Mars is the fourth planet from the Sun and the seventh
largest, much smaller than the Earth. Despite this small size, it has
a surface area that is about the same as the land area on Earth, so there
is plenty to explore! Not only this, but Mars has perhaps the most varied
and fascinating landforms of any of the rocky planets outside of the Earth.
These include the largest volcano in the solar system (Olympus Mons),
a massive canyon system called Valles Marineris that would stretch across
the entire North American continent, and Hellas Planitia, a huge impact
crater that would stretch halfway across North America! Mars is also famous
for its startling dichotomy: most of the craters are located in the Southern
hemisphere, while the plains and volcanoes are in the Northern hemisphere.
Unlike the Earth, Mars appears to lack active plate tectonics, and there
is no evidence of mountain building similar to that which we see on our
Mars follows a very elongated orbit around the Sun,
and therefore suffers from a large temperature variation throughout its
687 day long year. A Martian explorer would have to be equipped to cope
with temperatures ranging from as little as 133 K (-140 C, -220 F) to
almost 293 K (20 C, 70 F), depending on where they are and what time of
year it is. The average temperature is about 218 K (-55 C, -67 F). Mars
does not have a breathable atmosphere, so any explorer would have to be
equipped with breathing apparatus that would last for the full duration
of the mission. The Martian atmosphere is composed mostly of carbon dioxide
(95.3%) plus nitrogen (2.7%), argon (1.6%), oxygen (0.15%) and water (0.03%).
The average pressure on the surface of Mars is just 7 millibars (less
than 1% of Earth's), but varies with altitude, and is thick enough to
produce very strong winds and vast dust storms that have been know to
smother the entire planet for months.
As with the Earth, ice caps are present at both Martian
poles. On Mars, the ice caps are composed mostly of `dry ice' (frozen
carbon dioxide), although layers of water ice are also known to be present
in the North. It is not known if similar layers exist in the South. Many
scientists think that ther may also be water ice below the surface at
There is very clear evidence that, early in its history,
Mars was much more like Earth. Many of the surfaces show signs of water
erosion, including large floods and small river systems, so it is fairly
obvious that there was water on the surface at some time in the past.
This may even have taken the form of large lakes or oceans, but it does
not appear to have lasted long, and occurred a very long time ago (probably
about 4 billion years ago). This raises the possibility that at one time
the conditions necessary for life to originate were present on Mars. The
Viking landers performed experiments to try to determine the whether or
not life existed on Mars, with somewhat arguable results.
The interior of Mars cannot be observed directly,
and is difficult to estimate without carrying out extensive work on the
ground. However, scientists predict that the most likely scenario is a
dense core surrounded by a molten rocky mantle (probably a little denser
than the Earth's) on top of which is a thin crust.
Mars also has two tiny moons, called Phobos and Deimos,
which orbit very close to the surface. For further background reading
on Mars, see The Nine Planets webpages. This site also has several links
to other excellent pages on Mars.
Some questions that might be answered by sending a
manned mission to Mars are:
- Is there still active volcanism on Mars?
- How much water is there?
- Is, or was there any life on Mars?
- Are we yet able to send people as far afield as
- Do we have the technology to set up a semi-permanent
base on another world?
Try to think of some more yourself, and think of ways
we may be able to answer them…
Comparison of the landmasses of
Earth and Mars