An intimate tour of Earth's most impressive landscapes as captured by astronauts. Dr. Justin Wilkinson from NASA's astronaut team describes the special places that spacemen focus on whenever they get a moment.
Did liquid water once flow on Mars? Did the planet support life in any form? The answers may shed light on whether life-bearing planets are the norm in our galaxy run. Or is it a rare gem, with a unique make-up and history that allows it to support life.