructed by
better organizing humans at present levels of individual intelligence.
Several writers have suggested that human civilization, or some aspect
of it (e.g., the Internet, or the economy), is coming to function like a
global brain with capacities far exceeding its component agents. A prediction market
is sometimes considered as an example of a working collective
intelligence system, consisting of humans only (assuming algorithms are
not used to inform decisions).
A final method of intelligence amplification would be to directly enhance individual humans, as opposed to enhancing their social or reproductive dynamics. This could be achieved using nootropics, somatic gene therapy, or brain−computer interfaces.
However, Bostrom expresses skepticism about the scalability of the
first two approaches and argues that designing a superintelligent cyborg interface is an AI-complete problem.
Forecasts
Most surveyed AI researchers expect machines to eventually be able to
rival humans in intelligence, though there is little consensus on when
this will likely happen.
In a 2022 survey, the median year by which respondents expected
"High-level machine intelligence" with 50% confidence is 2061. The
survey defined the achievement of high-level machine intelligence as
when unaided machines can accomplish every task better and more cheaply
than human workers.
In 2023, OpenAI leaders Sam Altman, Greg Brockman and Ilya Sutskever published recommendations for the governance of superintelligence, which they believe may happen in less than 10 years.
In 2025, the forecast scenario AI 2027 led by Daniel Kokotajlo predicted rapid progress in the automation of coding and AI research, followed by ASI. In September 2025, a review of surveys of scientists and industry
experts from the last 15 years reported that most agreed that artificial
general intelligence (AGI), a level well below technological
singularity, will occur before the year 2100. A more recent analysis by AIMultiple reported that, “Current surveys of AI researchers are predicting AGI around 2040”.
Design considerations
Exploring the potential motivations of an artificial superintelligence, Bostrom distinguishes final goals and instrumental goals.
From the point of view of an agent, final goals are intrinsically
valuable, whereas instrumental goals are only useful for attaining final
goals. He proposed the "orthogonality thesis", which postulates that in
principle, virtually any final goal can be combined with virtually any
level of intelligence. Bostrom also introduced the concept of instrumental convergence, which postulates that certain instrumental goals (such as self-preservation,
resource acquisition or cognitive enhancement) increase the probability
of achieving final goals in a wide range of situations, and would thus
likely be pursued by a broad spectrum of intelligent agents.
William MacAskill argued that aligning
superintelligence with current human values could be catastrophic if
those values are permanently locked in and humanity still has moral
blind spots like slavery in the past.
Several proposals for an ASI's final goals have been put forward:
Coherent extrapolated volition (CEV) – The AI should have the values upon which humans would converge if they were more knowledgeable and rational.
Moral rightness (MR) – The AI should be programmed to do what is
morally right, relying on its superior cognitive abilities to determine
ethical actions.
Moral permissibility (MP) – The AI should stay within the bounds of
moral permissibility while otherwise pursuing goals aligned with human
values (similar to CEV).
Bostrom elaborates on these concepts:
instead of implementing humanity's coherent extrapolated
volition, one could try to build an AI to do what is morally right,
relying on the AI's superior cognitive capacities to figure out just
which actions fit that description. We can call this proposal "moral
rightness" (MR)...
MR would also appear to have some disadvantages. It relies on the
notion of "morally right", a notoriously difficult concept, one with
which philosophers have grappled since antiquity without yet attaining
consensus as to its analysis. Picking an erroneous explication of "moral
rightness" could result in outcomes that would be morally very wrong...
One might try to preserve the basic idea of the MR model while reducing its demandingness by focusing on moral permissibility: the idea being that we could let the AI pursue humanity's CEV so long as it did not act in morally impermissible ways.
The development of artificial superintelligence (ASI) has raised
concerns about potential existential risks to humanity. Researchers have
proposed various scenarios in which an ASI could pose a significant
threat:
Intelligence explosion and control problem
Some researchers argue that through recursive self-improvement, an
ASI could rapidly become so powerful as to be beyond human control. This
concept, known as an "intelligence explosion", was first proposed by I.
