An article that expands the implications of
this data is at:
http://www.space.com/13127-planet-mercury-revealed-nasa-messenger-spacecraft.html
It might be of use to someone trying to figure
what a Mercurian meteorite would be like:
"The composition of Mercury's surface is
substantially different from that of other
terrestrial planets, according to Messenger's
scans of the X-rays emanating from the
planet. For instance, Mercury's surface
possesses at least 10 times more sulfur,
or brimstone, than Earth or the moon...
The measured ratio of potassium, a volatile
element, to the non-volatile elements
thorium and uranium revealed levels
of volatile materials comparable to the
other terrestrial planets... Measurements
of gamma rays emanating from the planet's
surface also support theories that Mercury
originated from material comparable to that
of stony chondritic meteorites... Altogether,
this surface chemistry suggests the planet
formed from material now seen in certain
stony chondritic meteorites and cometary
dust particles... Nittler said. 'Our work is
showing that at some level, Mercury formed
from a different mix of these building
blocks than did the other terrestrial planets.' "
They don't say WHICH chondrites are the
"certain" stony chondritic meteorites, however.
Any guesses?
Let's Google Larry Nittler. Hmmm:
http://www.sciencemag.org/content/333/6051/1847.abstract
The abstract says: "the planet's surface differs
in composition from those of other terrestrial
planets. Relatively high Mg/Si and low Al/Si
and Ca/Si ratios rule out a lunarlike feldspar-
rich crust. The sulfur abundance is at least
10 times higher than that of the silicate portion
of Earth or the Moon, and this observation,
together with a low surface Fe abundance,
supports the view that Mercury formed from
highly reduced precursor materials, perhaps
akin to enstatite chondrite meteorites or
anhydrous cometary dust particles. Low Fe
and Ti abundances do not support the
proposal that opaque oxides of these elements
contribute substantially to Mercury's low and
variable surface reflectance."
Here's a more detailed account (from June, 2011,
with graphs) that speaks to what meteorites the
Mercurian surface might resemble:
http://planetary.org/blog/article/00003067/
" Other models proposed that it [Mercury] formed
from a specific kind of meteorite called CV chondrite
that are very very rich in metal. For the most part
these are not in detailed agreement with our
observations, but variants cannot be ruled out."
A polite way of saying "forget CV's."
Other models on which doubt is cast? A larger
version of Earth boiled down? No way. Mercury
stripped of crust by a giant impact? Well, that's
looking dubious, too.
Just waiting for more data...
Sterling K. Webb
-----------------------------------------------------------------
----- Original Message -----
From: "Ron Baalke" <[email protected]>
To: "Meteorite Mailing List" <[email protected]>
Sent: Thursday, September 29, 2011 2:29 PM
Subject: [meteorite-list] MESSENGER Revealing More Details About
PlanetMercury
Sept. 29, 2011
Dwayne Brown
Headquarters, Washington
202-358-1726
[email protected]
Paulette Campbell
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
240-228-6792
[email protected]
RELEASE: 11-330
NASA SPACECRAFT REVEALING MORE DETAILS ABOUT PLANET MERCURY
WASHINGTON -- NASA's MESSENGER spacecraft, the first to achieve orbit
around Mercury, is providing scientists new information about the
planet. The data show widespread flood volcanism similar to Earth,
clearer views of Mercury's surface, the first measurements of its
elemental composition, and details about charged particles near the
planet.
MESSENGER, or the MErcury Surface, Space ENvironment, GEochemistry,
and Ranging spacecraft, conducted 15 laps through the inner solar
system for more than six years before achieving the historic orbit
insertion March 18. The new results are reported in seven papers
published in Science magazine.
"MESSENGER's instruments are capturing data that can be obtained only
from orbit," says principal investigator Sean Solomon, of the
Carnegie Institution of Washington. "Mercury has many more surprises
in store for us as our mission progresses."
Scientists for decades had puzzled over whether Mercury had volcanic
deposits on its surface. New data show a huge expanse of volcanic
plains surrounding the planet's north polar region. These continuous
smooth plains cover more than six percent of the planet's total
surface. The deposits appear typical of flood lavas, or huge volumes
of solidified molten rock similar to those found in the northwest
United States.
"If you imagine standing at the base of the Washington Monument, the
top of the lavas would be something like 12 Washington Monuments
above you," said James Head of Brown University, the lead author of
one of the papers.
Scientists also have discovered vents or openings measuring up to 16
miles (25 kilometers) across that appear to be the source of some of
the large volume of very hot lava that has rushed across Mercury's
surface carving valleys and creating teardrop-shaped ridges in the
underlying terrain.
New images reveal landforms on Mercury suggesting a previously
unrecognized geological process. Images of bright areas appear to be
small, shallow, irregularly shaped depressions. The science team
adopted the term "hollows" for these features to distinguish them
from other types of pits seen on Mercury. Hollows have been found
over a wide range of latitudes and longitudes, suggesting that they
are fairly common across Mercury.
"Analysis of the images and estimates of the rate at which the hollows
may be growing led to the conclusion that they could be actively
forming today," says David Blewett of the Johns Hopkins University
Applied Physics Laboratory (APL) in Laurel, Md., lead author of one
of the reports.
Scientists also now have observations of the chemical composition of
Mercury's surface. The information is being used to test models of
Mercury's formation and further study the relationship between the
planet's tenuous atmosphere and surface makeup. Chemical measurements
reveal a higher abundance of potassium than previously predicted.
"These measurements indicate Mercury has a chemical composition more
similar to those of Venus, Earth, and Mars than expected," says APL's
Patrick Peplowski, lead author of one of the papers.
MESSENGER also has collected the first global observations of plasma
ions-- mostly sodium -- in Mercury's magnetosphere, the volume of
space near the planet dominated by Mercury's magnetic field. These
results reveal that Mercury's weak magnetosphere provides the planet
very little protection from the gusty solar wind, resulting is a very
hostile surface environment with extremes in space weather.
"We were able to observe the formation process of these ions, and it's
comparable to the manner by which auroras are generated in the
Earth's atmosphere near polar regions," said Thomas Zurbuchen of the
University of Michigan and lead author of one of the reports.
MESSENGER was designed and built by APL. The lab manages and operates
the mission for NASA's Science Mission Directorate (SMD) in
Washington. The mission is part of NASA's Discovery Program, managed
for SMD by the agency's Marshall Space Flight Center in Huntsville,
Ala.
For more information about the mission visit:
http://www.nasa.gov/messenger
-end-
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