Comet chunks to fly by Earth

CalliArcale · Apr 28, 2006

FYI, the profanity filter is also used to prevent the use of HTML to post inline images. To do this, certain strings have been blocked. s-r-c (minus the hyphens) is one of them, and unfortunately that appears to be the one that's giving you troubles. We had a troublemaker a while back who abused inline images to post porn, so that's why it's forbidden now. The best I can do for you is to say "sorry", because it's not going to be changed. <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>

CalliArcale · Apr 28, 2006

<blockquote>In reply to:<hr />If so, could internal stress alone account for such shattering? To my uninformed eye it looks more like it's been smashed to pieces by a fairly significant collision.<hr /></blockquote> Assuming comets are not uniform and are fairly porous (a popular but largely untested view -- Rosetta will help a lot in exploring this), then yes, internal stress could theoretically account for this. You've seen an ice cube crack when you dunk it in a glass of water, right? It's the same basic principle here, only on a bigger scale. Imperfections in the ice cube mean it expands unevenly, and this produces stress. Aiding the scattering of the bits is very likely the propulsive force of their own outgassing; they've been accelerating in the Hubble images in a way that is consistent with outgassing predominantly on the sunward side of the pieces. That's basically what's been proposed so far to explain what's happening here. This is an unparalleled opportunity to study a comet, because there is a lot you can learn from its breakup. <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>

tom_hobbes · Apr 28, 2006

Cheers Calli, that helps me to understand. I guess the various pieces have had long enough (over a decade?) to accelerate away from each other. <div class="Discussion_UserSignature"> I wish I could remember But my selective memory Won't let me - Mark Oliver Everett </div>

edawg · Apr 28, 2006

does anyone know where i can find out the orbital speed of the comet?Also any site dealing with orbital mechanics?How much orbital velocity change would we have to +/-? to park a chunk in L1?

tom_hobbes · Apr 28, 2006

Christ knows! Actually there's almost certainly someone here who knows and could work it out... <div class="Discussion_UserSignature"> I wish I could remember But my selective memory Won't let me - Mark Oliver Everett </div>

cyclonebuster · Apr 28, 2006

Well before SOHO was placed in the L1 lagrange orbit years ago we only thought just 2 or 3 comets a year flew into the sun. Well that all changed the number is actually at least 100 times that and the total count is over 1000 since it has been place there. Seems to me more chances of a collision happening.

tom_hobbes · Apr 29, 2006

I've seen the videos on the SOHO site over the last few years though I doubt most of them made it that far! Wouldn't they be melted and or vapourised long before arrival? <div class="Discussion_UserSignature"> I wish I could remember But my selective memory Won't let me - Mark Oliver Everett </div>

cyclonebuster · Apr 29, 2006

But not before it could have collided with another comet such as this!!

CalliArcale · May 1, 2006

Most likely, yes, the sungrazers (comets which go close to the sun) get vaporized. They're never seen again, anyway. <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>

edawg · May 1, 2006

got the link for the cali ice chunk?might be wheather related..whos goin to the isdc?

CalliArcale · May 2, 2006

An interesting target for backyard astronomers..... If you have favorable weather Sunday night (or early Monday morning for folks on the other side of the Atlantic), Fragment C of Comet 73P will pass very near the Ring Nebula in Lyra. The tail is expected to actually transit the Nebula. The pass will occur at 0300 UT Monday (10PM Sunday for folks in Central Daylight Time). Here's hoping for clear skies! <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>

cyclonebuster · May 2, 2006

http://abcnews.go.com/US/story?id=1826352

cyclonebuster · May 2, 2006

http://neo.jpl.nasa.gov/cgi-bin/db_shm?sstr=73P-AT May 11th is its closest approach if it were hit by another object we could be in for a bad time here for about a months period after that date.

