Page 36 - (DK) Eyewitness - Mars

Polar ice caps North
Polar Cap

After discovering the Martian polar
ice caps in 1666, astronomers watched
them grow larger in winter, smaller
in summer. Observers were sure this
was a freezing and melting process.
They thought Mars must be like
Earth, which has its own ice-
covered poles. Astronomers in the
19th century mistakenly believed
Martian canals were channeling
polar water to cities in drier regions.
In the late 20th century, space
missions showed the polar caps to
be encrusted with carbon dioxide
ice. The poles can be as cold as
195°F (-126°C). Over millions of years,
layer after layer of ice and dust have
been deposited on the poles. By drilling
through this ice, scientists may someday
study the layers and learn about changes
in the Martian climate.

SOUTH POLAR CAP
Viking 2 made this image of
the South Polar cap in 1977.
Permanently frozen, the carbon
dioxide ice cap stays about the
same size all year. Global
Surveyor data suggests a
subcap of water ice underlies
the cap. This water subcap is
not exposed because during
Mars’s closest approach to the
Sun the South Pole tilts away
and is in darkness.
0°W

HNu
Hd
HNu Apl Hd Nc

SOUTH POLE
90°W 270°W The white area on this
c
geologic map of the South
Pole represents carbon NORTH POLE OF MARS
dioxide ice deposits on the This artist’s illustration shows the Planum
region called Planum Australe. Boreum region, with the North Polar cap in
70°S Apl Blue areas are layered ice white. There are actually two caps, one
deposits—mixtures of soil, dust, permanent and one seasonal. The permanent
frost, and ice. Pink and purple cap, mainly water ice, is under a layer of
areas are smooth plains, and the carbon dioxide ice. This upper layer grows
Nc dark brown arc is the rim of the much larger in winter, then recedes as it
Prometheus impact basin. melts each summer.
180°W
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