Trojans and Comets of the Jupiter Group

In a recent paper (Rabe, 1970), I suggested that at least some comets of the Jupiter group may have originated from the relatively dense Trojan clouds that, according to a recent survey by the van Houtens and Gehrels (1970), seem to be associated with the equilateral points L4 and L5 of the Jupiter orbit. This suggestion was inspired by the finding that the periodic comet Slaughter-Burnham has been captured (or perhaps recaptured) into unstable or temporary “Trojan” librations lasting approximately 2500 yr and by the circumstance that the Jacobi “constants” of most Jupiter group comets have values between 3.0 and 2.5, or just in that range which would also be occupied by all known and unknown Trojans associated with Jupiter in stable or unstable librations involving heliocentric eccentricities up to about 0.5 and inclinations as large as 30°. Moreover, it is well known that nearly all comets of the Jupiter group are able to approach Jupiter rather closely, thus providing the possibility for such drastic orbital changes as temporary capture into, or escape from, librational motion of the Trojan type. All, presumably stable, orbits of actual Trojan planets presently known have eccentricities e not exceeding 0.15, but we also know that stable short-period librations with much larger e values do exist in the restricted Sun-Jupiter problem, so that even in the real, nonrestricted situation there should be a possibility for corresponding librations with these more substantial short-period components. These librations may be unstable but may have long lifetimes nevertheless. The case of P/Slaughter-Burnham has proved that such motions are indeed possible, even with an e as large as 0.52.