ON THE MISSING INTERSTELLAR COMETS

Comets are supposed to have been born in the outer part of the solar nebula and later thrown into their present location of the Oort cloud by perturbations of the giant planets. This process was inefficient and the majority of the comets were totally lost into the interstellar medium, instead of being trapped in the Oort cloud. Assuming stars in the solar neighbourhood to have formed in the same way as the Sun, one can find the number of interstellar comets and also estimate the expected number of detectable interstellar comets (McGlynn & Chapman 1989). In this work, using our present day knowledge of the local interstellar medium, we first calculate the population of interstellar comets. Then these calculations, combined with the detection probability and velocity distribution of the comets, as have been outlined by McGlynn & Chapman (1989), show that the expected number of detectable interstellar comet per century is less than one. Thus the nondetection of interstellar comets within the past 150 years or so, is nothing unusual and fully consistent with the existing models of the Oort cloud and solar system formation.