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----------------- 1778 - Mars and Venus, our Sister Planets.
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- Astronomers studying Mars are convinced that at some point in the planet’s history water flowed on its surface, or, an abundant liquid of some type flowed in the now dry river beds scattered over the planet’s surface.
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- Maybe even dry lake beds because ancient shorelines suggest this watery past. Because crater impacts scar the river beds astronomers conclude that the surface has been dry for 3.5 billion years. However, the watery surface must have lasted for 40 million years before disappearing.
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- Underground water aquifers likely exist today. However, due to Mar’s thin atmosphere any water quickly evaporates once it reaches the surface.
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- All things considered the belief today is that Mars experienced a substantial climate change some 600 million years after the planet formation. Volcanic eruptions may have been the cause of this drastic change. We don’t know?
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- Mars cooled faster because of its smaller volume and the iron core solidified dissipating the planet’s magnetic field. Without this magnetic shield the solar winds would have stripped away much of the Martian atmosphere. With a thin atmosphere all the surface water would have quickly evaporated into space.
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- If Mars were a larger planet it may have retained its earthlike existence. Instead the planet turned cold and dry, not a good home of living things.
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- Venus has a different story. It is similar in size to the Earth. Rather than a Mar’s thin atmosphere Venus has an intensely thick atmosphere. The abundance of carbon dioxide in the atmosphere traps the Sun’s reflection causing the surface temperatures to exceed 400 Centigrade ( 750F).
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- The thick atmosphere allows sulfur-dioxide and sulfuric-acid clouds to cover the planet.
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- Astronomers were amazed to find a lack of craters on the surface. Unlike the other rocky planets and moons. Venus must have some resurfacing forces hiding many old crater scars. In fact, the evidence suggests the entire planet has somehow turned itself inside-out.
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- In order for the Venus surface to be wiped clean it must have undergone a cataclysmic upheaval some 500 million years ago. One theory is that the Venusians crust grew so thick it trapped the planet’s heat inside and then flooded the surface with molten lava.
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- To better understand the evolution of Mars and Venus we need to look at the evolution of the Solar System. By measuring decay rates of radioactive elements in meteorites the birth of the Solar System is calculated to be 4.6 billion years ago.
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- Back then a molecular cloud had concentrated and began to collapse from 100 Astronomical Units in diameter. An AU is the distance between the Earth and the Sun today, 93 million miles.
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- As the cloud collapsed temperatures rose and the cloud began to rotate forming a relatively flat disk. The density of the rotating disk rose quickly. As rotation’s angular momentum increased the size of the disk decreased and dust and gas began colliding. A proto planetary spinning disk was formed.
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- After 50 million years the center of the disk gathered enough mass to cause nuclear fusion at its core. The Sun was born.
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- Father out in the disk planets, minor planets, and asteroids began to form. The Sun’s intense solar wind blew away the minor dust and debris. The giant gas planets that formed in the outer disk flung planetisimals out into the distant Oort Cloud. This gravitational disruption created a period of heavy bombardment of the inner rocky planets and moons.
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- Each planet’s environment depended on where it was orbiting in the disk. The Earth got lucky.
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- Other Reviews on Mars and Venus:
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- #1729 - Walk with Venus on a Starry Night. and several other Review #1706 to #587 listed in this about Venus.
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- #1630 - Water on Mars. Mars is only 10.6% the mass of the Earth. and other reviews #827, #384, #24 about Mars.
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----- 707-536-3272 ---------------------- Wednesday, May 27, 2015 -----
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