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Posted by Jan Panteltje on July 18, 2007, 4:28 am
Please log in for more thread options On a sunny day (Tue, 17 Jul 2007 21:55:27 +0100) it happened Aidan Karley
>> The _most_ likely explanation is that he meteorites were not from mars
>> in the fist place.
>> We need real samples
>>
> While agreeing with you on the need for sample return missions,
>the identification of certain meteorites as being form Mars is quite
>secure. The process of impact spalling fragments off the surface also
>melts small amounts of the rock on slip planes, fracture surfaces etc
>(unsurprisingly), and the high pressures in the impact drives bubbles of
>gas into this glass. Onec the rock fragment has wandered through space
>for a few millennia it hits the Earth's atmosphere, the surface is
>heated for a couple of seconds, then it crumps down into Antarctic snow
>or an Egyptian dog (allegedly, for the Nakhla meteorite) and is
>eventually found by a meteorite hunter. When the gas bubbles are
>identified in microscope thin sections (well, "thick sections" ; about
>0.1mm, polished but no cover slip) and zapped with an ion microprobe
>beam, the gas composition can be measured ... and is found to have a
>stable isotope composition matching that measured by the Viking landers,
>not what we find on Earth.
> If you're interested, I've got the papers detailing the process
>somewhere.
> Identification of Vesta-derived meteorites is a bit less secure,
>based on the IR reflection spectrum of the fresh meteorite surfaces
>matching that of Vesta. Once the plausibility of the process had been
>established by the identification of the Martian meteorites, the
>identification of other meteorites with Vesta had much less resistance.
>Plus, there are a number of asteroids in related orbits to Vesta which
>are interpreted as debris from a recent (last few million years) large
>impact on Vesta.
> The lunar-derived meteorites are uncommon, but securely
>identified by correlation against Apollo samples.
Thank you, sounds reasonable.
I made that remark inspired by yet an other posting in the trend of:
'and now we have to rethink completely about how planets and comets...'
as seen often posted by NASA in sci.astro.
Although I agree then methods you describe are very accurate with
a low margin of error I would personally like to see some
astronauts digging on mars :-)
It seems our view of how planets are formed is still changing, and that
would have some consequences for making statements where things come from.
No mars is not geologically dead, there is a picture somewhere of a geyser
like feature.. although some claim it is a dust devil...
We really need to go there an look.
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