That life inhabits Mars now is the only rational deduction from the observations in our possession; the only one which is warranted by the facts.

• In what ways is Mars similar to the Earth and in what ways is it different?
• What is the relationship between internal activity and Mars’s spectacular surface features such as its gigantic volcanos and immense canyon system?
• What can we learn about the history of Mars by studying its surface features?
• Has liquid water ever existed on Mars and, if so, where is that water today?
• Has Mars’s atmosphere always been as thin, dry, and cold as it is now?
• Is there any evidence of present or past life on Mars?