J. Good in 1965:
Let an ultraintelligent machine be
defined as a machine that can far surpass all the intellectual
activities of any man however clever. Since the design of machines is
one of these intellectual activities, an ultraintelligent machine could
design even better machines; there would then unquestionably be an
'intelligence explosion,' and the intelligence of man would be left far
behind. Thus the first ultraintelligent machine is the last invention
that man need ever make, provided that the machine is docile enough to
tell us how to keep it under control.
This scenario presents the AI control problem: how to create an ASI
that will benefit humanity while avoiding unintended harmful
consequences. Eliezer Yudkowsky argues that solving this problem is crucial before
ASI is developed, as a superintelligent system might be able to thwart
any subsequent attempts at control.
Unintended consequences and goal misalignment
Even with benign intentions, an ASI could potentially cause harm due
to misaligned goals or unexpected interpretations of its objectives.
Nick Bostrom provides a stark example of this risk:
When we create the first
superintelligent entity, we might make a mistake and give it goals that
lead it to annihilate humankind, assuming its enormous intellectual
advantage gives it the power to do so. For example, we could mistakenly
elevate a subgoal to the status of a supergoal. We tell it to solve a
mathematical problem, and it complies by turning all the matter in the
solar system into a giant calculating device, in the process killing the
person who asked the question.
Stuart Russell offers another illustrative scenario:
A system given the objective of
maximizing human happiness might find it easier to rewire human
neurology so that humans are always happy regardless of their
circumstances, rather than to improve the external world.
These examples highlight the potential for catastrophic outcomes even
when an ASI is not explicitly designed to be harmful, underscoring the
critical importance of precise goal specification and alignment.
Potential mitigation strategies
Researchers have proposed various approaches to mitigate risks associated with ASI:
Capability control – Limiting an ASI's ability to influence the world, such as through physical isolation or restricted access to resources.
Motivational control – Designing ASIs with goals that are fundamentally aligned with human values.
Ethical AI – Incorporating ethical principles and decision-making frameworks into ASI systems.
Oversight and governance – Developing robust international frameworks for the development and deployment of ASI technologies.
Despite these proposed strategies, some experts, such as Roman
Yampolskiy, argue that the challenge of controlling a superintelligent
AI might be fundamentally unsolvable, emphasizing the need for extreme
caution in ASI development.
Debate and skepticism
Not all researchers agree on the likelihood or severity of ASI-related existential risks. Some, like Rodney Brooks,
argue that fears of superintelligent AI are overblown and based on
unrealistic assumptions about the nature of intelligence and
technological progress. Others, such as Joanna Bryson, contend that anthropomorphizing AI systems leads to misplaced concerns about their potential threats.
Recent developments and current perspectives
The rapid advancement of LLMs and other AI technologies has
intensified debates about the proximity and potential risks of ASI.
While there is no scientific consensus, some researchers and AI
practitioners argue that current AI systems may already be approaching
AGI or even ASI capabilities.
LLM capabilities – Recent LLMs like GPT-4 have demonstrated
unexpected abilities in areas such as reasoning, problem-solving, and
multi-modal understanding, leading some to speculate about their
potential path to ASI.
Emergent behaviors – Studies have shown that as AI models increase
in size and complexity, they can exhibit emergent capabilities not
present in smaller models, potentially indicating a trend towards more
general intelligence.
Rapid progress – The pace of AI advancement has led some to argue
that we may be closer to ASI than previously thought, with potential
implications for existential risk.
As of 2024, AI skeptics such as Gary Marcus
caution against premature claims of AGI or ASI, arguing that current AI
systems, despite their impressive capabilities, still lack true
understanding and general intelligence. They emphasize the significant challenges that remain in achieving human-level intelligence, let alone superintelligence.
The debate surrounding the current state and trajectory of AI
development underscores the importance of continued research into AI
safety and ethics, as well as the need for robust governance frameworks
to manage potential risks as AI capabilities continue to advance.
Making territorial claims in space is prohibited by international space law, 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 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 racein 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.
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 and opposition to space colonization
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.
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.
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 that of 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 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:
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.
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.
Space colonization has been discussed as postcolonial continuation of imperialism and colonialism, 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.
In regard to the scenario of extraterrestrialfirst 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.
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 to overcome
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.
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 to consider
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
A computer-generated image from 2005 showing the distribution of mostly space debris in geocentric orbit with two areas of concentration: geostationary orbit and low 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.
