The Atacama Desert is the driest non-polar place on Earth, with some areas receiving no rain for over 400 years.

The Atacama Desert covers a 1,000-kilometer strip of land on the Pacific coast of South America. Its extreme aridity is caused by a double rain shadow. The Andes Mountains block moist Amazonian air from the east, while the Chilean Coastal Range prevents Pacific moisture from reaching the inland plateau. The cold Humboldt Current flowing along the coast also plays a critical role. This current cools the air above it, creating a thermal inversion that prevents the upward movement of air necessary for cloud formation and precipitation. Consequently, the region receives an average of only 15 millimeters of rain per year, though some weather stations have never recorded a single drop. According to records, the town of Calama experienced a legendary dry spell that lasted 401 years, ending only in 1971. This hyper-aridity makes the soil chemistry remarkably similar to that found on Mars. Because of these conditions, NASA’s Ames Research Center has used the Atacama since the early 2000s to test instruments for missions like the Viking and Curiosity rovers. Researchers study the 'microbial life' found in the desert's salt flats to understand how life might survive in the harsh conditions of other planets. The lack of water is so absolute that even the highest mountains in the region, reaching over 6,000 meters, remain completely free of glaciers. This unique geological and atmospheric combination makes the Atacama the oldest continuously dry desert on Earth.