The US space agency NASA is tracking two British explorers on a 3,650 kilometers journey across Antarctica to learn more about humanity's ability to survive on Mars. Explorers Justin Packshaw,57, and Jamie Facer Childs, 37 are on an 80-day trek across the southernmost continent as part of the Chasing the Light mission — a grueling expedition that could give a better understanding of the psychological and physical impact of other worlds on the human body and mind.