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1404 Lesson 9 Article 4 Mars.docx - Article 4: Mars General...

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Article 4: MarsGeneral CharacteristicsNo other planet has stirred the imagination of Earth-bound writers as much as Mars,with more fiction having been written about Mars than any other planet. In 1877,Giovanni Schiaparelli described dark surface markings seen in telescopic observationsas “canali” – Italian for channels. Later observers translated this word as “canals,” whichsuggested structures had been engineered and built, but by whom? The possibility oflife on Mars dominated the conversation during the early part of the 20th century. Today,Mars is probably one of the best-explored planets in the solar system, thanks to themany spacecraft that still operate on its surface. Although there are no “little greenMartians,” there is a serious effort to find signs of water that may indicate past bacteriallife.Perhaps our fascination with Mars has to do with its similarity to Earth. It has an axial tiltof 25 degrees, which gives it seasons much like our own. Polar ice caps that grow andshrink have been well-documented. Its revolution period is 1.88 years, which isunderstandable since its orbital distance is 1.5 AU. It takes 24 hours and 37 minutes tomake one rotation, and a Martian day is called a “sol.”While these physical properties make it quite like Earth, it is quite unlike Earth in someother respects. Its size is considerably smaller, its radius being about half that of Earth.Its mass is only 11% of Earth's mass, hence its density is considerably lower, 3.9 g/cm3.The Earth seems sandwiched between two planets that are like it in some respects, butvery different in others. There are not many similarities between Mars and Venus either.Surface FeaturesImages of Martian landscapes can easily be mistaken for some place on Earth. Evenwith the naked eye, Mars appears distinctly red, and through the telescope, its disk isclearly reddish orange. Chemical analysis has shown the surface soil is very rich in iron.The reddish color of the soil is due to iron oxide, which is literally “rust” produced by thereaction of the soil and the sparse atmosphere.Earth has plenty of iron also, but being a differentiated sphere, the heavy elements likeiron have sunk to the deeper regions and the lighter elements like silicon are on thesurface. On Mars, the low overall density and presence of iron on the surface indicatethe planet is not differentiated any more. It may have been in the past, when it couldhave had a magnetic field, but the planet has evolved to become solid. With no liquidinner core, there is no magnetism.Mars is larger than the Moon and Mercury, hence it should have more geologicalactivity. There are examples of impact cratering, volcanism, tectonics, and erosion. Anexample of impact cratering is the Hellas Basin, which is a large impact crater in thesouthern hemisphere. Crater counts suggest the southern are older than the northern1
plains. The two most dramatic features on Mars are Valles Marineris, which is anexample of tectonics, and Olympus Mons, which indicates volcanism.

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Term
Spring
Professor
Shahnaz Sokhansanj
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