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 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.
A contour plot of the gravitational potential of the Moon and Earth, showing the five Earth–Moon Lagrange points
Another near-Earth possibility are the stable Earth–Moon Lagrange pointsL4 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.
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 5.65×109 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 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), but
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.
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 colony is minimal.
Asteroids can provide enough material in the form of water, air,
fuel, metal, soil, and nutrients to support ten to a hundred trillion
humans in space. Many asteroids contain minerals that are inheriently
valuable, such as rare earths and precious metals. However, low gravity,
distance from Earth and disperse nature of their orbits make it
difficult to settle on small asteroids.
Giant planets
There have also been proposals to place robotic aerostats in the upper atmospheres of the Solar System's giant planets for exploration and possibly mining of helium-3, which could have a very high value per unit mass as a thermonuclear fuel.
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 a fusion
economy, with Saturn the most important and most valuable of the three,
because of its relative proximity, low radiation, and large system of
moons. On the other hand, planetary scientist John Lewis in his 1997 book Mining the Sky,
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 away. Furthermore, Uranus is an
ice giant, which would likely make it easier to separate the helium from the atmosphere.
Because Uranus has the lowest escape velocity of the four giant planets, it has been proposed as a mining site for helium-3. As Uranus is a gas giant without a viable surface, one of Uranus's natural satellites might serve as a base.
It is hypothesized that one of Neptune's satellites could be used for colonization. Triton'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 power.
Moons of outer planets
Artist's impression of a hypothetical ocean cryobot in Europa
Human missions to the outer planets would need to arrive quickly due
to the effects of space radiation and microgravity along the journey. In 2012, Thomas B. Kerwick wrote that the distance to the outer planets
made their human exploration impractical for now, noting that travel
times for round trips to Mars were estimated at two years, and that the
closest approach of Jupiter to Earth is over ten times farther than the
closest approach of Mars to Earth. However, he noted that this could
change with "significant advancement on spacecraft design". Nuclear-thermal or nuclear-electric engines have been suggested as a way to make the journey to Jupiter in a reasonable amount of time. Another possibility would be plasma magnet sails, a technology already suggested for rapidly sending a probe to Jupiter. The cold would also be a factor, necessitating a robust source of heat energy for spacesuits and bases. Most of the larger moons of the outer planets contain water ice, liquid water, and organic compounds that might be useful for sustaining human life.
Robert Zubrin
has suggested Saturn, Uranus, and Neptune as advantageous locations for
colonization because their atmospheres are good sources of fusion
fuels, such as deuterium and helium-3.
Zubrin suggested that Saturn would be the most important and valuable
as it is the closest and has an extensive satellite system. Jupiter's
high gravity makes it difficult to extract gases from its atmosphere,
and its strong radiation belt makes developing its system difficult. On the other hand, fusion power has yet to be achieved, and fusion
power from helium-3 is more difficult to achieve than conventional deuterium–tritium fusion. Jeffrey Van Cleve, Carl Grillmair, and Mark Hanna instead focus on Uranus, because the delta-v
required to get helium-3 from the atmosphere into orbit is half that
needed for Jupiter, and because Uranus' atmosphere is five times richer
in helium than Saturn's.
Jupiter's Galilean moons (Io, Europa, Ganymede, and Callisto) and Saturn's Titan
are the only moons that have gravities comparable to Earth's Moon. The
Moon has a 0.17g gravity; Io, 0.18g; Europa, 0.13g; Ganymede, 0.15g;
Callisto, 0.13g; and Titan, 0.14g. Neptune's Triton has about half the Moon's gravity (0.08g); other round moons provide even less (starting from Uranus' Titania and Oberon at about 0.04g).
Jupiter itself, like the other gas giants, has further
disadvantages. 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.
Radiation levels on Io and Europa are extreme, enough to kill unshielded humans within an Earth day. Therefore, only Callisto and perhaps Ganymede could reasonably support a human colony. Callisto orbits outside Jupiter's radiation belt. Ganymede's low latitudes are partially shielded by the moon's magnetic
field, though not enough to completely remove the need for radiation
shielding. Both of them have available water, silicate rock, and metals
that could be mined and used for construction.
