Comet debris

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Psnarf
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Comet debris

Post by Psnarf » Fri Oct 21, 2011 2:51 pm

News of tomorrow's meteor shower reminded me to ask: Does comet debris orbit the Sun following the host comet?
The dust can't be stationary because we'd pretty-much clear a path after a few years. Every year we pass through the comet trail, e.g., Halley's Comet, we get a shower, with a meteor frequency depending on which part of the debris trail we happen to hit that year. If the comet debris is in the same solar orbit as the host comet, does the host comet plunge through its own dust, growing denser each orbit?

http://science.nasa.gov/science-news/sc ... _orionids/

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Chris Peterson
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Re: Comet debris

Post by Chris Peterson » Fri Oct 21, 2011 3:14 pm

Psnarf wrote:News of tomorrow's meteor shower reminded me to ask: Does comet debris orbit the Sun following the host comet?
The dust can't be stationary because we'd pretty-much clear a path after a few years. Every year we pass through the comet trail, e.g., Halley's Comet, we get a shower, with a meteor frequency depending on which part of the debris trail we happen to hit that year. If the comet debris is in the same solar orbit as the host comet, does the host comet plunge through its own dust, growing denser each orbit?
Cometary dust is essentially in the same orbit as the parent body. However, it disperses with time for a variety of reasons- it was ejected outwards, it is subject to forces from solar wind and solar radiation, etc. So individual debris streams associated with specific perihelia (most material is released when the comet is closest to the Sun) drift apart somewhat. As material moves slightly inward or outward from the parent body orbit, it also drifts forward or backward, eventually filling the entire orbit with dust (but the dust will be thickest near the parent body, which is why we are more likely to experience strong meteor showers in the years near crossings of the comet with Earth's orbit).

Keep in mind some basic orbital dynamics: particles which drift into slightly sunward orbits move faster, those that drift outwards orbit slower. Those that stay exactly in the orbit of the nucleus are moving at the same speed as that nucleus, so there is nothing for the comet to "plunge" through. Everything in a given orbital path must have the same orbital velocity.

Although debris streams will eventually drift into the Sun, as long as they are dense enough to create detectable meteor showers they are sufficiently close to the orbit of the parent body that the path defining elements are the same. When I calculate the original orbit of a meteor from a shower, the elements are normally the same as those of the comet that created the shower.
Chris

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Psnarf
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Re: Comet debris

Post by Psnarf » Sun Oct 23, 2011 4:24 pm

Thank you for your explanation. I forgot that debris along the comet's path would orbit the sun at the same velocity as the comet. I need to read that book on celestial mechanics again.

The same sort of "forgetting the basics" as that dumb grandfather paradox of time travel. Whatever you do in the past will propagate at the speed of time, one second per second. Thus, those events can never catch up with the present. The time traveler who kills his grandfather before he met your grandmother can never catch up with the present 'now'. Even the knowledge of that event remains locked in the past. The same comet detritus won't be there the next time around. Each year we pass through a different part of the debris field.

Mebrayne Hertz