What's Going on With Comets?

CalliArcale · Mar 14, 2006

<blockquote>In reply to:<hr />calli, the "dark matter" the comet would be composed of is already accounted for when people do estimates of the dust cloud mass (from which they'd originate if they're there). It also falls into the "baryonic" cold dark matter. <hr /></blockquote> I was under the impression that current estimates did not show there being enough of it to form small bodies. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

Saiph · Mar 14, 2006

:::Shrugs::: I don't see any reason to say it can't happen. But I do see reasons to claim it isn't common. So if they are there, they've been accounted for indirectly (at least in part). If dust lanes and star forming regions can spawn brown dwarfs...those may come with their own cometary halos. So they haven't formed in isolation. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

bonzelite · Mar 14, 2006

calli, that is what is currently assumed. it may not be entirely accurate. comets may not be all from the same source. groups of them may be, but others may be lone wanderers. off campus formation may not be rock solid proven, but "weird crystals" whose structures are unidentifiable, lend credence to this idea. for example, it may be composed of elements and compounds commonly found throughout the solar system, like olivine or magnesium, yet arranged in an exotic fashion under possible conditions that cannot exist in the dead cold silence of interstellar space. the fact that the press release suggests molten conditions, and then on to mention from a distant star, is right away pointing this way. remove 'distant star' from the hypothesis and just look at the structures as examined. they determined that they were created under high heat. what could have done that? and the superfine dust structures and compositions of cometary nucei --where did all the dust come from other than from the galaxy itself, jam-packed with dust lanes? if you don't buy into exogenic/radioisotope decay heating, then what else is left but explosions (supernovae or EPH processes) and/or other suns? yes, Yevaud can debate that all such evidence points just as easily to local on-campus formation. then that would entail some comets having been created by Sol. which is entirely possible. i'm less inclined to believe that due to a myriad of observed factors such as cometary orbits, extremely long-period comets --to the point that the period is non-existent--passing through only once, exotic particle structures, formation of structures under molten conditions. it creates an extrasolar picture for me because i want to believe in it, admitedly.

yevaud · Mar 14, 2006

Remember that when they say "weird," they aren't stating it's something never before seen. What they're saying is "not expected," specifically in the amounts seen. They were quite specific about that to my understanding. It's already known that material that formed in the inner solar system has migrated outwards via a number of mechanisms. So all that was a real surprise was that the quantity of it. Can there be material captured from extrasolar sources? Yes, certainly. But the amount is expected to be very low. Interstellar space is vast, and the chances of as much material deriving from there as has been mentioned is very unlikely. Further (not that this precludes it), it would be a huge coincidence if Wild2 turned out to be entirely of extrasolar origin. As I'd mentioned, it just plain isn't neccessary; there's already a large reservoir of material available right here. Now, hedging their bets, they did make mention of extrasolar sources for Wild2. That's expected, because it is possible; just very, very unlikely, particularly in the amounts neccessary to comprise an entire comet. Remember that comets do accrete other material during their lifetimes. I'd be very surprised if one could be comprised of 100% pristine, non-solar origin, even if one was discovered. There's nothing wrong about "believing" in the possibility, but you have to look at the odds first. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

siriusmre · Mar 14, 2006

<blockquote>In reply to:<hr />If comets are the remains of some fragmented planet...then should we not expect to see strong biases in their orbital parameters? Obviously there is one bias: they all have extremely elliptical orbits. (This is practically the definition of a comet.) But this isn't enough by itself. They seem to come from all over. Obviously we need to find more comets and better map the outer solar system to really get down to the meat of this, but the fact that they don't show a strong trend in their orbits seems, to me, to make it unlikely that they could all have once been part of a single object.<hr /></blockquote> Maybe. I agree, though, that more study is needed. It strikes me, though, that, even though I do not favor the EPH, your point that "[t]hey seem to come from all over" would seem to me to be consistent with something like an exploding planet. Wouldn't an explosion throw material in many directions? I am not sure how you can conclude that it is unlikely that they were part of some exploding object because they do not show a particular orbital bias, whereas I would expect things to be quite scattered as a result of exploding. Of course, the energies imparted to these fragments would depend on HOW this hypothetical planet got exploded in the first place (if, indeed, it did). <div class="Discussion_UserSignature"> </div>

