On the probability that a comet that has escaped from another solar systemwill collide with the Earth

Stars pass the Sun all the time, and many of these stars may have their own planetary systems and their own 'Oort cloud' of comets. We consider a stra ightforward problem in which the planetary system of the passing star is id entical to the planetary system of the Sun, and also the cloud of comets is identical to the Oort cloud of the Solar system. We calculate (1) the rate of loss of comets from this other planetary system, (2) the frequency of p assage of other stars at a minimum distance r(0) and at a constant velocity v(0) relative to the Sun, (3) the number and velocity distribution of come ts coming from the passing star and impacting our planetary system, and fin ally (4) the number of cometary collisions with the Earth resulting from th is process.