ORIGIN OF THE SOLAR SYSTEM JEANS 159 



originally liquid and those which were originally gaseous, the cor- 

 responding boundary case on the other half of the chain being Nep- 

 tune. Thus we can conjecture that Mercury and Venus were born 

 liquid or solid, that the earth and Neptune were born partly liquid 

 and partly gaseous, and that Mars, Jupiter, Saturn, and Uranus were 

 born gaseous. 



We have already noticed that Mars and Uranus both have masses 

 which are too small for their positions in the sequence of planets. If 

 the planets Avere born out of a filament of continuously varying 

 density, the mass of Mars at birth ought to have been intermediate 

 between that of the earth and that of Jupiter, and similarly the mass 

 of Uranus at birth ought to have been intermediate between that of 

 Neptune and that of Saturn. We have, however, just seen reasons 

 for conjecturing that the two anomalous planets. Mars and Uranus, 

 were the two smallest planets to be bom in the gaseous state; they 

 would, therefore, be likely to lose more mass by dissipation of their 

 outer layers than any of the other planets. Let us introduce the sup- 

 position that Mars, and to a lesser degree Uranus, lost large parts of 

 their mass by dissipation into space; let us suppose that they are 

 mere fragments of what were originally much more massive planets, 

 then all anomalies disappear, and the pieces of the puzzle begin to 

 fit together in a very gratifying manner. 



Nevertheless, and in spite of the high promise which the tidal 

 theory seems to hold out, it is far too early to claim that it can finally 

 explain the origin of our system. Its claim to consideration at pres- 

 ent is rather that, so far as I know, it provides the only theory of 

 that origin which is not open to obvious and insuperable objections. 



