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Many believe space colonization is a desirable and perhaps inevitable step in the future of humanity. Mars is the focus of much speculation and serious study about possible colonies. It is the easiest planet to reach from Earth in terms of energy (delta V) requirements, but a trip there would require several months in space.

Similarity to Earth

While Earth is most like neighboring Venus in bulk composition, Mars' similarities to Earth are ultimately 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 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 points at Cygnus, not Ursa Minor.
• Mars has an atmosphere. While 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 and ESA's Mars Express confirm the presence of water on Mars. Mars appears to have in significant quantities all the elements necessary to support life.

Differences

There are differences, of course, between Earth and Mars:

• The surface gravity on Mars is only one third that of Earth. 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 minus 63°C and a low of minus 140°C.
• There are no standing bodies of liquid water on the surface of Mars.
• Because Mars is further from the Sun, the level of solar energy reaching the surface (the solar constant) is only about half of what reaches the Earth or the Moon.
• Mars' orbit is more eccentric than Earth's, exacerbating temperature and solar constant variations.
• The atmospheric pressure on Mars is too low for humans to survive without pressure suits.
• The Martian atmosphere consists mainly of carbon dioxide. However the partial pressure of CO₂ at the surface of Mars is some 52 times higher than on Earth, possibly allowing Mars to support plant life.
• Mars has two moons and they are much smaller and closer to the planet than Earth's Moon. Phobos and Deimos might prove useful as places to test concepts for colonizing the asteroids.

Habitability

A human being would not survive more than a minute or so on the surface of Mars without protective equipment. However, conditions on Mars are much closer to habitability than the furnace-hot temperatures on Mercury and Venus, the cryogenic cold of the outer planets or the hard vacuum of the Moon and asteroids. 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) The pressure at that altitude is about the same as on the surface of Mars. Extreme cold in the Arctic and Antarctic match all but the most extreme temperatures on Mars. Also, there are deserts on Earth that look similar to Martian terrain.

Ultimately, some groups have speculated, Mars might one day be transformed so as to allow a wide variety of living things, including humans, to survive unaided on Mars' surface. The practicality of terraforming is still unclear, and its ethics are also disputed.

Radiation

Mars has no global geomagnetic field comparable to Earth's. Combined with a thin atmosphere, this increases the amount of ionizing radiation that reaches 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, apparently because SPEs are directional. This would imply that a network of spacecraft in orbit around the Sun would 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.

Communication

Communications with Earth are relatively straightforward during the half-sol when the Earth is above the Martian horizon. NASA included communications relay equipment in several of its Mars orbiters, so Mars already has communications satellites. However, they will likely have worn out and need to be replaced long before any colonization expeditions are mounted.

Communication can be difficult for a few days every synodic period, around the time of superior conjunction when the Sun is directly between Mars and Earth. The round trip communication delay due to the speed of light ranges from about 6.5 minutes at closest approach to 44 minutes at superior conjunction. Ordinary voice conversation with Earth may never be possible, but other means of communication, such as e-mail and voice mail may pose less difficulty.

Ordinary two-way radios may work well over line of sight distances. Mars has an ionosphere, but it is not clear to what extent it could be used to reflect long distance high frequency communications between points far apart on the Martian surface.

In any case, a constellation of communications satellites, perhaps including a satellite conveniently located to avoid difficulties during superior conjuction, would be a minor expense in the context of a full-blown Mars colonization program.

Possible locations for colonies

Mars can be broken into 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.

Midlands

File:MarsOpportunityLandingSite.jpg

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 becomes available. As on Earth, the further one goes from the equator, the greater the seasonal climate variation one encounters.

Valles Marineris

File:ValMarinerisPIA00422 modest.jpg

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 from the canyon, indicating it was once flooded. The exposed walls of the canyon could offer a window into Martian geologic history, much as the walls of Earth's Grand Canyon provide.

Concerns

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

• some worry about contamination of the planet with Earth life. The question of whether life once existed or exists now on Mars has not been settled. See Life on Mars.
• many believe Mars might be more economically explored by robots, though arguably this does not necessarily preclude later colonisation.
• others suggest the Moon as a more logical first location for a planetary colony, perhaps using it as a staging area for future manned missions to Mars, despite the Moon's extreme poverty in several of the key elements required for life, most notably hydrogen, nitrogen and carbon (50 - 100 ppm).

See also

• Exploration of Mars
• Mars
• MarsDrive
• Mars Analogue Research Station Programme
• Mars in fiction
• Mars Society
• NASA's Vision for Space Exploration
• Red Colony
• Solar system
• Space colonization in popular culture
• Terraforming
• The Case for Mars

References

• Crossman, Frank. On to Mars: Colonizing a New World. Burlington, Ontario: Apogee Books. ISBN 1496-6921. {{cite book}}: Unknown parameter |coathors= ignored (help)
• Zubrin, Robert. The Case for Mars: The Plan to Settle the Red Planet and Why We Must. New York, New York: Touchstone. ISBN 0-684-83550-9. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

External links

• The Planetary Society
• Red Colony web site
• The Case for Mars
• MarsDrive Consortium
• 4Frontiers Corporation
• Mars Foundation
• Mars Society

• Mars
• Mars Society
• Space colonization