[meteorite-list] NWA 482

From: Dennis Beatty <apollocollector_at_meteoritecentral.com>
Date: Tue, 26 Jan 2010 11:37:47 -0800
Message-ID: <BLU0-SMTP9887C39D9F4139786D5AE1B65E0_at_phx.gbl>

Is there any reason to believe that one side might be more prone to
impacts than the other??

Dennis Beatty

On Jan 26, 2010, at 11:14 AM, Randy Korotev wrote:

> At 00:54 26-01-10 Tuesday, you wrote:
>> Randy, why did you write that there is no scientific evidence that
>> any particular lunar meteorite originates from the lunar farside?
>
>
> Dear Walter and list:
>
> We don't know exactly where on the Moon any lunar meteorite comes
> from. It has, nevertheless, become fashionable, if not obligatory,
> for lunar meteorite scientists to speculate where a new lunar
> meteorite might come from in a regional sense when they write papers
> about them. I've done it myself.
>
> The people who understand the dynamics of these things tell me that
> the chance of having a rock achieve escape velocity from the farside
> is the same as from the nearside. Any rock that leaves the Moon has
> the same chance of landing on Earth. Some of this is discussed in a
> recent (and much too long) paper:
>
> http://epsc.wustl.edu/~rlk/papers/korotev_et_al_2009_m&ps_intermediate_iron.pdf
>
> To me this all means that half the lunar meteorites must come from
> the farside, we just don't know which ones.
>
> What we do know is that NWA 482 is highly feldspathic (~80%
> plagioclase) and poor in radioactive elements like Th (thorium). We
> know from orbital measurements that a larger fraction of the surface
> material on the farside is feldspathic and low in Th than for the
> nearside. The nearside has more basalts and most of the Th-rich
> stuff. So, on the basis of chemical composition, NWA 482 has a >50%
> chance of being from the farside. But, the same argument applies to
> the other 32 feldspathic lunar meteorites. Surely, some feldspathic
> lunar meteorites come from the nearside. NWA 4936/5406, for
> example, is very similar in composition to soil from the Apollo 16
> site on the nearside.
>
> The corresponding argument is that most of the basaltic (lun-b)
> meteorites come from the nearside because most of the mare basalts
> are exposed on the nearside. We also can say that Th-rich
> meteorites like SaU 169 and Dhofar 1442 must come the anomalously Th-
> rich region in the northwest quadrant of the nearside known as the
> Procellarum KREEP Terrane. But again, the source crater for none of
> the lunar meteorites has been established with certainty. An impact
> making a 1-km-crater can launch a lunar meteorite.
>
> Randy Korotev
>
>
> ______________________________________________
> Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
Received on Tue 26 Jan 2010 02:37:47 PM PST