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(Steve Willner) wrote in message ...
In article , (John Curtis) writes: My reference claims that the largest constituent(next to hydrogen) of planetay nebulae is carbon monoxide. http://soral.as.arizona.edu/sofia2/node4.html. As Henry pointed out, "planetary nebulae" (ejecta of old, evolved stars) are not the same as "proto-planetary nebulae," or more common, "proto-planetary disks." In any case, the page you cite describes the molecular outflow, not the planetary nebula itself. The nebula itself is ionized and has only trace molecules associated with dust grains. CO2 is not a factor unless the temperature of the central star exceeds 370000 K . There's something wrong here. A hot central star will dissociate all molecules, including CO. Significantly, CO2 was detected in the form of calcium carbonate, which not only implies aqueous origin but also a source of oxygen(water) for the conversion of CO into CO2 How did we jump from CO to CO2? My interpretation is that CO ignites readily to form CO2. CO + 1/2O2 --- CO2 Oxygen was derived from the lysis of water. Also, where was calcium carbonate detected, and what is the evidence? In the dust shell. http://www.spaceref.com/news/viewpr.html?pid=7153 John Curtis |
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In article ,
(John Curtis) writes: Significantly, CO2 was detected in the form of calcium carbonate, which not only implies aqueous origin but also a source of oxygen(water) for the conversion of CO into CO2 How did we jump from CO to CO2? My interpretation is that CO ignites readily to form CO2. CO + 1/2O2 --- CO2 Oxygen was derived from the lysis of water. Also, where was calcium carbonate detected, and what is the evidence? In the dust shell. http://www.spaceref.com/news/viewpr.html?pid=7153 Taking the last point first, the original reference is by Kemper et al., 2002 Nature 415, 295. The main point of the (quite interesting!) paper is that the carbonate they detect is evidence for a non-aqueous formation process. The timescale (10^4 years) and amount of carbonate present (=30 earth masses) are claimed to rule out the usual aqueous formation processes. More generally, CO is quite abundant in molecular outflows -- it is the most abundant molecule after H2. That's because CO has high energy of formation. CO2 is much less stable and much less abundant than CO. Neither molecule will exist in significant abundance inside an ionized region. Molecules are destroyed very quickly by UV radiation, but solid particles (silicates typically being most abundant) can last awhile before they are destroyed. The chemistry of molecular outflows and clouds differs quite a lot from usual laboratory chemistry. Densities are vastly lower, and usually there is lots of UV light around. The fact that CO and O both exist does not mean they will combine. In fact, I deliberately wrote O and not O2. SWAS did not detect O2 outside the solar system despite extensive searching and prior expectations that molecular oxygen should be abundant enough to be detected. (SWAS did detect O2 in Earth's atmosphere, so the instrument was working properly.) I'm no longer sure what the original point of this thread was, but perhaps it's useful to clear up some misconceptions about molecular outflows. -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
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