CalliArcale · May 2, 2006

Not likely. (See other thread.) <img src="/images/icons/wink.gif" /> Short answer: it's already breaking up; any fragments from a collision will probably continue on a path very similar to what they're already on, and thus miss the Earth. (On this path anyway. I don't know how much uncertainty there is about future orbits.) <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>

edawg · May 2, 2006

when an ice cube cracks sometimes lil chunks shoot of on random trajectories +orbital mechanics =? i can't do the math but the theory makes sense anyone?

harmonicaman · May 2, 2006

A lot of big scopes are keeping an eye on things and we'll know more in a few months. It's still a bit too early to tell how big of a footprint the comet debris will cover on future passes and if the Earth is in any danger; right now things look good and there is a wide margin of safety. Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. - Douglas Adams (1952 - 2001), "The Hitchhiker's Guide to the Galaxy"

CalliArcale · May 2, 2006

<blockquote>In reply to:<hr />when an ice cube cracks sometimes lil chunks shoot of on random trajectories +orbital mechanics =? i can't do the math but the theory makes sense <hr /></blockquote> You should see the Hubble pics. It's awesome -- you can see the chunks are moving apart in that sort of fashion. Click here for video. The unknown factor is how much *delta-vee was applied to each chunk by whatever process broke it off. Scientists can make educated guesses, but it's a bit like trying to determine cause of death with a body that wasn't recovered for months; you just don't have all the information, and even where the clues do exist, they're obscured by bigger damage that occured after death (like decay). In this case, the problem is one of distance; the comet was much further away when it broke up. Time is an issue too; the initial breakup began years ago, first being observed in '95 (IIRC). So watching how the chunks move will narrow the field, because it'll show how much delta-vee was imparted to the chunks, which should limit the possibilities for how they broke up and how quickly. * delta-vee = change in velocity; it's the technical term for how much overall propulsive effect was had on the object; a very important term in celestial mechanics <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>

cyclonebuster · May 2, 2006

So lets calculate how far apart they will be in 2022 and if any of the debris crosses Earths orbit.

dmjspace · May 3, 2006

CalliArcale said: Good grief! They aren't saying that at all. From the link *you* provided: They said *exactly* that: "In 1995, Comet 73P/Schwassmann-Wachmann 3 did something unexpected: it fell apart. For no apparent reason, the comet's nucleus split into at least three 'mini-comets' flying single file through space." "Unexpected" is the operative word here. As SiriusMrE pointed out, comets that break up do so at the wrong time, under dirty snowball premises, at least. The EPH says that comets are mutually orbiting debris fields, with multiple main nuclei. This is a significant difference from the standard model. The EPH predicts a shrinking gravitational sphere of influence for the nuclei, a situation which causes the nuclei to become unbound. It requires no other mechanism. There is relatively little guesswork involved with the EPH. "The most likely explanation is thermal stress, with the icy nucleus cracking like an ice cube dropped into hot soup: the comet broke apart as it approached the Sun after a long sojourn the frigid outer solar system," he explains. "If this is truly what happened, then the debris cloud should be expanding slowly, and there will be no strong meteor shower." The dirty snowball model didn't expect the comet to break up, because it assumes it is a single nucleus object. This explanation actually derives from the "dirty snowball" concept. It is grossly unfair to the scientists to claim that the breakup of this comet defies the standard model, even more so when you purport to be paraphrasing an article which does not support your assertion that this is totally unexpected. According to the article, "[The comet] did something unexpected: it fell apart." Does this wording not fit the idea that the breakup was unexpected? There is no d

cyclonebuster · May 3, 2006

So it is possible that another object impacted this object and broke it apart. If this is so then it is possible to have a fragment hit us this time around.

