FORMA TION OF ME TEORl TES '3 7 5 



Let two stars be assumed to be attended by secondaries like 

 those of the sun, and to pass each other near enough to initiate 

 serious disturbances in the orbits of the planets and satellites of 

 the two systems. It is not necessary that this disturbance shall 

 be so great as to bring about a disruptive approach of any of 

 these bodies at once, but merely that this shall be the ulterior 

 effect, which may be long delayed. The two systems need not 

 necessarily invade each other's actual limit, that is, the two 

 suns need not approach each other within the sum of the radii 

 of the orbits of their outermost planets.' For example, in the 

 ideal case of two solar systems, it is not necessary that the 

 orbits of the two Neptiuies shall actually cut each other. If the 

 undisturbed orbits merely touch each other, or even closely 

 approach each other, it seems clear that if Neptune be at the time 

 coming toward the point of such ideal contact, or near approach, 

 the attraction of the passing sun, together with Neptune' s own 

 momentum, will carr)^ the planet far beyond the limit of its own 

 ideal orbit into the sphere of dominant influence of the passing 

 sun. At the same time, the paths of the inner orbits of both 

 systems will be distorted in a quite irregular way, dependent on 

 their various positions in their several orbits. The transfer of 

 an outermost planet from one system to another under these con- 

 ditions of general disturbance, or any other radical change in 

 the orbits of the outer planets, will cjuite certainly lead on to 

 other disturbances of orbit, some of which may sooner or later 

 lead to disruptive approach, though the result of such a compli- 

 cation is beyond the reach of precise prediction. 



A still more remote approach between two systems in which 

 the only result is a pronounced elongation of the orbits of the 

 two systems, may ultimately result in close approaches, for, if 

 the orbit of any of the planets of the two systems be elongated 

 so that its perihelion distance is less than the aphelion distance 

 of the next inner planet, or its aphelion distance greater than the 

 perihelion distance of the next outer planet, a disruptive 



' In the illustrative examples it is assumed for convenience that the planes of the 

 systems are normal to the systems' lines of movement. 