Although Io's volcanism and tidal heating constitute valuable resources, exploiting them is probably impractical. Europa is rich in water (its subsurface ocean is expected to contain over twice as much water as all Earth's oceans together) and likely oxygen, but metals and minerals would have to be imported.
If alien microbial life exists on Europa, human immune systems may not
protect against it. Sufficient radiation shielding might, however, make
Europa an interesting location for a research base. The private Artemis Project
drafted a plan in 1997 to colonize Europa, involving surface igloos as
bases to drill down into the ice and explore the ocean underneath, and
suggesting that humans could live in "air pockets" in the ice layer. Ganymede and Callisto are also expected to have internal oceans. It might be possible to build a surface base that would produce fuel for further exploration of the Solar System.
In 2003, 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.
HOPE estimated a round trip time for a crewed mission of about 2–5
years, assuming significant progress in propulsion technologies.
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.
The magnetic field of Jupiter and co-rotation rotation enforcing currents
Ganymede is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere, 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.
The Keck Observatory announced in 2006 that the binary Jupiter trojan617 Patroclus,
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, may be feasible in the not-so-distant future. This could make colonization of the Moon, Mercury and main-belt asteroids more practical.
Saturn
Saturn's radiation belt is much weaker than Jupiter's, so radiation
is less of an issue here. Dione, Rhea, Titan, and Iapetus all orbit
outside the radiation belt, and Titan's thick atmosphere would
adequately shield against cosmic radiation.
The small moon Enceladus is also of interest, having a subsurface
ocean that is separated from the surface by only tens of meters of ice
at the south pole, compared to kilometers of ice separating the ocean
from the surface on Europa. Volatile and organic compounds are present
there, and the moon's high density for an ice world (1.6 g/cm3) indicates that its core is rich in silicates.
On 9 March 2006, NASA's Cassini space probe found possible evidence of liquid water on Enceladus. 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 clathrates
– 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.
Authors like Robert Zubrin have offered that Saturn is the most important and valuable of the four gas giants in the Solar System,
because of its relative proximity, low radiation, and excellent system
of moons. He named Titan as the best candidate on which to establish a
base to exploit the resources of the Saturn system.
He pointed out that Titan possesses an abundance of all the elements
necessary to support life, saying "In certain ways, Titan is the most
hospitable extraterrestrial world within our solar system for human
colonization."
To consider a colony on Saturn's largest moon Titan, protection against the extreme cold must be a primary consideration. Titan offers a gravity of approximately 1/7 of Earth gravity, in the
same range as Earth's Moon. Atmospheric pressure at the surface of the
planet is about 1.5x that of the surface of the Earth; there is however,
no oxygen present in the environment. The atmosphere is about 95%
nitrogen and 5% methane. Some estimates suggest that abundant energy resources on Titan could
power a colony with a population size of the United States.
The dense atmosphere of Titan shields the surface from radiation
and would make any structural failures problematic, rather than
catastrophic. With an oxygen mask and thermal clothing protection,
humans could roam Titan's surface in the dim sunlight. Or, given the low
gravity and dense atmosphere, they could float above it in a balloon or
on personal wings.
Freeman Dyson proposed that trans-Neptunian objects, rather than planets, are the major potential habitat of life in space. 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.
Diagram of the Stanford Torus-based world ship described in World Ships – Architectures & Feasibility Revisited paper, also considering the detailed design of Stanford Torus as described in Space Settlements: A Design Study book
Beyond the Solar System colonization targets might be identified in the surrounding stars. The main difficulty is the vast distances to other stars.
To reach such targets travel times of millennia would be
necessary, with current technology. At average speeds of even 0.1% of
the speed of light (c) interstellar expansion across the entire Milky Way galaxy
would take up to one-half of the Sun's galactic orbital period of
~240,000,000 years, which is comparable to the timescale of other
galactic processes. Due to fundamental energy and reaction mass consideration such speeds
would be with current technology limited to small spaceships. If
humanity would gain access to a large amount of energy, on the order of
the mass-energy of entire planets, it may become possible to construct
spaceships with Alcubierre drives.
The following are plausible approaches with current technology:
A generation ship
which 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 was complete, so none of the initial crew
would be expected to survive to arrive at the destination, assuming
current human lifespans.
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.
