Page 306 - NS-2 Textbook

ASTRONOMY 301

haze rises above each polar region during the 'winter sea- 40 degrees warmer due to absorption of the Sun's rays.
sons. The polar regions grow and shrink during the win- But because of the thin atmosphere, the air a few feet
ters, which appear to be similar to Earth seasons. The above the ground may be as much as 80 degrees cooler
Martian polar ice is thought to be composed of frozen than the smface itself. The daily temperature range of
carbon dioxide and frozen water vapor. about 170 degrees would be extremely uncomfortable, if
Fierce seasonal Martian winds whip up huge dust not fatal, to Earth's higher organisms. The polar regions
storms of the pinkish-colored iron oxide that covers about seem to have fairly constant temperatures of about -190
three-fourths of the Martian surface. The windstorms degrees F.
may rage for months, at speeds of up to 300 miles per Mars is about twice the diameter of the Moon and
hour, covering much of the planet with swirling reddish about half that of Earth. While Earth has a smface area of
and yellowish dust clouds. The dust of Mars is extremely 197 million square miles, Mars is only about one-quarter
fine, something like fine talcum powder. This dust some- that size, 55", million square miles. Mars' gravity is only
times is carried 35 miles above the planet's surface. about one-third (0.38) of Earth's. TIlat means a person
Huge inactive volcanoes are present on the Martian weighing 150 pounds on Earth would weigh only about
surface. Nix Olympica (Snow of Olympus) is the size of 57 pounds on Mars.
the state of Nebraska. It rises 15 miles above the sur- Two NASA Viking spacecraft landed safely on Mars
rounding terrain and has a main crater 40 miles in diam- in 1976. Carrying cameras, sensors, and radio-con-
eter. A volcano named South Spot has the largest vol- trolled arms, one Viking retrieved and analyzed sam-
canic crater on Mars, measuring 75 Iniles across. ples of Martian soil and rocks in a series of on-board
Temperatures on Mars range from near 32 degrees F chemical tests. The analyses were sent back to Earth. In
in summer in the early afternoon to -135 degrees F just what has been the most detailed search for life on Mars
before sunrise. The surfaces of the darker areas may be

An intriguing view of the alleged "face on Mars" taken by one of
A close-up of the great Martian volcano Nix Olympica. This volcanic the Viking orbiters in 1976. Subsequent pictures of the same area
mountain rises 15 miles above the surface and is more than 370 taken by later Mars orbiters left little doubt that this was only a
miles wide at its base. transitory wind-erosion effect. NASA