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

From: bernd.pauli at paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: 18 Jun 2010 16:47:09 UT
Message-ID: <DIIE.0000000A00004CC5_at_paulinet.de>

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
Received on Fri 18 Jun 2010 12:47:09 PM PDT