[meteorite-list] Mercury data

From: Carl Agee <agee_at_meteoritecentral.com>
Date: Sun, 19 Jun 2011 10:16:35 -0600
Message-ID: <BANLkTinVEVipD-0fA-iEAFux=7QVBb-_5A_at_mail.gmail.com>

Of course it's still early days on understanding the Mercury data
coming back from Messenger, but I think there are a few simple things
that can be said about the two geochemical graphs that were part of
the press release. The major element graph of Al/Si versus Mg/Si
clearly shows that the measured Mercurian surface is similar to
basaltic and mantle rocks from the Earth. They plot along the Earth
array and look to be a bit more olivine-rich than mid-ocean ridge
basalts, but not as olivinerich as mantle peridotites, perhaps more
like Archean Earth komatiites. The measured Mercurian surface is NOT
delpleted in aluminum, like Martian basalts or Angrites. Also,
Messenger is clearly not measuring rocks like the lunar anorthositic
highlands. The major element that is still missing from this puzzle is
iron. The data do not say anything about the FeO content of the
Mercurian surface -- this is a pretty big deal, and until that is
known it will difficult to know exactly what we are looking at -- let
alone if there is a match for any known meteorite type.

The potassium/thorium plot shows that Mercury is a lot like the other
terrestrial planets in terms of volatile element content. It seems to
be closest to the K/Th of Mars which is quite surprising, since Mars
is thought to be the most volatile rich of the rocky planets. This
runs counter to the idea that the inner solar system is chemically
zoned with volatile elements concentrated out at Mars and lower in
towards the Sun. But who knows? Maybe Mercury formed farther from the
Sun and migrated inwards.

There was a brief mention of substantial amounts of sulfur, but no
data in the multimedia press release, so it would be interesting to
know what they mean by "substantial amounts". Also, why do they think
it is in the form of sulfide and not sulfate?

See how important these missions of planetary exploration are and how
fragmentary our understanding is?

Just my opinion....

Carl Agee

Carl B. Agee
Director and Curator, Institute of Meteoritics
Professor, Earth and Planetary Sciences
MSC03 2050
University of New Mexico
Albuquerque NM 87131-1126
Tel: (505) 750-7172
Fax: (505) 277-3577
Email: agee at unm.edu
Received on Sun 19 Jun 2011 12:16:35 PM PDT

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