bonzelite · Mar 14, 2006

There's nothing wrong about "believing" in the possibility, but you have to look at the odds first. i can agree with that. i am biased to extrasolar. i admit that. if they did form from fiery hellish conditions, they'd have had to have migrated from Sol. what are some ideas, then, if any, about their highly eccentric, highly elongated, orbits? such traits beckon the assumption of capture. just questions.

yevaud · Mar 14, 2006

Well, remember that this is material incorporated as part of a comet. It doesn;t mean, per se, that the comet itself originated within the inner solar system. Which is to say, yes sure, comets are a mixed bag of materials. The volatiles originating from the KBO, Oort cloud, or yes, even extrasolar. And a lot of the other material is accreted over a long period of time. As to the elongated orbits: perturbations and interaction with other bodies. After all, something generally kicks these objects out of semi-stable orbits in the locations mentioned. Over time, they end up in the orbits we see today. (Another minor mechanism is outgassing of the comet as it approaches the sun - this alters it's trajectory somewhat) <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

jatslo · Mar 14, 2006

What odds? Are you privileged to information that the rest of us are not privileged to see, because I don't really see anyone presenting actual numbers, do you? If you have stats from a statistician, then please fork them over. I will see what I can find, as well. Of course, lots of hypothecations will undoubtedly be rejected in the coming days, weeks, months, and/or years, but we can still dissect them nevertheless. Let's quantify please; you seem to have a desire to do so.

yevaud · Mar 14, 2006

Jatslo, have you ever contemplated exactly how vast space is? For example, suppose the cometary material is supposed to have derived from Rigel Kent. That's so far that it takes light alone over 4 years to reach us from there. And yet, if one buys into the belief that most comets derive from extrasolar sources, one has to convince themselves that somehow, even though solar systems are specks in the void, a huge number of them ended up here. How? <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

jatslo · Mar 14, 2006

Here are some stats, if not ping away; I'll be back: COMET StatisticsIf you are interested in statistics from Spring 2005 COMET administration, click here. Spring 2005, Admissions Offers. If you are interested in admissions ... www.comfsm.fm/comet/statistics.htm - 13k - Cached - Similar pages Comet HalleyHalley's Comet Statistics. Perihelion distance: 0.587 AU; Orbital eccentricity: 0.967; Orbital inclination: 162.24°; Orbital period: 76.0 years ... www.solarviews.com/eng/halley.htm - 11k - Cached - Similar pages Mickey Mantle Statistics - Baseball-Reference.comMickey Charles Mantle (The Mick, The Commerce Comet, or Muscles) ... Statistics may come from our work, the Baseball Databank, or other sources including ... www.baseball-reference.com/m/mantlmi01.shtml - 68k - Cached - Similar pages PSIgate - Physical Sciences Information Gateway: Search/Browse ResultsA brief history of Halley's comet is given, together with details of spacecraft that have visited the comet, comet statistics, images, and an animation of ... www.psigate.ac.uk/roads/cgi-bin/psisearch. pl?term1=Halley's+Comet&subject=All&limit=0 - 18k - Cached - Similar pages Cometary statistics (from comet) -- Encyclopædia BritannicaCometary statistics (from comet) The Catalog of Cometary Orbits, compiled by Marsden, remains the standard reference for orbital statistics. www.britannica.com/eb/article-54343 - 56k - Cached - Similar pages

yevaud · Mar 14, 2006

<img src="/images/icons/laugh.gif" /> You nut, you! The first link is to an entrance exam form for a school in Micronesia! Heheheh. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

jatslo · Mar 14, 2006

There are four or five @ www.solarviews.com/eng/halley.htm , and they are all testable. Halley's Comet Statistics: Perihelion distance: 0.587 AU Orbital eccentricity: 0.967 Orbital inclination: 162.24° Orbital period: 76.0 years Next perihelion: 2061 Diameter: 16 x 8 x 8 km

