[meteorite-list] Wandering Gas Giants & Nakhla Dogs

From: Michael L Blood <mlblood_at_meteoritecentral.com>
Date: Sat Aug 26 12:43:39 2006
Message-ID: <C115C82C.2DBEF%mlblood_at_cox.net>

Hi Rob, Ron & all,
        To hell with Gas Giants - I am forever indebted to
Ron for his brilliant debate as to the possibility (However
remote) of the Nakhla Dog! Ron revived the hope that the
Nakhla Dog actually existed and took one on the cabesa.
Long live the dog!
        Michael
        

on 8/26/06 4:59 AM, Rob McCafferty at rob_mccafferty_at_yahoo.com wrote:

> This is another wonderful link from Ron. A remarkable
> theory which I would never have considered or even
> believed had I not read it.
>
> Thanks once again to you Ron for providing us with
> these real gems.
>
> Rob McC
>
> --- Ron Baalke <baalke_at_zagami.jpl.nasa.gov> wrote:
>
>>
>>
> http://www.psrd.hawaii.edu/Aug06/cataclysmDynamics.html
>>
>> Wandering Gas Giants and Lunar Bombardment
>> Planetary Science Research Discoveries
>> August 24, 2006
>>
>> --- Outward migration of Saturn might have triggered
>> a dramatic increase
>> in the bombardment rate on the Moon 3.9 billion
>> years ago, an idea
>> testable with lunar samples.
>>
>> Written by G. Jeffrey Taylor
>> Hawai'i Institute of Geophysics and Planetology
>>
>> There may have been a dramatic event early in the
>> history of the Solar
>> System--the intense bombardment of the inner planets
>> and the Moon by
>> planetesimals during a narrow interval between 3.92
>> and 3.85 billion
>> years ago, called the late heavy bombardment, but
>> also nicknamed the
>> lunar cataclysm. The evidence for this event comes
>> from Apollo lunar
>> samples and lunar meteorites. While not proven, it
>> makes for an
>> interesting working hypothesis. If correct, what
>> caused it to happen?
>>
>> A group of physicists from the Observatoire de la
>> C??te d'Azur (Nice,
>> France), GEA/OV/Universidade Federal do Rio de
>> Janeiro and Observat??rio
>> Nacional/MTC (Rio de Janeiro, Brazil), and the
>> Southwest Research
>> Institute (Boulder, Colorado) conducted a series of
>> studies of the
>> dynamics of the early Solar System. Alessandro
>> Morbidelli, Kleomenis
>> Tsiganis, Rodney Gomes, and Harold Levison simulated
>> the migration of
>> Saturn and Jupiter. When the orbits of these giant
>> planets reached the
>> special condition of Saturn making one trip around
>> the Sun for every two
>> trips by Jupiter (called the 1:2 resonance), violent
>> gravitational
>> shoves made the orbits of Neptune and Uranus
>> unstable, causing them to
>> migrate rapidly and scatter countless planetesimals
>> throughout the Solar
>> System. This dramatic event could have happened in a
>> short interval,
>> anywhere from 200 million years to a billion years
>> after planet
>> formation, causing the lunar cataclysm, which would
>> have affected all
>> the inner planets.
>>
>> References:
>>
>> * Tsiganis, K., R. Gomes, A. Morbidelli, and H.
>> F. Levison (2005)
>> Origin of the orbital architecture of the
>> giant planets of the
>> Solar System. Nature, v. 435, p. 459-461.
>> * Morbidelli, A., H. F. Levison, K. Tsiganis,
>> and R. Gomes (2005)
>> Chaotic capture of Jupiter's Trojan asteroids
>> in the early Solar
>> System. Nature, v. 435, p. 462-465.
>> * Gomes, R., H. F. Levison, K. Tsiganis, and A.
>> Morbidelli (2005)
>> Origin of the cataclysmic Late Heavy
>> Bombardment period of the
>> terrestrial planets. Nature, v. 435, p.
>> 466-469.
>>
>>
> ------------------------------------------------------------------------
>>
>> The Lunar Cataclysm
>>
>> There are lots of really old lunar rocks. Ferroan
>> anorthosites, which
>> were the first to accumulate from the ocean of magma
>> surrounding the
>> Moon when it formed, crystallized 4.45 billion years
>> ago (see PSRD
>> article The Oldest Moon Rocks
>>
> <http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html>.)
>> However, many, many rocks formed by melting during
