[meteorite-list] Odyssey of a Moon Rock (SAU 169)

From: Peter Marmet <p.marmet_at_meteoritecentral.com>
Date: Thu Jul 29 16:58:36 2004
Message-ID: <410965E6.D2901B74_at_dplanet.ch>

Hi list,

just a reminder:

For more photos of the exhibition at the NHM in Bern and pictures of the
?front and back side? of SaU 169

go to: http://www.marmet-meteorites.com/id2.html


Ron Baalke wrote:

> http://www.nature.com/news/2004/040726/full/040726-9.html
> Odyssey of a Moon rock
> Mark Peplow
> nature.com
> July 29, 2004
> Chemical analysis illuminates 4-billion-year history of desert meteorite.
> A lucky find in the desert of Oman has allowed scientists to reconstruct
> the most detailed ever history of a lunar meteorite. Their results
> reveal that the rock has had a violent life, enduring at least four
> collisions before it even left the Moon.
> The meteorite, called Sayh al Uhaymir 169, was discovered by Edwin Gnos
> and colleagues from the University of Bern, Switzerland, during a field
> trip to Oman in 2002. It is one of about 30 Moon meteorites that have
> been found on Earth since 1979.
> The team has worked out that the rock came from the Lalande impact
> crater on the Moon, an area just a few kilometres across. It is the
> first time that scientists have been able to pinpoint the birthplace of
> a lunar meteorite with such precision.
> The researchers' best clue came from unusually high levels of the
> radioactive element thorium in the meteorite. "The chemistry of this
> rock is quite unusual. There's no other rock quite like this, either as
> a meteorite or as collected on the Apollo missions," says Gnos.
> The team used a detailed map of lunar thorium created by NASA's Lunar
> Prospector probe in 1998-99 to work out that the rock must have come
> from somewhere in the Mare Imbrium (Sea of Showers), which forms the
> right eye of the 'man in the Moon'. Other mineral data pinpointed the
> location as Lalande.
> Rocky ride
> Gnos and his team determined the history of Sayh al Uhaymir 169 by
> comparing the ratios of radioactive elements within the rock. As
> radioactive elements decay they change into different elements. For
> example, over millions of years uranium eventually becomes lead, so the
> ratio of uranium to lead helps to reveal how long it is since the rock
> crystallised.
> Any major impact melts parts of the rock, resetting the radioactive
> clock in those areas. So comparing the ages of crystals in different
> parts of the rock shows when and how severely it has been battered.
> During the meteorite's time in space it was also bombarded with cosmic
> rays, which altered its chemical composition, leaving a distinct
> signature of its journey to Earth.
> The team's analysis suggests that the rock was caught up in the enormous
> impact that created Mare Imbrium, which Gnos estimates to have happened
> about 3.9 billion years ago. The rock was then bounced through the
> Moon's crust by two more impacts, 2.8 billion and 200 million years ago,
> that may have been caused by colliding asteroids.
> A final impact just 340,000 years ago knocked the rock off the Moon
> altogether, and it floated through space before crashing to Earth about
> 10,000 years ago. It has probably lain undisturbed in the Omani desert
> ever since.
> Gnos calculates an age for the Imbrium crater that is slightly older
> than lunar samples collected by the Apollo missions had suggested. They
> dated the impact to about 3.85 billion years ago. The new date is
> important for planetary scientists who use the craters of the Moon as a
> pictorial calendar that shows how many meteorites there were in our
> Solar System at different stages in the last 4 billion years.
> Gnos's team will go back to Oman to look for more meteorites at the end
> of this year.
> References
> 1. Gnos E., et al. Science, 305. 657 - 659 (2004).
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Received on Thu 29 Jul 2004 05:02:30 PM PDT

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