1. Earth-Mars Comparison
This image compares Mars and Earth in their correct relative sizes. Mars (diameter 6790 kilometers) is only slightly more than half the size of Earth (diameter 12750 kilometers). Note the difference in color between the two planets. Almost 70% of Earth's surface is covered by liquid water. In contrast, Mars now has no liquid water on its surface and is covered with bare rock and dust. The four dark circles in the Mars image are the Tharsis shield volcanos (slide #10). Africa is at the center of the Earth image.
From Viking Orbiter Views of Mars, NASA SP-441, p. 14