Speculations on the Comet's Last Stand
Monday, May 29 2006 @ 10:00 am EDT
Contributed by: bobmoody
Comet 73P/Schwassmann-Wachmann 3 (S-W 3) has all but disappeared after it's most recent passage through the inner solar system. It's fair to say that this was its final such trip. All that will remain for the immediate future is for the rocky, silicate materials that had been bound up inside it to slowly dissipate and spread out. It may be possible for some of this material to burn out in Earth's outer atmosphere as little meteors in their final blazes of glory.
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| Comet S-W 3 and the Ring Nebula on May 8th. Photo courtesy Mike Holloway, Holloway Comet Observatory, Van Buren, AR. |
Not being someone who is especially enamored with comets, it may have passed by Earth this time without my ever having thought twice about it. But comet 73P/Schwassmann-Wachmann 3 made me take notice this time, made me wonder a little more than usual about comets in general, and about this particular one more than most others.
Professional astronomers were expecting it to pass through the inner sanctum of the solar system in late 1995 as an uninspiring object barely even visible to all but the largest amateur telescopes. Yet, in October of 1995, S-W 3 was recovered and at first mistaken for a new comet due to it appearing several hundred times brighter than had been expected. Why was that?
The answer became obvious when professional observatories imaged the comet and discovered that it had split into at least four pieces. When events such as this occur, there is usually a large amount of deeply buried pristine material suddenly released to reflect more sunlight and make these objects brighter than expected. The frozen gasses sublimate into a bigger coma than normal, and any solid particles of rock and metal are freed to reflect even more sunlight and lend their own contribution to the overall effect.
Once I had started reading the magazine articles about this comet's return, and after Mike Holloway had sent me some images he'd taken earlier this year, I began to get interested in what might happen this time. After the successful NASA mission to smash a projectile into comet 9P/ Temple 1 on the Deep Impact mission last year, I saw the images of that comet's exterior and was surprised by how smooth and "solid" looking it was. Of course, Temple was a much bigger comet than S-W 3 to begin with.
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| Fragment B of comet S-W 3. A composite of 8 X 8 sec exposures by Arkansas Sky Observatories and Dr. P. Clay Sherrod taken on May 19, 2006. Note in the inset image the small trailing fragment which had just been released and is beginning to drift away from the larger piece. |
But as I kept reading about S-W 3's approach and realized that it was continuing to break up into even more fragments, I imagined that its appearance may have have been something more similar to that of asteroid Itokawa, the "rubble-pile" of rocks and dust that the Japanese asteroid sample return mission had revealed to us early this year.
No one knows why S-W 3 is breaking up as much as it is, but I had to wonder whether or not it had ever have been a very compacted or compressed object to begin with. Maybe it was simply a loose conglomerate of numerous small pieces barely held together by weak gravity to begin with. Or, maybe it had met up with a small asteroid sometime in its past and that impact could have caused numerous fractures throughout its mass. The slight gravitational influence of the Sun or some other planet may have been all that was needed to cause the fragmentation effect and help make it ready to crumble away during this particular trip inwards toward the Sun.
Whatever the reason, S-W 3 is basically dissolving right before our eyes, providing astronomers with a rare opportunity to see how such processes work. We need to study how asteroids and comets are held together in order to eventually use our technology to deflect one sometime in the future. The last thing the human race wants to see is a Shoemaker-Levy 9 type object breaking up and striking Earth with one or more catastrophic impacts. Earth's very existence may depend on such knowledge.
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| S-W 3 and its trail of 45 fragments from Spitzer Space Telescope. Infrared images were responsible for detecting the (now) more than 60 fragments, large and small, of this fragile comet. |
The orbiting infrared Spitzer Space Telescope captured the image at left revealing about 45 of the more than 60 (so far) fragments, and shows the brightest fragment "C" near the top, while next-brightest fragment "B" follows fairly closely behind amid the remaining trail of debris. This image was from the Astronomy Picture of the Day for May 13, 2006. Another spectacular image was on APOD for May 4, 2006 which had actually been taken by Hubble Space Telescope on April 18 right after a huge fragmentation event. By clicking on this link above you can see that that image shows graphically what enormous amounts of debris and gas are expelled from the comet during such massive fragmentation events. That debris cloud would be absolutely chock full of dust particles of all sizes as well.
It may well be that Comet 73P/Schwassmann- Wachmann 3 goes down in history as a comet that taught us much about cometary structure due to its ongoing disintegration right in front of the world's collective eyes. Its final gasp may turn out to be a rich shower of meteors on one or more dates sometime in the future. I, for one, hope it does.
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| My image of a nice, bright meteor with a "terminal burst" as it flashed out of existence at the end of its flight. Myself and 4 others watched and counted more than 900 meteors that cold November evening in 1998. About 20%-25% produced meteors like this one or a little brighter. |
Its just my personal choice, but I enjoy a good meteor show over the slow graceful weeks-long sweep of a great comet's tail any day. Some comets even cross through the constellations over many months time. Maybe that's odd to some amateurs, but what if, just maybe on some distant evening, there comes a meteor shower like we saw during the Leonid storm of November 18, 1998? What if every 5th or 6th meteor is bright enough to light up the ground and at least half of those become as bright as full-moonlight? That's the way it was on that evening now 8 years gone. They came in spurts and every few minutes I actually saw a tiny speck of light moving rapidly against the background stars until it dipped deeply enough into the thicker atmosphere to suddenly, dramatically, flare up into brilliance for just a few seconds causing shouts of joy and wonder to all who were lucky enough to see them.
That's what I hope for from this comet, that some spectacular end is in store for the final remains of Comet 73P/Schwassmann-Wachmann 3. Something similar to those Leonids in '98 would be especially nice to see before my time is done. There are already estimates that this might happen on May 31st, 2022. I hope I'm still around then, because I'd enjoy seeing that, immensely!
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