Comet Trails and Meteors

[Papa Surf]

I understand that annual meteor showers come from streams of dust left behind by passing comets. Do these streams stay in one place? Shouldn't they be orbiting the sun just like Earth and if so why do we cross through these trails at all :confused:?

[Hornblower]

I understand that annual meteor showers come from streams of dust left behind by passing comets. Do these streams stay in one place? Shouldn't they be orbiting the sun just like Earth and if so why do we cross through these trails at all :confused:?

These particles are in orbits similar to the orbit of the parent comet. Because of perturbations both gravitational and nongravitational (radiation pressure, etc.), the orbits of the individual particles get smeared out over time, so for older swarms the Earth may take several days to cross the full extent of the swarm.

[matthewota]

In addition, the shower hapens when the Earth's orbit intersects with the meteor stream's orbit.

[Jens]

I understand that annual meteor showers come from streams of dust left behind by passing comets. Do these streams stay in one place? Shouldn't they be orbiting the sun just like Earth and if so why do we cross through these trails at all :confused:?

Two things orbiting the same body can intersect. Remember those two satellites that collided a few months ago? They were both orbiting the earth, but their orbits intersected. It can happen because their orbits are not parallel (say, one is orbiting N-S and the other E-W) or it can happen because the eccentricity is different (say one is in a fairly circular orbit whereas the other is very elliptical).

[ngc3314]

To fill out some of the earlier replies - material that leaves a comet goes into separate orbits. In a simple two-body system it is a principle of gravitational mechanics that a perturbed orbit (say, perturbed by being ejected from the comet driven by gas pressure, or the relatively brief effects of sunlight pressure) returns through the point of perturbation. So all these slightly different orbits converge again where the orbit is nearest the sun, albeit at different times. So the material gets spread out along a region around the comet orbit, narrowing most closely near the comet's perihelion. This we see meteor showers even when the comet isn't in that part of its orbit. (Working out the structure of the debris streams in detail has only recently gotten far beyond numerical guesswork).

[Papa Surf]

Thanks for the great replies.

So all the common, annual meteor showers come from only comets that passed through somewhere along the earths orbit?

[antoniseb]

So all the common, annual meteor showers come from only comets that passed through somewhere along the earths orbit?

To our knowledge this is true, and most of the known annual showers each have a particular comet that is associated with it.