(meteorobs) Meteorite pix
mexicodoug at aim.com
mexicodoug at aim.com
Fri Dec 5 04:28:48 EST 2008
"Perhaps the excitement over the piece under examination is the chance
it
might be a product of the Jupiter-Asteroid collision which may have
caused
additional isotopes to be formed in the asteroid fragments."
Hello Larry,
It is very unlikely that such a scenario is being considered. Are you
referring to Shoemaker-Levy 9 and suggesting that after collision with
Jupiter, it swam out of that intense gravitational field and
atmosphere, then navigated with JPL slingshot precision to Earth 15
years later in the form of intact rocks with a density greater than
quartz :-)
The journey from the asteroid belt (source so far of all ordinary
chondrites for which orbits have been determined) to Earth delivery
seems to be without exception a more than 1,000,000 year long dynamic.
This lower limit has been been supported by the previously described
cosmic ray exposure ages as well as CR fission tract densities.
A more likely explanation is that whoever related the story of
"unusually high radioactivity", didn't accurately follow that it simply
was a pristine specimen and typical meteorite - a good candidate for
doing cosmic ray exposure testing via isotope concentrations and ratios
to try to ferret out this info, to gather whatever information shakes
out. Or maybe the Saskatchewan cold was affecting the performance of
an unwitting geiger counter that had been rusty in storage a while that
someone stuck by the rock in the field.
Or maybe it was a general statement that anythings in space have a
trace amount of systemmatic radioactivity dependent on their history
and not present on Earth due to magnetic and atmospheric shielding of
CRs. Meteoroids in situ present greater dangers to astronauts visiting
them when the cosmic rays hit the astronauts directly due to no
magnetic protection or atmosphere around the meteoroid, as well as the
worse ejected immediate byproducts from the surface for any asteroid
miners. It is this active cosmic ray particle bombardment and
byproduct dangers in space that is hard for many of the public to
separate from the supposed "radioactivity" of space material, i.e.,
meteorites, in the popular press. Once on Earth, the light bulb gets
turned off- well in this case the cosmic particle bulb and it is a
passive process pesists for a very tiny concentration of isotopes.
As Chris also mentioned, this is a trace amount. Any claims anywhere
near approaching a dangerous threshhold would raise quite a few
scoffing eyebrows among meteoriticists... It has a whole lot less than
the radon accumulating basements many list members live on top
of...anyway this is my understanding FWIW, which you already seem to
have acknowledged ... still, it might make a good plot for a Canadian
horror flick explaining that Canadians' teeth will fall out whether
they look for "highly radioactive" Unwin meteorites or go back to
playing hockey. Can't win :)
Best wishes, Great Health,
Doug
-----Original Message-----
From: stange <stange34 at sbcglobal.net>
To: Global Meteor Observing Forum <meteorobs at meteorobs.org>
Sent: Fri, 5 Dec 2008 12:22 am
Subject: Re: (meteorobs) Meteorite pix
Acknowledged Chris.
Perhaps the excitement over the piece under examination is the chance
it
might be a product of the Jupiter-Asteroid collision which may have
caused
additional isotopes to be formed in the asteroid fragments.
Larry
----- Original Message -----
From: "Chris Peterson" <clp at alumni.caltech.edu>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: 2008/12/04 10:08
Subject: Re: (meteorobs) Meteorite pix
> The only difference between cosmic rays in the Solar System and
outside it
> is that locally you have a slightly higher rate of relatively low
energy
> particles from the Sun. The planets have no effect at all. By most
> standards, almost no meteorites would be considered "radioactive",
> although
> most natural materials, meteorites included, have some low background
> activity. Most radioactive isotopes present when the objects formed
have
> long since decayed to very low levels, and regardless of location,
the
> rate
> of cosmic ray impacts and occasional conversion of material to
radioactive
> species is far too low to result in significant radioactivity in bulk.
>
> Chris
>
> *****************************************
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
>
>
> ----- Original Message -----
> From: "stange" <stange34 at sbcglobal.net>
> To: <meteorobs at meteorobs.org>
> Sent: Thursday, December 04, 2008 10:52 AM
> Subject: (meteorobs) Meteorite pix
>
>
>> Is it thought that meteroids entering the solar system from a travel
>> through
>> the galaxy would not be radioactive from encountering primarily
higher
>> energy cosmic rays, but those meteoroids formed (within) the solar
system
>> and coming from orbits within the asteroid belt would be radioactive
from
>> isotope formation due to planetary magnetic focussing of lower energy
>> cosmic
>> rays?
>>
>> Is my understanding correct that rates and velocities of cosmic
radiation
>> that cause isotope formation, would be dramatically different in
these
>> two
>> situations?
>
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