jcdenton,<br /><br />It is very unlikely that unprotected humans will ever be able to survive on Mars. Terraforming is a hypothetical method of gradually transforming an environment into one similiar to Earth's. The process may take centuries, and is likely to require enourmous investment. Terraforming Mars is a romantic ideal, with no practical purpose.<br /><br />Someday, humans will live on Mars, Mercury, the Moon, Ganymede, Titan, and possibly Venus. With adequate supplies of energy, humans can live anywhere, and will, if the race is to survive. We will create life support systems, just like we do on Earth. I'll bet that where you live, most houses have heating systems, or cooling systems, or both. Without air conditioning, much of Arizona is uninhabitable by unprotected humans in the summer. A naked human being in Michigan in January does not have much life expectancy.<br /><br />There are already people on Earth who rarely are exposed to the natural environment. They go into their garage, get in their car, open the garage door, start the car, drive to an underground, climate controlled garage, get out of their car, walk to an elevator, and ride to the floor that their office is on. In the evening, the process is reversed. Certainly, this is an extreme example, but this is the direction that we are headed. We are evolving into a narrow range of temperature tolerance, inability to withstand direct sunlight, and eventually will require an artificial environment no matter where we live. As long as we maintain the ability to create that environment, we will be able to live anywhere.<br /><br />Discussions of what the space program should focus on next are being distorted by romantic ideals which have no basis in fact. Mastering the Moon means mastering the majority of the environments that we are ever likely to face. Living on Mars will be much more like living on the Moon than it will be like living on Earth, at least for the forseeable future. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>