[meteorite-list] Meteorite from Oman Records Its Lunar Launch Site and Detailed History (SAU 169)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Jul 29 16:30:08 2004
Message-ID: <200407292029.NAA25954_at_zagami.jpl.nasa.gov>

>From Lori Stiles, UA News Services, 520-621-1877
July 29, 2004

Scientists have pinpointed the source of a meteorite from the moon for the
first time. Their unique meteorite records four separate lunar impacts.

They are the first to precisely date Mare Imbrium, the youngest of the large
meteorite craters on the moon. That date, 3.9 billion years ago, is a new
key date for lunar and even terrestrial stratigraphy, the scientists say,
because life on Earth would have evolved only after heavy meteorite
bombardment ended.

Geologists who found the meteorite and scientists from Swiss, Swedish,
German, British, and Arizona laboratories who analyzed the unique stone
report their work in the July 30 issue of Science. Swiss geologist Edwin
Gnos is first author of the article titled "Pinpointing the Source of Lunar
Meteorite: Implications for the Evolution of the Moon."

Contact Information
A.J. Tim Jull 520-621-6816 jull_at_email.arizona.edu
Note - Contact Jull between July 30-Aug. 7 in Brazil at the Sofitel Hotel
+55 21 25251232 and Aug. 7-9 in Argentina at the Sheraton International
Hotel Iguazu +54 3757 49180.

Edwin Gnos (++41) 31 631 84 93 (office) (++41) 31 631 39 36 (lab)

Related Web sites
SaU 169 meteorite - http://illite.unibe.ch/sau169/
NSF - Arizona AMS Lab - http://www.physics.arizona.edu/ams/index.html

Gnos, Ali Al-Kathiri and Beda Hofmann found the 206-gram (7-ounce) meteorite
in Oman on Jan. 16, 2002. The geologists were on a joint meteorite search
expedition sponsored by the Government of Oman, the Natural History Museum
of Berne and the University of Berne.

"The desert in Oman is the new place to find meteorites," said A.J. Tim Jull
of the University of Arizona in Tucson. Jull directs the National Science
Foundation - Arizona Accelerator Mass Spectrometry (AMS) Laboratory. He
analyzed beryllium and carbon isotopes that told how long the meteorite was
in space after it was launched from the moon and how long ago it fell to
Earth at Oman.

Scientists who've acquired the special permits needed to search for
meteorites in Oman and North Africa during the past half-dozen years have
been amply rewarded, Jull said. Seven of the 30 known lunar meteorites have
been found in Oman, and five have been found in North Africa. One was found
in Australia and the rest have been found in Antarctica. Hot or cold, arid
climates preserve meteorites from quickly weathering, Jull noted.

Gnos, Al-Kathiri and Hofmann recognized in the field that the meteorite was
of lunar or martian origin because it wasn't magnetic. Meteorites from
planetary bodies don't contain metal. And, typical of lunar rocks, it was
greenish colored and contained white angular feldspar inclusions.

But when they tested it with a Geiger counter, they found it was no typical
lunar rock. They found it contained high levels of radioactive uranium,
thorium and potassium. Gamma ray-spectroscopy lab tests told them that the
ratios between these elements fit only one enigmatic group of lunar rocks
called "KREEP," the acronym of K for potassium, REE for rare earth
elements, and P for phosphate.

"At that moment, it was clear that the rock had something to do with the
large Imbrium impact basin, the right eye of the man in the moon," Gnos et
al. report on the Web at http://www.geo.unibe.ch/sau169 . The Imbrium impact
basin on the lunar nearside is the only area where KREEP rocks are found.
KREEP rocks are known both from samples returned by the Apollo missions and
by NASA's Lunar Prospector Orbiter radioactivity survey in 1998-99.

The scientists conducted a battery of laboratory tests to piece together a
detailed history of the meteorite, named Sayh al Uhaymir (SaU) 169. They
summarize SaU 169's history:

* At 3.909 billion years ago, plus or minus 13 million years ? An asteroid
collides with the moon, forming the 1160 km (720-mile) diameter Imbrium
impact basin. Crushed and molten rocks mix and solidify to form the main
rock type in meteorite SaU 169.

* At 2.8 billion years ago - A meteorite hits the moon, forming the 25 km
(15-mile) diameter Lalande crater south of the Imbrium basin. The impact
blasts material, including the main rock type in SaU 169, from depth and
deposits it as an ejecta blanket around the crater. The ejecta there mixes
with other lunar soil.

* At 200 million years ago - Another impact brings the rock that will become
a meteorite to within a half-meter (20 inches) of the lunar surface.

* At less than 340,000 years ago - Another impact hits the moon, producing a
crater a few kilometers in diameter and ejects SaU 169 from the moon. The
scientists studied NASA images and identified a young, 3 km (1.8-mile)
diameter crater 70 km (43 miles) north-northeast of Lalande as the
meteorite's likely launch site. Jull measured beryllium 10 in SaU 169 and
determined the meteorite's moon-to-Earth transit time at around 300,000
years. He also measured carbon 14 in SaU 169, which shows the meteorite
fell in present-day Oman around 9,700 years ago, plus or minus 1,300 years.

"Without the Apollo and Luna sampling programs, and especially the huge
advance in knowledge of the Moon acquired during investigations in the last
20 - 30 years, we would only be able to tell that SaU 169 is an exceptional
lunar rock," the scientists said on their Website. "Without background
information from such missions as Clementine and Lunar Prospector, we could
never have linked ages and chemical data with lunar surface information."

"SaU is a rock which demonstrates impressively how rocks can travel, like a
ping-pong-ball, from one body to another," they said.
Received on Thu 29 Jul 2004 04:29:15 PM PDT

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