# Astronomy:Colonization of Mars

Short description: Proposed concepts
An artist's conception of a human Mars base, with a cutaway revealing an interior horticultural area

The colonization of Mars (or settlement of Mars[1]) has received interest from public space agencies and private corporations, and been extensively explored in science fiction writing, film, and art.

Organizations have proposed plans for a human mission to Mars, the first step towards any colonization effort, but no person has set foot on the planet nor have any return journeys been achieved. However, landers and rovers have successfully explored the planetary surface and delivered information about conditions on the ground.

Reasons for colonizing Mars include curiosity, the potential for humans to provide more in-depth observational research than uncrewed rovers, economic interest in its resources, and the possibility that the settlement of other planets could decrease the likelihood of human extinction. Difficulties and hazards include radiation exposure during a trip to Mars and on its surface, toxic soil, low gravity, the isolation that accompanies Mars' distance from Earth, a lack of water, and cold temperatures.

Commitments to researching permanent settlement have been made by public space agencies—NASA, ESA, Roscosmos, ISRO, the CNSA, among others—and private organizations—SpaceX, Lockheed Martin, and Boeing.

## Mission concepts and timelines

Since the 20th century, there have been several proposed human missions to Mars both by government agencies and private companies.

Most of the human mission concepts as currently conceived by national governmental space programs would not be direct precursors to colonization. Programs such as those being tentatively planned by NASA, Roscosmos, and ESA are intended solely as exploration missions, with the establishment of a permanent base possible but not yet the main goal.

Colonization requires the establishment of permanent habitats that have the potential for self-expansion and self-sustenance. Two early proposals for building habitats on Mars are the Mars Direct and the Semi-Direct concepts, advocated by Robert Zubrin, an advocate of the colonization of Mars.[2]

At the February 2017 World Government Summit, the United Arab Emirates announced a plan to establish a settlement on Mars by 2117, led by the Mohammed bin Rashid Space Centre.[3][4]

SpaceX has proposed the development of Mars transportation infrastructure in order to facilitate the eventual colonization of Mars. The mission architecture includes fully reusable launch vehicles, human-rated spacecraft, on-orbit propellant tankers, rapid-turnaround launch/landing mounts, and local production of rocket fuel on Mars via in situ resource utilization (ISRU). SpaceX's aspirational goal (As of 2017) was to land their cargo Starships on Mars by 2024 and the first 2 crewed starships by 2026.[5][6][needs update]

## Comparisons between Earth and Mars

Atmospheric pressure comparison
Location Pressure
Olympus Mons summit 72 Pa (0.0104 psi) (0.0007 atm)
Mars average 610 Pa (0.088 psi) (0.006 atm)
Hellas Planitia bottom 1.16 kPa (0.168 psi) (0.0114 atm)
Armstrong limit 6.25 kPa (0.906 psi) (0.0617 atm)
Mount Everest summit[7] 33.7 kPa (4.89 psi) (0.3326 atm)
Earth sea level 101.3 kPa (14.69 psi) (1 atm)

### Gravity and size

The surface gravity of Mars is just 38% that of Earth. Although microgravity is known to cause health problems such as muscle loss and bone demineralization,[8][9] it is not known if Martian gravity would have a similar effect. The Mars Gravity Biosatellite was a proposed project designed to learn more about what effect Mars' lower surface gravity would have on humans, but it was cancelled due to a lack of funding.[10]

Mars has a surface area that is 28.4% of Earth's, which is only slightly less than the amount of dry land on Earth (which is 29.2% of Earth's surface). Mars has half the radius of Earth and only one-tenth the mass. This means that it has a smaller volume (≈15%) and lower average density than Earth.

### Magnetosphere

Due to the lack of a magnetosphere, solar particle events and cosmic rays can easily reach the Martian surface.[11][12][13]

### The atmosphere

Atmospheric pressure on Mars is far below the Armstrong limit at which people can survive without pressure suits. Since terraforming cannot be expected as a near-term solution, habitable structures on Mars would need to be constructed with pressure vessels similar to spacecraft, capable of containing a pressure between 30 and 100 kPa. The atmosphere is also toxic as most of it consists of carbon dioxide (95% carbon dioxide, 3% nitrogen, 1.6% argon, and traces totaling less than 0.4% of other gases, including oxygen).

