The Evolution of the Universe 15 



of these "freakish" conditions set the scene for the origin of hfe; 

 hence it is pertinent to investigate the manner in which the solar 

 system came into being. 



The solar system consists of the sun, the nine planets which 

 revolve around it, and moons revolving around six of the planets. 

 The four small planets, Mercury, Venus, Earth, and Mars are closest 

 to the sun; the four giant planets, Jupiter, Saturn, Uranus, and 

 Neptune are located at much greater distances with the small planet 

 Pluto beyond them. 



According to earlier theories, the entire system resulted from a 

 giant gas cloud, the edges gradually separating into gas rings 

 around the resulting inner cloud. This inner cloud gradually con- 

 densed, more and more, until the pressure raised the heat of the 

 interior to the point at which nuclear reactions occurred, giving 

 the sun its present fiery nature. The gas rings were thought to have 

 condensed into the planets. When the mechanics of the solar system 

 were better known, however, it was discovered that the great 

 distance of the giant planets from the sun combined with their 

 relatively rapid orbital motion made this speculation untenable. The 

 same circumstances also disprove the theory that explosions in the 

 sun shot out huge gas balls which condensed to form the planets, 

 or that another star passed sufficiently close to the sun as to tear 

 away part of it in the form of a gas-dust cloud which, in turn, 

 formed the planets (Jones, 1940). 



According to the present consensus, the solar system arose from 

 a pair of stars which were close together. Such twin stars are 

 abundant in the galaxy. There is disagreement about the exact 

 mechanics involved in the formation of the final (present) products 

 in the system from such a twin origin. Some believe that when 

 these twins were still gas-dust clouds, the larger (which became 

 the sun) captured the smaller one in its gravitational field, and 

 that the latter evolved into the planets. Others believe that the 

 smaller star was the sun, and that the larger was a giant star. Giant 

 stars burn with great rapidity and end by exploding as super-novae. 

 According to this last theory, the sun's twin exploded in this fashion, 

 blowing most of its mass far out into the galaxy but leaving behind 

 a cloud composed chiefly of the giant's core of heavier elements. 

 This cloud was then captured by the sun's gravitational field and 

 evolved into the planets (Hoyle, 1950). On the basis of its radio- 

 active materials, a meteorite presumably formed in this cloud has 

 been calculated to be 4.95 billion years old. The meteorite fell in 

 Richardton, N.D., in 1919 (Reynolds, 1960). 



