I'm not sure why you thought there was a definition that requires L5
and L6 chondrites to come from different parent asteroids... there
isn't. Questions like this are open to investigation. Isotopic data
show that the different petrologic types of L chondrites all
experienced a major shock event around 500 million years ago, which
means that at least many of them came from a single parent
body. Similarly, different petrologic types of H chondrites show
evidence for a break-up event around 7.5 million years ago. There is
still debate over the importance of "onion shell" vs. "rubble pile"
models of the asteroids, but not so much over whether the different
petrologic types come (or came) from a single asteroid.
jeff
At 11:40 PM 9/8/2009, Dave Gheesling wrote:
All,
Pete's question re: pallasites reminds me of one I've been meaning to throw
out to the group for a while. I believe that, by definition, L6's come from
one parent body and L5's, say, come from another. It's clear why breccias
might simply be an association of the two. But I've seen cross section
illustrations of hypothetical asteroids more than once which indicate a
transitional progression from L3 material at the exterior/crust through L4,
then L5, and eventually to L6 at the center/core. Presumably this is due to
insulative properties and the like towards the interior which allow more
heat from radioactivity to build up, etc, but this also seems to indicate a
single parent body. I'm sure Sterling & Co. might have a field day with
this one, and I'm looking forward to any responses out there...
Thanks much,
Dave
Dave Gheesling
IMCA #5967
www.fallingrocks.com
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