This thin atmosphere does not filter out ultraviolet sunlight, which causes instability in the molecular bonds between atoms. For example, ammonia (NH3) is not stable in the Martian atmosphere and breaks down after a few hours.[14] Also due to the thinness of the atmosphere, the temperature difference between day and night is much larger than on Earth, typically around 70 °C (125 °F).[15] However, the day/night temperature variation is much lower during dust storms when very little light gets through to the surface even during the day, and instead warms the middle atmosphere.[16]

### Water and climate

Water on Mars is scarce, with rovers Spirit and Opportunity finding less than there is in Earth's driest desert.[17][18][19]

The climate is much colder than Earth, with mean surface temperatures between 186 and 268 K (−87 and −5 °C; −125 and 23 °F) (depending on the season and latitude).[20][21] The lowest temperature ever recorded on Earth was 184 K (−89.2 °C, −128.6 °F) in Antarctica.

Because Mars is about 52% farther from the Sun, the amount of solar energy entering its upper atmosphere per unit area (the solar constant) is only around 43.3% of what reaches the Earth's upper atmosphere.[22] However, due to the much thinner atmosphere, a higher fraction of the solar energy reaches the surface as radiation.[23][24] The maximum solar irradiance on Mars is about 590 W/m2 compared to about 1000 W/m2 at the Earth's surface; optimal conditions on the Martian equator can be compared to those on Devon Island in the Canadian Arctic in June.[25] Mars' orbit is more eccentric than Earth's, increasing temperature and solar constant variations over the course of the Martian year. Mars has no rain and virtually no clouds, so although cold, it is permanently sunny (apart from during dust storms). This means solar panels can always operate at maximum efficiency on dust-free days.

Global dust storms are common throughout the year and can cover the entire planet for weeks, blocking sunlight from reaching the surface.[26][27] This has been observed to cause temperature drops of 4 °C (7 °F) for several months after the storm.[28] In contrast, the only comparable events on Earth are infrequent large volcanic eruptions such as the Krakatoa event which threw large amounts of ash into the atmosphere in 1883, causing a global temperature drop of around 1 °C (2 °F). These dust storms would affect electricity production from solar panels for long periods, and interfere with communications with Earth.[16]

#### Temperature and seasons

Mars has an axial tilt of 25.19°, similar to Earth's 23.44°. As a result, Mars has seasons much like Earth, though on average they last nearly twice as long because the Martian year is about 1.88 Earth years. Mars' temperature regime is more similar to Earth's than all other planets‘ in the solar system. While generally colder than Earth, Mars can have Earth-like temperatures in some areas and at certain times.

### Soil

The Martian soil is toxic due to relatively high concentrations of chlorine and associated compounds, such as perchlorates, which are hazardous to all known forms of life.[29][30]

### Survivability

Plants and animals cannot survive the ambient conditions on the surface of Mars.[31] However, some extremophile organisms that survive in hostile conditions on Earth have endured periods of exposure to environments that approximate some of the conditions found on Mars.

### Length of day

The Martian day (or sol) is very close in duration to Earth's. A solar day on Mars is 24 hours, 39 minutes and 35.244 seconds.[32]

## Conditions for human habitation

An expedition-style crewed mission would operate on the surface, but for limited amounts of time
Dust is one concern for Mars missions

Conditions on the surface of Mars are closer to the conditions on Earth in terms of temperature and sunlight than on any other planet or moon, except for the cloud tops of Venus.[33] However, the surface is not hospitable to humans or most known life forms due to the radiation, greatly reduced air pressure, and an atmosphere with only 0.16% oxygen.

