Ice on Comet Tempel 1

bonzelite · Feb 14, 2006

the primary constituent of the tail in Comet Halley is C02 laden silicate dust and not liquid water. there is certainly ice present in the dust, as there is on the moon in some places, but the primary material is not a gush of water. a luminous comet tail is primarily, as we continue to glean data, ionized dust in which ice is but one part of a complex silicate particle. again, there is no dirty snowball. to imply that the data only shows "huge volumes of water" is misleading and not true. this gives the impression that the comet is primarily an ice-laden body like Enceladus when, in reality, is more similar to a common asteroid.

telfrow · Feb 14, 2006

The ratio observed in the tail of Halley's Comet, IIRC, was 1 to 1, water vapor to dust. Not bad for someone with the intelligence of an "average ape," huh? <div class="Discussion_UserSignature"> Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild. - Tennyson </div>

bonzelite · Feb 14, 2006

not enough, homie. this common ape says ain't no water ice body, baby. ain't no big water carrier. dirty snowman is dead. moving on now to better things. time for dinner.

telfrow · Feb 14, 2006

The discovery of gas and dust jets being emitted from the nucleus suggested that only about 10% of the surface was active. [Emphasis added] The chemical composition of the gas changes with distance from the nucleus in a complex chain of chemical reactions. The 'parent molecules' at the beginning of this chain reflect the composition of the nucleus. As expected, water (H20) was found to be the dominant (80%) parent molecule. Other parent molecules are carbon monoxide (CO) at 10%, carbon dioxide (CO2) at 2.5%, CH4 (7%), NH3 and at the 0.1% level HCN and various hydrocarbon (C2Hn, C3Hm). Iron (Fe) and Sodium (Na) were also found, and S2 and H2S are strongly suspected to be other parent molecules. [Emphasis added] The cometary gas is ionized by solar ultraviolet radiation, by electrons and by charge exchange with the solar-wind plasma. A large number of ionic species were identified, among them H30+ (the most dominant ion near the nucleus), H20+, OH+, C+. CH+, 0+, Na+, C2+, S+ and Fe+. At the time of the Giotto encounter on 14 March 1986 at about 0.9AU heliocentric distance, comet P/Halley emitted about 18 metric tons (19.8 tons) of gas every second, together with the emission of dust, which was of nearly the same order, an estimated 30 metric tons (33 tons) of material was released every second by the nucleus. [Emphasis added] Link So nearly 20 tons of gas per second was emitted from about 10% of the nucleus, with 80% of the gas emitted identified as water. That's 16 tons per second of water from just 10% of the surface. Not enough? For what? <div class="Discussion_UserSignature"> Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild. - Tennyson </div>

bonzelite · Feb 14, 2006

telfrow, it's not enough to make the comet into the ice ball that everyone wishes for. the data you provide misleads the reader to believing that the comet is mostly water and it is not. specific to Halley: http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=26418 http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31878 Science Results Horst Uwe Keller "We discovered that a comet is not really a 'dirty snowball' since dirt is dominant, not ice," said Horst Uwe Keller of the Max Planck Institut für Aeronomie, Katlenburg-Lindau, Germany. "Instead of being spherical like a warm snowball, a comet nucleus is elongated. The physical structure of a comet's interior is defined by its dust content rather than its ice content." The data from the plasma and ion mass spectrometers indicated that the surface of Comet Halley is covered in a layer of organic (carbon-rich) material./safety_wrapper>

yevaud · Feb 14, 2006

And yet (from the second link you provide): Water accounted for about 80% by volume of all of the material thrown out by the comet. There were also substantial amounts of carbon monoxide (10%), carbon dioxide (2.5%) methane and ammonia. Traces of other hydrocarbons, iron and sodium were also found <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

telfrow · Feb 14, 2006

You beat me to it. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild. - Tennyson </div>

mlorrey · Feb 14, 2006

Tempel is considered an old comet partly because of its albedo and partly because its orbit is so circular. It takes a lot of passes to turn an extremely eccentric orbit into a circular one.

bonzelite · Feb 14, 2006

And yet (from the second link you provide): Water accounted for about 80% by volume of all of the material thrown out by the comet. exactly. i don't see your "gotcha" factor. i said that the data is misleading upon first read. it does not mean the comet is mostly water. it is mostly dirt with a little ice. it's nucleus content is not defined by the water blowoff. what don't you understand about this: "The physical structure of a comet's interior is defined by its dust content rather than its ice content." /safety_wrapper>

yevaud · Feb 14, 2006

Well, there's a very real problem with that. How are they determining the composition of Halley? It can be only one of two ways, given what they've stated in the articles. One, they're using the Comet's Albedo, and trying to ballpark from there. And there lies a serious problem. Surface composition tells little of what the underlying material present is. The data from the plasma and ion mass spectrometers indicated that the surface of Comet Halley is covered in a layer of organic (carbon-rich) material. Somehow they've extrapolated internal composition from the surface layer. Two, they're using spectroscopic analysis of the emitted material. If so, then I default right back to the composition of the material: 80% water. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

telfrow · Feb 14, 2006

"[Comet 9P/Tempel 1] is like a sponge, with a lot of cavities," agrees Horst Uwe Keller, an astronomer at the Max-Planck Institute for Solar System Research in Germany. He observed the event with Europe's Rosetta spacecraft and says the discovery confirms previous observations suggesting other comets are also porous. "When you touch it, it just crumbles under your hands."" Link <div class="Discussion_UserSignature"> Made weak by time and fate, but strong in will to strive, to seek, to find and not to yeild. - Tennyson </div>

bonzelite · Feb 14, 2006

If so, then I default right back to the composition of the material: 80% water. for some reason unknown, you must be in a state of denial of this assessment, then: Horst Uwe Keller "We discovered that a comet is not really a 'dirty snowball' since dirt is dominant, not ice," said Horst Uwe Keller of the Max Planck Institut für Aeronomie, Katlenburg-Lindau, Germany. "Instead of being spherical like a warm snowball, a comet nucleus is elongated. The physical structure of a comet's interior is defined by its dust content rather than its ice content." what do you not understand about that statement?

yevaud · Feb 14, 2006

A state of denial...hey, that's pretty good. *Ahem* Edit: going to redact and reexplain here. The determined density for Tempel1 is quite low. Highly porous, with an estimated density only 60% of that of H20 ice. Carbonaceous or metal-rich materials would have a much higher density, and were they to predominate in the overall makeup of the comet, we'd know it. Clearly, given what we know and saw, they don't here. Couple this with the detected plume of ejected material, of which I believe your own sourse said "80% water" (along with other expected and unexpected material), and I believe a very solid argument can be made for the "Dirty Snowball" model in this case. A surprise: The comet also shows layering of different structures, with each segment 20 to 30 m deep. "We went into this mission talking about the so-called icy conglomerate model—a chunk of ice and dirt and organic gunk, all mixed together," Veverka says. "But instead, we have this frozen onion (NASA Science News)." I could even buy a mechanism whereby a small amount of some rocky/metallic material acts as a "seed crystal" for the growth (accretion) of comets over time, in the same way hail is built up (not that it appears neccessary in the formation and evolution of comets, but I'll speculate a bit here). But even so, that overall density for Tempel1 kills the "Snowy Dirtball" line of reasoning right there. It's far too low for that kind of dense material to predominate. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

bonzelite · Feb 15, 2006

more on comet Halley: http://spaceguard.esa.int/tumblingstone/issues/num20/eng/giotto4.htm (cached) http://64.233.179.104/search?q=cache:AtsD-lTwkrIJ:spaceguard.esa.int/tumblingstone/issues/num20/eng/giotto4.htm+Horst+Uwe+Keller,+comet+halley&hl=en&gl=us&ct=clnk&cd=1&client=safari excerpt: Of particular importance for the quest of cometary origin are isotopes. The ratio of deuterium (a heavy isotope of hydrogen) and hydrogen (D/H) in cometary water was found to be much higher than the typical value of material in the solar system and in particularly in the oceans of the earth. Therefore, the notion that the terrestrial oceans and atmosphere are the result of a bombardment with comets in the early stages of the solar system can be refuted. Not more than 10 % of our water could be of cometary origin. Cometary water has to come from ice that condensed on grains. During the formation of water molecules on the surfaces of grains in space the heavy deuterium atoms are slowly enriched compared to their concentration in the gas because the lighter hydrogen atoms can more easily leave the grains again.3.2.2 The dustThe volatile compounds found in the coma essentially confirmed our conception, with the possible exception of the D/H ratio. The dust revealed more surprises. First of all it was found that the cometary nucleus contained much more dust than previously assumed and determined from remote observations with telescopes. The ratio of volatiles (ices) to dust (non-volatiles) was found to be one or even smaller. With other words most of the material in a cometary nucleus is non-vo

exoscientist · Feb 15, 2006

Yevaud, the 80% by volume water vapor figure does not necessarily contradict a largely dust model if the characterization is being made by *mass*. For instance air at sea level, which is pretty dense as far as gases go, has density of 1.2 kg/m^3 whereas solid minerals or dust might be expected to have a density in the range of 1500 to 2500 kg/m^3. With the comets weak gravity we would expect the density of the gases to be even less than that of air. I think it's pretty well accepted now there is more dust in comets that water. How much more depends on the comet. - Bob Clark <div class="Discussion_UserSignature"> </div>

siriusmre · Feb 16, 2006

<blockquote>In reply to:<hr />Tempel is considered an old comet partly because of its albedo and partly because its orbit is so circular. It takes a lot of passes to turn an extremely eccentric orbit into a circular one.<hr /></blockquote> And how, exactly, do they *know* what Tempel's initial orbital trajectory was? Also, what's the connection between age and albedo? Is it that old comets have low albedo? What's the explanation for that? It seems to me that that kind of explanation relies on many, many unsubstantiated--and unsubstantiatable--assumptions. <div class="Discussion_UserSignature"> </div>

