I understand that meteor showers are due to the Earth passing through the debris left by a comet, but shouldn’t the Earth clear out any lingering meteors after a few revolutions?
In: Planetary Science
A few things. First, most orbits aren’t completely planar. Just look at our moon in that we sometimes get an eclipse during a new/full moon and sometimes we don’t. Second, the particles ejected from the comet aren’t statically floating there. Many have some momentum from when they were ejected but not enough to escape the sun’s orbit. As a result, by the time Earth revolves around the sun, it’s going through a slightly different area of the debris field and a lot of the debris that wasn’t originally in the path of Earth has moved into it.
Give it enough time, and the debris will eventually be cleared out. But time on an astronomical scale is a long, long time for humans.
The debris from the comets still orbit the Sun in the orbit that the comet had. So while the Earth do clear out a tunnel in the debris field these debris would have continued on their orbit and be well outside the Earth’s orbit when the Earth comes around to the same spot again. But more debris is coming inn from the outer solar system in the orbit of the comet and will impact the Earth.
As I understand it, as a layman. As we travel through space, we follow a regular path. So we go through the same cosmic “neighborhoods”. In which the debris sits. 
>shouldn’t the Earth clear out any lingering meteors after a few revolutions?
This question grossly underestimates the size of Earth’s orbit. It’s not like a table with some crumbs you can brush off with your arm, it’s like a gymnasium that you’re sweeping with a toothpick.
You’re driving slowly around the block, it takes you one year to do a lap.
One of your neighbors always leaves a mess on the road in front of their house. Every year you drive past their house and hit a bunch of crap they left on the road. It just depends on the year as to how much stuff is there or if you hit it or not.
In astronomy words. Your annual trip around the block/sun runs through a debris field.
The particles that form the meteor shower are not just sitting there in space. Rather, they follow approximately the same orbit as the comet they came from, albeit with a spread of some millions of miles. Earth, by comparison, is tiny and only sweeps out a tiny portion of this cloud of meteoroids.
Because the perseid showers result from the debris of comet swift-tuttle, which ( could be wrong) has an orbital period of 133 years, and an approximate orbit circumference of 2 billion kilometers, so it has time to throw off a lot of material, both approaching and leaving the near sun part of the orbit. It’s also 16 miles across, so it has a lot of mass it can lose, and all of the material it loses is also orbiting the sun. so it’s not like a static ring that the earth can clear out in one year.
The Leonids occur from the same process but from the comet tempel-tuttle, which has a 33 year orbit, and I believe that both comet start shedding material when the get about the same distance from the sun as the asteroid belt.
Edit: reworded better.
That cloud of meteors is huge, comprised of tiny particles, and regularly gets refilled.
The comet orbits the Sun, just on a very stretched orbit that takes centuries. Each time it flies by the Sun, it sheds more dust for the Perseids.
Earth is a relatively tiny target on a stellar scale (look up “earth and moon distance to scale” to get just how much void there is around us). Each year thousands of comet dust specks burn up in the Earth’s atmosphere, but they are millions upon millions more that miss our planet to hit it another year.
And when the comet returns in 200 years, there will be even more.
**The whole debris field is orbiting too. Every year we take a different track through it.**
The stuff the debris came from was orbiting, so even debris that breaks off maintains the orbit because there’s nothing stopping it.
So every year the Earth takes a different track through it. It’s not sitting there stationary and we take the same trajectory through it each year. We might eventually clear the whole thing but not not any time soon. The point is it’s not just one Earth-sized path through the debris we’d have to clear out.
yo it’s like a cosmic game of dodgeball. earth passes through this junk every year cause comets leave trails of crumbs. so we get these showers that are pretty cool… can’t complain
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