CalliArcale · Mar 14, 2006

<blockquote>In reply to:<hr />It strikes me, though, that, even though I do not favor the EPH, your point that "[t]hey seem to come from all over" would seem to me to be consistent with something like an exploding planet. Wouldn't an explosion throw material in many directions?<hr /></blockquote> Yes, it would throw material in many directions. However, conservation of matter applies. The object would almost certainly be in motion relative to the Sun. Its pieces will continue along much the same path. Depending on the force of the explosion, they will vary somewhat, and over a great amount of time and many interactions with other objects, their orbits will shift, but most of them should still stay along a similar path, at least vaguely. For a real-world example of what I mean, it is widely believed that a moon of Saturn was somehow fragmented into billions of tiny pieces, producing the ring system. Although the fragments must have been propelled outwards in many directions, there is a very strong bias in the orbits of the fragments today, producing the very visually pleasing effect of Saturn's rings. Basically, it comes down to a question of how much delta-vee is imparted on a given fragment of the original object by the explosion. If the object is rotating, that will also have an effect, by the way -- it will tend to fly apart mostly along what used to be its equatorial plane. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

robnissen · Mar 14, 2006

"have you ever contemplated exactly how vast space is? . . . And yet, if one buys into the belief that most comets derive from extrasolar sources, one has to convince themselves that somehow, even though solar systems are specks in the void, a huge number of them ended up here. How?" You are missing one thing: space is not static. While its true that the closest star is now over 4 light years away, that is not always the case. The sun has orbited around the Milky Way approximately 20 times, during that orbit, some stars are nearer, some are farther. Indeed, there was a story on Space. com about a star passing within 1 light year of the sun in the near (geologically speaking) future. As the Oort cloud is hypothesized to exend 2 light years, there would certainly be much interchange of materials when that star passes the sun. In addition, the current model suggests that the sun was born in a star nursery with many other stars. Those stars could have easily exchanged comets and other material. Do I think most comets came from other star systems? No. Is it likely that some came from other star systems? Absolutely.

CalliArcale · Mar 14, 2006

<blockquote>In reply to:<hr />if you don't buy into exogenic/radioisotope decay heating, then what else is left but explosions (supernovae or EPH processes) and/or other suns?<hr /></blockquote> Lots is left. I just don't think there's enough radioisotopes out there to account for it. More study is known to be sure, but I just don't think there's evidence to support radiogenic heating to this degree. Most likely, I would think the stuff formed someplace other than inside the comet, and later became incorporated into the comet's structure. Perhaps these materials are actually older than the comet itself. That's impossible to know at this point, of course, but intruiging all the same. Perhaps there are more complex substances in protoplanetary nebulas than we tend to think. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

siriusmre · Mar 14, 2006

I have to agree with Yevaud on this one. The image of the solar system that I like that gives one the sense of how widely separated things are in space; space is not as densely populated as some of us may think. For this analogy, imagine that one AU is one inch. At this scale, Sol would be 1/100th of an inch in diameter; Earth would be even tinier, at 1/100th the size of Sol. The entire system, out to the orbit of Pluto, would be able to be held in the outstretched arms of Yao Ming. At this scale, the nearest star would be FOUR MILES away, even in our relatively densly populated region of the galaxy! <img src="/images/icons/shocked.gif" /> The distances are truly vast. <div class="Discussion_UserSignature"> </div>

