PLANETARY EVOLUTION 



course of its planetary development. It was 

 otherwise with the ancestral ring of the aster- 

 oids. This thinnest and weakest of rings started 

 on its independent career at a distance of only 

 240,000,000 miles from Jupiter — the planet 

 whose gravitative force is more than twice that 

 of all the other planets put together. Under 

 such circumstances it would seem impossible 

 that a planet could be formed. The asteroid 

 ring must have been liable to rupture, not only 

 from the causes which affect all planet-forming 

 rings alike, but also from the strain exerted upon 

 it, now in one part and now in another, by 

 Jupiter's attraction. The fragments of a ring, 

 torn asunder by such a cause, would not con- 

 tinue to occupy the same orbit — they would 

 be dragged from the common path in various 

 directions and to various distances, according 

 to the ever-changing position of the disturb- 

 ing body. Henceforward, instead of chasing 

 directly on each other's heels, they would rush 

 along in eccentric, continually intersecting paths, 

 and there would thus be no opportunity for 

 consolidation, except in the case of two frag- 

 ments meeting each other at the intersection of 

 their orbits. As a final result we should have, 

 not one good-sized planet, but a multitude of 

 tiny planets, with intersecting orbits exhibiting 

 great differences in eccentricity. All this is true 

 of the group of asteroids. While the mean 

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