The Science behind the Experiment
July 21st, 2010
To understand what we’re up to here, you need to know a bit about meteors. They come from comets. A comet is, in the words of a famous astronomer, a "dirty snowball": a big hunk of frozen gases with dust, dirt, and bits of rock mixed in. Most comets -- and there are, in Carl Sagan’s words, "billions and billions" of them -- are way out beyond Pluto, orbiting the sun very slowly. Every now and then one of them gets bumped out of its orbit by gravitational perturbations and starts a long, slow fall towards the sun. Once it gets near the sun, the heat of the sunlight causes the frozen gases on its surface to melt away (actually, they sublimate: go directly from solid to gas); those gases are then pushed away from the comet by the pressure of sunlight, forming its tail.
The little bits of dust and dirt trapped inside the comet are liberated by the melting process, and they spread out like the gases. Because they’re all going at slightly different speeds, they move ahead of or behind the comet in its orbital path. Moreover, that orbital path can be disturbed by the gravity of the planets (usually Jupiter is the culprit), and the comet gets caught in an orbit close to the sun, taking a few decades to orbit, not returning to the dark and distant region from which it came.
So the comet leaves a trail of dust and dirt in its wake, and if the earth happens to cross that trail of dust and dirt, the little bits of dust and dirt hit our atmosphere and burn up -- which we see as meteors. We see the same family of meteors each year on the same date, because the earth comes back to the same place in its orbit.
Here’s the big question we’re attempting to help answer: when the meteors are liberated from the surface of the comet, do they peel off one by one or do they break off in groups? If they peel off one by one, then the meteors will appear randomly in the sky, but if they break off in groups, then we’ll see the groups as bunches of meteors falling together -- and that might give us a clue about how comets (and thus, the solar system) were formed.
Now, you’re probably thinking, why don’t you just go outside and watch the meteors and see if they’re coming in bunches? Astronomers have been doing that for decades now and they’ve always come up with a negative answer. The reason for this is that the earth is moving through space so fast that, if an observer were underneath a bunch of meteors, they’d be carried away from it before being able to see much of that bunch. It’s kind of like driving past a sprinkler spraying water into the street; you go by so fast that you get only a quick spot of water, not a steady stream.
Now at last I can explain the significance of this experiment: what we’re doing is putting together a whole caravan of cars to drive by the sprinkler and combine their observations into a coherent whole. With lots of observers spread out all over the map, we can get a much bigger picture of the meteor stream than we could get with just one observer.
This would have been impossible just ten years ago. It is made possible by the convergence of four technologies: laptop computers; email; blogs for recruiting thousands of observer; and Internet time standards.
The whole thing could be a bust. It could be cloudy all over the Northern Hemisphere on August 11-12. Minor irregularities in the observations might make it impossible to cross-correlate the data. We might discover that there’s nothing to see -- the meteors are all just randomly distributed. But even that will be a useful contribution to science.