Colonization of Mars

Mars

Mars is the focus of much speculation and serious study about possible human colonization. Its surface conditions and the availability of water make it arguably the most hospitable of the planets in this solar system, other than Earth. The Moon has been proposed as the first location for human colonization, but unlike Earth's moon, Mars has the potential capacity to host human and other organic life. With an environment suitable for colonization, and potential for alteration into a stable ecosystem in the far future, Mars is considered by most scientists, including Stephen Hawking,^[1] as the ideal planet for future colonization and renewal of life. The colonization of Mars is a thought-provoking subject that captures the imagination of many people in science and science-fiction. The project of colonizing Mars provides a useful thought experiment for contemplating the future of humanity.

Getting there

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. Modified transfer trajectories that cut the travel time down to seven or six 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 exponentially increasing amount of fuel, and is not feasible with chemical rockets, but could become feasible with advanced propulsion technologies not in current use, such as VASIMR,^[2] and nuclear rockets, the latter of which could potentially cut the trip time down to about two weeks.^[3]

Relative similarity to Earth

Space colonization

Mercury
Venus
Earth
- Moon
- Lagrange points
Mars
Ceres
Asteroids

Outer solar system

Jupiter
- Europa
- Callisto
Saturn
- Titan
Pluto
Trans-Neptunian Objects

While Earth is most like its inner neighbor Venus in bulk composition, Mars' similarities to Earth are arguably more compelling when considering colonization. These include:

The Martian day (or sol) is very close to Earth's. A Mars solar day is 24 hours 39 minutes 35.244 seconds. (See timekeeping on Mars.)

Mars has a surface area that is 28.4% of Earth's, 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 is less volumous and less dense than Earth.

Mars has an axial tilt of 25.19°, compared with Earth's 23.44°. As a result, Mars has seasons much like Earth, though they last nearly twice as long because the Martian year is about 1.88 Earth years. The Martian north pole currently points at Cygnus, not Ursa Minor.

Mars has an atmosphere. While very thin (about 0.7% of Earth's atmosphere), it provides some protection from solar and cosmic radiation and has been used successfully for aerobraking of spacecraft.

Recent observations by NASA's Mars Exploration Rovers, ESA's Mars Express and NASA's Phoenix Lander confirm the presence of water ice on Mars. Mars appears to have significant quantities of all the elements necessary to support Terran-based life.^[4]

Differences from Earth

The surface gravity on Mars is only a little more than one third that of Earth's. It is not known if this level is high enough to prevent the health problems associated with weightlessness.

Mars is much colder than Earth, with a mean surface temperature of -63°C and a low of -140°C. The lowest temperature ever recorded on earth was −89.2 °C by a scientist who was based in Antarctica.

There are no standing bodies of liquid water on the surface of Mars.

Because Mars is farther from the Sun, the amount of solar energy reaching the upper atmosphere (the solar constant) is only about half of what reaches the Earth's upper atmosphere or the Moon's surface. However, the solar energy that reaches the surface of Mars is not impeded by a thick atmosphere like on Earth, so that solar energy at the surface of Earth or Mars is largely the same.

Mars' orbit is more eccentric than Earth's, exacerbating temperature and solar constant variations.

The atmosphere on Mars, in its current condition, is too low for humans to survive without pressure suits. Since terraforming can not 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 a third and a whole bar.

The Martian atmosphere consists mainly of carbon dioxide. Because of this, even with the reduced atmospheric pressure, the partial pressure of CO₂ at the surface of Mars is some 52 times higher than on Earth.

Mars has a very weak magnetosphere, so it deflects solar winds poorly.

Habitability

Conditions on the surface of Mars are much closer to habitability than the surface of any other planet or moon, as seen by the extremely hot and cold temperatures on Mercury, the furnace-hot surface of Venus, or the cryogenic cold of the outer planets and their moons. Only the cloud tops of Venus are closer in terms of habitability to Earth than Mars is.^[5] There are natural settings on Earth where humans have explored that match most conditions on Mars. The highest altitude reached by a manned balloon ascent, a record set in May 1961, was 34,668 meters (113,740 feet).^[6] The pressure at that altitude is about the same as on the surface of Mars.^[7] Extreme cold in the Arctic and Antarctic match all but the most extreme temperatures on Mars.

