Look for clues about the author’s purpose in this passage about Mars. In the spring and summer, some areas of the Martian surface darken and turn a greenish-blue hue. In autumn and winter, the same areas turn a yellowish-brown hue. The best time to observe these changes is when the white polar caps start to melt. At this time, the Martian dark areas remind one of Earth's moist soil. What is the author’s purpose in writing this paragraph?
