What's the cause of a meteor shower? Why are clumps of rock complied together and consistent year round?

Question

Were they once part of a large asteroid that broke up and scattered?

Answer 1

< from Wikipedia>

The causes of meteor showers



Comets are like "dirty snowballs" made up of ice and rock, orbiting the Sun. Each time a comet swings by the Sun in its orbit, some of its ice or other volatile vapourises and a certain amount of debris, or cometary fragments, may be shed. As the debris streams from the comet, it forms the comet's visible tail. The solid pieces of debris are a form of meteoroid. The meteoroids spread out along the entire orbit of the comet to form a meteoroid "stream". As the Earth orbits the Sun, its orbit sometimes takes us through a meteoroid stream and a meteor shower ensues. The meteoroids encounter Earth's atmosphere at high speed. As the meteoroids streak through the atmosphere, ram pressure causes the particles to burn and incandesce, forming meteors. When the meteoroid stream is particularly dense, we occasionally see a spectacular "meteor storm." The comets that spawn most known meteor showers have been identified.

Irish astronomer George Johnstone Stoney (1826-1911), collaborating with British astronomer Arthur Matthew Weld Downing (1850-1917), and independently Adolf Berberich of the Königliches Astronomisches Rechen Institut (Royal Astronomical Computation Institute) in Berlin, Germany, had apparently first offered in the 1890s the idea of a meteoroid stream or trail, when they calculated how meteroids, once freed from the comet and traveling at low speeds relative to the comet, would drift mostly in front of or behind the comet after completing one orbit. The effect is simple orbital mechanics - the material drifts only a little laterally away from the comet while drifting ahead or behind the comet because some particles make a wider orbit than others. [1] These dust trails are sometimes observed in comet images taken at mid infrared wavelengths (heat radiation), where dust particles from the previous return to the Sun are spread along the orbit of the comet (see figures).

The gravitational pull of the planets determines where the dust trail would pass by Earth orbit, much like a gardener directing a hose to water a distant plant. Most years, those trails would miss the Earth altogether, but in some years the Earth is showered by meteors.

In 1985, E. D. Kondrat'eva and E. A. Reznikov of Kazan State University first correctly identified the years when dust was released responsible for several past Leonid meteor storms. In anticipation of the 1999 Leonid storm, Robert H. McNaught[2] and David Asher[3], and Esko Lyytinen of Finland, were first to apply this method in the West. [4][5] Peter Jenniskens has published predictions for future dust trail encounters, resulting in a "meteor storm" or "meteor outburst", for the next 50 years. [6]

Over longer periods of time, the dust trails can evolve in complicated ways. One effect is that the orbits of some repeating comets, and meteoroids leaving them, are in resonant orbits with Jupiter or one of the other large planets - so many revolutions of one will equal another number of revolutions of the other. So over time since Jupiter will have the same relative position intermittently and it will tend to pull meteoroids into keeping that relative position. This creates a shower component called a "filament".

A second effect is a close encounter with a planet. When the meteoroids pass by Earth, some are accelerated (making wider orbits), others are decelerated (making shorter orbits), resulting in gaps in the dust trail in the next return (like opening a curtain, with grains piling up at the beginning and end of the gap). Also, Jupiter's perturbation can change sections of the dust trail dramatically, especially for short period comets, when the grains approach the big planet at their furthest point along the orbit around the Sun, moving most slowly. As a result, the trail has a clumping, a braiding or a tangling of crescents, of each individual release of material.

The third effect is that of radiation pressure which will push less massive particles into orbits further from the sun - while more massive objects (responsible for bolides or fireballs) will tend to be affected less by radiation pressure. This makes some dust trail encounters rich in bright meteors, others rich in faint meteors. Over time, these effects disperse the meteoroids and create a broader stream. The meteors we see from these streams are part of annual showers, because Earth encounters those streams every year at much the same rate.

When the meteoroids collide with other meteoroids in the zodiacal cloud, they lose their stream association and become part of the "sporadic meteors" background. Long since dispersed from any stream or trail, they form isolated meteors, not a part of any shower. These random meteors will not appear to come from the radiant of the main shower.

Answer 2

They are the trails of tiny sand grains (not clumps of rock) left behind by comets. They don't scatter; they remain in the comet's original orbit.

Answer 3

I think they are actually tiny dust sized particles that have been blown off of comets by the Sun's solar winds. At least in some cases. Basically, we pass through the tail of a comet.

Answer 4

Every year, in early August, the earth passes through the trail left by the Swift-Tuttle comet's tail, which is made up of dust, rock and various other debris.  The earth's gravity invariably grabs up some of this debris, which is pushed away from the comet by solar winds, and pulls it into our atmosphere, where it burns up during re-entry and is incinerated before it can make it to the ground.  This is why meteors appear as streaks of light in the night sky -- they're tiny fragments of rock and dust being heated to extreme temperatures.  Because our orbit is constant, we know when to expect all of this to happen.

Answer 5

Comet Swift-Tuttle swings around in an orbit that intersects the Earth near August 12 each year.  As the comet goes around, stuff boils off the comet in jets and creates a tail.  But it also creates a stream of stuff that spreads over the entire orbit.  The Earth plows into this stream each summer.  But it doesn't just smack into it once for a few minutes, because this stream also spreads out in size.  So the Earth smacks into this stuff for a couple weeks, with a peak on August 12th.

The bits of stuff are very small.  Most are the size of a grain of sand, but can be as large as a pea.

There is a suggestion that the thing that slammed into Tunguska in 1908 was a piece of comet Enke.  If such a piece of Swift-Tuttle were to slam into the Earth, it would make it a less than peachy day for at least some.

But at the moment, you are still more likely to be shot in the face by d**k Cheney than killed by something from space, statistically speaking.