On March 21, 2007, in remarks at JPL's High-Tech Conference for Small Business, NASA Deputy Administrator Shana Dale said, "We also hope to discover if Mars can provide a second home for humans—an extension of our civilization—40 million miles from Earth."^[8]

Terraforming of Mars

An artist's conception of a terraformed Mars

Main article: Terraforming of Mars

Some groups have speculated that Mars might one day be transformed so as to allow a wide variety of living things, including humans, to survive unaided on Mars' surface.^[9] Others make a variety of objections to doing so, some relating to technical feasibility, and others to desirability.

Radiation

Mars has no global geomagnetic field comparable to Earth's. Combined with a thin atmosphere, this permits a significant amount of ionizing radiation to reach the Martian surface. The Mars Odyssey spacecraft carried an instrument, the Mars Radiation Environment Experiment (MARIE), to measure the dangers to humans. MARIE found that radiation levels in orbit above Mars are 2.5 times higher than at the International Space Station. Average doses were about 22 millirads per day (220 micrograys per day or 0.8 gray per year). A three year exposure to such levels would be close to the safety limits currently adopted by NASA. Levels at the Martian surface would be somewhat lower and might vary significantly at different locations depending on altitude and local magnetic fields.

Occasional solar proton events (SPEs) produce much higher doses. Astronauts on Mars could be warned of SPEs by sensors closer to the Sun and presumably take shelter during these events. Some SPEs were observed by MARIE that were not seen by sensors near Earth due to the fact that SPEs are directional. This would imply that a network of spacecraft in orbit around the Sun might be needed to ensure all SPEs threatening Mars were detected.

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 will study its effects on living organisms along with shielding techniques.^[10] There is some evidence that this kind of low level, chronic radiation is not quite as dangerous as once thought; and that radiation hormesis occurs.^[11] The consensus among those that have studied the issues is that radiation levels, with the exception of the SPEs, that would be experienced on the surface of Mars, and whilst journeying there, are certainly a concern, but are not thought to prevent a trip from being made with current technology.^[12]

Communication

Communications with Earth are relatively straightforward during the half-sol when the 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 aphelion of Mars minus perihelion of Earth) to 22 minutes at the largest possible superior conjunction (approximated by perihelion of Mars plus perihelion of Earth). 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.^[13] A satellite at either of the Earth-Sun L4/L5 Lagrange points could serve as a relay during this period to solve the problem, or even a constellation of communications satellites, which would be a minor expense in the context of a full-blown Mars colonization program.

Robotic precursors

The path to a human colony could be prepared by robotic systems such as the Mars Exploration Rovers Spirit and Opportunity. 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 measured in 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.

Early human missions

See also: Vision for Space Exploration

Early human missions to Mars, such as those being tentatively planned by NASA, ESA, and other national space agencies, would not be direct precursors to colonization. They are intended solely as exploration missions, as the Apollo missions to the Moon were not planned to be sites of a permanent base.

Colonization requires the establishment of permanent bases that have potential for self-expansion. A famous proposal for building such bases is the Mars Direct plan, advocated by Robert Zubrin.^[3] The Mars Society has established the Mars Analogue Research Station Programme at sites Devon Island in Canada and in Utah, USA, to experiment with different plans for human operations on Mars, based on Mars Direct.

Economics

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 provide the rationalization for continued settlement of the planet.

Mars' reduced gravity together with its rotation rate makes possible the construction of a space elevator with today's materials, although the low orbit of Phobos will present engineering challenges.

A major economic problem is the enormous up-front investment required to establish the colony and perhaps also terraform the planet.

Some early Mars colonies might specialize in developing local resources for Martian consumption, such as water and/or ice.

Another main inter-Martian trade good during early colonization could be manure.^[14] 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. However, the Phoenix lander has discovered that the Martian soil could possibly sustain life already.^[15]

Solar power will possibly be the main power source for a Martian colony, although solar insolation (the amount of solar radiation that reaches mars) is on average only 42% of that on Earth. Excess energy gathered in the day can be stored in batteries for back-up power and nightly use. A Martian colony will need large amounts of energy for heating the habitats and greenhouses, since temperatures are much lower compared to Earth. Alternatively, nuclear reactors could provide power for colonies. Heating requirements could be lowered if the colonists use domes to trap solar heat.

