Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES
Hello Sterling, List, Sterling, your summarizing our (still so fragmentary) knowledge on our solar system in general and on the origin of carbonaceous chondrites in particular, is very much appreciated. I am not at all expert in cosmology, just, as a chemist, interested in the constitution of the various cc's related to their origin, namely the place (within the primitive solar nebula or with respect to the (proto) sun), where they first formed and place where their parent bodies were approximately located when they collided. It is certain that the chemistry, mineralogy or composition of a material (here a carbonaceous chondrite), which is a priori universally the same in a laboratory on Earth or somewhere in the remote space, obviously depends on the physical, thermodynamic or kinetic parameters that characterize their environment. So that the analysis of a specific meteorite can tell us much about such parameters that characterize(d) selective parts of our solar system. I have a couple of somewhat naive questions that you possibly can at least partly answer. 1) Among the ungrouped C chondrites are Coolidge, Loongana 001, Belgica 7904, Adelaide and Açfer 094, perhaps some other, my list being probably not exhaustive. Are these meteorites all different in constitution so that they are just thrown to the ungrouped class, or do they have some common charcteristics that could be later used to create a new group ? In other words, can we claim that their parent body is the same, or just belongs to a common family or are so far all their parent bodies thought to be different (and, of course, unknown) ? 2) Same question about the group of the three meteorites Kakangari, Lewis Cliff 87232 and Lea County 002, that are at the edge of the achondrite class, although an isotopic analysis suggests some close similarities with CR or even CH groups. 3) Does the fact that Tagish Lake was reported to contain the highest % of carbon ever measured in a cc, namely 5.81% (if my data are correct), still fit the assumption that TL belongs to the CI group and that it can originate from Sun's photosphere ? Also, first analyses of TL suggested its possible cometary origin but it seems that more refined data challenged that statement. Does one have today a better guess about the parent body of CI's in general and of TL in particular ? I know of a recent study (March 2006) that suggested, as CI's parent bodies, asteroïds of type P or D, thus orbiting beyond Saturn, at the edge of Kuyper belt. Any comment on that ? Thank you very much again! Best wishes to all, Zelimir A 19:54 21/09/2006 -0500, vous avez écrit : Hi, E.P., The truth is we really don't know what comets and asteroids actually are, or whether there's a real distinction between them, or if they are just keywords derived (mistakenly) from the two extremes of a continuous spectrum of bodies with every intermediate state fully represented. There are comets that die and turn into asteroids, and there are asteroids that suddenly develop a coma and become comets. But the two terms may not be a descriptions of two essentially different classes of bodies at all. After we sample and/or visit 50 or 100 of them, we'll have a much better idea... The association of carbonaceous chondrites with comets is supposed by many, but not ever demonstrated. No meteorite has ever been definitively linked to a comet. There are no known samples of cometary material. (We may have it, but if we do, we don't know it...) On the chance that CC's may be linked to cometary material or be similar to it... Here's a summary on Carbonaceous Chondrites (quickly ripped from the Net, not my data-leaky brain). The metal content runs from 50% for Bencubbinites, 15% for CH type, down to about 1% for other classes. Some classes have clearly never been warmed about 50 degrees absolute; some people have suggested that the CH class formed intra-Mercurially. Obviously, all carbon containing meteorites didn't start out in the same single nursery! Another indicator that the heresy that the early system was very well stirred might be true. Carbonaceous chondrites account for about 3% of all known chondrites. They are classified according to the proportion and size of the chondrules they contain (one rare subclass lacks chondrules). The average contents of CC's are: Carbon, 2.0%; Metals, 1.8%; Nitrogen, 0.2%; Silicates, 83.0%; Water, 11.0%. At most, they can be 20% water and can contain as much as 4% carbon. Carbonaceous Chondrites contain around 5% kerogen. The sub-classes are: CI chondrites, only a handful of which are known, are named for the Ivuna meteorite. They have very few chondrules and are composed mostly of crumbly, fine-grained material that has been changed a lot by exposure to water on the parent asteroid. As a result of this aqueous alteration, CI chondrites contain up to 20% water in addition to various minerals altered in the presence
Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES
Hello Larry, In the case of carbonaceous chondrites, I believe your inference that Just being in an orbit that takes them near the Earth would warm them up to 100 c or so is way too high, and that the right number in direct Sunlight hovers around freezing (0 degrees C). There is that other related subject of whether chondritic meteorites are cool to touch when they land...but I'm not going there... To reach 100 C, by just being in an orbit near X, taking a carbonaceous chondrite as a model, I believe you would need to be a third of the way closer to Mercury's orbit from Venus' in today's Solar System. You mention Spitzer data. For comets on epic journeys through the Solar System, which have possibly been orbiting over 4.5 Billion years through all phases of development, there are many possible alternate sources of meaningful temporary heating during this history that could account for the gentle-moderate heating you mention, likely reasonable sized impacts and more so, shock heating from barreling through precursor Solar nebula components from their own soup they were formed out of in situ, not to mention other lower probabilities over time that chance favors. Maybe you meant something else? Even a lump of nickel iron is hard pressed to make 100 C in the Sunshine in Earth's neighborhood in outer space. The high volatiles concentrations in carbonaceous chondrites are supportive of what I say, I think, though of course they are NOT conclusive. Best wishes, Doug P.S. The Andromeda Galaxy, which dwarfs our own, may even collide with the Milky Way in 3 Billion years, two-thirds of the Sun's current age. Larry wrote: Hi Sterling: Not a bad summary. However, do not know where you got the heated above 50 absolute. Much too low. Just being in an orbit that takes them near the Earth would warm them up to 100 c or so. Some clearly have not been heated much above that, but at the same time, since they contain water of hydration, they had to be warm enough to have had liquid water (clays are an alteration product). Until the Spitzer observations of Deep Impact, it was thought by many people (but not all) that one would not find hydrated silicates in comets (too cold). There is still some question about the Spitzer observations, but have not seen anything is the Lunar and Planetary Science Conference last March. Larry Quoting Sterling K. Webb [EMAIL PROTECTED]: Hi, E.P., The truth is we really don't know what comets and asteroids actually are, or whether there's a real distinction between them, or if they are just keywords derived (mistakenly) from the two extremes of a continuous spectrum of bodies with every intermediate state fully represented. There are comets that die and turn into asteroids, and there are asteroids that suddenly develop a coma and become comets. But the two terms may not be a descriptions of two essentially different classes of bodies at all. After we sample and/or visit 50 or 100 of them, we'll have a much better idea... The association of carbonaceous chondrites with comets is supposed by many, but not ever demonstrated. No meteorite has ever been definitively linked to a comet. There are no known samples of cometary material. (We may have it, but if we do, we don't know it...) On the chance that CC's may be linked to cometary material or be similar to it... Here's a summary on Carbonaceous Chondrites (quickly ripped from the Net, not my data-leaky brain). The metal content runs from 50% for Bencubbinites, 15% for CH type, down to about 1% for other classes. Some classes have clearly never been warmed about 50 degrees absolute; some people have suggested that the CH class formed intra-Mercurially. Obviously, all carbon containing meteorites didn't start out in the same single nursery! Another indicator that the heresy that the early system was very well stirred might be true. Carbonaceous chondrites account for about 3% of all known chondrites. They are classified according to the proportion and size of the chondrules they contain (one rare subclass lacks chondrules). The average contents of CC's are: Carbon, 2.0%; Metals, 1.8%; Nitrogen, 0.2%; Silicates, 83.0%; Water, 11.0%. At most, they can be 20% water and can contain as much as 4% carbon. Carbonaceous Chondrites contain around 5% kerogen. The sub-classes are: CI chondrites, only a handful of which are known, are named for the Ivuna meteorite. They have very few chondrules and are composed mostly of crumbly, fine-grained material that has been changed a lot by exposure to water on the parent asteroid. As a result of this aqueous alteration, CI chondrites contain up to 20% water in addition to various minerals altered in the presence of water, such as clay-like hydrous phyllosilicates and iron oxide in the form of magnetite. They also harbor organic matter, including polycyclic aromatic hydrocarbons (PAHs) and amino acids, which makes them
Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES
Hi Doug: Tell this to the astronauts in their space suits. I wish I still had access to my old thermal model programs so that I could give you real answers, but I will do my best. If you look up the surface temperture of the day side of the Moon, you get 107 degrees C. However, the noon temperture is well above 120 C (130 C ?). The mean and high temperture of an object is dependent on: Distance from the Sun Its reflectance (how much sunlight it absorbs) How fast it is rotating The size of the particles that make up the material (sand vs. rock) The lower the albdeo, the more sunlight you absorb, the hotter you get. The faster you rotate and the rockier your surface, the more heat you dump out the night side, so the lower your highest temperture. The Moon's day/night cycle is 29 days (slow) and its reflectance is 12%, so it gets fairly hot at noon. A typical NEO will rotate much faster, but if a C asteroid, it will have a much lower albedo (maybe 5% or 6%, but that really is not that much more energy since the absorbed energy is 88% vs 95%). Still, the asteroid will reach average daytime tempertures very close to 100 degrees C. The interior will be cooler (insulated), but will still be warm depending on the object's mean distance from the Sun. If anything is hard pressed to get above freesing at the Earth's distance, why does it get so hot on the surface of the Earth in the summer even though the Earth reflects 30% of the light that hits it? Go stand outside in July and tell me you are cold! Remember that the volatiles (water) are lcked in the minerals themselves (clays) and can withstand vacuum and moderate heating with being lost to space. Larry Quoting MexicoDoug [EMAIL PROTECTED]: Hello Larry, In the case of carbonaceous chondrites, I believe your inference that Just being in an orbit that takes them near the Earth would warm them up to 100 c or so is way too high, and that the right number in direct Sunlight hovers around freezing (0 degrees C). There is that other related subject of whether chondritic meteorites are cool to touch when they land...but I'm not going there... To reach 100 C, by just being in an orbit near X, taking a carbonaceous chondrite as a model, I believe you would need to be a third of the way closer to Mercury's orbit from Venus' in today's Solar System. You mention Spitzer data. For comets on epic journeys through the Solar System, which have possibly been orbiting over 4.5 Billion years through all phases of development, there are many possible alternate sources of meaningful temporary heating during this history that could account for the gentle-moderate heating you mention, likely reasonable sized impacts and more so, shock heating from barreling through precursor Solar nebula components from their own soup they were formed out of in situ, not to mention other lower probabilities over time that chance favors. Maybe you meant something else? Even a lump of nickel iron is hard pressed to make 100 C in the Sunshine in Earth's neighborhood in outer space. The high volatiles concentrations in carbonaceous chondrites are supportive of what I say, I think, though of course they are NOT conclusive. Best wishes, Doug P.S. The Andromeda Galaxy, which dwarfs our own, may even collide with the Milky Way in 3 Billion years, two-thirds of the Sun's current age. __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES
There are no known samples of cometary material. Don't forget we have samples of Comet Wild 2 collected by Stardust! Ron Baalke __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES
Whoops! I should have said fell-to-Earth samples. Of course, if it won't fall to Earth, then we just have to go get it! Sterling K. Webb - - Original Message - From: Ron Baalke [EMAIL PROTECTED] To: Meteorite Mailing List meteorite-list@meteoritecentral.com Sent: Friday, September 22, 2006 11:06 AM Subject: Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES There are no known samples of cometary material. Don't forget we have samples of Comet Wild 2 collected by Stardust! Ron Baalke __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES
