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Mars
in Society and Culture 
Mars
has always played a significant role in human
society. The early Greeks noted that unlike the
other planets, Mars sometimes seemed to reverse
its direction across the sky. This
"contrary" motion suggested disorder
and anarchy to the Greeks, which, along with its
reddish color, led them to name the planet after
Ares, their god of war. The Romans later changed
the planet’s name
to that of their god of war, Mars, and the name
has remained ever since.
Read
History in
"Solar System" page to know how
Mars helped us understand the motion of planets.
Also
Read Explorers on
the red Planet: Man to Mars
{Below-
Related links and photos.}
Background
Mars
has attracted the attention and imaginations of
observers for thousands of years. The first
serious observations of the Martian surface were
conducted by Schiaparelli in 1877, whose work
was expanded upon by Lowell in 1890. Until the
dawn of the space age in the early 1960’s,
telescopic observations were the only way we
could study Mars. Even the best telescopes,
however, must still look up through the Earth’s
atmosphere in order to see out into space. It’s
a lot like trying to watch clouds from the
bottom of a swimming pool: the objects are
there, but they are fuzzy, wavering, and hard to
make out. If we want to conduct serious
observations of another planet, we need to go
there.
Mars
In Solar System
Mars
is a world of puzzles. It is both very similar
to and very different from our own Earth. Mars
is the fourth planet from the Sun and orbits at
a distance one and a half times that of Earth’s
orbit. As a result, Mars receives much less
light and heat from the Sun than the Earth does,
so it is much colder. Also, unlike the Earth,
Mars has a very thin low-pressure atmosphere
which is unable to retain what heat it does
receive. Because of the temperatures and
pressures on the Martian surface today, water
cannot exist in liquid form. Mars today is
therefore a dry, frozen desert.
Similarities
and Differences--Earth and Mars
Mars is similar to earth in a number of
important ways. It has an axial tilt of 23.98
degrees, very similar to Earth's 23.44 degrees.
Mars therefore has seasons, just like Earth,
with cold winters and warm
summers. mars' rotation period, its
"day", is 24 hours, 37 minutes again
almost exactly the same as Earth's. Like Earth,
Mars has ice caps at both poles. It has clouds,
winds, dust storms, volcanoes, and channels. For
many years, Venus was considered as twin of
Earth. Unlike Mars, Venus is very similar in
size and mass as Earth and therefore has very
similar gravity. But Venus is a hothouse,
with temperatures soaring to hundreds of degrees
centigrade and atmospheric pressures high enough
to crush our toughest metals like tin cans.
Mars, on the other hand, could one day
conceivably be changed to be more like Earth
through advanced engineering known as
"terraforming". In many aspects Mars
is a much hospitable environment than Venus,
making it an obvious target for our
imaginations.
But Mars is very different from Earth as well.
Surface temperatures on Mars range from hundreds
of degrees centigrade below zero in winter to
nearly freezing (0º
C) in the summer. Because Earth's orbit is
nearly circular, our seasons are virtually the
same in both hemispheres. Mars travels in more
elliptical orbit around the sun than does the
other planets, so it is 20% closer to the Sun
during southern summer than it is in Northern
summer. This results in very long, relatively
warm southern summers and very long, cold
northern winters. Mars has an atmospheric
pressure less than seven -tenths of one percent
of Earth's, far too low to sustain most forms of
life as we know it. The Southern ice cap is
mostly of frozen Carbon dioxide (dry ice), not
water. Much of the surface of Mars is covered
with craters much like the Moon. All of these
differences make Mars a world unto itself,
rather than twin of Earth or other planet.
The northern and southern hemispheres of Mars
are very different. In general, the south is
heavily clustered, while the north is made up
mainly of smooth dark plains. There are many
exceptions to this general rule, for example,
Hellas Planitia (planitia are smooth, low plains
or basins) lies in southern hemisphere and, at 3
km below "datum", is the deepest basin
on Mars.
The word "datum" is used rather than
"sea level" because, obviously, mars
currently has no seas! the datum is defined as
the altitude at which the atmospheric pressure
is 6.1 millibars (6.1 thousandths of the sea
level pressure on Earth). The planet isn't
either. There is a very large bulge in the crust
located around 113º
west longitude. This region, called the Tharsis
Bulge, is home to the largest volcanoes on Mars
– and in the entire Solar System. The southern
hemisphere reveals the ancient cratering record
of impacts early in the Solar System’s
history. On Earth, this record has been
virtually erased by the effects of volcanoes,
wind, and water. Planets such as
Mercury died young, ceasing geological activity
not long after the period of major impacts.
Mars, however, was geologically active for most
of the life of the Solar System – the great
volcano Olympus Mons was probably active just
thirty million years ago – so has examples of
young terrain in the north right alongside the
ancient cratered terrain in the south. In many
ways, Mars uniquely records the history of the
Solar System in its surface features.
SOURCE-JPL(NASA)
& ASU
Picture Olympus Mons from GSFC
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