[meteorite-list] Mercurian Meteorites (was: Rocks from Space Picture of the Day - June 16, 2010)

From: cdtucson at cox.net <*cdtucson_at_meteoritecentral.com*> Date: Fri, 18 Jun 2010 13:16:58 -0400 Message-ID: <20100618131658.2IX2S.806287.imail_at_fed1rmwml4101> · cdtucson_at_meteoritecentral.com

--
Carl or Debbie Esparza
Meteoritemax
---- bernd.pauli at paulinet.de wrote: 
> Greg S. inquired:
> 
> "I heard that possible meteorites from Mercury should contain very little
> (or no) free iron. Is this true? I think the one pictured here and NWA 2999
> do contain some free iron."
> 
> 
> Hello Greg and List,
> 
> I thought this summary of the "Summary and Conclusions" part of Love's article
> might be of interest because it partly answers your question about Mercury's iron:
> 
> Summary:
> 
> - orbital evolution of Mercurian material to Earth-crossing orbits possible
> - efficiency probably < 1% of that computed for Mars
> - a ~ 10% chance that a mercurian rock could exist in current meteorite collections
> - may possess an unusual isotopic composition
> - rocks from Mercury probably low in volatiles
> - Mercury bulk composition moderately enriched in refractory oxides of Al, Ti, and Ca
> - FeO contents not more than ~ 5%, and possibly much lower
> - Mercurian regolith breccias:
>   - rich in micrometeorite craters
>   - rich in exogenic chondritic materials
>   - rich in agglutinates
>   - rich in impact vapor deposits
>   - lower solar-wind content than similar lunar soils
>   - implanted gas may be fractionated by interaction with Mercury's global magnetic field
> - a uniquely high solar-to-galactic cosmic-ray damage track ratio of surfac rocks
> - launch-induced shock damage may be comparable to or greater than in martian meteorites
> - no match of these predicted properties of mercurian rocks in current meteorite groups
> - misclassified mercurian meteorites most likely differentiated, low-FeO objects such as
>   lunar anorthosites and aubrites
> 
> Reference:
> 
> LOVE S.G. et al. (1995) Recognizing mercurian meteorites (MAPS 30-3, 1995, 269-278).
> 
> .........................................................................................
> 
> There are some scientists who favor enstatite chondrites but there's a problem with that:
> Mercury's mean density is about 5.4 g/cm^3, whereas enstatite chondrites have a density
> of about 3.4-3.7 g/cm^3.
> 
> In 2002, H. Palme proposed that NWA 011 (and paired material like NWA 4587) might be
> a fragment of Mercury but the high FeO content of this meteorite would point toward
> a parent body with a small metallic iron core. Mercury, however, is believed to have
> a large iron core.
> 
> Best wishes,
> 
> Bernd
> 
> 
> 
> 
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