CalliArcale · Mar 14, 2006

You're right. That is very important to remember. My favorite illustration of it is this: The Pale Blue Dot It's part of this mosaic: Solar System Portrait The solar system looks awfully sparse at this distance. (Voyager 1 was 4 billion miles from Earth when it took the pictures.) <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

siriusmre · Mar 14, 2006

<blockquote>In reply to:<hr />For a real-world example of what I mean, it is widely believed that a moon of Saturn was somehow fragmented into billions of tiny pieces, producing the ring system. Although the fragments must have been propelled outwards in many directions, there is a very strong bias in the orbits of the fragments today, producing the very visually pleasing effect of Saturn's rings.<hr /></blockquote> Mmm. We can barely say with any amount of certainty what exactly did happen to produce the rings of Saturn--and they're still intact! This is revealed by your statement: "it is widely believed that a moon of Saturn was somehow fragmented into billions of tiny pieces, producing the ring system." Key words here: "believed" and "somehow." The fact is that no one really knows how those rings were formed, and if they were formed in the same way that a hypothetical exploding planet would have met its demise; i.e., did the moons in Saturn's rings explode, or were they disintegrated in some other way? It's still going on, and we still cannot tell! An planetary fragments and the pulverization of bodies in Saturn's rings MAY, in fact, be due to the same process, but it MAY have nothing to do with exploding, per se. <blockquote>In reply to:<hr />Basically, it comes down to a question of how much delta-vee is imparted on a given fragment of the original object by the explosion.<hr /></blockquote> That was part of my point. I also think that it would depend on the nature and cause of the "explosion." <div class="Discussion_UserSignature"> </div>

bonzelite · Mar 14, 2006

the void is beyond human capture. it is immense beyond immensity. comets may be swarming the void, as a plague of locusts.

CalliArcale · Mar 14, 2006

I only brought up Saturn's rings as an example of a system which shows characteristics consistent with possibly being part of a larger body that has since broken up. It is certain that they are younger than the planet, due to their orbital characteristics, so it's a very reasonable hypothesis. <blockquote>In reply to:<hr />That was part of my point. I also think that it would depend on the nature and cause of the "explosion."<hr /></blockquote> Yeah. That would influence the delta-vee. It's basic orbital mechanics, essentially. Lots of math. The upside is that you can write software models to figure out what it's likely to do given a range of explosions/impacts/gravitational disruptions/whatever. However, even if it was an explosion sufficient to scatter them REALLY widely, they should still show trends in their orbital parameters. Now, the search would be complicated by the fact that known comets certainly have interacted gravitationally with major planets. It's not usually possible to tell what orbit they used to be on. In the end, it's going to require finding a cometary resevoir (if one exists) where they are still orbiting in more primordial paths. (I.e. closer to where they were when they were formed, however that occured.) The amount of energy required to not only fragment a body such that it stays permanently fragmented and doesn't end up as a really complicated planetary system is enormous -- and just as prone to underestimation as the sheer vastness of space. And even in that sort of an explosion, they'll still end up on very similar paths. That's the biggest problem with asteroid deflection schemes such as depicted in the movie "Armageddon" -- even if you could blow up the asteroid, the bits are still gonna hit you. (And now their force will be spread out over a much larger area.) To scatter the bits so much and change their orbits so much would require a phenomenal amount of en <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

jatslo · Mar 14, 2006

The further away the source is makes the Earth that much more unlikely to get slammed, for if the source is close, the buckshot is packed closer together. How long will it take for the buckshot to get here?

bonzelite · Mar 14, 2006

good point. the odds diminsh the farther out you go. or do they? this is beginning to give me a headache. more questions are raised, daily, than answered.

yevaud · Mar 14, 2006

this is beginning to give me a headache. more questions are raised, daily, than answered. "Welcome to the Wonderful Wide World of Science. The thrill of victory; the agony of defeat." <img src="/images/icons/wink.gif" /> That's the appeal. An ever moving frontier. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

Saiph · Mar 14, 2006

no no no, the agony of victory...as it only opens up more details to be pinned down. The thrill of defeat...as it actually closes a line of questioning. Feels like you did something. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

yevaud · Mar 14, 2006

A Marine named Sid: "The victory of defeat and the defeat of victory. Booyah!" <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

What's Going on With Comets?

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