We have been going to space for nearly 40 years now, but it has always been for temporary stays in orbit. However, three astronauts have now moved into the International Space Station (ISS) for a four-month stay, marking the beginning of a decade and a half of a permanent human presence in space. The arrival of these three astronauts at the ISS on Nov. 2, 2000, sparked one NASA official to remark, "We're going into space forever with people first circling this globe, and then we're going to Mars...."

An artist's concept of how a Mars colony may look on a terraformed Mars.

Why would we ever want to go to Mars? As pictures beamed back from planetary probes and rovers since 1964 have shown, Mars is a desolate, lifeless planet with seemingly little to offer humans. It has a very thin atmosphere and no signs of existing life -- but Mars does hold some promise for the continuation of the human race. There are more than six billion people on Earth, and that number continues to grow unabated. This overcrowding, or the possibility of planetary disaster, will force us to eventually consider new homes in our solar system, and Mars may have more to offer us than the photos of its barren landscape now show.

Recently, NASA probes have discovered hints to a warmer past on Mars, one in which water may have flowed and life might have existed. With fluvial evidence mounting that water may still exist in a frozen state on Mars, there are many who suggest that the human race could one day make Mars its second home. Such an effort to colonize Mars would begin with altering the current climate and atmosphere to more closely resemble that of Earth's. The process of transforming the Martian atmosphere to create a more habitable living environment is called terraforming. In this edition of How Stuff Will Work, you will find out why Mars is the ideal candidate for colonization, and how we plan to terraform the red planet for human habitation.