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

Abstract

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 straightforward problem in which the planetary system of the passing star is identical 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 passage of other stars at a minimum distance r0 and at a constant velocity v0 relative to the Sun, (3) the number and velocity distribution of comets coming from the passing star and impacting our planetary system, and finally (4) the number of cometary collisions with the Earth resulting from this process.