[meteorite-list] Use of magnets for meteorite hunting
From: rochette <rochette_at_meteoritecentral.com>
Date: Thu Apr 22 10:23:45 2004
>P.S. Perhaps a compass can be used as a "weaning" device?
>It generates a minimal magnetic field, and yet is sensitive
>enough to detect most H- and L-chondrites.
yes compass is able to detect (by a small deviation from N when you
approach the stone) the magnetization of a say L or H. But it is tricky.
The problem is that the effect is quite different in the natural state and
on a piece that has already been submitted to high field (touching with a
magnet or lightning stroke). For example a LL after magnet exposure make a
larger deviation on the compass than a H in its natural state
and then: >> It can easily discriminate between LL and L, L and H or even
>> and howardite, for example.
>Ahhh, but what about weathering? If you can't see into the interior
>of a meteorite, you'll know nothing about its weathering grade. The
>range of responses corresponding to the various weathering grades of
>an H (for instance) will easily intersect that of the L's and probably
>even unweathered LL's. Presumably similar difficulties will be
>encountered with achondrites. --Rob
Right again (but I was told that efficient communication should convey only
one message per time!). So lesson 2 is: a strongly (W2-3) weathered H is as
magnetic as a fresh L....
then Mark says:
>Hi Robert and list
>I'm curious about this latent magnetic field. If its anything like that used
>for paleomag, of what real interest is it except that the meteorite came
>from a body large enough to develope a magnetic field which, if my
>understanding of magnetics is fair enough would only tell you the body
>developed a field. And this may be debatable if there was enough heat around
>the area where the meteorite came from that the field isn't "set in stone"
>because of a major impact or something ripped the parent body apart (as may
>be the case with irons and mesosiderites and such). If the rock is still
>plastic when this occurs, the field is subject to many other factors and may
>not even represent the parent body's field anyway.
There are instances where this paleomagnetic signal is of high interest,
but of course it's very complicated and a lot of meteorites are rather dumb
in this field. But taking the example of martians, the paleomagnetic signal
of SNC has triggered many scientific publications (among which 3 in Science
I guess) discussing for example the low temperature transfer of ALH84001
from Mars to Earth and thus the possibility that Earth may have already
been contaminated by martian bugs in the past (see e.g.:
y controversial, I warn you!).
Unfortunately every Saharan or Omani SNC has been tested with a magnet and
therefore are definitively useless to investigate further this issue.
Received on Wed 05 Mar 2003 03:05:26 AM PST