3Mars and Earth share many features. Maybe one day, cities full of people will be another thing they share! But how similar are the planets, really? Which features aid in supporting human life, and which will make colonization more difficult? Find out what kinds of preparations are underway to make living on Mars possible. Full-color photos give readers a look at this future vacation destination. 21st Century sidebars discuss technological advancements, hypothesize future endeavors and inventions, and solve problems and challenges astronauts might face. An activity at the end lets readers think about what they learned in a hands-on way.