Possible locations for colonies

Mars can be considered in broad regions for discussion of possible colony sites.

Polar regions

Mars' north and south poles once attracted great interest as colony sites because seasonally-varying polar ice caps have long been observed by telescope from Earth. Mars Odyssey found the largest concentration of water near the north pole, but also showed that water likely exists in lower latitudes as well, making the poles less compelling as a colony locale. Like Earth, Mars sees a midnight sun at the poles during local summer and polar night during local winter.

Equatorial regions

Mars Odyssey found natural caves near the volcano Arsia Mons. Yet, the size and shape of the caves are unknown. Scientists suspect water ice on the ground of the caves. Colonists could possibly benefit from both shelter from radiation and ice reservoirs. Geothermal energy is also suspected in the equatorial regions.

Midlands

Eagle Crater, as seen from Opportunity

The exploration of Mars' surface is still underway. The two Mars Exploration Rovers, Spirit and Opportunity, have encountered very different soil and rock characteristics. This suggests that the Martian landscape is quite varied and the ideal location for a colony would be better determined when more data become available. As on Earth, the further one goes from the equator, the greater the seasonal climate variation one encounters.

Valles Marineris

Valles Marineris, the "Grand Canyon" of Mars, is over 3,000 km long and averages 8 km deep. Atmospheric pressure at the bottom would be some 25% higher than the surface average, 0.9 kPa vs 0.7 kPa. The canyon runs roughly east-west, so shadows from its walls should not interfere too badly with solar power collection. River channels lead to the canyon, indicating it was once flooded.

Advocacy

Making Mars Colonization a reality is advocated by several groups with different reasons and proposals. One of the oldest is the Mars Society. They promote a NASA program to accomplish human exploration of Mars and have set up Mars analog research stations in Canada and the United States. Another group is Marsdrive. MarsDrive is dedicated to private initiatives for the exploration and settlement Mars.

Concerns

Besides the general criticism of human colonization of space (see space colonization), there are specific concerns about a colony on Mars:

Mars has a gravity 0.38 times that of the earth and a density of the atmosphere of 1% that on earth.^[16] The stronger gravity than the Moon and the presence of aerodynamic effects makes it more difficult to land heavy, crewed spacecraft with thrusters only, yet the atmosphere is also too thin to get very much use out of aerodynamic effects for braking and landing. Landing piloted missions on Mars will require a braking and landing system different from anything used to land crewed spacecraft on the Moon or robotic missions on Mars.^[17]

The question of whether life once existed or exists now on Mars has not been settled, raising concerns about possible contamination of the planet with Earth life. See Life on Mars.

Advocates of a return to the Moon say the Moon is a more logical first location for a first planetary colony, perhaps using it as a staging area for future manned missions to Mars. However, the moon has no atmosphere, no analogous geology and a much greater temperature range and rotational period. These differences make Mars more in common with Earth than the Moon. Antarctica or desert areas of Earth provide much better training grounds at vastly lesser cost. Also, the Moon has extreme poverty in several of the key elements required for life, most notably hydrogen, nitrogen and carbon (50 - 100 ppm), as well as the high delta-v required for takeoff and landing.^[18]

It is unknown whether Martian gravity can support human life in the long term (all experience is at either ~1g or zero gravity). Space medicine researchers have theorized on whether the health benefits of gravity rise slowly or quickly between weightlessness and full Earth gravity. One theory is that sleeping chambers built inside centrifuges would minimize the health problems. The Mars Gravity Biosatellite experiment is due to become the first experiment testing the effects of partial gravity, artificially generated at 0.38 g to match Mars gravity, on mammal life, specifically on mice, throughout the life cycle from conception to death.^[19]

Mars' escape velocity is 5 km/s, which, though less than half that for Earth, is reasonably high compared to the Moon's 2.38 km/s or the negligible escape velocity of most asteroids.^[20] This could make physical export trade from Mars to other planets and habitats less viable economically.

There is likely to be little economic return from the colonization of Mars whilst Lunar and Near Earth Asteroid industry is likely to be exporting to Earth^[21]