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© Copyright 2000, Jim Loy
Above is a map of Mars, apparently prepared from Viking Orbiter images. I have adjusted the color, and labeled a few features. The three most amazing features are the polar ice caps (not shown), Olympus Mons (a huge shield volcano), and the Valles Marineris (a huge canyon). The Tharsis Montes is a string of three volcanoes. Elysium Mons is a volcano. The Planatia are planes, the Terras are rougher highlands. There are quite a few impact craters. I have labeled three large ones, Cassini, Schiaparelli, and Huygens.
At one time, Mars was considered likely to have life on it. A few astronomers saw canals, often running straight for thousands of miles. Mars' surface darkened during the summer. Clearly that showed plant life. But Mars turned out to be the coldest, driest of deserts, with not enough air to support life. There is now no evidence of plants. There are no canals. So why did people see canals? Mostly, it was probably wishful thinking. A person can see strange things just at the limit of visibility.
Mars is called the red planet. It looks red from Earth,
and its soil and rocks are mostly reddish in color, from iron oxide. Mars has a
little over half the diameter of Earth. That makes its surface area a little
over one-fourth that of Earth. Since much of the Earth is covered with water,
Mars actually has almost as much land area as Earth. There are unmistakable
signs that there was water on Mars in the relatively recent past. Apparently
underground water has been melted now and then, to gush out and flow on the
surface before evaporating. Prominent features are a few volcanoes (including
Olympus the tallest mountain known in the universe), the Valles Marineris
(Mariner Valley shown above left in a photo from NASA's Viking 2 orbiter) a
huge thousand mile long canyon, and many meteor craters. The poles are covered
in white, probably both water ice and carbon dioxide ice. The atmosphere is
very thin, and mostly carbon dioxide. There are sometimes huge, planet-wide
dust storms.
Mars has two tiny, oblong shaped moons (Phobos and Diemos), probably captured minor planets (asteroids). They were discovered by Hall, in 1877. Phobos orbits mars in less than one martian day, while Diemos orbits in more than one day; so from the surface of Mars, they appear to be going in opposite directions.
There are still chances that there is some life on Mars. The clues are few, but ambiguous. We will have to wait and see.
The seasons vary greatly in length and from northern
hemisphere to southern hemisphere, because of the tilt of the planet, and
because of the great eccentricity of the orbit. In the north, summer lasts 183
days (but it is cooler than the southern summer because the sun is much farther
away), and winter lasts 158 days. And the polar ice caps vary greatly in size.
On the right is a particularly good photo taken from Earth (from
Broderbund's ClickArt).
Here are some data about Mars: