[meteorite-list] Recognizing a Venusian meteorite
From: Popocatept_at_aol.com <Popocatept_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:35 2004 Message-ID: <195.216dee21.2cc9ed53_at_aol.com> Sterling, Interesting theory about Venus's atmosphere being blown off by a monster impactor. Here is my objection: Where did the 100 bar carbon dioxide atmosphere come from? Could one monster impactor blow off the existing atmosphere and yet at the same time deposit a new one? Seems a stretch. I suggest a different scenario. Mars is enriched in Argon 40 compared to earth for the same reason it is enriched in deuterium. The lighter elements are lost to space as a function of Mars's lesser gravity. Venus has a tremendous amount of CO2, Argon 36 neon, etc, because it atmosphere was not blown off into space by a giant impactor. On the contrary it was earth's atmosphere that was lost to space. Therefore using Earth's ratio of Ar 36/40 as a standard is misleading. What was the giant impactor responsible for the loss of earth's atmosphere. A good candidate is the impactor that created the moon. In any case, a young crystallization age of less than 500 million years would eliminate all sources, except Venus and Mars. Mike Fowler "E.J" wrote: > Howard Wu wrote: > > Still the question was how would we recognize a venusian meteorite? > Great question to ponder. The best way to identify a Venus Stone would be by the Argon isotope ratios. Argon-36 is the "natural" original isotope of Argon from the solar nebula. Argon-40 is formed by the radioactive decay of Potassium. It forms in the stone body of a planet and is released to the atmosphere by volcanic action, or "out-gassing." On Earth, most of our Argon is isotope 40, thanks to our active little rockball, and there is very little "natural" Argon. The 40:36 isotope ratio is 296 to 1. On Mars, there is even less "natural" Argon. The 40:36 isotope ratio for Mars is 2750 +/- 500 to 1 (Is Mars more volcanic than the Earth? Hmmmm.). So far, it all fits with those nice theories about volatiles and nebulas (which, you call tell by my tone, I distrust profoundly). Therefore, we would expect a ratio of 200:1 for Venus or maybe even 100:1, right? Here's where reality gets in its licks. First, there's 50 to 100 times more Argon and Neon in Venus' atmosphere than we would expect, huge amounts! Where in the H*** did that come from? Second, the 40:36 isotope ratio is 1 to 1, more or less. That is, they are present in roughly equal amounts. Say what? Well, maybe all the noble gasses are enriched? Nah, they're not. This demonstrates that the abnormal Argon did not come from the "old" solar nebula. The two "explanations" left and they're both whacky: 1) Venus has no Potassium in the planet at all, so there is no Argon 40! This goes against everything. No Potassium!!! That's Crazy. And 2) Venus has never had any kind of volcanic activity at all, ever, period. That's even Crazier, since we can radar-map a huge of what appear to be volcanic features on Venus. My personal theory is that Venus had its entire native atmosphere blown off by a whopping big impactor 480,000,000 years ago, an impactor that completely melted Venus' crust, resurfaced the planet, and left a lot of its own volatiles behind as a new atmosphere to mix with the residues of the melted crust. Hey, I said it was whopping big, didn't I? So, what you do is a rare gas analysis of the suspected Venus meteorite, and if the Argon 40:36 ratio is the same, then Venusian meteorite is its name, as Johnny Cochran would say. Sterling K. Webb Received on Thu 23 Oct 2003 10:49:55 PM PDT |
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