[meteorite-list] Mercurian Meteorites (was: Rocks from Space Picture of the Day - June 16, 2010)
bernd.pauli at paulinet.de
bernd.pauli at paulinet.de
Fri Jun 18 12:47:09 EDT 2010
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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