One of the few perpetually ice-free regions in Antarctica, the McMurdo Dry Valleys are home to some of the coldest and driest exposed land on Earth. These properties make the Dry Valleys so unusual that they more closely resemble Mars than they do most of Earth, and therefore make a great research station for planetary scientists who can't yet buy a ticket to Mars.

According to Joseph Levy, a geologist at Portland State University pictured here in green, Antarctica's Taylor Valley approximates the surface conditions on Mars roughly three billion years ago.