Mars

Four billion years ago was a warm and wet planet, possibly supporting
life. Spacecraft that once orbited Mars tells us liquid water once flowed
on the planet\'s surface. Today Mars is a cold, dry, desertlike world with a
thin atmosphere. Without any water on the Martian surface (The main
thing all life must have) no living life that we no of can survuve on Mars.
More than 20 years ago the Mariner and Viking missions failed to find
evidence that life exists on Mars\'s surface, although all the chemical
elements needed for life were present. That result inspired a biologist
Robert D. MacElroy to consider seriously whether Mars\'s environment
could be made hospitable to colonization by Earthings. Since then, several
scientists, using climate models and ecological theory, have said “it is
posssible,” with today\'s technology, we could transform the climate on the
planet Mars, making it suitable once more for life. Macelroy said “such an
experiment would allow us to examine, on a grand scale, how biospheres
grow and evolve. And it would give us the opportunity to spread and study
life beyond Earth. “
Many of the key elements to live on Mars are similiar to those of Earth.
On both planets the length of day is about 24 hours. Mars also experiences
seasons, as the planet\'s axis is tilted to a similar degree as Earth\'s. Because
Mars is farther from the sun, a Martian year is almost twice the length of
an Earth year, but plants should be able to adapt to such a difference. One
unalterable difference between Earth and Mars is gravity: Martian gravity
is about one third that of Earth\'s. How life would adapt to reduced gravity
is unknown. It is likely, however, that microbes and plants would adjust
easily to Martian gravity, and some animals too.
Other planets and moons in our solar system also might be considered
potential sites for life, including , and . Each of these bodies, however,
possesses some basic physical parameter that is inconsistent with
habitability. Titan and Europa are satellites that are too far from the sun to
support our life. Venus is too close, and its extremely dense atmosphere
makes the planet much too hot for life. The planet rotates so slowly that its
day is equal to about four months on Earth, which might make life difficult
for plants. The technology needed to alter these planets and satelites are
well beyond are technonlogy.
Mars is currently too cold, too dry and its carbon dioxide atmosphere is
too thin to support life. And this can be altered by a combination of
human intervention and biological changes. If we were to make Mars in a
thicker carbon dioxide atmosphere, with a surface pressure one to two
times that of air at sea level on Earth, the planet would naturally warm
above the freezing point of water . Adding a bit of to the atmosphere
would help satisfy the metabolic needs of plants and microbes. And the
small amount of oxygen that would be produced from the photochemical
degradation of carbon dioxide could create a rudimentary but effective
ozone shield for the rejuvenated planet. This carbon dioxide atmosphere
would support plant life, but would not contain enough oxygen for
animals. (Humans also) Although humans would need to carry a supply of
breathable air with them, a carbon dioxide Mars would still be a much
kinder, gentler place than today\'s Mars. The higher temperatures and
atmospheric pressure would make space suits and biodomes unnecessary.
And the natural growth of plants would allow the cultivation of farms and
forests on Mars\'s surface, this would provide food for humans and
animals.
To make Mars suitable for animals and humans, its atmosphere would
have to be made more similar to , which is composed primarily of
nitrogen, with oxygen levels close to 20 percent and carbon dioxide levels
less than 1 percent. The process of generating such an Earth- like,
oxygen-rich environment would be much more difficult than simply
thickening Mars\'s atmosphere. But to make Mars livable, generating a
carbon dioxide atmosphere would probably be the first step. Bringing the
exact air we need to breathe from Earth would be impractical. For
example, the amount of nitrogen needed to create a breathable atmosphere
on Mars is more than a million billion tons. The space shuttle can carry
only about 25 tons into low Earth orbit. That means if Mars does not have
the necessary amount of nitrogen, it is not within human capabilities to
bring it there. Unfortunately, we do not yet know how much of each of
these key ingredients Mars has hidden below its surface. We do know that
the