As John H. Jenkins has noted, Asimov's novels typically are set either on Earth ("Pebble in the Sky", "The End of Eternity", "The Caves of Steel"), or on fictional extrasolar planets ("The Currents of Space", "The Naked Sun", the Foundation series). The major exceptions are the Lucky Starr novels, which take place among the familiar worlds of the Solar System. "David Starr: Space Ranger" is the only Asimov novel set on Mars, and the picture of Mars that he draws is accurate, if optimistic, based on what was known in 1951. Asimov's Martian atmosphere is one-fifth as dense as Earth's and lacks oxygen. He does not mention the famous Martian canals, though the novel's fissures might allude to these.