Conceptual illustration of nine stages of terraforming Mars.
Terraforming is the process by which an uninhabitable environment is altered into an Earth-like environment that terrestrial plants and even humans could survive i.e., planetary engineering.
Mars and Venus have both been considered as candidates for terraforming.
However, to actually take a planet and alter its natural environment to create a more terrestrial friendly one is a complicated process, one that is not in our near future.
Timescale: To terraform a planet like Mars would mean the initial stages might take decades or centuries and to transform the entire planet into an Earth-like habitat would take several millennia.
Nevertheless, scientists have considered the possibilities:
MARS--Could we terraform and then colonize Mars?
Mars seems to be the most likely
candidate for terraforming because it is most Earth-like to begin with -
the temperature range overlaps that of Earth, H2O is present, and
the length of the day is similar enough that organisms adapted to a 24-hour
day/night cycle could adapt. (This is a fortunate coincidence -- the
day on Venus is more than 200 Earth days long!)
We have already determined that liquid water needs to stay liquid on the surface of a planet for it to be habitable----->surface temp needs to be greater than 0 C for at least part of the year for the kind of life we think of as typical to form and thrive.
Recall: the temp on Mars rises above
0°C at the equator. BUT the average temp at the surface is 50-60 C below
freezing. Even when the temperature on Mars does rise above freezing,
the very thin atmosphere means the water does not remain liquid, but quickly
evaporates and refreezes.
So---->to terraform Mars would
mean we would need to raise the daytime surface temp to at or above
freezing for at least part of the year on at least part of the planet. We
also would need to give Mars a thicker atmosphere, both to give plants enough
CO2 to use and to give animals oxygen to breathe.
How do we do this?
2. One alternative gases to CO2 to raise the atmospheric temp is NH3. Ammonia is a very efficient greenhouse gas but to obtain it we would need to convert nitrogen in the atmosphere and we don't possess that technology yet. An alternative would be to deliberately crash ammonia-rich asteroids or comets into Mars (deliberately crashing things into Mars comes up again and again in terraforming studies!)
3. Another possible greenhouse
gas is water vapor -- it is actually responsible for the majority of the greenhouse
effect on Earth! Like CO2 , water is present on Mars, though
the exact amounts are unknown. Once again, melting the ice caps could
release greenhouse gases into the atmosphere, or deliberately crashing comets
into Mars could provide a supply of water. Once again this can be done
at least partly with materials already present on Mars, and without creating
an atmosphere hostile to human or other animal life.
"a drastic modification of Martian conditions can be achieved using 21st century technology. The Mars so produced will closely resemble the conditions existing on the primitive Mars. Humans operating on the surface of such a Mars would require breathing gear, but pressure suits would be unnecessary. With outside atmospheric pressures raised, it will be possible to create large dwelling areas by means of very large inflatable structures. Average temperatures could be above the freezing point of water for significant regions during portions of the year, enabling the growth of plant life in the open. The spread of plants could produce enough oxygen to make Mars habitable for animals in several millennia. More rapid oxygenation would require engineering efforts supported by multi-terrawatt power sources. It is speculated that the desire to speed the terraforming of Mars will be a driver for developing such technologies, which in turn will define a leap in human power over nature as dramatic as that which accompanied the creation of post-Renaissance industrial civilization. " --from http://www.users.globalnet.co.uk/~mfogg/zubrin.htm
The terraforming of Venus has also been considered, though it would be even more difficult than terraforming Mars:
How could the temp of Venus be brought down to a more clement level?
The Ethical Implications
Is it right to terraform? Should we alter a natural environment?
These questions are philosophically interesting but they also bear on reality.
Some of the tricky issues are:
Does Mars as a planet have any intrinsic value in and of itself?
Is there less intrinsic worth in
a planet that is devoid of life than in one with an active biosphere?
Is Mars more valuable as a unique
planet than as an "imitation Earth"?
Some of these arguments have analogs
here on Earth. Imagine you could make it possible for twice as many
people to live in Arizona, by flooding the Grand Canyon.
Would the additional living space for humans outweigh the loss of a unique geological formation?
Should we access and use the resources that are available there or should we leave them as they are?
ARGUMENTS PRO TERRAFORMING MARS:
1) Even a thick (nonbreathable) CO2 atmosphere would allow people walk on mars with just simple breathing apparatus rather than full space suits.
2) Local biomass would be critical for colonists
3) Would provide a uniting project for all of the Earth.
4) Would allow life to survive on Mars if something really bad happened to Earth
5) New technologies would be developed
6) These technologies would likely also help Earth's environment as well.
7) Planets with life on them are more important than those that do not.
8) Better use of funds than building
up military stockpiles.
ARGUMENTS CON TERRAFORMING MARS
1) The time scales are longer than the world economic order needed to support the effort.
2) The economic benefits would be less than than the costs for a very long time.
3) Such an effort would take away Earth's "best and brightest" from important terrestrial projects and problems
4) It is not possible to prove today that Mars is devoid of life. Therefore, such a terraforming project would possibly wipe-out indigenous martian biota.
5) It is better to leave Mars as it is for scientific and aesthetic reasons.
6) We might fail and make Mars less hospitable than it is today.
7) We have done poorly here on Earth, why would we be able to make Mars into a new "earth".
8) Political or legal roadblocks might exist.
9) Who gets to live on Mars? Who owns it? Who controls it Earth or Mars?
10) The future of the Mars biosphere
cannot be predicted or controlled possibly leading to failure.