MadSci Network: Astronomy
Query:

Re: Origins of the Campo Del Cielo Meteorite

Date: Thu Sep 30 07:58:26 2010
Posted By: Matthew Buynoski, Process Integration Engineer (retired)
Area of science: Astronomy
ID: 1285797842.As
Message:

Hello, Ryan!

Positive meteorite origin identification can be done in some cases, but not necessarily in others.  For 
example, some meteorites have included gas compositions that match the isotopic ratios found in the 
Martian atmosphere, thus strongly implying they were blasted off of Mars during an impact event. 

This metorite has had analysis done on it; see http://www.campometeorites.com/history.htm.  Here's a 
quote from that site:

         "The cosmic radiation age was found to be ~14 million years, which is very low compared to other    
       odtahedrites (Nyquiest et al. 1967).
           "Perry (1944) presented several photomicrographs; one of them (plate 48) undoubtedly show 
       cliftonite, a graphite crystal aggregate, and troilite as stated in the text. Curvello's (1958: 40) 
       application of the aragonite twinning law in this supposedly troilite crystal is therefore invalid. Park 
       et al. (1966) discussed some millimeter-sized silicate inclusions and showed that they consisted of 
       forsterite, chrome diopside, enstatite and oligoclase, decreasing in frequency in that order, and 
       further identified chromite, graphite, troilite and sphalerite, mostly in complex intergrowths. One of 
       the first publications on dislocations in meteorites by thin-film transmission electron microscopy 
       showed that Campo del Cielo had an immobile dislocation network of high density (Ashbee & 
       Vassamillet 1966). Bunch & Cassidy (1968) discussed the numerous deformation structures and 
       found one fragment in particular with indications of heavy plastic flow and recrystallized kamacite. 
       Clarke & Jarosewich (1969) reported a number of excellent analyses (6.7% Ni), the first to be made 
       since the misleading ones performed generations earlier and showing only 5.1–5.9% Ni (Cohen 
       1898a; Duclous 1929). Reed (1965; 1969) found 6.2–6.6% Ni and 670 ppm P in the kamacite.
           "In 1966, the 1,998 kg El Taco mass was cut in the Max Planck Institut, Mainz. The critical 
       process of making such a large section (about 110 x 40 cm) was carried out under the direction of 
       Professor H. Hintenberger, using a combination of close parallel 1.2 inch drilling holes and sawing. 
       Two slices were prepared.
          "Nyquist et al (1967), Hintenberger et al (1969) and Schultz et al (1971) determined the rare 
       gases, while Mason (1967) gave a photograph of the newly cut El Taco specimen and discussed the 
       silicate inclusions of iron meteorites in general. Wlotzka & Jarosewich (1969) examined the silicate 
       inclusions in detail. Podosek (1971) presented the argon analyses on a silicate inclusion, and 
       potassium ages calculated by the 40Ar – 39Ar method. He estimated a K–Ar age of 4.6 x 10(9) 
       years and found evidence of a later heating event 3.4 x 10(9) years ago."

Since no one doing the analyses seems to have determined an exact origin, we can suppose that the 
evidence here does not support one.  My best guess is that this was a fragment from the interior of a 
larger body that suffered a collision some 14 million years ago (thus explaining the cosmic radiation 
age), and that body's composition implies (my personal guess, not a fact) it is from the asteroid belt 
between Mars and Jupiter.  

You may wish to get the book "From Stone to Star" by Claude Allegre, which contains within it a whole 
lot of interesting information on meteroite analysis and how it is done.





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