The year is 2033 and the first crewed mission to Mars has landed on the Red Planet, but things have gone wrong. They’ve overshot their basecamp by 75 kilometres (46 miles) and the mission commander, Ben Sawyer, has been injured and blood is pooling in his lungs. The only chance to save him is for the crew of the Daedalus to attempt to drive to basecamp where he can be treated with medical equipment stored there. As mission control on Earth watch and listen helplessly, the time delay between Earth and Mars meaning they’re hearing things happen 40 minutes after they have on the surface of the Red Planet, the drive back to camp suffers disaster when their exploration vehicle suffers a blown axle. The only chance is to walk the final 16 kilometres (10 miles) before nightfall and temperatures plunge to –70 degrees Celsius (-94 degrees Fahrenheit) and the power drains from their suits’ batteries. Can they make it and save both their commander and themselves?
When humans eventually do fly to Mars, their mission will be fraught with danger. As Ann Druyan, who was Carl Sagan’s wife, say during the episode, “there’s suspense in whether we can survive on a world not meant for us.”
The theme of the episode is how the human body adapts to space, focusing on Scott Kelly’s Year in Space mission between 2015 and 2016, when the astronaut spent 12 months on the International Space Station, while his twin brother Mark remained on Earth, allowing medical technicians to compare how the time spent in space affected Scott’s body compared to Mark’s. The absence of gravity can affect the human body in so many ways from respiratory to cardiovascular, muscular to the immune system. Then, after 7 months of flying to Mars, the human body has to suddenly readjust to gravity in the hostile environment of the red planet, while psychologically the astronauts have to cope with being so far away from their families and everything they know on Earth, with only their fellow astronauts for company and to keep each other safe.