In 2012, it was reported that some lichen and cyanobacteria survived and showed remarkable adaptation capacity for photosynthesis after 34 days in simulated Martian conditions in the Mars Simulation Laboratory (MSL) maintained by the German Aerospace Center (DLR).[34][35][36] Some scientists think that cyanobacteria could play a role in the development of self-sustainable crewed outposts on Mars.[37] They propose that cyanobacteria could be used directly for various applications, including the production of food, fuel and oxygen, but also indirectly: products from their culture could support the growth of other organisms, opening the way to a wide range of life-support biological processes based on Martian resources.[37]

Humans have explored parts of Earth that match some conditions on Mars. Based on NASA rover data, temperatures on Mars (at low latitudes) are similar to those in Antarctica.[38] The atmospheric pressure at the highest altitudes reached by piloted balloon ascents (35 km (114,000 feet) in 1961,[39] 38 km in 2012) is similar to that on the surface of Mars. However, the pilots were not exposed to the extremely low pressure, as it would have killed them, but seated in a pressurized capsule.[40]

Human survival on Mars would require living in artificial Mars habitats with complex life-support systems. One key aspect of this would be water processing systems. Being made mainly of water, a human being would die in a matter of days without it. Even a 5–8% decrease in total body water causes fatigue and dizziness and a 10% decrease physical and mental impairment (See Dehydration). A person in the UK uses 70–140 litres of water per day on average.[41] Through experience and training, astronauts on the ISS have shown it is possible to use far less, and that around 70% of what is used can be recycled using the ISS water recovery systems. (For instance, half of all water is used during showers.[42]) Similar systems would be needed on Mars but would need to be much more efficient, since regular robotic deliveries of water to Mars would be prohibitively expensive (the ISS is supplied with water four times per year). Potential access to on-site water (frozen or otherwise) via drilling has been investigated by NASA.[43]

### Effects on human health

Main page: Astronomy:Effect of spaceflight on the human body

Mars presents a hostile environment for human habitation. Different technologies have been developed to assist long-term space exploration and may be adapted for habitation on Mars. The existing record for the longest consecutive space flight is 438 days by cosmonaut Valeri Polyakov,[44] and the most accrued time in space is 878 days by Gennady Padalka.[45] The longest time spent outside the protection of the Earth's Van Allen radiation belt is about 12 days for the Apollo 17 moon landing. This is minor in comparison to the 1100-day journey to Mars and back[46] envisioned by NASA for possibly as early as the year 2028. Scientists have also hypothesized that many different biological functions can be negatively affected by the environment of Mars colonies. Due to higher levels of radiation, there are a multitude of physical side-effects that must be mitigated.[47] In addition, Martian soil contains high levels of toxins which are hazardous to human health.

#### Physical effects

The difference in gravity may negatively affect human health by weakening bones and muscles. There is also risk of osteoporosis and cardiovascular problems. Current rotations on the International Space Station put astronauts in zero gravity for six months, a comparable length of time to a one-way trip to Mars. This gives researchers the ability to better understand the physical state that astronauts going to Mars would arrive in. Once on Mars, surface gravity is only 38% of that on Earth. Microgravity affects the cardiovascular, musculoskeletal and neurovestibular (central nervous) systems. The cardiovascular effects are complex. On Earth, blood within the body stays 70% below the heart, but in microgravity this is the not case due to nothing pulling the blood down. This can have several negative effects. Once entering into microgravity, the blood pressure in the lower body and legs is significantly reduced.[48] This causes legs to become weak through loss of muscle and bone mass. Astronauts show signs of a puffy face and chicken legs syndrome. After the first day of reentry back to earth, blood samples showed a 17% loss of blood plasma, which contributed to a decline of erythropoietin secretion.[49][50] On the skeletal system which is important to support our body's posture, long space flight and exposure to microgravity cause demineralization and atrophy of muscles. During re-acclimation, astronauts were observed to have a myriad of symptoms including cold sweats, nausea, vomiting and motion sickness.[51] Returning astronauts also felt disoriented. Journeys to and from Mars being six months is the average time spent at the ISS. Once on Mars with its lesser surface gravity (38% percent of Earth's), these health effects would be a serious concern.[52] Upon return to Earth, recovery from bone loss and atrophy is a long process and the effects of microgravity may never fully reverse.

