National Geographic : 1939 Jul
NEWS OF THE UNIVERSE Photographs from Lowell Observatory WHEN SPRING COMES ON MARS, THE POLAR CAP SHRINKS, GREEN AREAS GROW Changes caused by advancing spring and summer are revealed strikingly in these telescopic photographs. Left to right, top to bottom, the pictures show how the white cap at the south pole (top of planet), probably snow, gradually dwindles. At the same time, dark, blue-green regions in the Martian tropics increase. Many astronomers believe this represents the growth of vegetation (Color Plate IV and page 14).