acourt@BBN-VAX.ARPA ("Anthony J. Courtemanche") (01/24/86)
> Remember the inverse-square law, and the distances in the outer Solar > System: those effects are going to be pretty small. If I'm not mistaken, resonances with planets are responsible for the "Kirkwood gaps" in the asteroid belt (the one between Mars and Jupiter, I think). The asteroid belt is not uniform but has several rings where there are no asteroids at all. Computer simulation at M.I.T. has convinced some people that if there were any any asteroids in the Kirkwood gaps, after some period of time they would eventually settle into non-Kirkwood gap orbits. If planetary resonances can explain this structuring of the asteriod belt, I don't think it is too far fetched that planetary resonances can sling Trojan asteroids into earth-crossing orbits. I am not necessarily a beleiver but I don't think it is outrageous. Disclaimer: I disclaim this disclaimer. --Anthony Courtemance acourt@bbn-vax.arpa
henry@utzoo.UUCP (Henry Spencer) (01/26/86)
> If I'm not mistaken, resonances with planets are responsible for > the "Kirkwood gaps" in the asteroid belt... Computer simulation at > M.I.T. has convinced some people that if there were any any asteroids > in the Kirkwood gaps, after some period of time they would eventually > settle into non-Kirkwood gap orbits... That's right. Incidentally, it was known long before the MIT simulations; Kirkwood published his findings in the late 19th century, I believe. > If planetary resonances can > explain this structuring of the asteriod belt, I don't think it > is too far fetched that planetary resonances can sling Trojan asteroids > into earth-crossing orbits... We're still talking about different orders of magnitude, though. The Kirkwood-gap asteroids have their orbits changed only slightly, to the point where they are no longer in resonance with Jupiter. Moving a Trojan asteroid into an Earth-crossing orbit is a vastly larger change. This does not sound plausible to me. Moving it out of the Trojan point, okay, but that's still a very long way from an Earth-crossing orbit. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
cramer@kontron.UUCP (Clayton Cramer) (01/28/86)
> > Remember the inverse-square law, and the distances in the outer Solar > > System: those effects are going to be pretty small. > > If I'm not mistaken, resonances with planets are responsible for > the "Kirkwood gaps" in the asteroid belt (the one between Mars and > Jupiter, I think). The asteroid belt is not uniform but has several > rings where there are no asteroids at all. Computer simulation at > M.I.T. has convinced some people that if there were any any asteroids > in the Kirkwood gaps, after some period of time they would eventually > settle into non-Kirkwood gap orbits. If planetary resonances can > explain this structuring of the asteriod belt, I don't think it > is too far fetched that planetary resonances can sling Trojan asteroids > into earth-crossing orbits. I am not necessarily a beleiver but I don't > think it is outrageous. > > --Anthony Courtemance Correct. The Kirkwood Gaps are caused by resonances between the asteroid belt and Jupiter. Anything at a harmonic revolutionary period with Jupiter (1/2, 1/3, 1/4, 1/5 the period of Jupiter) will be pulled closer to Jupiter. The harmonics associated with the planets further out are less important both because the gravitional pull is smaller (both for distance and planetary mass reasons), and because the smaller the harmonic, the less often the planet and the asteroid are in opposition. (The 1/5 harmonic would only be in opposition to Jupiter every 60 Earth years, as opposed to the 1/2 harmonic, which is in opposition every 12 Earth years). The Cassini Division in Saturn's rings exists because of the harmonic period with Titan (I think). *** REPLACE THIS LINE WITH YOUR MESSAGE ***