"Before MARS" tells the dramatic backstory of Hana and Joon Seung, identical twin sisters who will grow up to be central characters in the upcoming global event series, "MARS" on the National Geographic Channel. Set in the present day, "Before MARS" focuses on the young twins' move to a small town and the events that will one day inspire Hana to join humankind's first expedition to another planet.

In 2033, the first human mission to Mars enters the red planet's atmosphere but the crew of the Daedalus faces a life-threatening emergency when the ship's landing system goes offline. The crew's commander risks his life to fix the problem as mission control monitors back on Earth. In the present-day documentary, SpaceX attempts to land the world's first reusable rocket in order to pioneer the critical technology that will help humans reach Mars.