siriusmre · Feb 16, 2006

As for all this talk about the "water" content of comet coma, astronomer Fred Whipple (1986 Bruce Medalist) had this to say about comet coma material in his book The Mystery of Comets: "The inner coma of a comet is a chemical factory! This leaves us confused as to whether the materials we detect come unchanged directly from the nucleus or were manufactured near the surface. Fortunately, the tools for analysing this horrendously complicated problem have become available in recent decades. "[...] "From our vantage point on Earth, which is so distant from comets, we can observe only the end products of the chemical factory after they have escaped hundreds or thousands of kilometres into space, where the gas is so rare that collisions no longer count. Thus the complicated gas-phase chemistry disguises the composition of the original ices in a comet. [Emphasis added.]" So, it is entirely possible--if not probable--that there is some kind of chemistry going on very near or at the surface of comets--which we will soon discover are simply asteroids with eccentirc orbits. Further, I agree with bonzelite that it is misleading and disengenuous to state as fact that there are large volumes of water in comet coma. Scientists are not actually detecting water, but the OH hydroxyl radical. And, while scientists hold that photolysis, the mechanism by which H2O is supposedly boken down by solar UV light, produces leftover hydrogen, it is not clear, though, that photolysis can actually break down water in this way. No one seems to have done the lab work yet. We do know, however, that electrolysis is the easiest way to split the water molecule to produce hydrogen. Perhaps something like that is happening. If material is being electrically sputtered off of the surface of the comet nucleus, the ch <div class="Discussion_UserSignature"> </div>

yevaud · Feb 16, 2006

The Chief Spectroscopic team at the University of Maryland would tend to disagree. UMD Deep Impact Spectroscopy <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

dmjspace · Feb 16, 2006

exoscientist said: I think it's pretty well accepted now there is more dust in comets that water. How much more depends on the comet. Given that asteroids are up to 20% interstitial ice, the line between comets and asteroids has become hopelessly blurred. There is no such thing as a dirty snowball, only icy dirtballs of varying flavors.

yevaud · Feb 16, 2006

That last may well be so. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

colesakick · Feb 16, 2006

"A much different vantage point on the water question is possible. The unsolved mysteries of the comet will find direct answers in an electrical exchange—the transaction between a negatively charged comet nucleus and Sun. In fact there are many avenues for generating OH if you allow for electric discharge and “sputtering” by protons to remove silicates, carbonates, and other rock minerals, together with organic molecules, from the comet’s surface. The sputtering technology is well established in industrial applications, and such events would be the trademark of an electric comet. No other model could account for the phenomena. And anything suggestive of electric sputtering could only come as a surprise to astronomers, who have never dreamt of such a thing. The electric theorists repeatedly remind us that surprises are the key to discovery: the findings that have most astonished astronomers are high energy events—extreme ultraviolet light emissions, x-ray emissions, million degree temperatures, supersonic jets, explosive and unpredictable outbursts even beyond the orbits of Jupiter and Saturn, the violent break-up of comets (including the surprising speed at which the parts sometimes separate), and the complete disintegration of comet nuclei millions of miles from the Sun. The very things that comet researchers did not anticipate are the predictable effects of an electric comet." http://www.thunderbolts.info/tpod/2005/arch05/00current.htm <div class="Discussion_UserSignature"> Intellectual honesty means being willing to challenge yourself instead of others </div>

yevaud · Feb 16, 2006

I'm going to ask you very nicely to cease posting EU concepts here. While there are some well-known electric phenomena in Space Physics, this subject has been flogged to death and found to have no merit in a scientific sense. Or, for that matter, in a scientific forum. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

colesakick · Feb 16, 2006

Early results of what the tail is made of led to this comment: "But the first day was as exciting as I'd anticipated," says Bland. "And to actually find something wacky straight off was way more than I expected." http://www.nature.com/news/2006/060213/full/060213-2.html We won't know why its wacky until they all agree how to report it. <div class="Discussion_UserSignature"> Intellectual honesty means being willing to challenge yourself instead of others </div>

yevaud · Feb 16, 2006

We won't know why its wacky until they all agree how to report it. And the Deep Impact Spectroscopic Team isn't "reporting it?" Oh good God... <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

bonzelite · Feb 16, 2006

In fact there are many avenues for generating OH if you allow for electric discharge and “sputtering” by protons to remove silicates, carbonates, and other rock minerals, together with organic molecules, from the comet’s surface. The sputtering technology is well established in industrial applications, ^^^ this is correct. whether it happens in comets has yet to be accepted or confirmed, but the statement is sound and scientific. surprises are the key to discovery: ^^^also correct. and modern science presently accepts surprises in terms only of pre-existing politically accepted ideas. how sad, a crying shame. the polarized opinions in this thread, despite the growing mountain of evidence that comets are primarily dust and not gushing water vessels, is testament to that.

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