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Lesson 4-A

Page history last edited by Chai Nakpiban 11 years, 2 months ago

Formation of the Solar System

Between existing stars is “the vacuum of space.” However, it is far from being a pure vacuum because it is populated with clouds of dust and gases. A cloud of dust and gas in space is called a nebula (nebula = cloud; plural: nebulae). A nebula, shown in Figure 3, often consists of 92 percent hydrogen, 7 percent helium, and less than 1 percent of the remaining heavier elements. For some reason not yet fully understood, these thin gaseous clouds begin to rotate slowly and contract gravitationally. As the clouds contract, they spin faster. For an analogy, think of ice skaters—their speed increases as they bring their arms near their bodies.



Figure 3 - Formation of the Solar System According to the Nebular Hypothesis

A solar system began as an enormous cloud of dust and gases made up mostly of hydrogen and helium with a small percentage of heavier elements.

B This cloud, called a nebula, started to rotate and collapse toward the center of the cloud. Heat was generated at the center, which eventually formed the sun.

C Cooling of the nebula caused rocky and metallic materials to form tiny solid particles. D Repeated collisions of these particles resulted in the formation of asteroid-sized bodies.

E These asteroids eventually combined to form the four inner planets—Mercury, Venus, Earth, and Mars. The lighter materials and gases combined farther away from the center to form the four outer planets—Jupiter, Saturn, Uranus, and Neptune.



Nebular Theory

Scientific studies of nebulae have led to a theory concerning the origin of our solar system. According to the nebular theory, the sun and planets formed from a rotating disk of dust and gases. As the speed of rotation increased, the center of the disk began to flatten out, as shown in Figure 3. Matter became more concentrated in this center, where the sun eventually formed.



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