>> huge impact events,
>> which we call "impact melt breccias," have ages that
>> fall into a narrow
>> time interval, between 3.92 and 3.85 billion years.
>> This apparent
>> clustering of ages was first noticed in the
>> mid-1970s by Faroud Tera,
>> Dimitri Papanastassiou, and Gerald Wasserburg
>> (Caltech) who concluded
>> that the ages record an intense bombardment of the
>> Moon. They called it
>> the "lunar cataclysm" and proposed that it
>> represented a dramatic
>> increase in the rate of bombardment of the Moon
>> around 3.9 billion years
>> ago. More recent work on lunar samples and lunar
>> meteorites generally
>> confirms that there is a dearth of ages for impact
>> melts older than 3.9
>> billion years (see PSRD article Lunar Meteorites and
>> the Lunar Cataclysm
>>
> <http://www.psrd.hawaii.edu/Jan01/lunarCataclysm.html>.)
>>
>> [lunar basins with ages]
>>
>> The ages of five basins on the Moon have been
>> determined. Other basins
>> are known to be younger than Nectaris and older than
>> Orientale, so at
>> least 12 basins formed between >3.80 and 3.90
>> billion years ago.
>> Possibly almost all 45 lunar basins formed during
>> this time period.
>>
>>
> ------------------------------------------------------------------------
>>
>> The Cataclysm Skeptics Club
>>
>> The lunar cataclysm is an established, solid idea.
>> Or is it? No, say the
>> voices from the critics' corner. Randy Korotev
>> (Washington University in
>> St. Louis) is skeptical of the whole idea, as was
>> his late colleague
>> Larry Haskin. Korotev thinks we have a hideous
>> sampling problem, and
>> that the Apollo sites were all too close to the
>> Imbrium impact basin.
>> Imbrium is 1300 kilometers in diameter and tossed
>> its continuous ejecta
>> over an area twice that size; see image below. (The
>> basalt flows
>> composing Mare Imbrium make up a thin veneer that
>> covers only part of
>> the impact basin.) They say that all the impact melt
>> breccias we have
>> are associated with the Imbrium impact. No wonder
>> they all have the same
>> age--they were all made by one gigantic event.
>>
>> [map of Imbrium ejecta]
>>
>> The dark blue area surrounding Imbrium basin on this
>> map shows Don
>> Wilhelms' interpretation of the extent of primary
>> ejecta for the Imbrium
>> basin. The Apollo 16 landing site marked with a "+"
>> is at the edge of
>> this geologic unit. Apollo 15 site is inside the
>> unit and the Apollo 17
>> landing site is just outside the boundary. There are
>> some uncertainties
>> in the positions of the boundaries of the units.
>>
>> Most lunar scientists do not agree with this
>> hardnosed interpretation.
>> They point out that many of the samples of impact
>> melts cluster into
>> geochemical groups that have distinctive ages.
>> Although the ages do not
>> vary much from cluster to cluster, they do differ
>> beyond experimental
>> uncertainties. Nevertheless, it is difficult to
>> prove the Imbrium-only
>> hypothesis wrong... and really hard to convince
>> Randy Korotev that he
>> should abandon the idea and embrace the cataclysm
>> interpretation!
>>
>> The skeptics do have some rock data on their side. A
>> group of
>> feldspar-rich impact melt breccias from the Apollo
>> 16 landing site have
>> ages between 4.09 and 4.14 billion years, averaging
>> 4.12 billion years.
>> This is substantially older than the narrow
>> cataclysm range. If these
>> ages represent the age of an impact, it shows that
>> impacts certainly
>> took place before 3.9 billion years. And if the ages
>> represent the age
>> of a basin, such as the Nectaris basin a few hundred
>> kilometers to the
>> east, then it casts great doubt on the cataclysm
>> hypothesis. The
>> feldspar-rich composition of these rocks is
>> consistent with remote
>> sensing observations of the lunar highlands
>> surrounding
> === message truncated ===
>
>
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Received on Sat 26 Aug 2006 12:43:08 PM PDT