Published online by Cambridge University Press: 14 August 2015
A simplified form of the Jacobi integral in the three-body system Sun-Jupiter-comet or asteroid provides an excellent method for discriminating between cometary and asteroidal orbits. Omitting the librating bodies, unambiguous separation is obtained for all known objects with reliable orbital data, i.e., about 600 comets and 1800 asteroids. The only exception is the peculiar asteroid 944 Hidalgo – which is presumably a comet. The intermediate region is occupied exclusively by bodies revolving in resonance with Jupiter, and the value of the libration argument yields a sharp secondary criterion in these cases. Besides the direct perturbational capture of long-period comets from high-eccentricity orbits into Jupiter's family, a ring of nearly circular orbits between Jupiter and Saturn is suggested as another significant source of short-period comets. For these comets the subsequent operation of nongravitational effects gives a better chance of injection into small orbits of the Apollo type and for the formation of short-period meteor streams. Some phenomena (the outbursts of P/Schwassmann-Wachmann 1, the probable recent splitting of one parent body into P/Whipple and P/Shajn-Schaldach) give reasons for speculation about the population of this region, too distant for the discovery of typical asteroids or comets, by interplanetary particles up to sizeable solid bodies.