Ever thought of living on Mars? Will humans ever be able to live on other planets? Former NASA astronaut Dr. Dave Williams is the person to ask.  It turns out that Earth is a pretty good place to live. Finding other habitable environments in space is no easy task: temperatures on Mercury are ten times hotter than on Earth; winter on Neptune lasts about forty years, and Uranus is ten billion miles (sixteen billion kilometers) away. But there is one planet that looks promising: Mars. Even though it takes six months to get there, Mars most closely resembles Earth. So what would it take to make it habitable—and what would life look like there?