[meteorite-list] Recognizing a Venusian meteorite

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:35 2004
Message-ID: <3F98B411.F1A98BCC_at_bhil.com>

Gee,
    You mean, we could have been a nice "normal" planet like Venus if it wasn't for
the sheer bad luck of getting that ol' Devil Moon delivered to our doorstep?
    Shucks, I hate to think of having to miss those 100-bar CO2 breezes, particularly
the ones with that whiff of fresh Argon, when I get up in the morning and trundle
down to the nearest stream to get a cup of molten lead right from the source...
    I could go for the idea, except for one other old problem: the water. The total
water content of Venus is about one bucket of warm spit. If that's "normal," then how
could the proto-Moon impactor deliver world-wide oceans to the Earth? And if all the
water here now outgassed from the Earth, why didn't as much water outgas from Venus?
It should still be there, since it's almost impossible to transport water high enough
in the Venusian atmosphere for it to escape...
    If a giant Venusian impactor was a 200 km. comet, it would certainly have enough
CO2 for Venus' new atmosphere, BUT, again, where'd the water go??! On the other hand,
if the impactor were a rocky body and pre-impact Venus had a substantial surface
accumulation of carbonates... No problem.
    There a nice study by Zahnle and Sleep, "Impacts and the Early Evolution of
Life," which despite its title is really about modelling mega-impacts. They start
with "little" mega-impacts like the ones that obliterate all life on Earth and work
up to the really big ones, like "Boils All The Oceans" and "Planets With An
Atmosphere of Rock Vapor"! They have a talent for thinking Big and Nasty. And they
demonstrate that we still have to stretch our minds to understand impacts as big as,
say, the one that produced the Imbrium basin on the Moon. The Earth should have
suffered about 18 that size.
    The real problem is that Venus is a bitch! (Pardon my Pig Latin, although I
suppose the ancient Romans would agree.) Everything we learn about it raises three
more questions than it answers. We are at the important stage of enlarging our
ignorance, something you have to do before you learn anything. Great stuff,
ignorance.
    You are definitely right about one thing: the Earth is not "normal." It's so wet;
it has no stable surface, with all those strange tectonics going on all the time;
it's accompanied by a "double" planet in virtually the same orbit; and it's infested
by a jillion different kinds of molecular parasites: it is one weird place!
    Still, I'm enjoying my stay there...

Sterling
--------------------------------------------
Popocatept_at_aol.com wrote:

> 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
>
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Received on Fri 24 Oct 2003 01:09:39 AM PDT