Mars
'
Mars' is the focus of much speculation and serious study about possible 'human colonization'. Its surface conditions and the likely availability of water make it arguably the most hospitable of the planets in this solar system, other than
Earth.
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 would require an exponentially increasing amount of delta V, and are not feasible with standard
chemical rockets, but could become feasible with more advanced propulsion technologies, such as
nuclear rockets, which could feasibly cut the trip time down to about two weeks.
[1]
Relative similarity to Earth
While Earth is most like neighboring
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, being less dense.
★ 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 and
ESA's
Mars Express confirm the presence of
water on Mars. Mars appears to have significant quantities of all the
elements necessary to support Terran-based 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 -63
°C and a low of -140°C.
★ 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. If Mars were to be
terraformed, significantly less
sunlight would reach the surface.
★ 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; habitable structures on Mars will 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 CO
2 at the surface of Mars is some 52 times higher than on Earth, possibly allowing Mars to support some plant life. Most higher plants cannot survive without a minimum level of
oxygen, however.
★ Mars has no
magnetosphere to deflect
solar winds.
Habitability
Physiologically, Mars' atmosphere may be considered a
vacuum. An unprotected human being would lose consciousness in about 20 seconds and would not survive more than a minute or so on the surface of Mars without a
space suit.
Still, conditions on Mars are much closer to habitability than the extremely hot and cold temperatures on
Mercury, the furnace-hot surface of
Venus, or the
cryogenic cold of the
outer planets. Only the cloud tops of Venus are closer in terms of habitability to Earth than Mars is. There are natural settings on Earth where humans have explored that match most conditions on Mars. 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."
[2]
Terraforming of Mars
Main articles: 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.
[3] The practicality of
terraforming is still unclear, and its
ethics are disputed.
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 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.
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.
[1] The general 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.
[1]
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 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. Real-time conversation with Earth, such as
telephone is not possible, but other means of communication, such as
e-mail and
voice mail pose no difficulty. 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. It should be remembered that the vast majority of exploration and colonization of Earth was conducted without the benefit of real-time communication with "home". Also a satellite at either of the Earth-Sun L4/L5
Lagrange points could serve as a relay during this period.
Ordinary
two-way radios or even
cell phones will work well over
line of sight distances and their range can be extended using
radio repeaters on high ground or towers. Mars has an
ionosphere that might be used to reflect radio communications between points farther apart on the Martian surface, somewhat like
short wave communication on Earth. The peak
plasma frequency in the Martian ionosphere is about 1 MHz (at about 150 km),
[6] suggesting that would be the
maximum usable frequency for such communications.
In any case, a constellation of communications satellites, perhaps including a
Lagrangian point satellite located to avoid difficulties during superior conjunction, would be a minor expense in the context of a full-blown Mars colonization program.
Robotic precursors
The path to a Mars colony will be prepared by
robotic systems such as the
Mars Exploration Rovers Spirit and Opportunity. These systems will help locate resources, such as ground water or ice, that will help a colony to grow and thrive. The lifetimes of these systems will 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.
Robotic systems will 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 manned bases
As with the first manned missions to the Moon, early manned missions to Mars may
be tentative steps, sometimes referred to as Flags and Footprints. A real progression
towards colonization will be the establishment of permanent bases which begin to
establish an infrastructure from which other activities can grow. One proposal
for early manned landings on Mars with a live-off-the-land approach is
Mars Direct
as advocated by
Robert Zubrin.
[1] An active effort is also underway to simulate
these early bases with the
Mars Analogue Research Station Programme at
Devon Island
in Canada and with a more frequently used site in
Utah, USA.
Economics
As with early colonies in the
New World, economics are a crucial aspect to a colony's success. Whereas
North American colonies established
a trade in timber, furs, and other raw materials, the early Martian colonies will
need to develop local resources both for internal consumption and, perhaps, for export. These
resources will certainly include water and/or ice. In the slightly longer term, the reduced
gravity well of Mars versus that of the Earth may improve the economics of lifting
materials from the surface. This reduced gravity together with Mars' rotation rate makes possible the construction of a
space elevator, although there is the problem of the low orbit of its moon
Phobos.
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.
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 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 from the canyon, indicating it was once flooded.
Martian moons
While not strictly part of Mars itself, the moons are attractive for some kind of presence. The
delta-v from the moons to an Earth return trajectory is low, and the moons may possess rocket propellant such as water ice in the rock. If so, they could act as refueling points for vehicles returning to Earth, and would be economically viable to periodically return propellant and other material to
cislunar space. This could help pay for Martian surface settlement.
Concerns
Besides the general criticism of human colonization of space (see
space colonization), there are specific concerns about a colony on Mars:
★ A gravity 0.38 times that of the earth and a density of the atmosphere of 1% that on earth
ref means that a shuttle or parachute touches down at 3.8 times the speed on earth. Therefore the cargo is dumped out the back in low level flight and uses retro rockets to slow down even more. The rockets need to produce 2.3 times the thrust compared to the moon. In the sky crane concept the real cargo is then dumped down from the rocket stage and decelerated by a
winch and then lands with its wheels. Precise navigation helps to hit some sort of natural runway. For some reason this does not scale well with vehicle size and between mach 5 and mach 0 a safety gap opens.
[8]
★ 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, despite the Moon's extreme poverty in several of the key elements required for life, most notably hydrogen, nitrogen and carbon (50 - 100 ppm).
[9]
★ 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. 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.
[10]
★ Humans born and raised on Mars would probably have difficulty adapting to gravity on Earth, should they travel there.
★ 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.
[11] This could make physical export trade from Mars to other planets and habitats less viable economically.
See also
★
Exploration of Mars
★
In-Situ Resource Utilization
★
Mars
★
Mars Direct
★
MarsDrive
★
Mars Analogue Research Station Programme
★
Mars in fiction
★
Mars Society
★
NASA's
Vision for Space Exploration
★
Red Colony
★
Solar system
★
Terraforming
★
The Case for Mars
Notes
1. The Case for Mars:The Plan to Settle the Red Planet and Why We Must, , Robert, Zubrin, Touchstone, , ISBN 0-684-83550-9
2.
Remarks as Prepared for Delivery By the Honorable Shana Dale, NASA Deputy Administrator
3. http://www.users.globalnet.co.uk/~mfogg/zubrin.htm
4. The Case for Mars:The Plan to Settle the Red Planet and Why We Must, , Robert, Zubrin, Touchstone, , ISBN 0-684-83550-9
5. The Case for Mars:The Plan to Settle the Red Planet and Why We Must, , Robert, Zubrin, Touchstone, , ISBN 0-684-83550-9
6. http://www-mars.lmd.jussieu.fr/granada2006/abstracts/Picardi_Granada2006.pdf
7. The Case for Mars:The Plan to Settle the Red Planet and Why We Must, , Robert, Zubrin, Touchstone, , ISBN 0-684-83550-9
8. [1]
9. http://www.space-frontier.org/PressReleases/2002/20021017moonmars.html
10. http://www.marsgravity.org/
11. http://pds.jpl.nasa.gov/planets/
References
★ Frank Crossman and Robert Zubrin, editors, ''. Apogee Books Space Series, 2002, ISBN 1-896522-90-4.
★ Robert Zubrin, ''
The Case for Mars: The Plan to Settle the Red Planet and Why We Must'', Simon & Schuster/Touchstone, 1996, ISBN 0-684-83550-9
External links
★
The Planetary Society
★
Red Colony web site
★
MarsDrive Consortium
★
4Frontiers Corporation
★
Mars Foundation
★
Mars Society
★
Google Mars
★
TLU Mission to Mars
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