Hi Sterling: Not a bad summary. However, do not know where you got the heated above 50 absolute. Much too low. Just being in an orbit that takes them near the Earth would warm them up to 100 c or so. Some clearly have not been heated much above that, but at the same time, since they contain water of hydration, they had to be warm enough to have had liquid water (clays are an alteration product). Until the Spitzer observations of Deep Impact, it was thought by many people (but not all) that one would not find hydrated silicates in comets (too cold). There is still some question about the Spitzer observations, but have not seen anything is the Lunar and Planetary Science Conference last March. Larry Quoting Sterling K. Webb [EMAIL PROTECTED]: Hi, E.P., The truth is we really don't know what comets and asteroids actually are, or whether there's a real distinction between them, or if they are just keywords derived (mistakenly) from the two extremes of a continuous spectrum of bodies with every intermediate state fully represented. There are comets that die and turn into asteroids, and there are asteroids that suddenly develop a coma and become comets. But the two terms may not be a descriptions of two essentially different classes of bodies at all. After we sample and/or visit 50 or 100 of them, we'll have a much better idea... The association of carbonaceous chondrites with comets is supposed by many, but not ever demonstrated. No meteorite has ever been definitively linked to a comet. There are no known samples of cometary material. (We may have it, but if we do, we don't know it...) On the chance that CC's may be linked to cometary material or be similar to it... Here's a summary on Carbonaceous Chondrites (quickly ripped from the Net, not my data-leaky brain). The metal content runs from 50% for Bencubbinites, 15% for CH type, down to about 1% for other classes. Some classes have clearly never been warmed about 50 degrees absolute; some people have suggested that the CH class formed intra-Mercurially. Obviously, all carbon containing meteorites didn't start out in the same single nursery! Another indicator that the heresy that the early system was very well stirred might be true. Carbonaceous chondrites account for about 3% of all known chondrites. They are classified according to the proportion and size of the chondrules they contain (one rare subclass lacks chondrules). The average contents of CC's are: Carbon, 2.0%; Metals, 1.8%; Nitrogen, 0.2%; Silicates, 83.0%; Water, 11.0%. At most, they can be 20% water and can contain as much as 4% carbon. Carbonaceous Chondrites contain around 5% kerogen. The sub-classes are: CI chondrites, only a handful of which are known, are named for the Ivuna meteorite. They have very few chondrules and are composed mostly of crumbly, fine-grained material that has been changed a lot by exposure to water on the parent asteroid. As a result of this aqueous alteration, CI chondrites contain up to 20% water in addition to various minerals altered in the presence of water, such as clay-like hydrous phyllosilicates and iron oxide in the form of magnetite. They also harbor organic matter, including polycyclic aromatic hydrocarbons (PAHs) and amino acids, which makes them important in the search for clues to the origin of life in the universe. It remains uncertain whether they once had chondrules and refractory inclusions that were later destroyed during the formation of hydrous minerals, or they lacked chondrules from the outset. CIs have never been heated above 50°C, indicating that they came from the outer part of the solar nebula. They are especially interesting because their chemical compositions, with the exception of hydrogen and helium, closely resemble that of the Sun's photosphere. They thus have the most primitive compositions of any meteorites and are often used as a standard for gauging how much chemical fractionation has been experienced by materials formed throughout the solar system. CM chondrites are named for the Mighei meteorite that fell in Mykolaiv province, Ukraine, in 1889.They contain small chondrules (typically 0.1 to 0.3 mm in diameter) and similar-sized refractory inclusions. They also show less aqueous alteration than, and about half the water content of, CI chondrites. Like CIs, however, they contain a wealth of organic material - more than 230 different amino acids in the case of the famous Murchison meteorite. Comparisons of reflectance spectra point to the asteroid 19 Fortuna or, possibly, the largest asteroid, 1 Ceres, as candidate parent bodies. CV chondites are named for the Vigarano meteorite that fell in Italy in 1910. They resemble ordinary chondrites and have large, well-defined chondrules of magnesium-rich olivine, often surrounded by iron sulfide, in a dark-gray matrix of mainly iron-rich olivine. They
Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES
