"Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local name for the red planet. Long after Burroughs' stories were published, Mars has continued to capture the imagination of science fiction writers as a popular location for extraterrestrial adventures. This dramatic picture of a crescent Mars was taken by NASA's Viking 2 spacecraft in 1976.