Assuming the creation of cometary nuclei in cool, dense, molecular interstellar clouds, we modelled their dynamical evolution in the collapsing protosolar nebula. We demonstrated that a significant number of cometary nuclei remained at large heliocentric distances at the end of the collapse, if the peak of supposed Maxwell-Boltzmann distribution of the initial velocities of the nuclei was not lower than about m s-1 (and not higher than a few hundreds of meters per second; an excess of this upper limit was improbable and was not looked for). We assumed that the neighbouring protostars, forming together with the protosun in a common association, scattered the velocities of cometary nuclei, therefore the cloud of comets at large heliocentric distances could actually be a remnant from the era when the protosolar nebula started its collapse or, maybe, even from an era of interstellar cloud - a birth cloud of the protosolar nebula. Unfortunately, it is impossible to make a reliable quantitative estimate of the the peak of velocity distribution.
In spite of this uncertainty, there is a chance to prove the theory with the help of future analysis of some of its consequences. For example, it sets up new initial conditions at the accretion of planets and reduces the estimated number of interstellar comets. Thus, it may provide a new way how to solve or to avoid some problems that have occurred in the theories of comet as well as planet origin.
In contrast with the primordial theory assuming the creation of comets within planet formation, the suggested theory assumes the creation of comets earlier, already within star formation or even before it. If the theory is proved, it will be possible, studying the Oort cloud comets, to improve the model of protosolar nebula collapse (to determine free parameters of this process) and, furthermore, to gain some new details on the early stage of protosun formation.
© European Southern Observatory (ESO) 2000
Online publication: September 5, 2000