Many people believe that 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. Mars is the easiest planet to reach from Earth in terms of energy (delta V) requirements. Still, a trip to Mars requires several months in space.

Similarity to Earth

Of all the extraterrestrial bodies known to date, Mars is the most like Earth. Similarities include:

• the Martian day (or sol) is very close to Earth's. A Mars solar day is 24 hours 39 minutes 35.244 seconds[1]. See Time, date and astronomy 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 Mars year is about 1.88 Earth years.
• 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 aerodynamic braking of spacecraft.
• Recent observations by NASAs Mars Exploration Rovers and ESA's Mars Express confirm the presence of water on Mars. Mars appears to have 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 1/3 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 -63 Celsius and a low of -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 that at the Earth and 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 long 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 wthout 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. And there are deserts on Earth that look similar to Martian terrane.

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. It is now thought that water exists in lower lattitudes 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 winter.

Midlands

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 is best determined after more data becomes 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 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. Ancient river channels lead from the canyon, indicating it was once flooded. The exposed walls of the canyon could provide 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 that could precede any colonization activity.
• 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.

See also

• Colonization of the Moon
• Exploration of Mars
• Mars Analogue Research Station Programme
• Mars in fiction
• Mars Society
• NASA's Vision for Space Exploration
• Solar system
• Terraforming
• The Case for Mars

External links

• The Planetary Society
• Red Colony web site
• The Case for Mars