[meteorite-list] Recognizing a Venusian meteorite

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:35 2004
Message-ID: <3F98801D.92545517_at_bhil.com>

"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
----------------------------------------------

>
> As a "lay" astrogeologist here is "an" answer as I see it. So far we
> only have the direct sampling of the Venusian atmosphere by the Soviet
> mission. The isotope ratios of the Venusian atmosphere will help in
> confirming meteorites from the Mercury Venus Zone. The analysis will
> initially lie in the differences in isotopic ratios between Mars and
> Venus, I feel. Age of formation will be equally important. We need a
> mission to Venus again!
>
> We know that there is a gradient of " heavy to light" elements produced
> by a presolar shockwave(s) that swept elements outward from the center.
> This is why the inner planets are stony-irons and the outer ones are
> gaseous. Having higher "momentum / inertia"moments, the heavier
> elements tended to remain in the inner solar system while lighter
> elements rode the bow wave to the outer edges. Of course all the atoms
> of each element were not completely segregated, none-the -less there was
> a measurable sorting. We know this from measuring values against the
> elemental abundance of the solar system. The"elemental abundance" is a
> calculation of all elements against each other such that we know the
> ratio of each individual element to all the others or, in another way,
> we know their individual percentage in the entire mass of the soar system.
>
> Along with the afore mentioned distribution/concentration of elements,
> is a subset distribution within the isotopes of individual elements.
> For example, from each area of concentration in the solar system for
> oxygen, the ratio of isotopes such as Oxygen 16, 17, and 18 as they
> relate to each other vary. Specifically, they vary with the distance
> they are from the center of the solar system. The lighter the isotope,
> the more distantly it moved toward the outer edge of the solar system.
> The Earth Moon ratio has been determined. This is one of the means we
> used to identify lunar meteorites. Similar ratios were used to identify
> Martian meteorites based on Viking Lander measurements.
>
> Igneous rocks from Earth and Mars pretty much contain the same minerals
> so we rely on isotopic ratios and radioisotope ages to shore up our
> findings. In like manner, that is how the determination of a Veneusian
> meteorite will happen. While the jurry is out on Mercury, some think it
> was captured and its orbit of formation lies elsewhere, (isotopic ratios
> may not be what is expected from a planetoid forming close to the solar
> center), Venus is another story. It is certianly a differenteated body
> and recently volcanicaly active. Any Enstatite chondrite (E,EH,EL)
> can't be from Mercury nor Venus. Likewise the age of
> formation/crystallization for Venuisan material will likely be much less
> younger than asteroidal material.
>
> So Venusian material will likely be isotopically weighted toward Oxygen
> 18 and will have a crystallization age closer to Martian material but I
> am guessing under 2 but less than 3-3.5 billion years.
>
> Regards,
> Elton
>
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Received on Thu 23 Oct 2003 09:27:58 PM PDT