The distances between galaxies are on the order of a million times
farther than those between the stars, and thus intergalactic
colonization would involve voyages of millions of years via special
self-sustaining methods.
Implementation
Building colonies in space would require access to water, food, space, people, construction materials, energy, transportation, communications, life support, simulated gravity, radiation
protection, migration, governance and capital investment. It is likely
the colonies would be located near the necessary physical resources. The
practice of space architecture
seeks to transform spaceflight from a heroic test of human endurance to
a normality within the bounds of comfortable experience. As is true of
other frontier-opening endeavors, the capital investment necessary for
space colonization would probably come from governments, an argument made by John Hickman and Neil deGrasse Tyson.
In space settlements, a life support system must recycle or import
all the nutrients without "crashing." The closest terrestrial analogue
to space life support is possibly that of a nuclear submarine.
Nuclear submarines use mechanical life support systems to support
humans for months without surfacing, and this same basic technology
could presumably be employed for space use. However, nuclear submarines
run "open loop"—extracting oxygen from seawater, and typically dumping carbon dioxide overboard, although they recycle existing oxygen. Another commonly proposed life-support system is a closed ecological system such as Biosphere 2.
Although there are many physical, mental, and emotional health risks
for future colonists and pioneers, solutions have been proposed to
correct these problems. Mars500, HI-SEAS,
and SMART-OP represent efforts to help reduce the effects of loneliness
and confinement for long periods of time. Keeping contact with family
members, celebrating holidays, and maintaining cultural identities all
had an impact on minimizing the deterioration of mental health. There are also health tools in development to help astronauts reduce
anxiety, as well as helpful tips to reduce the spread of germs and
bacteria in a closed environment. Radiation risk may be reduced for astronauts by frequent monitoring and focusing work to minimize time away from shielding. Future space agencies can also ensure that every colonist would have a
mandatory amount of daily exercise to prevent degradation of muscle.
Cosmic rays and solar flares create a lethal radiation environment in space. In orbit around certain planets with magnetospheres (including Earth), the Van Allen belts
make living above the atmosphere difficult. To protect life,
settlements must be surrounded by sufficient mass to absorb most
incoming radiation, unless magnetic or plasma radiation shields are
developed. In the case of Van Allen belts, these could be drained using orbiting tethers or radio waves.
Passive mass shielding of four metric tons per square meter of surface area will reduce radiation dosage to several mSv or less annually, well below the rate of some populated high natural background areas on Earth. This can be leftover material (slag) from processing lunar soil and
asteroids into oxygen, metals, and other useful materials. However, it
represents a significant obstacle to manoeuvering vessels with such
massive bulk (mobile spacecraft being particularly likely to use less
massive active shielding). Inertia would necessitate powerful thrusters to start or stop rotation,
or electric motors to spin two massive portions of a vessel in opposite
senses. Shielding material can be stationary around a rotating
interior.
Psychological adjustment
The monotony and loneliness that comes from a prolonged space mission
can leave astronauts susceptible to cabin fever or having a psychotic
break. Moreover, lack of sleep, fatigue, and work overload can affect an
astronaut's ability to perform well in an environment such as space
where every action is critical.
A range of different models of transplanetary or extraterrestrial
governance have been sketched or proposed. Often envisioning the need
for a fresh or independent extraterrestrial governance, particularly in
the void left by the contemporarily criticized lack of space governance
and inclusivity.
It has been argued that space colonialism would, similarly to terrestrial settler colonialism, produce colonial national identities.
Federalism has been studied as a remedy of such distant and autonomous communities.
Space activity is legally based on the Outer Space Treaty, the main international treaty. But space law has become a larger legal field, which includes other international agreements such as the significantly less ratified Moon Treaty and diverse national laws.
Many articles of the Outer Space Treaty prevent the legal colonization of outer space. The Outer Space Treaty established the basic ramifications for space
activity in article one: "The exploration and use of outer space,
including the Moon and other celestial bodies, shall be carried out for
the benefit and in the interests of all countries, irrespective of their
degree of economic or scientific development, and shall be the province
of all mankind." And continued in article two by stating: "Outer space,
including the Moon and other celestial bodies, is not subject to
national appropriation by claim of sovereignty, by means of use or
occupation, or by any other means."