Because of so much radiation reaching Mars' surface, the planet has lost its inner dynamo despite its far distance from the Sun compared to Earth. Due to this, Mars has a weaker global magnetosphere than Earth does. Combined with a thin atmosphere, this permits a significant amount of ionizing radiation to reach the Martian surface. There are two main types of radiation risks to traveling outside the protection of Earth's atmosphere and magnetosphere: galactic cosmic rays (GCR) and solar energetic particles (SEP). Earth's magnetosphere protects from charged particles from the Sun, and the atmosphere protects against uncharged and highly energetic GCRs. There are ways to mitigate against solar radiation, but without much of an atmosphere, the only solution to the GCR flux is heavy shielding amounting to roughly 15 centimeters of steel, 1 meter of rock, or 3 meters of water, limiting human colonists to living underground most of the time.[53]

The Mars Odyssey spacecraft carries an instrument, the Mars Radiation Environment Experiment (MARIE), to measure the radiation. MARIE found that radiation levels in orbit above Mars are 2.5 times higher than at the International Space Station. The average daily dose was about 220 μGy (22 mrad)—equivalent to 0.08 Gy per year.[54] A three-year exposure to such levels would exceed the safety limits currently adopted by NASA,[55] and the risk of developing cancer due to radiation exposure after a Mars mission could be two times greater than what scientists previously thought.[56][57] Occasional solar proton events (SPEs) produce much higher doses, as observed in September 2017, when NASA reported radiation levels on the surface of Mars were temporarily doubled, and were associated with an aurora 25-times brighter than any observed earlier, due to a massive, and unexpected, solar storm.[58] Building living quarters underground (possibly in Martian lava tubes) would significantly lower the colonists' exposure to radiation.

Comparison of radiation doses—includes the amount detected on the trip from Earth to Mars by the RAD on the MSL (2011–2013).[59][60][61]

Much remains to be learned about space radiation. In 2003, NASA's Lyndon B. Johnson Space Center opened a facility, the NASA Space Radiation Laboratory, at Brookhaven National Laboratory, that employs particle accelerators to simulate space radiation. The facility studies its effects on living organisms, as well as experimenting with shielding techniques.[62] Initially, there was some evidence that this kind of low level, chronic radiation is not quite as dangerous as once thought; and that radiation hormesis occurs.[63] However, results from a 2006 study indicated that protons from cosmic radiation may cause twice as much serious damage to DNA as previously estimated, exposing astronauts to greater risk of cancer and other diseases.[64] As a result of the higher radiation in the Martian environment, the summary report of the Review of U.S. Human Space Flight Plans Committee released in 2009 reported that "Mars is not an easy place to visit with existing technology and without a substantial investment of resources."[64] NASA is exploring a variety of alternative techniques and technologies such as deflector shields of plasma to protect astronauts and spacecraft from radiation.[64]

#### Psychological effects

Due to the communication delays, new protocols need to be developed in order to assess crew members' psychological health. Researchers have developed a Martian simulation called HI-SEAS (Hawaii Space Exploration Analog and Simulation) that places scientists in a simulated Martian laboratory to study the psychological effects of isolation, repetitive tasks, and living in close-quarters with other scientists for up to a year at a time. Computer programs are being developed to assist crews with personal and interpersonal issues in absence of direct communication with professionals on Earth.[65] Current suggestions for Mars exploration and colonization are to select individuals who have passed psychological screenings. Psychosocial sessions for the return home are also suggested in order to reorient people to society.

