IS MARS LIKE OUR EARTH?

[font:441e=&quot]Mars is the fourth planet
from the Sun in our Solar System. It looks like a reddish star in the sky. Mars
is named after the god of war in Roman mythology. Its red colour and the
strange markings that can be seen with a telescope have fascinated people for
centuries. Early science-fiction stories invented Martians that lived there,
but several spacecraft have visited the planet without finding one. Scientists
are still working on the question: is there life on Mars?[/font]


[font:441e=&quot]Mars is 227.9 million
kilometres from the Sun—about one-and-a-half times as far away from the Sun as
we are. Its diameter is just over half that of Earth. It has two moons—Phobos
and Deimos. They are oddly shaped rocky bodies and are probably captured
asteroids.[/font]


[color:441e=#FFC000][font:441e=&quot]IS MARS LIKE OUR EARTH?[/font][/color]


[font:441e=&quot]In some ways, Mars does seem rather like our
own planet. Mars takes about the same time as the Earth to turn on its axis,
although it takes a bit longer to go round the Sun—nearly two of our Earth
years. Mars has icy polar caps that grow bigger in winter and shrink in summer,
though they are made mainly of frozen carbon dioxide, not frozen water. In 1976
the American Viking Lander spacecraft sent back pictures of the surface that
show reddish rocks, a pink sky and a landscape that could be a desert here on Earth.
Mars has old volcanoes, ridges, canyons and what look like dried-up river beds,
rather like parts of Earth. Yet in other ways, Mars is very different.[/font]


[color:441e=#FFC000][font:441e=&quot]WHAT IS IT LIKE ON MARS?[/font][/color]


[font:441e=&quot]The atmosphere of Mars is thin, and mainly made up
of carbon dioxide. There is a big difference in temperature between night and
day, but on average it is very cold, about -33 degrees Celsius. Much of the
surface is littered with rocks and fine dust, eroded from old volcanic craters.
Sometimes the wind whips up the dust into big dust storms. The red colour of
the rocks comes from the surface reacting with oxygen. It is a kind of rusting.[/font]


[font:441e=&quot]Since 1999 astronomers have been building up a detailed
map of the surface of Mars. The American space agency NASA sent the Mars Global
Survey spacecraft into orbit around the planet and it has sent back some
astonishing views. Craters cover much of the south of the planet, and parts of
the north seem to be covered by volcanic lava flows. There are huge extinct
volcanoes in the region called Tharsis—the biggest is called Olympus Mons.
Another amazing sight, south of the Martian equator, is Valles Marineris, a
spectacular system of canyons.[/font]


[font:441e=&quot]Mars shows lots of signs of activity in the
past, from volcanoes, and from water—the signs of sudden floods and edges of
what may once have been lakes. Today it seems to be cold and dead, just a big
wind-blown desert.[/font]


[color:441e=#FFC000][font:441e=&quot]IS THERE LIFE ON MARS?[/font][/color]


[font:441e=&quot]There is no evidence for life on Mars at all at
the moment. The atmosphere is so thin that it cannot block ultraviolet light from
the Sun, as our ozone layer does on Earth. Strong ultraviolet light would
damage life. It is also too cold for liquid water to exist on the surface. The
Viking Landers, and Sojourner, a little robot rover sent out by Mars Pathfinder
in its 1997 landing, all tested the Martian soil. None of the samples they
tested showed any trace of the organic (carbon-based) molecules connected with
life.[/font]


[font:441e=&quot]In 2002 another spacecraft, Mars Odyssey, discovered
crystals of ice (frozen water, not the usual frozen carbon dioxide) just under
the Martian surface. New missions will go to Mars to probe further. There may
not be any Martians, but perhaps they may find some Martian bacteria. Even that
would be a very big discovery. It would show that life has also evolved outside
our Earth.[/font]


[b][font:441e=&quot]Microsoft Encarta 2007.
1993-2006 Microsoft Corporation. All rights reserved.[/font][/b]