The atmosphere of Mars is one hundred times less dense than that of the Earth. This makes the observation of its surface relatively easy.
Mars probably has a small core of solid iron. This is surrounded by a mantel of rock and a solid crust. The red colored Mars has been visited by numerous probes, which have provided detailed images of the planet's surface. Different types of landscape were found. While the northern hemisphere consists mainly of lower plains and relatively young craters, the southern hemisphere is covered by high plateaus featuring numerous large old craters.
There are huge volcanoes, which are, however, no longer active. The highest peak is Mons Olympus. It is 27,000 meters high and has a diameter of 600 kilometers. Its mighty lava streams can be traced for hundreds of kilometers.
Not far from it lies the Tharsis region with Arsia Mons, Ascraeus Mons and Pavonis Mons. A huge mass of lava with a height of 6000 meters has formed here. South of that lies a great trench which stretches for over a sixth of the entire circumference of Mars (approx. 5000 kilometers). It is over 100 kilometers wide in places.
Three probes passed Mars in the 1960s, revealing only a barren landscape of craters. In 1971, Mariner 9 examined Mars again and came up with a surprise. Besides clefts and craters, channels and furrows were discovered, which could only have been formed by water.
Should water have existed in its liquid form on Mars, then the planet must once have been cloaked in a denser and warmer atmosphere. It probably contained a high percentage of carbon dioxide, which caused the temperature to fall so drastically that the water was trapped in the crust as permafrost. Had any life existed on Mars, the strong UV radiation from the Sun would have killed it.
In 1976 two Viking_probes with laboratories on board were launched in a renewed attempt to find life on Mars. However, after the final analysis the results were negative.
The red appearance of Mars is explained by the soil samples, which were taken at that time. The water that once existed on the surface had a high iron content, and left behind rust particles when it froze into the ground. In 1996, the Global Surveyer Mars probe was launched. It reached the planet's orbit in September of that year and mapped the surface of Mars by means of special camera. First results also indicate that, contrary to earlier opinions, the planet actually does have a magnetic_field. Further Mars missions are planned by NASA. Japan and Russia also plan to send probes to Mars.
