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Mars is the fourth planet from the Sun and is
commonly referred to as the Red Planet. The rocks, soil and sky have a red or pink hue.
The distinct red color was observed by stargazers throughout history. It was given its
name by the Romans in honor of their god of war. Other civilizations have had similar
names. The ancient Egyptians named the planet Her Descher meaning the red one.
Before space exploration, Mars was considered the best candidate for harboring
extraterrestrial life. Astronomers thought they saw straight lines crisscrossing its
surface. This led to the popular belief that irrigation canals on the planet had been
constructed by intelligent beings. In 1938, when Orson Welles broadcasted a radio drama
based on the science fiction classic War of the Worlds by H.G. Wells, enough people
believed in the tale of invading Martians to cause a near panic.
Another reason for scientists to expect life on Mars had to do with the apparent seasonal
color changes on the planet's surface. This phenomenon led to speculation that conditions
might support a bloom of Martian vegetation during the warmer months and cause plant life
to become dormant during colder periods.
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In July of 1965, Mariner 4, transmitted 22 close-up pictures of Mars. All that was
revealed was a surface containing many craters and naturally occurring channels but no
evidence of artificial canals or flowing water. Finally, in July and September 1976,
Viking Landers 1 and 2 touched down on the surface of Mars. The three biology experiments
aboard the landers discovered unexpected and enigmatic chemical activity in the Martian
soil, but provided no clear evidence for the presence of living microorganisms in the soil
near the landing sites. According to mission biologists, Mars is self-sterilizing. They
believe the combination of solar ultraviolet radiation that saturates the surface, the
extreme dryness of the soil and the oxidizing nature of the soil chemistry prevent the
formation of living organisms in the Martian soil. The question of life on Mars at some
time in the distant past remains open.
Other instruments found no sign of organic chemistry at either landing site, but they did
provide a precise and definitive analysis of the composition of the Martian atmosphere and
found previously undetected trace elements.
Atmosphere
The atmosphere of Mars is quite different from that of Earth. It is composed primarily of
carbon dioxide with small amounts of other gases. The six most common components of the
atmosphere are:
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Carbon Dioxide (CO2): 95.32%
Nitrogen (N2): 2.7%
Argon (Ar): 1.6%
Oxygen (O2): 0.13%
Water (H2O): 0.03%
Neon (Ne): 0.00025 %
Martian air contains only about 1/1,000 as much water as our air, but even this small
amount can condense out, forming clouds that ride high in the atmosphere or swirl around
the slopes of towering volcanoes. Local patches of early morning fog can form in valleys.
At the Viking Lander 2 site, a thin layer of water frost covered the ground each winter.
There is evidence that in the past a denser martian atmosphere may have allowed water to
flow on the planet. Physical features closely resembling shorelines, gorges, riverbeds and
islands suggest that great rivers once marked the planet.
Temperature and Pressure
The average recorded temperature on Mars is -63° C (-81° F) with a maximum temperature
of 20° C (68° F) and a minimum of -140° C (-220° F).
Barometric pressure varies at each landing site on a semiannual basis. Carbon dioxide, the
major constituent of the atmosphere, freezes out to form an immense polar cap, alternately
at each pole. The carbon dioxide forms a great cover of snow and then evaporates again
with the coming of spring in each hemisphere. When the southern cap was largest, the mean
daily pressure observed by Viking Lander 1 was as low as 6.8 millibars; at other times of
the year it was as high as 9.0 millibars. The pressures at the Viking Lander 2 site were
7.3 and 10.8 millibars. In comparison, the average pressure of the Earth is 1000
millibars.
For new pictures of the surface of Mars from
the Spirit Rover Mission please
click here.
New pictures of the planet Mars
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