Some scientists think we should skip the moon and head straight for Mars. One of the most outspoken supporters of this strategy is Robert Zubrin, founder and president of the Mars Society. In 1996, he laid out the details of a Mars Direct mission, which could serve as a template for manned travel to the red planet.
Here's how it would play out: The first launch would carry an unmanned Earth Return Vehicle, or ERV, to Mars. The ERV would contain a nuclear reactor, which provided the power for a chemical-processing unit capable of manufacturing propellant using compounds found in the Martian atmosphere. Two years later, another unmanned ERV would launch and head for a second landing site. At the same time, a manned spacecraft would make the journey and touch down near the first ERV. The crew would stay on Mars for 18 months, exploring the planet and conducting experiments until it was time to return to Earth using fuel manufactured on-site. As the crew members departed, another team would arrive, and the process would repeat itself so that a string of bases was established.
Long-term settlement of Mars, however, would require a transformation of the planet, a process known as terraforming. Terraforming involves warming Mars to more Earth-like conditions. The only way to do this realistically is to build soil-processing units that pump super-greenhouse gases, such as methane and ammonia, into the Martian atmosphere. These gases would absorb solar energy and warm the planet, triggering the release of carbon dioxide from the soil and polar ice caps. As carbon dioxide builds in the atmosphere, atmospheric pressure would increase, additional warming would occur and oceans would form. Eventually, colonists would be able to survive without spacesuits, although they would still need to wear oxygen tanks.
After several decades of terraforming, the red planet might look just as blue and watery as our home planet. After several more, it might be transformed completely into an Earth-like, oxygen-rich environment. If and when that occurs, it will be able to support a thriving colony of humans, some of whom will undoubtedly turn their faces toward the sky and dream of traveling to the remote corners of the solar system.