Hi, Larry, List, E.P. Just another brain-slip; should read 50 degrees C! Hydration commences as nebular temperatures drop below 120 degree C. Yeah, that's a warm and cuddly 50 C, not 50 K. Brr... At low pressures that's steam, not water, down to 160-165 K. after which it's ice. Like Mars, no ponds, no rivers, but oddly, the relative humidity is always 100%. It's so muggy... I'm glad it was just a typo; means I don't have to read chemistry... Normally, hydration means lots of water, like magnesium sulfate brines on Europa and Ganymede. Lots of meteorites have hydrated minerals (amphibole), Martians (Nakhlites) have a wide variety of hydrated minerals. E-class asteroids have a spectral feature that has been interpreted as hydrated minerals. And to modify the old saying, Where there's clay, there's water... Sterling K. Webb -- - Original Message - From: Larry Lebofsky [EMAIL PROTECTED] To: Sterling K. Webb [EMAIL PROTECTED] Cc: E.P. Grondine [EMAIL PROTECTED]; meteorite-list@meteoritecentral.com Sent: Thursday, September 21, 2006 9:12 PM Subject: Re: [meteorite-list] COMETS AND CARBONACEOUS CHONDRITES Hi Sterling: Not a bad summary. However, do not know where you got the heated above 50 absolute. Much too low. Just being in an orbit that takes them near the Earth would warm them up to 100 c or so. Some clearly have not been heated much above that, but at the same time, since they contain water of hydration, they had to be warm enough to have had liquid water (clays are an alteration product). Until the Spitzer observations of Deep Impact, it was thought by many people (but not all) that one would not find hydrated silicates in comets (too cold). There is still some question about the Spitzer observations, but have not seen anything is the Lunar and Planetary Science Conference last March. Larry Quoting Sterling K. Webb [EMAIL PROTECTED]: Hi, E.P., The truth is we really don't know what comets and asteroids actually are, or whether there's a real distinction between them, or if they are just keywords derived (mistakenly) from the two extremes of a continuous spectrum of bodies with every intermediate state fully represented. There are comets that die and turn into asteroids, and there are asteroids that suddenly develop a coma and become comets. But the two terms may not be a descriptions of two essentially different classes of bodies at all. After we sample and/or visit 50 or 100 of them, we'll have a much better idea... The association of carbonaceous chondrites with comets is supposed by many, but not ever demonstrated. No meteorite has ever been definitively linked to a comet. There are no known samples of cometary material. (We may have it, but if we do, we don't know it...) On the chance that CC's may be linked to cometary material or be similar to it... Here's a summary on Carbonaceous Chondrites (quickly ripped from the Net, not my data-leaky brain). The metal content runs from 50% for Bencubbinites, 15% for CH type, down to about 1% for other classes. Some classes have clearly never been warmed about 50 degrees absolute; some people have suggested that the CH class formed intra-Mercurially. Obviously, all carbon containing meteorites didn't start out in the same single nursery! Another indicator that the heresy that the early system was very well stirred might be true. Carbonaceous chondrites account for about 3% of all known chondrites. They are classified according to the proportion and size of the chondrules they contain (one rare subclass lacks chondrules). The average contents of CC's are: Carbon, 2.0%; Metals, 1.8%; Nitrogen, 0.2%; Silicates, 83.0%; Water, 11.0%. At most, they can be 20% water and can contain as much as 4% carbon. Carbonaceous Chondrites contain around 5% kerogen. The sub-classes are: CI chondrites, only a handful of which are known, are named for the Ivuna meteorite. They have very few chondrules and are composed mostly of crumbly, fine-grained material that has been changed a lot by exposure to water on the parent asteroid. As a result of this aqueous alteration, CI chondrites contain up to 20% water in addition to various minerals altered in the presence of water, such as clay-like hydrous phyllosilicates and iron oxide in the form of magnetite. They also harbor organic matter, including polycyclic aromatic hydrocarbons (PAHs) and amino acids, which makes them important in the search for clues to the origin of life in the universe. It remains uncertain whether they once had chondrules and refractory inclusions that were later destroyed during the formation of hydrous minerals, or they lacked chondrules from the outset. CIs have never been heated above 50°C, indicating that they came from the outer part of the solar nebula. They are especially interesting because their chemical compositions, with the exception of hydrogen and helium, closely resemble
