Colonization of Mars

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]

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

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 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.[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]

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 Krakatoa which threw large amounts of ash into the atmosphere in 1883, causing a global temperature drop of around 1 °C (2 °F). Perhaps more importantly, these storms affect electricity production from solar panels for long periods, as well interfering with communications with Earth.[16]

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. And Mars' orbit is more eccentric than Earth's, increasing temperature and solar constant variations over the course of the Martian year.

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

Although there are some extremophile organisms that survive in hostile conditions on Earth, including simulations that approximate Mars, plants and animals generally cannot survive the ambient conditions present on the surface of Mars.[31]

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,[43] and the most accrued time in space is 878 days by Gennady Padalka.[44] 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[45] planned by NASA as soon 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.[46] In addition, Martian soil contains high levels of toxins which are hazardous to human health.

The difference in gravity would 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 effects the cardiovascular, musculoskeletal and neurovestibular (central nervous) systems. The cardiovascular effects are complex. On earth, blood within the body stays 70% below the heart, and in microgravity this is 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.[47] This causes legs to become weak, lose muscle, bone mass, are called “chicken like” 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.[48][49] 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.[50] Returning astronauts also felt disorientated. 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.[51] Upon return to Earth, recovery from bone loss and atrophy is a long process and the effects of microgravity may never fully reverse.

Mars has a weaker global magnetosphere as Earth does as it has lost its inner dynamo which significantly weakened the magnetosphere which is the cause of so much radiation reaching the surface despite its far distance from the Sun compared to Earth. 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.[52]

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.[53] A three-year exposure to such levels would exceed the safety limits currently adopted by NASA,[54] and the risk of developing cancer due to radiation exposure after a Mars mission could be two times greater than what scientists previously thought.[55][56] 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.[57] 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).[58][59][60]

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.[61] 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.[62] 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.[63] 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."[63] NASA is exploring a variety of alternative techniques and technologies such as deflector shields of plasma to protect astronauts and spacecraft from radiation.[63]

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.[64] 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.

Artist's conception of the process of terraforming Mars as discussed in some works of science fiction

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.[65]

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.[66] 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,[67] and nuclear rockets. In the former case, a trip time of forty days could be attainable,[68] and in the latter, a trip time down to about two weeks.[3] 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.[69][70]

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.[71]

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.[72] 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.[73]

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.[74] A space elevator on Phobos (a Martian moon) has also been proposed.[75]

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 whilst 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.

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,[78] 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.[79]

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.[80] 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.[81] 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.

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.

Although there are no immediate prospects for the large amounts of money required for any space colonization to be available given traditional launch costs,[89] there is some prospect of a radical reduction to launch costs in the 2020s, which would consequently lessen the cost of any efforts in that direction. With a published price of US$62 million per launch of up to 22,800 kg (50,300 lb) payload to low Earth orbit or 4,020 kg (8,860 lb) to Mars,[90] SpaceX Falcon 9 rockets are already the "cheapest in the industry".[91] SpaceX's reusable plans include Falcon Heavy and future methane-based launch vehicles including the Starship. 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.[92]

Alternative funding approaches might include the creation of inducement prizes. For example, the 2004 President's Commission on Implementation of United States Space Exploration Policy suggested that an inducement prize contest should be established, perhaps by government, for the achievement of space colonization. One example provided was offering a prize to the first organization to place humans on the Moon and sustain them for a fixed period before they return to Earth.[93]

Mars Odyssey found what appear to be natural caves near the volcano Arsia Mons. It has been speculated that settlers could benefit from the shelter that these or similar structures could provide from radiation and micrometeoroids. Geothermal energy is also suspected in the equatorial regions.[94]

Several possible Martian lava tube skylights have been located on the flanks of Arsia Mons. Earth based examples indicate that some should have lengthy passages offering complete protection from radiation and be relatively easy to seal using on-site materials, especially in small subsections.[95]

Hellas Planitia is the lowest lying plain below the Martian geodetic datum. The air pressure is relatively higher in this place when compared to the rest of Mars.

Space colonization in general has been discussed as continuation of imperialism and colonialism, [109] especially regarding Mars colonial decision making and reasons for colonial labor[110] and land exploitation have been questioned with postcolonial critique. Seeing the need for inclusive[111] 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 and bigotry.[112]

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.[113][114][115]

The predominant perspective of territorial colonization in space has been called surfacism, especially comparing advocacy for colonization of Mars opposed to Venus.[116]

The logo and name of the Lunar Gateway references the St. Louis Gateway Arch, associating Mars with the American frontier.[117]

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 crewmembers 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 impede 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 an unborn child in space would be more susceptible to solar radiation, which would likely have a negative effect on its cells and genetics.[118] During a long trip to Mars, it is likely that members of craft may engage in sex due to their stressful and isolated environment.[119]