### Terraforming

Artist's conception of the process of terraforming Mars as discussed in some works of science fiction
Main page: Astronomy:Terraforming of Mars

Various works of fiction put forward the idea of terraforming Mars to allow a wide variety of life forms, including humans, to survive unaided on Mars' surface. Some ideas of possible technologies that may be able to contribute to the terraforming of Mars have been conjectured, but none would be able to bring the entire planet into the Earth-like habitat pictured in science fiction.[66]

### Minimum size of a colony

To be self-sustaining, a colony would have to be large enough to provide all the necessary living services. These include[67]

• Ecosystem management: producing appropriate gases, controlling air composition pressure and temperature, collecting and producing water, growing food and processing organic wastes.
• Energy production: this includes extracting methane for vehicles and if photovoltaic cells are used to produce energy this would include the extraction and processing of silicates, to augment or replace any original equipment.
• Industry: extracting and processing appropriate ores, manufacturing tools and other objects; producing clothes, medicine, glass, ceramics, plastics.
• Building: even if the base is constructed before arrival, it will need frequent adaptation according to the evolution of the settlement as well as inevitable replacement.
• Social activities: this includes raising children and educating them, health care, preparing meals, cleaning, washing, organizing the work and making decisions. Time for sport, culture and entertainment can be minimized but not eliminated.

As the number of individuals grows, both activities and objects can be shared between them. Growth also will offset the risks of collapse of the society, caused by sudden deaths, accidents, infertility or inbreeding. But this may not prevent mortal combat between different groups of individuals, or the loss of efficiency due to inappropriate social organization.

By mathematical modelling of the time spent by people on these issues and by keeping things simple, Salotti concludes that the minimum number for a colony on Mars is 110.[67] This is close to other studies of the genetic problems involved in the longer journey to Proxima Centauri b (6,000+ years).[68]

## Transportation

### Interplanetary spaceflight

Rendezvous, an interplanetary stage and lander stage come together over Mars
Mars (Viking 1, 1980)

Mars requires less energy per unit mass (delta V) to reach from Earth than any planet except Venus. Using a Hohmann transfer orbit, a trip to Mars requires approximately nine months in space.[69] Modified transfer trajectories that cut the travel time down to four to seven months in space are possible with incrementally higher amounts of energy and fuel compared to a Hohmann transfer orbit, and are in standard use for robotic Mars missions. Shortening the travel time below about six months requires higher delta-v and an increasing amount of fuel, and is difficult with chemical rockets. It could be feasible with advanced spacecraft propulsion technologies, some of which have already been tested to varying levels, such as Variable Specific Impulse Magnetoplasma Rocket,[70] and nuclear rockets. In the former case, a trip time of forty days could be attainable,[71] and in the latter, a trip time down to about two weeks.[2] In 2016, a University of California, Santa Barbara scientist said they could further reduce travel time for a small robotic probe to Mars down to "as little as 72 hours" with the use of a laser propelled sail (directed photonic propulsion) system instead of the fuel-based rocket propulsion system.[72][73]

During the journey the astronauts would be subject to radiation, which would require a means to protect them. Cosmic radiation and solar wind cause DNA damage, which increases the risk of cancer significantly. The effect of long-term travel in interplanetary space is unknown, but scientists estimate an added risk of between 1% and 19% (one estimate is 3.4%) for males to die of cancer because of the radiation during the journey to Mars and back to Earth. For females the probability is higher due to generally larger glandular tissues.[74]

### Landing on Mars

Painting of a landing on Mars (1986)

Mars has a surface gravity 0.38 times that of Earth, and the density of its atmosphere is about 0.6% of that on Earth.[75] The relatively strong gravity and the presence of aerodynamic effects make it difficult to land heavy, crewed spacecraft with thrusters only, as was done with the Apollo Moon landings, yet the atmosphere is too thin for aerodynamic effects to be of much help in aerobraking and landing a large vehicle. Landing piloted missions on Mars would require braking and landing systems different from anything used to land crewed spacecraft on the Moon or robotic missions on Mars.[76]

If one assumes carbon nanotube construction material will be available with a strength of 130 GPa (19,000,000 psi) then a space elevator could be built to land people and material on Mars.[77] A space elevator on Phobos (a Martian moon) has also been proposed.[78]

## Equipment needed for colonization

Colonization of Mars would require a wide variety of equipment—both equipment to directly provide services to humans and production equipment used to produce food, propellant, water, energy and breathable oxygen—in order to support human colonization efforts. Required equipment will include:[2]

