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Volcanic Places on Mars

Mars is only about one-half the size of Earth and yet has several volcanoes that surpass the scale of the largest terrestrial volcanoes. The most massive volcanoes are located on huge uplifts or domes in the Tharsis and Elysium regions of Mars. The Tharsis dome is 4,000 kilometers (2,500 miles) across and rises to 10 kilometers (6.2 miles) in height. Located on its northwest flank are three large shield volcanoes:

Ascraeus Mons, Pavonis Mons and Arsia Mons. Beyond the dome's northwest edge is Olympus Mons, the largest of the Tharsis volcanoes. Sattellite image Olympus Mons is classified as a shield volcano. It is 24 kilometers (15 miles) high, 550 kilometers (340 miles) in diameter and is rimmed by a 6 kilometers (4 miles) high. It is one of the largest volcanoes in the Solar System.

By comparison the largest volcano on Earth is Mauna Loa which is 9 kilometers (6 miles) high and 120 kilometers (75 miles) across.

Mars has many interesting geological features on its surface that first became apparent with Mariner 9, were subsequently studied by the Viking missions, and many of which now are visible from the Hubble Space Telescope. Enormous Shield Volcanoes In the previous section we saw an image of Mars with 3 large volcanoes on the left limb of the image. The volcanoes on Mars are now extinct, but they indicate a preceding period of significant Martian volcanism. Such volcanoes are called shield volcanoes, because they look like shields.

For reference, the largest shield volcano on the Earth is Mauna Loa, which is only about 200 km across its base, and the 25 km height of Olympus Mons is about 2 1/2 times the height of Mount Everest. This raises the interesting issue of why Mars in its past developed a few very large shield volcanoes, while on the Earth the more normal pattern is for volcanoes to develop in strings of smaller volcanoes. As we shall see, the answer is thought to lie in plate tectonics

Mars has its fair share of volcanic landforms, including the largest known volcano in the solar system, Olympus Mons

The Interior of Mars

The current understanding of the interior of Mars suggests that it can be modeled with a thin crust, similar to Earth's, a mantle and a core. Using four parameters, the Martian core size and mass can be determined. However, only three out of the four are known and include the total mass, size of Mars, and the moment of inertia. Mass and size was determined accurately from early missions. The moment of inertia was determined from Viking lander and Pathfinder Doppler data, by measuring the precession rate of Mars. The fourth parameter, needed to complete the interior model, will be obtained from future spacecraft missions. With the three known parameters, the model is significantly constrained. If the Martian core is dense (composed of iron) similar to Earth's or SNC meteorites thought to originate from Mars, then the minimum core radius would be about 1300 kilometers. If the core is made out of less-dense material such as a mixture of sulfur and iron, the maximum radius would probably be less than 2000 kilometers.