Page 26 - (DK) Eyewitness - Mars

Martian atmosphere

The “air,” or atmosphere, of Mars is much thinner
than Earth’s, and is 95 percent carbon dioxide. Earth’s
atmosphere is 78 percent nitrogen, 21 percent oxygen.
The average Martian surface temperature is a bitterly
cold minus 81°F (-63°C). In the upper Martian
atmosphere, water and carbon dioxide vapors freeze
and form high clouds. Other clouds appear over Mars
when springtime winds puff dust into the air, causing
great storms. Most of the grit settles down again, but
fine reddish dust stays suspended in the atmosphere’s
lowest level—the “troposphere.” Dust colors the sky a
LOSING AIR IN NOACHIAN TIMES rose-orange. In the polar regions, suspended dust
Billions of years ago, meteor impacts blasted away much
of the Martian atmosphere. Since then, air has continued mingles with icy vapors and turns to snowy frost
to escape because the planet’s gravity is just a third of that covers the ground.
Earth’s. Weak gravity allows gases to vanish into space.
Mars loses more atmosphere in winter, when carbon
dioxide freezes to the polar caps, but in spring the carbon
dioxide ice becomes a gas again.
MARTIAN ATMOSPHERE Structure
SUNRISE THROUGH A HAZE Composition
Martian air glows red in this artist’s view of dawn as
seen from orbit. Tiny particles bearing iron oxide float Carbon dioxide about 95% Thermosphere
in the atmosphere, absorbing and scattering blue light Nitrogen about 2.7%
but allowing red rays to get through. Mars’s 81 miles/
atmospheric pressure—the weight of its atmosphere— Argon about 1.6% 130 km
is only 1/143 of Earth’s.
Oxygen, carbon monoxide,
water vapor, and other Stratosphere Thin clouds of frozen
gases about 0.7% carbon dioxide
Clouds of water
25 miles/ ice particles
40 km
Troposphere
Suspended red, iron-rich dust;
fog of water ice particles