Mars greenhouses feature in many colonization designs, especially for food production and other purposes
Various technologies and devices for Mars are shown in the illustration of a Mars base
• Food production spaces and equipment.
• Propellant production equipment, generally thought to be hydrogen and methane through the Sabatier reaction[79] for fuel—with oxygen oxidizer—for chemical rocket engines
• Fuels or other energy source for use with surface transportation. Carbon monoxide/oxygen (CO/O2) engines have been suggested for early surface transportation use as both carbon monoxide and oxygen can be straightforwardly produced by zirconium dioxide electrolysis from the Martian atmosphere without requiring use of any of the Martian water resources to obtain hydrogen.[80]
• Off-planet communication equipment
• Equipment for moving over the surface—Mars suit, crewed rovers and possibly even Mars aircraft.

### Basic utilities

In order to function at all the colony would need the basic utilities to support human civilization. These would need to be designed to handle the harsh Martian environment and would either have to be serviceable while wearing an EVA suit or housed inside a human habitable environment. For example, if electricity generation systems rely on solar power, large energy storage facilities will also be needed to cover the periods when dust storms block out the sun, and automatic dust removal systems may be needed to avoid human exposure to conditions on the surface.[28] If the colony is to scale beyond a few people, systems will also need to maximise use of local resources to reduce the need for resupply from Earth, for example by recycling water and oxygen and being adapted to be able to use any water found on Mars, whatever form it is in.

### Communication with Earth

Communications with Earth are relatively straightforward during the half-sol when Earth is above the Martian horizon. NASA and ESA included communications relay equipment in several of the Mars orbiters, so Mars already has communications satellites. While these will eventually wear out, additional orbiters with communication relay capability are likely to be launched before any colonization expeditions are mounted.

The one-way communication delay due to the speed of light ranges from about 3 minutes at closest approach (approximated by perihelion of Mars minus aphelion of Earth) to 22 minutes at the largest possible superior conjunction (approximated by aphelion of Mars plus aphelion of Earth). Real-time communication, such as telephone conversations or Internet Relay Chat, between Earth and Mars would be highly impractical due to the long time lags involved. NASA has found that direct communication can be blocked for about two weeks every synodic period, around the time of superior conjunction when the Sun is directly between Mars and Earth,[81] although the actual duration of the communications blackout varies from mission to mission depending on various factors—such as the amount of link margin designed into the communications system, and the minimum data rate that is acceptable from a mission standpoint. In reality most missions at Mars have had communications blackout periods of the order of a month.[82]

A satellite at the L4 or L5 Earth–Sun Lagrangian point could serve as a relay during this period to solve the problem; even a constellation of communications satellites would be a minor expense in the context of a full colonization program. However, the size and power of the equipment needed for these distances make the L4 and L5 locations unrealistic for relay stations, and the inherent stability of these regions, although beneficial in terms of station-keeping, also attracts dust and asteroids, which could pose a risk.[83] Despite that concern, the STEREO probes passed through the L4 and L5 regions without damage in late 2009.

Recent work by the University of Strathclyde's Advanced Space Concepts Laboratory, in collaboration with the European Space Agency, has suggested an alternative relay architecture based on highly non-Keplerian orbits. These are a special kind of orbit produced when continuous low-thrust propulsion, such as that produced from an ion engine or solar sail, modifies the natural trajectory of a spacecraft. Such an orbit would enable continuous communications during solar conjunction by allowing a relay spacecraft to "hover" above Mars, out of the orbital plane of the two planets.[84] Such a relay avoids the problems of satellites stationed at either L4 or L5 by being significantly closer to the surface of Mars while still maintaining continuous communication between the two planets.

