[meteorite-list] No Need To Fly To The Moon For Lunar Soil (Lunar Meteorite Dhofar 025)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat May 14 21:24:37 2005
Message-ID: <200505150123.j4F1NwX11240_at_zagami.jpl.nasa.gov>

http://www.physorg.com/news4093.htm

No Need To Fly To The Moon For Lunar Soil
PhysOrg.com
May 13, 2005

It is not necessary to fly to the Moon to get lunar soil even if the
sample is required from the other side of this planet. A meteorite
originating from the other side of the Moon has recently got into the
hands of scientists. The meteorite investigation required precision
instruments and grants from the Russian Foundation for Basic Research
and the B?ro F?r Wissenschaftlich-Technische Zusammenarbeit Des
?sterreichischer Austauschdienst (Bureau for Scientific and Technical
Collabration of Austrian Exchange Service).

A piece of lunar soil (its weight being slightly less than one kilogram)
was knocked out by a meteorite blow and later fell on the Earth. Judging
by a microparticle of zircon mineral the specialists not only calculated
its age, but also made conclusions about the event that had taken place
on the Moon at that time. It has appeared that about 2 billion years ago
the rock containing a particle of zircon endured some planetary
cataclysm and melted, and 500 thousand years ago a piece of rock was
thrown away from the lunar surface into space by a meteorite blow.

Meteorite Dhofar 025 was found in 2000 in the desert on the Arabian
Peninsula (Oman). It weights 751 grams and consists of breccia -
sintered fragments of various minerals from lunar continents. Several
years were spent on investigation of this celestial stone. To determine
its age, the researchers of four Russia institutes jointly with Austrian
colleagues found a microscopical grain of zircon in it - the mineral
consisting of oxides of zirconium, lead, thorium and uranium.

The isotopic composition in the two sections of this tiny speck was
investigated on the SHRIMP mass-spectrometer. The researchers were
interested in ratio of stable isotopes of lead 206, 207, 208 and
radioactive isotopes of uranium - 238 and 235. The grain was extracted
from the core of meteorite, i.e. it had been isolated from the
environment while the meteorite was lying on the Earth. That allowed the
researchers to compare quantitative ratios of isotopes with known and
dated rocks of the Earth and the Moon and to determine the age of
meteorite. On the Earth, for example, zircon contained in gabbro from
Eastern Australia was accepted as the standard for the uranium-lead
relation.

Geochemists discovered that zircon from Dhofar 025 was of the same age
as others, already known lunar rocks - i.e. 4.3 to 4.4 billion years,
but its composition had changed approximately 2 billion years ago. Most
likely, that is the consequence of a powerful blow by a meteorite, as a
result breccia was formed out of granite which contained zircon being
investigated. This result, by the way, coincided with radiation age of
meteorite calculated by isotopes of noble gases. Breccia was formed and
carried out to the surface of the planet as a result of some
catastrophe, and gases started to accumulate in it . However, that was
not the meteorite bombardment well-known to researchers, to which the
visible part of the Moon was exposed to 3.9 billion years ago.
Consequently, the specialists believe that Dhofar 025 is nothing but a
sample of lunar soil from the other part of the planet.

It is not for the first time that lunar meteorites were found in the
region of Dhofar. Among the findings are, for example, Dhofar 305, 307
and others. Altogether, there were about 50 such meteorites found on the
Earth. However, within thousands of years spent on the Earth with its
oxygen atmosphere, under rain and sunshine, with temperature differences
and in contacts with microorganisms that excrete deleterious substances,
debris of the moon became gradually destroyed and by our time it turned
out to be fairly contaminated by "terrestrial' atoms, it oxidized and
lost part of original components. From this point of view, the integral
Dhofar 025 meteorite is considered unique by the researchers.

Source: Informnauka (Informscience) Agency
Received on Sat 14 May 2005 09:23:57 PM PDT