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Nov10-09, 07:34 PM
P: 2
First off, love the site and I use it all the time to get my mind working and I really appreciate everyone who puts the time in to answer questions and contribute their two cents to questions that are, at the moment, unanswerable.

My question is regarding meteor showers and what mechanisms allow them to consistently occur at the same moment in the earth's orbit year after year. I guess the crux of my question concerns how ejected materials from comets is able to hold a stationary position in the solar system so that the earth passes through the cloud at a predictable time. I'm hoping that a better understanding of this question will help me establish a more intuitive understanding of orbital motion and the effects of gravity on small bodies. The are a few sub questions that I've come up with while trying to figure this out. To simplify (I hope) I've used the Perseid meteor shower as a discussion case:

1. From what I've read the Perseids are ejected material from the passage of Comet Swift-Tuttle which has an orbital period of about 133 years. Additionally, wikipedia says that much of the material entering Earth's atmosphere during the Perseids comes from a passage of Swift-Tuttle approximate 1000 years ago. My question here is how has Swift-Tuttle's orbit been consistent enough over a thousand years that it passes through roughly the same spot in the solar system 8 orbits in a row. When I picture this I imagine large bodies in the solar system coming close enough to perturb it's orbit.
2. Why is it that material "ejected" from the comet remains stationary after a thousand years? It seems that material "ejected" from the comet would still have a velocity which would cause it to scatter. I could possibly buy that it scatters together in a cloud but this would seemingly throw off the timing of Earth encountering the cloud.
3. How is it that after 1000 passages of Earth through the filament cloud there is still material left for Earth to capture? It seems like, due to the fact that the Earth passes through the filament cloud every 1 year and the cloud only gets renewed every 133 years, Earth should clear out an empty swath of space in the filament cloud and thus turn the Perseids into an event that happens every 133 years.
4. How does the gravity of the sun affect the material left behind by Swift-Tuttle? If we were to launch a space mission inside of the Earth-Sun L1 point and leave a car-sized object there with 0 velocity wouldn't we see it begin to accelerate toward the sun (plainly wouldn't an object not interacting with any other bodies interact with the largest gravity well in the galaxy)?

thanks for all of your help in advance!
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