## Robotic precursors

Astronauts approach Viking 2 lander probe

The path to a human colony could be prepared by robotic systems such as the Mars Exploration Rovers Spirit, Opportunity, Curiosity and Perseverance. These systems could help locate resources, such as ground water or ice, that would help a colony grow and thrive. The lifetimes of these systems would be years and even decades, and as recent developments in commercial spaceflight have shown, it may be that these systems will involve private as well as government ownership. These robotic systems also have a reduced cost compared with early crewed operations, and have less political risk.

Wired systems might lay the groundwork for early crewed landings and bases, by producing various consumables including fuel, oxidizers, water, and construction materials. Establishing power, communications, shelter, heating, and manufacturing basics can begin with robotic systems, if only as a prelude to crewed operations.

Mars Surveyor 2001 Lander MIP (Mars ISPP Precursor) was to demonstrate manufacture of oxygen from the atmosphere of Mars,[85] and test solar cell technologies and methods of mitigating the effect of Martian dust on the power systems.[86][needs update]

Before any people are transported to Mars on the notional 2020s Mars transportation infrastructure envisioned by SpaceX, a number of robotic cargo missions would be undertaken first in order to transport the requisite equipment, habitats and supplies.[87] Equipment that would be necessary would include "machines to produce fertilizer, methane and oxygen from Mars' atmospheric nitrogen and carbon dioxide and the planet's subsurface water ice" as well as construction materials to build transparent domes for initial agricultural areas.[88]

## Economics

Iron–nickel meteorite found on Mars' surface (Heat Shield Rock)

As with early colonies in the New World, economics would be a crucial aspect to a colony's success. The reduced gravity well of Mars and its position in the Solar System may facilitate Mars–Earth trade and may provide an economic rationale for continued settlement of the planet. Given its size and resources, this might eventually be a place to grow food and produce equipment to mine the asteroid belt.

Some early Mars colonies might specialize in developing local resources for Martian consumption, such as water and/or ice. Local resources can also be used in infrastructure construction.[89] One source of Martian ore currently known to be available is metallic iron in the form of nickel–iron meteorites. Iron in this form is more easily extracted than from the iron oxides that cover the planet.

Another main inter-Martian trade good during early colonization could be manure.[90] Assuming that life doesn't exist on Mars, the soil is going to be very poor for growing plants, so manure and other fertilizers will be valued highly in any Martian civilization until the planet changes enough chemically to support growing vegetation on its own.

Solar power is a candidate for power for a Martian colony. Solar insolation (the amount of solar radiation that reaches Mars) is about 42% of that on Earth, since Mars is about 52% farther from the Sun and insolation falls off as the square of distance. But the thin atmosphere would allow almost all of that energy to reach the surface as compared to Earth, where the atmosphere absorbs roughly a quarter of the solar radiation. Sunlight on the surface of Mars would be much like a moderately cloudy day on Earth.[91]

### Economic drivers

Space colonization on Mars 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.

### Colonialism

Space colonization in general has been discussed as continuation of imperialism and colonialism,[112] especially regarding Mars colonial decision making and reasons for colonial labor[113] and land exploitation have been questioned with postcolonial critique. Seeing the need for inclusive[114] and democratic participation and implementation of any space and Mars exploration, infrastructure, or colonialization, many have called for dramatic sociological reforms and guarantees to prevent racism, sexism, and other forms of prejudice.[115]

The narrative of space exploration as a "New Frontier" has been criticized as unreflected continuation of settler colonialism and manifest destiny, continuing the narrative of colonial exploration as fundamental to the assumed human nature.[116][117][118]

The predominant perspective of territorial colonization in space has been called surfacism, especially comparing advocacy for colonization of Mars opposed to Venus.[119][120]

The logo and name of the Lunar Gateway references the St. Louis Gateway Arch, associating Mars with the American frontier.[121]

### Dangers to pregnancy

One possible ethical challenge that space travelers might face is that of pregnancy during the trip. According to NASA's policies, it is forbidden for members of the crew to engage in sex in space. NASA wants its crew members to treat each other like coworkers would in a professional environment. A pregnant member on a spacecraft is dangerous to all those aboard. The pregnant woman and child would need additional nutrition from the rations aboard, as well as special treatment and care. The pregnancy would impinge on the pregnant crew member's duties and abilities. It is still not fully known how the environment in a spacecraft would affect the development of a child aboard. It is known however that a fetus would be more susceptible to solar radiation in space, which would likely have a negative effect on its cells and genetics.[122] During a long trip to Mars, it is likely that members of craft may engage in sex due to their stressful and isolated environment.[123]

