The Topography of Mars
Earth vs. Mars
Although often described as a desolate planet, Mars is full of stunning topographical suprises. Earth's Grand Canyon and Mount Everest are impressive, but they are nothing next to Valles Marineris and Olympus Mons, their counterparts on Mars. Though the Red Planet is only half the size of the Earth, the sheer size of its geographic features are amazing. To better understand the scale we're talking about, we need to take a tour of Mars' surface, which has two types of regions separated by a ridge of mountains. To the north are lowlands, whose topography has been shaped by lava flows that have made the surface smooth. The south, in contrast, is mountainous, with many meteorite impact craters, some of which are enormous.
Let's begin our guided tour with Olympus Mons, which would dwarf Mount Everest were they to be placed side by side. Olympus Mons, which means Mount Olympus, takes its name from the home of the ancient Greek gods. At 27 km high, three times taller than Everest, it is, in fact, the tallest mountain known to exist anywhere in the solar system. Olympus, which is of volcanic origin, is by no means the only huge mountain on Mars. The Tharsis plateau where Olympus Mons is located is home to three more volcanoes, each more impressive than the last. Earth's mountains seem to pale in comparison.
Named after the Mariner 9 science team Valles Marineris is also much larger than the Earth's Grand Canyon. The Valles Marineris, or Mariner Valley, is about four times deeper and nine times longer than the USA's Grand Canyon. It also has a subsystem of smaller canyons that extend over more than a fifth of the planet's surface. As far as we know, this makes Mars home to the largest canyon in the solar system.
Among Mars' other huge geographical features is the Hellas Planitia impact basin. This giant impact crater is thought to have been formed 3.9 billion years ago when an enormous meteorite collided with Mars. With a diameter of 2300 km, Hellas Planitia (Latin for "the Plains of Greece") is the largest crater on Mars. At nine kilometres deep, it is also the planet's lowest point, four kilometres below reference level. That reference level, called the datum, is comparable to mean sea level on Earth and has been established using pressure and temperature data. The difference between the highest and lowest points on Mars, Olympus Mons and Hellas Planitia, is 31 km, whereas barely 20 km separates the summit of Mount Everest from the bottom of the Mariana Trench.
The plains of Mars fall into two categories: the planitiae and the maria. Although there is no water on Mars, some regions are called maria (Latin for "seas"), because the first astronomers believed they were under water. Far from being flooded, the surface of these regions is rocky and covered with stones, which makes them look darker. The best known of these dark regions are Mare Erythraeum, Mare Sirenum, Aurorae Sinus and Syrtis Major, the latter being the largest dark region visible from Earth. Syrtis Major apparently owes its name to Herschel, a famous astronomer who thought its shape resembled that of a dog. The lighter regions are called planitiae or plains, which accounts for their names, Arabia Terra and Amazonis Planitia. These vast areas are thought to be covered in dust and sand rich in iron oxide. Strong winds that blow the sand and dust around can change the configuration of these dark and light plains, forming new patterns on the surface of Mars. However, the planet's features do remain relatively unchanged over the years.
This description of the topography of Mars, also called areography, was made possible by the Mars Global Surveyor and Mars Reconnaissance Orbiter probes, which have been mapping the Red Planet since 1996. Our knowledge of Mars' impressive topography stretches back just over ten years. This allows us make precise choices when it comes to landing sites for the various missions to Mars, thereby ensuring that Mars probes land successfully.
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