CHAPTER XII 



THE ORIGIN AND EVOLUTION OF THE SOLAR SYSTEM 



283. The sequence of events to be expected in a mass of astronomical 

 matter left solely to the influence of its own rotation has now been traced out 

 with tolerable completeness. 



Of the five uniformities of structure mentioned in our introductory chapter 

 we have found that two fall naturally into their places in the scheme of evolu- 

 tion of a rotating mass, these two being the spiral nebulae and the binary 

 and multiple stars. Two others, namely the planetary and ring nebulae and 

 the globular and moving star-clusters, seem at least to be capable of explana- 

 tion in terms of a rotational theory of evolution, although our interpretation 

 of these formations was largely conjectural. 



The fifth uniformity was that observed in the solar system, and for this 

 no place has been found in the rotational scheme of evolution. It is true 

 that we found ( 257) that planets might possibly form out of the atmosphere 

 thrown off equatorially from a rotating mass of gas, but several objections 

 present themselves against any attempt to explain the origin of our solar 

 system in this way primarily the objection that the next stage in evolution 

 ought to be for the central mass to break up into an ordinary binary star, 

 whereas our sun and planets are not binary. Also the arrangement of the 

 components of typical multiple stars such as can have been formed by rotation 

 (cf. fig. 45, p. 265) does not in the least resemble that observed in the solar 

 system. 



Such considerations alone would throw doubt on a rotational theory of the 

 evolution of our solar system. Beyond these there is the objection already 

 referred to in 14, that the total angular momentum of our system appears, 

 at first sight at least, to be much too small for the system ever to have broken 

 up by rotation. We proceed to examine this supposed objection in the light 

 of the theoretical knowledge we have now obtained as to the conditions for 

 rotational break-up to occur. 



THE ROTATIONAL THEORY 



284. For an incompressible and homogeneous mass of fluid, rotational 

 break-up cannot commence until after the configuration has passed the 

 Maclaurin-Jacobian point of bifurcation ; at this 



018712 . (588). 