Buzz Aldrin, the Apollo 11 astronaut and second person to set foot on the Moon, has recommended human Mars missions

Mars colonization is advocated by several non-governmental groups for a range of reasons and with varied proposals. One of the oldest groups is the Mars Society who promote a NASA program to accomplish human exploration of Mars and have set up Mars analog research stations in Canada and the United States. Mars to Stay advocates recycling emergency return vehicles into permanent settlements as soon as initial explorers determine permanent habitation is possible.

Elon Musk founded SpaceX with the long-term goal of developing the technologies that will enable a self-sustaining human colony on Mars.[105][124] Richard Branson, in his lifetime, is "determined to be a part of starting a population on Mars. I think it is absolutely realistic. It will happen... I think over the next 20 years," [from 2012] "we will take literally hundreds of thousands of people to space and that will give us the financial resources to do even bigger things".[125]

Author Robert Zubrin has been a major advocate for Mars exploration and colonization for many years. He is a member of the Mars society and has authored several fiction and nonfiction books about the subject. In 1996 he wrote The Case for Mars: The Plan to Settle the Red Planet and Why We Must. He continues to advocate for Mars and space exploration with his most recent book being The Case for Space: How the Revolution in Spaceflight Opens Up a Future of Limitless Possibility.

In June 2013, Buzz Aldrin, United States engineer and former astronaut, and the second person to walk on the Moon, wrote an opinion, published in The New York Times , supporting a human mission to Mars and viewing the Moon "not as a destination but more a point of departure, one that places humankind on a trajectory to homestead Mars and become a two-planet species".[126] In August 2015, Aldrin, in association with the Florida Institute of Technology, presented a "master plan", for NASA consideration, for astronauts, with a "tour of duty of ten years", to colonize Mars before the year 2040.[127]

## In fiction

A few instances in fiction provide detailed descriptions of Mars colonization. They include:

• The Expanse (2016-2021) airing originally on Syfy, then Amazon Prime
• ‘’ Colony One Mars: A SciFi Thriller’’ (2016), by Gerald Kilby
• The Space Between Us (2016 film), by Peter Chelsom
• Mars (2016) by National Geographic
• John Carter (2012), by Mark Andrews
• The Martian (2011), by Andy Weir (and the 2015 film, directed by Ridley Scott)
• Mr. Nobody (2009), by Jaco Van Dormael
• Tom and Jerry: Blast Off to Mars (2005) animated science fiction comedy film by Warner Bros. Animation and Turner Entertainment
• Aria (2002–2008), by Kozue Amano
• First Landing (2002), by Robert Zubrin
• Mars Diaries (2000), by Sigmund Brouwer
• Martian Gothic (2000), developed by Creative Reality for Microsoft Windows and Coyote Developments for PlayStation, published by TalonSoft for Microsoft Windows and Take-Two Interactive for PlayStation
• Mars Underground (1997), by William K. Hartmann
• Climbing Olympus (1994), by Kevin J. Anderson
• The Martian (1992) and Return to Mars (1999), by Ben Bova
• Total Recall (1990), by Paul Verhoeven
• Icehenge (1985), the Mars trilogy (Red Mars, Green Mars, Blue Mars, 1992–1996), and The Martians (1999), by Kim Stanley Robinson
• Man Plus (1976), by Frederik Pohl
• The Destruction of Faena (1974), by Alexander Kazantsev
• We Can Remember It for You Wholesale (1966), by Philip K. Dick
• The Sands of Mars (1951), by Arthur C. Clarke
• The Martian Chronicles (1950), by Ray Bradbury
• Red Planet (1949), by Robert A. Heinlein

## Interactive Mars map

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## References

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