Paul Joss, of the Institute for Advanced Study in Princeton, NJ, gives a value of 70 as an average.("On the Origin of Short-Period Comets," Astronomy and Astrophysics, 1-273, June, 1973).I do not claim to be an expert in the fields involved. Short-period comets Short period comets disinagrate rather quickly due to interaction with the sun while in the inner portion of the solar system.Several references gave conflicting values, from dozens to hundreds, of the number of orbits to be expected.First, of the three astronomy books mentioned, only this one mentioned comets as a source and another, as mentioned above, discountsd small particles almost entirely.This leads me to believe that the comet source theory might not be an agreed upon answer.
Because of the forward motion of an object in orbit around the sun, the sun's radition strikes it at an angle and exerts a backwards force. In the case particles on the order of 1 mm or less in diameter, this force degrades the orbit, causing the particle to fall into the sun within thousands to a few million years.About 1950, Jan Ort of the Netherlands postulated a cloud of comets orbiting the sun far outside the planets.Note that, although observed comet orbits are consistent with such a cloud, there is no direct evidence of its existence: the presence of the comet source is derived from the need for such a source in an old universe.He gives the likely source for these particles to be comets, since we know that comets can create meteors.This sounds plausible, but there are a few difficulties.Also, since there has been controversy on the net, unless otherwise indicated, all references and quotes are taken from works which I have personally examined.Any conclusions not specifically quoted are my own and may not agree with those who supply the facts on which I base them.Second, the distribution of meteors resulting from comets is highly non-uniform around the earth's orbit, while the particles which cause the zodical light must be uniformly distributed.Lastly, and most importantly, the theory that the particle supply is constantly being replenished must make another assumption: that the rates of supply and of destruction into the sun are roughly equal.Comets are supposedly diverted from the reservoir by the influence of passing stars.The question is whether or not enough comets will be supplied by this mechanism to agree with observations.