Did you know...
...that evidence from the Mars Pathfinder mission suggests that the surface of Mars was subject to massive flooding at one time in the planet's ancient past?
...that the "canals" of Mars, now known to be an optical illusion, were once touted as evidence of extraterrestrial intelligence?
...that Mars has a volcano (Olympus Mons) which is 500-600 km in diameter and 25 km high?
...that the number of UFO sightings consistantly increases when Mars is nearest to Earth?
...that scientists named some of the rocks they found near the two Viking landings?
Mars, often called "The Red Planet," is the fourth closest planet to our Sun. Its scarlet hue caused it to be named for the Roman God of War. In size, Mars has about half the diameter of Earth and twice that of the Moon. In pre-Space Age times, people thought that Mars must be almost exactly like Earth. The perception of Mars was of a planet with its own polar ice caps and water supply, temperatures like our planet, and possibly even life.
Don't let the red color fool you; Mars is actually a cold planet. Mars travels in a pretty eccentric orbit, which means that at times it is far from the Sun, making it even colder. The angle of Mars's axis is such that it has four seasons. Of course, a year on Mars is about 23 of our months long, and its 6-month winter gets down around -100 degrees Celsius!
The surface of Mars, at first glance, looks cratery like the Moon or Mercury. If you take a closer look, you'll find many more complex features on it. Mars's surface is probably one of the most complex and interesting in the solar system. Volcanic and tectonic marks show that the surface underwent dramatic lava eruptions many millions of years ago. Mars has a large bulge (around 4000 km) named Tharsis. Another notable feature on Mars's surface is Olympus Mons, which is 24 km tall.
There is a lot of evidence to suggest that Mars once had water on its surface. Stream beds and canyon channels are abundant, but they are now empty. The water that used to be on Mars's surface could have come from an icy meteorite landing on the surface or volcanic eruptions. There certainly aren't any oceans around now. In fact, if you picked up one of Earth's oceans and dropped it down on Mars, it wouldn't last long because of Mars's unstable atmospheric and thermal conditions.
Mars does have an atmosphere, but it is much different from Earth's. It is almost all carbon dioxide. There are traces of oxygen and water vapor in the atmosphere, but only very small amounts. Mars got its atmosphere from the gas released by volcanoes, just as Earth did. In some seasons, the carbon dioxide in the atmosphere gets so cold that it freezes into frosty solid globs of dry ice. Clouds and even cyclones occur in Mars's atmosphere. But overall, the atmosphere is much thinner and less stable than Earth's.
Mars has two moons, Phobos and Deimos. Phobos is the closer and larger of the two. Does the name "Phobos" sound scary to you? Well, it should. The word "phobos" meant "fear" to the Romans; kind of like "phobias" in English. Phobos was the name of the mythological character who drove Mars's chariot. Phobos and Deimos are two of the ugliest moons around. Deimos looks like a giant potato, and Phobos looks like an egg-shaped asteroid.
Mars Today - NASA site, info
The Planet Mars: History of Observation and Discovery - Online Book
Planet Mars - Exploration & Missions
* Photo credit - NSSDC Photo Gallery