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.
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]
Space colonization |
Outer solar system
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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:
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]
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.
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]
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.
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 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.
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.
Mars can be considered in broad regions for discussion of possible colony sites.
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.
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.
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, 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.
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.
Besides the general criticism of human colonization of space (see space colonization), there are specific concerns about a colony on Mars:
A few instances in fiction provide detailed descriptions of Mars colonization. They include:
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