Observing Projects 8E Surveying the Martian Geography Quadrant 2 Centered on 135 Degrees

In this project, we'll continue highlighting surface features on Mars, this time moving 90 degrees further to the west. Here is where we find Mars' most dramatic surface features. Here we are looking at Mars with the 135-degree meridian centered and we are scanning the surface 45 degrees either side of the central meridian.

At about 30 degrees south latitude is a large dark area called Mare Sirenum. This is a rugged and heavily cratered highland zone. This is the most prominent feature in this quadrant that is easily visible. On the extreme northwest edge of Mare Sirenum is a 130-kilometer wide ancient crater called Gusev. Here scientists studying images from Mars Global Surveyor believed that they have viewed the telltale signs of flowing water on the ancient surface and for this reason the crater was targeted as the first landing site for the Mars Exploration Rover Program. The rover Spirit bounced to a landing here on the night of January 4, 2004. South of Mare Sirenum the terrain brightens again rapidly as we come to a higher region called Phaethontis. As you scan further south towards the polar region, the terrain gives way to the flat area that we saw in quadrant one, Mare Australe, which extends about one-third of the way around the planet from where we saw it originate.

Scanning back to the equator is where we find Mars' crowning glory of features. The Tharsis Montes are three of the largest volcanic structures in the solar system and they would be the largest if it were not for what looms to the northwest. The three Tharsis volcanoes each tower twice the height of Mount Everest and each would completely cover the state of New York. These are called shield volcanoes. They are built up from below by magma pushing up weak spots in the Martian curst. On Earth, the ability of such mountains to build is limited by the presence of tectonic motion in the crust, which over millions of years will carry the building volcano away from the hot spot in the mantle beneath it. But on Mars there are no plate tectonics so the Tharsis range was able to build for as long as the volcanic pressures were present because the building mountain never moves. The mountains however barely subtend one arc second when Mars is at a median opposition diameter. That is big enough to be viewed in an 8-inch or larger telescope but conditions need to be perfect. Yet there is something bigger still to see.

Just to the northwest of the Tharsis is the solar system's largest mountain, Olympus Mons. Olympus Mons is thrust up on a base which itself towers more than a kilometer above the surrounding plains. The total height of the caldera above the surrounding plains is more than 80,000 feet and the volcano is large enough to cover the entire state of Texas! Olympus Mons was formed in the same manner as the Tharsis Montes. The uplifting of these four mountains stretched and split the Martian crust and created the Valles Marineris over to the east. This was a blow to those who thought that the massive canyon system might have been formed by flowing water.

Several large plains sit to the north of Olympus Mons. The large dark area is called Arcadia. Arcadia appears to be flat and smooth like much of the rest of the Martian lowlands. Arcadia is shaped like a downward pointing arrowhead coming out of the north polar region. The bright area to the east of Arcadia is a plain called Ceraunius. The bright area to the west of the arrowhead is called Diacria. All of these areas are part of the Martian northern lowlands. North of this area, low flat plains continue until reaching the polar cap area.

After viewing the first half of the Martian surface, one interesting thing becomes apparent. The color of the terrain seems to have little bearing upon its elevation. Dark markings appear at both highlands and lowland areas of the planet. The difference in relative reflectivity of the rock and dust of that given area is what causes the dark markings. Though Mars is a small world, half the size of Earth, that has not stopped it from building geological features that are Olympian in size.

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