CalliArcale · May 3, 2006

<blockquote>In reply to:<hr />The dirty snowball model didn't expect the comet to break up, because it assumes it is a single nucleus object.<hr /></blockquote> As the article goes on to explain, the dirty snowball model DOES expect comets to break up. The observed breakup of comets (this is far from the first to do so) was a major factor in the development of the theory. What scientists don't know is exactly what caused the comet to break up in this particular instance (thermal stress or a collision are the two leading theories), or why it broke up when it did. This is not because the dirty snowball model doesn't expect breakup. This is because the dirty snowball model is not psychic. It doesn't know where fracture lines happen to be within comets, how long they've been in their current orbits prior to first observation, whether or not some undetected minor planet smacked into 73P back in '95, and so on. You really are reading far too much into the word "unexpected". If a person runs a red light in front of me and I find that unexpected, does this mean I had an incorrect model of human behavior? No. It simply means I didn't anticipate this particular person running the red light at that particular time. "Unexpected" doesn't mean "gosh, this completely blows away everything we ever thought true." It simply means "unexpected". BTW, one of the leading variants of the "dirty snowball" holds that comets are loose rubble piles, so you are severely mischaracterizing the model. <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>

llivinglarge · May 3, 2006

Shoemaker-Levy 9 broke up due to Jupiter's tidal forces... Can a similar circumstance be at work here?

dmjspace · May 3, 2006

CalliArcale said: What scientists don't know is exactly what caused the comet to break up in this particular instance (thermal stress or a collision are the two leading theories), or why it broke up when it did. This is not because the dirty snowball model doesn't expect breakup. This is because the dirty snowball model is not psychic. No, it's because the dirty snowball model has so many variables, it can't decide on what will happen or when. It can't predict when breakups occur. It can't predict what comets are made of (are they rubble piles, or are they solid masses, do they have satellites or don't they, etc., etc., etc.). You really are reading far too much into the word "unexpected". And you are vastly underestimating the importance of the repeated instances of "unexpected" observations regarding comets. Virtually every new observation produces a fundamental shock to the snowball model. You may call that a model under refinement. I call it one that is severely flawed. BTW, one of the leading variants of the "dirty snowball" holds that comets are loose rubble piles, so you are severely mischaracterizing the model. You're citing this as a strength of the model? Variants? The more version of a model that exist, the closer it is to worthlessness, scientifically speaking. Again, there is no doubt snowball proponents will find a way to explain 73P's behavior. Even in the article link I cited, the astronomers are busy covering their butts: *if* 73P broke up due to thermal stress, its debris will be moving slowly; *if* it was hit by an interplanetary boulder, it will be moving quickly. Slowly, quickly. Both are acceptable. The model makes no specific predictions. (Actually, as I and another poster pointed out--and you edited out so as to not have to address it--the d

CalliArcale · May 4, 2006

<blockquote>In reply to:<hr />Slowly, quickly. Both are acceptable. The model makes no specific predictions. (Actually, as I and another poster pointed out--and you edited out so as to not have to address it--the dirty snowball model *does* make predictions about when such breakups should occur. It has been wrong about the timing. This is a failed prediction, not just the usual non-prediction that characterizes the standard model.) <hr /></blockquote> What did I edit out??? Are you seriously accusing me of censorship? The dirty snowball model should be able to correctly predict when a comet will break up -- if a lot is known about the particular comet. How long has it been dipping into the inner solar system? Has it collided with anything? What is the particular distribution of material within the comet? (The dirty snowball expects them to be variable. You seem to think of this as a flaw, although I fail to see why.) Since these data points are unknown for virtually all comets, it is unreasonable to expect the dirty snowball model to make predictions about exactly when a particular comet will fracture. Your objections to the dirty snowball are noted, and fair. However, I disagree that they are the showstoppers you think they are. But while your objections are fair, I think your mischaracterization of the article is grossly unfair -- to say nothing of your accusation that I edited out somebody's post so as to spare me the inconvenience of responding to it. I would never EVER do something as despicable as that <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>

paulanderson · May 4, 2006

I noticed that one of the fragments, 73P/Schwassmann-Wachmann 3-BD, is listed here as having a Minimum Miss Distance of only 0.04 LD / 0.00010 AU (very close, about 4% of the distance to the moon): http://tinyurl.com/pcfe8 The Nominal Miss Distance is still much greater though, so a hit may still be unlikely, I hope. Closest approach is on May 11.

Comet chunks to fly by Earth

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