Space colonization can roughly be said to be possible when the necessary methods of space colonization become cheap enough
(such as space access by cheaper launch systems) to meet the cumulative
funds that have been gathered for the purpose, in addition to estimated
profits from commercial use of space.
Overcoming access-to-space barriers
Although there are no immediate prospects for the large amounts of
money required for space colonization to be available given traditional
launch costs, there is some prospect of a radical reduction to launch costs in the
2010s, which would consequently lessen the cost of any efforts in that
direction. With a published price of US$56.5million per launch of up to 13,150 kg (28,990 lb) payload to low Earth orbit, SpaceXFalcon 9 rockets are already the "cheapest in the industry". Advancements currently being developed as part of the SpaceX reusable launch system development program
to enable reusable Falcon 9s "could drop the price by an order of
magnitude, sparking more space-based enterprise, which in turn would
drop the cost of access to space still further through economies of
scale." If SpaceX is successful in developing the reusable technology, it would
be expected to "have a major impact on the cost of access to space",
and change the increasingly competitive market in space launch services.
Experts have debated on the possible use of money and currencies in
societies that will be established in space. The Quasi Universal
Intergalactic Denomination, or QUID, is a physical currency made from a
space-qualified polymer PTFE
for inter-planetary travelers. QUID was designed for the foreign
exchange company Travelex by scientists from Britain's National Space
Centre and the University of Leicester. Other possibilities include the incorporation of cryptocurrency as the primary form of currency, as suggested by Elon Musk.
Socio-economic issues
Human spaceflight has enabled only temporarily relocating a few privileged people and no permanent space migrants.
The societal motivation for space migration has been questioned
as rooted in colonialism, questioning the fundamentals and inclusivity
of space colonization.
Colonies on the Moon, Mars, asteroids, or the metal-rich planet Mercury, could extract local materials. The Moon is deficient in volatiles such as argon, helium and compounds of carbon, hydrogen and nitrogen. The LCROSS impacter was targeted at the Cabeus crater
which was chosen as having a high concentration of water for the Moon. A
plume of material erupted in which some water was detected. Mission
chief scientist Anthony Colaprete estimated that the Cabeus crater
contains material with 1% water or possibly more. Water ice
should also be in other permanently shadowed craters near the lunar
poles. Although helium is present only in low concentrations on the
Moon, where it is deposited into regolith by the solar wind, an estimated million tons of He-3 exists over all. It also has industrially significant oxygen, silicon, and metals such as iron, aluminium, and titanium.
Launching materials from Earth is expensive, so bulk materials for colonies could come from the Moon, a near-Earth object (NEO), Phobos, or Deimos. The benefits of using such sources include: a lower gravitational force, no atmospheric drag
on cargo vessels, and no biosphere to damage. Many NEOs contain
substantial amounts of metals. Underneath a drier outer crust (much like
oil shale), some other NEOs are inactive comets which include billions of tons of water ice and kerogen hydrocarbons, as well as some nitrogen compounds.
Recycling of some raw materials would almost certainly be necessary.
Energy
Solar energy
in orbit is abundant, reliable, and is commonly used to power
satellites today. There is no night in free space, and no clouds or
atmosphere to block sunlight. Light intensity obeys an inverse-square law. Hence, the solar energy available at distance d from the Sun is E = 1367/d2 W/m2, where d is measured in astronomical units (AU) and 1367 watts/m2 is the energy available at the distance of Earth's orbit from the Sun, 1 AU.
In the weightlessness and vacuum of space, high temperatures for industrial processes can easily be achieved in solar ovens
with huge parabolic reflectors made of metallic foil with very
lightweight support structures. Flat mirrors to reflect sunlight around
radiation shields into living areas (to avoid line-of-sight access for
cosmic rays, or to make the Sun's image appear to move across their
"sky") or onto crops are even lighter and easier to build.
Large solar power photovoltaic cell arrays or thermal power
plants would be needed to meet the electrical power needs of the
settlers' use. In developed parts of Earth, electrical consumption can
average 1 kilowatt/person (or roughly 10 megawatt-hours per person per year.) These power plants could be at a short distance from the main
structures if wires are used to transmit the power, or much farther away
with wireless power transmission.
