(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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