To travel to Mars, astronauts will have to complete about 8,750 Columbus voyages of distance, assuming that Mars and Earth are at their closest points in their respective orbits around the Sun, a position they take once every two years. While the distance is vast, the fuel cost is not as much greater as it looks; the terrain from the Moon to Mars is milder than that from Earth to the Moon. (Calculation based on Columbus’s first voyage, from his journal, edited by Clements R. Markham.)