A major export of the initial space settlement designs was anticipated to be large solar power satellites (SPS) that would use wireless power transmission (phase-locked microwave
beams or lasers emitting wavelengths that special solar cells convert
with high efficiency) to send power to locations on Earth, or to
colonies on the Moon or other locations in space. For locations on
Earth, this method of getting power is extremely benign, with zero
emissions and far less ground area required per watt than for
conventional solar panels. Once these satellites are primarily built
from lunar or asteroid-derived materials, the price of SPS electricity
could be lower than energy from fossil fuel or nuclear energy; replacing
these would have significant benefits such as the elimination of greenhouse gases and nuclear waste from electricity generation.
Transmitting solar energy wirelessly from the Earth to the Moon
and back is also an idea proposed for the benefit of space colonization
and energy resources. Physicist Dr. David Criswell, who worked for NASA
during the Apollo missions, proposed the idea of using power beams to
transfer energy from space. These beams, microwaves with a wavelength of
about 12 cm, would be almost untouched as they travel through the
atmosphere. They could also be aimed at more industrial areas to keep
away from humans or animal activities. This would allow for safer and more reliable methods of transferring solar energy.
In 2008, scientists were able to send a 20 watt microwave signal from a mountain on the island of Maui to the island of Hawaii. Since then JAXA
and Mitsubishi have been working together on a $21 billion project to
place satellites in orbit which could generate up to 1 gigawatt of
energy. These are the next advancements being done today to transmit energy wirelessly for space-based solar energy.
However, the value of SPS power delivered wirelessly to other
locations in space will typically be far higher than to Earth.
Otherwise, the means of generating the power would need to be included
with these projects and pay the heavy penalty of Earth launch costs.
Therefore, other than proposed demonstration projects for power
delivered to Earth, the first priority for SPS electricity is likely to be locations in
space, such as communications satellites, fuel depots or "orbital
tugboat" boosters transferring cargo and passengers between low Earth
orbit (LEO) and other orbits such as geosynchronous orbit (GEO), lunar orbit or highly-eccentric Earth orbit (HEEO).The system will also rely on satellites and receiving stations on Earth
to convert the energy into electricity. Because this energy can be
transmitted easily from dayside to nightside, power would be reliable
24/7.
Nuclear power
is sometimes proposed for colonies located on the Moon or on Mars, as
the supply of solar energy is too discontinuous in these locations; the
Moon has nights of two Earth weeks in duration. Mars has nights,
relatively high gravity, and an atmosphere featuring large dust storms to cover and degrade solar panels. Also, Mars' greater distance from the Sun (1.52 astronomical units, AU) means that only 1/1.522 or about 43% of the solar energy is available at Mars compared with Earth orbit. Another method would be transmitting energy wirelessly to the lunar or
Martian colonies from solar power satellites (SPSs) as described above;
the difficulties of generating power in these locations make the
relative advantages of SPSs much greater there than for power beamed to
locations on Earth. In order to also be able to fulfill the requirements
of a Moon base and energy to supply life support, maintenance,
communications, and research, a combination of both nuclear and solar
energy may be used in the first colonies.
For both solar thermal and nuclear power generation in airless
environments, such as the Moon and space, and to a lesser extent the
very thin Martian atmosphere, one of the main difficulties is dispersing
the inevitable heat generated. This requires fairly large radiator areas.
Space manufacturing could enable self-replication. Some consider it the ultimate goal because it would allow an exponential increase in colonies, while eliminating costs to, and dependence on, Earth. It could be argued that the establishment of such a colony would be Earth's first act of self-replication. Intermediate goals include colonies that expect only information from
Earth (science, engineering, entertainment) and colonies that just
require periodic supply of light weight objects, such as integrated circuits, medicines, genetic material and tools.
Sustaining a population
In 2002, the anthropologistJohn H. Moore estimated that a population of 150–180 would permit a stable society to exist for 60 to 80 generations—equivalent to 2,000 years.
In 2020, Jean-Marc Salotti proposed a method to determine the
minimum number of settlers to survive on an extraterrestrial world. It
is based on the comparison between the required time to perform all
activities and the working time of all human resources. For Mars, 110
individuals would be required.
