THE SOLAR SYSTEM — LOVELL 291 



many aspects of these lunar and planetary studies which can be 

 achieved only by the physical presence of instruments carried in space 

 probes. Lunik II crashed its instruments onto the lunar surface. 

 Soon we may expect control to be exercised in the final stages of flight. 

 Then either a soft landing can be made and the instruments main- 

 tained in working order on the lunar surface, or the probe can be 

 placed in close orbit around the moon. Then we shall have the poten- 

 tial for studying the lunar atmosphere and magnetic field (if any 

 exists) ; and for making detailed measurements on the lunar surface, 

 which may well have a decisive influence on many outstanding con- 

 flicts of opinion. The history of many eons of time is contained on 

 the lunar surface, which must be almost untouched by erosion. Is 

 there, for example, an identity of material between the meteorites 

 which crash to earth and the surface of the moon ? The anal3^sis of 

 certain meteorites made by Urey seems to indicate that at some stage 

 in their history they must have gone through processes of heating 

 which could occur only in the interior of a body of lunar size ; and that 

 these meteorites which we handle today are the result of a shattering 

 of these moons in collision. If this is correct there must, at some 

 stage in the evolution of the solar system, have been at least 10 objects 

 the size of the present moon which eventually disintegrated in mutual 

 collisions. It seems that these lunar investigations may well hold 

 the key to a major problem in the evolution of the solar system. 



THE ORIGIN OF THE SOLAR SYSTEM 



Various forms of evidence indicate that the earth is about 4,500 

 million years old. In the first half of tliis century we believed that the 

 earth and the planets were torn out of the sun in the form of great 

 tongues of solar gas by the gravitational attraction of a passing star. 

 The wandering star passed on its journey and eventually after eons of 

 time the molten gas cooled down and formed the planets and the earth. 

 One significant feature of this theory was that the close encounter of 

 two stars in this way must be an extremely rare accident and in spite 

 of the trillions of stars in the universe the solar system was probably 

 imique. Today we are aware of reasons why the earth and the planets 

 could not have been torn from the sun in this way. For example, 

 98 percent of the mass of the entire solar system is in the sun, but 

 98 percent of the angular momentum of the system resides in the 

 planets. Since the division of angular momenta must have occurred 

 at the time of formation of the solar system, this represents an im- 

 possible situation. Gaseous material torn out from the sun with that 

 distribution of momenta would dissipate quickly and could not possibly 

 have aggregated into planets. 



Today we believe that the solar system was formed in quite a differ- 

 ent way. Originally, the sun, which is an average star, was probably 



