[Lonesome in Massachussets]

Thanks for input. I am a natural skeptic and I haven’t “done the math(s)”, though I’m perfectly capable of doing so. It just seems counter intuitive, especially if its in orbital resonance with Jupiter, it should be in a direct, rather than retrograde, orbit and the vector sum of the velocities should be smaller than if they were in quadrature, i.e., smaller than the sum of the squares.

I think what I am missing is the added energy obtained by falling from “infinity” to earth. There still doesn’t seem to be enough energy in the orbits, though.

[ETL]

The comet apparently has an exceptionally elongated (elliptical) orbit. Perhaps that explains why it moves so especially fast when it approaches the sun and earth.

"Based on their observations, and those of other astronomers who began tracking the comet's highly elongated orbit, it was calculated that Swift-Tuttle would make its next appearance during the 1980s. They were close. Japanese astronomer Tsuruhiko Kiuchi rediscovered the comet in 1992.

Aside from its unusual orbit, Swift-Tuttle is also significant as the host body of the Perseids meteor shower, one of the most prominent in the northern sky.

Oh, and there's one more thing.

Comets come and go, literally, but Swift-Tuttle's orbit is of particular interest to us earthlings since astronomers calculate that it is very likely to strike either the Earth or the moon on its next pass. They've even zeroed in on a date: Aug. 14, 2126."

http://www.wired.com/science/discoveries/news/2007/07/dayintech_0716
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109P/Swift-Tuttle:

http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=109p;orb=1;cov=0;log=0;cad=0#orb