A Red Planet
Viewed from Earth, Mars is reddish in color. The ancient Greeks and Romans named the
planet after the god of war. They may have associated the planet with war because its red
color reminded them of blood. Mars appears red because the surface of the planet really is
a reddish-orange rust color, due to large amounts of iron in the soil. Mars has only a very
thin atmosphere, made up mostly of carbon dioxide.
Surface Features
Mars is home to the largest mountain in the solar system—Olympus Mons, shown inFigure
25.16. OlympusMonsisashieldvolcano, similartothevolcanoesthatmakeuptheHawaiian
islands on Earth. Olympus Mons is about 27 km (16.7 miles/88,580 ft) above the normal
Martian surface level. That makes it more than three times taller than Mount Everest. At
its base, Olympus Mons is about the size of the entire state of Arizona!
Figure 25.16: The Martian volcano Olympus Mons is the largest mountain in the solar
system. ( 29 )
Mars also has the largest canyon in the solar system, Valles Marineris (Figure 25.17).
This canyon is 4,000 km (2,500 miles) long, as long as Europe is wide, and one-fifth the
circumference of Mars. The canyon is 7 km (4.3 miles) deep. By comparison, the Grand
Canyon on Earth is only 446 km (277 miles) long and about 2 km (1.2 miles) deep.