Of all the planets in our solar system, Mars is the most suitable for human life. But there is a problem - cold. Also there is weaker gravity than on Earth, more radiation from the Sun and much less oxygen. A journey to Mars takes about nine months. People would survive if robots would built underground homes. There would be big greenhouses, too and these would have a temperature warm enough to grow plants. Surprisingly, when a space magazine wrote about a future colony on Mars, more then 400 people wanted to be a part of it.