Anatomy of Mars Help (page 2)
Introduction to the Anatomy of Mars
The Red Planet is about 53 percent the diameter of Earth, roughly 6,800 kilometers (4,200 miles). This would put Mars neatly between Earth and the Moon in size if the three orbs could be lined up next to one another (Fig. 6-2). If you were to stand on Mars and look toward the horizon, you would see a strangely foreshortened vista. Similarly, standing on top of one of the highest mountains, you would be able to perceive the curvature of the planet.
The smaller size of Mars, combined with a density somewhat lower than that of Earth, produces a less intense gravitational field than the one we know. Your weight on Mars would be 37 percent of your weight on Earth. If you weigh 160 pounds here, you would weigh 59 pounds there. You would be able to throw a baseball much farther on Mars than you can on Earth. While golf-loving astronauts might not be able to drive a ball as far on Mars as they did on the Moon, they would do better than they can on Earth. A golf course on Mars would have to be much larger than one on Earth, and to make things more interesting, there would be no shortage of boulders and sand traps.
There is evidence that the crust of Mars is thicker than that of Earth. There is also evidence that the Martian mantle historically has been less active than that of Earth.
The surface area of a sphere is proportional to the square of the diameter, whereas the volume is proportional to the cube of the diameter. Mars, being approximately half the diameter of Earth, has one-quarter the surface area but only one-eighth the volume. This means that the surface-area-to-volume ratio of Mars is twice as great as that of Earth, causing Mars to cool off faster after its formation along with the rest of the Solar System. All these factors have combined to create a world where the crust does not move very much.
On Earth, crustal plates float around over the mantle, so volcanoes move gradually away from the hot spots underneath. On Mars, however, little or no such movement has occurred, so some volcanoes have built themselves up to enormous proportions. The crowning glory of the Martian volcanoes is Olympus Mons (Mount Olympus), which is 24 kilometers (15 miles) tall and measures 600 kilometers (370 miles) in diameter at its base.
Mars is pitted in some places with impact craters. In fact, when Mariner 4 took the first close-up photographs of Mars in 1965, coming within 9,800 kilometers (6,100 miles) of the surface, craters seemed to dominate the landscape. This led astronomers to believe that Mars might be as desolate as our own Moon. It was up to later missions to demonstrate otherwise. An entire planet cannot be characterized by looking at only one spot. Suppose an alien civilization were to send a probe past Earth and happened to obtain photographs of only the Sahara Desert?
The southern hemisphere of Mars consists of highlands, and this is where most of the impact craters are found. The northern hemisphere, in contrast, is several kilometers lower in elevation and appears flooded over by the lava from volcanic eruptions. Various parts of the surface have a dusky gray, almost green appearance. This greenish cast was seen by the first people who looked at Mars through “spy glasses.” The dark regions, along with illusory straight dark lines that seemed to lead from them toward the polar ice caps, led some respected scientists to believe that Mars must be home to an intelligent civilization.
Numerous probes followed Mariner 4 , and with each new set of photographs and data, the hope for finding life on Mars diminished. Many scientists believe there is an abundance of water locked up on Mars in the form of permafrost beneath the surface. Some water ice also appears in the polar caps. In addition to water ice, during the polar winters there is frozen carbon dioxide (dry ice) in the polar caps, particularly the southern cap, which endures a longer winter.
Dried-up riverbeds are the most interesting features seen on the surface of Mars. After careful analysis, most geologists have agreed that these marks could only have been made by running water. One theory is that Mars was at one time covered to some extent by a shallow sea or perhaps by large glaciers that melted during a series of volcanic eruptions.
Atmosphere And Weather
Mars has oxygen, but almost all of it is bound up with elements in the surface and with carbon in the atmosphere. The result is a rusty world, with an atmosphere consisting almost entirely of carbon dioxide (CO 2 ). The barometric pressure at the surface of Mars is less than 1 percent of the pressure on Earth. Were it not for the fact that CO 2 is a heavy gas, the atmosphere of Mars would be even thinner than this.
Despite the thin air on Mars, weather occurs, and it can be extreme. Winds aloft can reach speeds of around 400 kilometers per hour (250 miles per hour); near the surface, they commonly rise to 120 kilometers per hour (75 miles per hour). It would be a mistake to say that such winds are of “hurricane force” because the thin air on Mars produces far less wind pressure for a given wind speed than the air on Earth. However, dust particles from the surface are picked up and travel right along with the wind, blowing high up into the atmosphere, where they at times shroud the planet completely. During these massive dust storms, which can be accompanied by lightning, the surface features of the planet practically disappear. As seen from the surface, such a storm would produce a dark red sky, obscuring the sun and casting an evil gloom over the landscape.
One of these planetwide dust storms was indirectly responsible for the discovery of the four largest Martian volcanoes. These include Olympus Mons (already mentioned as the largest mountain on the planet), Ascraeus Mons, Pavonis Mons , and Arsia Mons . As the storm abated, the dust gradually settled. The peaks of the volcanoes were seen first; more and more of them appeared as the Martian sky regained its characteristic clarity.
High clouds, similar to cirrostratus and cirrus clouds on Earth, are sometimes observed on Mars. In addition, Olympus Mons is occasionally shrouded in a thin veil of cloud, in much the same way as high mountains are cloud-covered on Earth. These Martian clouds are far less substantial than their Earthly counterparts, and scientists doubt that they produce much, if any, precipitation. However, they do produce a sort of fog at the top of Olympus Mons. Standing inside the caldera of this monstrous mountain on a foggy morning, you might for a moment imagine yourself in the Namib Desert on the southwestern African coast.
Practice problems of this concept can be found at: Mars Practice Problems
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