Several private companies have announced plans toward the colonization of Mars. Among entrepreneurs leading the call for space colonization are Elon Musk, Dennis Tito and Bas Lansdorp.
Involved organizations
Organizations that advocate for space colonization include:
Blue Origin and Jeff Bezos
are pursuing plans for space colonization starting with a base on the
moon. Blue Origin is developing the New Glenn launcher to significantly
reduce access to space cost with use of a re-useable booster and is
building the Blue Moon lunar lander.
The National Space Society
(NSS) is an organization with the vision of people living and working
in thriving communities beyond the Earth. The NSS also maintains an
extensive library of full-text articles and books on space settlement.
The British Interplanetary Society (BIS) promotes ideas for the exploration and use of space, including a Mars colony, future propulsion systems (see Project Daedalus), terraforming, and locating other habitable worlds. In June 2013 the BIS began the SPACE project to re-examine Gerard
O'Neill's 1970s space colony studies in light of the advances made since
then. The progress of this effort were detailed in a special edition of
the BIS journal in September 2019.
Biosphere 2 is a test habitat on Earth for space flight.
Many space agencies
build "testbeds", which are facilities on Earth for testing advanced
life support systems, but these are designed for long duration human spaceflight, not permanent colonization.
The most famous attempt to build an analogue to a self-sufficient settlement is Biosphere 2, which attempted to duplicate Earth's biosphere.
An artist's view of a terraformed Mars centered on Valles Marineris. Tharsis is visible on the left side. This transformation was imagined in science fiction author Kim Stanley Robinson's Mars Trilogy but also studied by scientists including Robert Zubrin. Robinson and Zubrin are both members of the Mars Society.
Space colonization is a recurring theme in science fiction. NASA began to assess space colonization issues as early as 1975 with
their Space Settlements Design Study. The report directly acknowledges
the foundation of various ideas for colonization in science fiction. It
quotes author Robert Salkeld and highlights the role of the precursors
of science fiction alongside the founders of astronautics, where for
example Jules Verne rubs shoulders with Constantin Tsiolkovsky.
Indeed, colonization as a fictional theme and colonization as a
research project are not independent. Research feeds fiction and fiction
sometimes inspires research. Many of the most fascinating ideas in
science originated not in the laboratory but in the minds of such
science fiction writers as Arthur C. Clarke and Ray Bradbury. Clarke's
1945 article on communications satellites was the original idea behind
modern communications satellites. Bradbury's The Martian Chronicles
explores the exploration and settlement of Mars and has been attributed
as the main inspiration behind NASA's many missions to Mars. Communicators and tricorders from the science fiction of Star Trek are
said to be inspirations for cell phones and wireless medical triage
devices. Fiction inspired innovation and invention to develop new technologies.
Communications, governance principles, and advanced technological
devices, all speculated by science fiction, are all precursors to
survival of an extraterrestrial colony. The European Space Agency ITSF project (Innovative Technologies in
Science Fiction for Space Applications) study offers similar
consideration for the cross-fertilization between fiction and science.
Science fiction writer Norman Spinrad
highlights the role of science fiction as a visionary force that
spawned the conquest of space, a term he believes betrays its
imperialist tendencies, and the colonization of space. He also shows that political scientist and science fiction writer Jerry
Pournelle, in wanting to revive the conquest of space for this purpose
in the early 1980s, actually launched the Reagan administration's
Strategic Defense Initiative project, which he considers a failure,
because instead of the military program reviving the space program, the
opposite happens: the $40 billion cost of the program is actually taken
away from the construction of a base on the Moon.
One of the great names in science fiction, Arthur C. Clarke, a supporter of Marshall Savage's ideas, announced in a 2001 article, the date appearing in one of his most famous titles 2001: A Space Odyssey, that by 2057 there would be humans on the Moon, Mars , Europa, Ganymede, Titan and in orbit around Venus, Neptune and Pluto. Contemporary science fiction has extended the colonization vision further. The TV series The Expanse
which is based on a series of novels of the same name by James S. A.
Corey, addresses the politics and conflict of humanity hundreds of years
in the future after it has colonized the solar system and Mars has
become an independent military power. In Theresa Hutchin's essay on the
series in 2021, comparisons are drawn between the fiction of the story
and the reality of current corporate led development of space
exploration activities.
