[meteorite-list] NWA 2999 - A Case for Mercury? or not?

From: Larry Lebofsky <lebofsky_at_meteoritecentral.com>
Date: Tue Dec 20 18:45:27 2005
Message-ID: <1135122318.43a8978ea2a6b_at_hindmost.LPL.Arizona.EDU>

Michael:

Mercury may not have a crust! What we see on the "surface" is more mantle-like
than crust-like in composition. In one theory, the crust and upper mantle were
stripped away by early impacts. Could angrites be the stripped-off crust?

Also, while there are lava-filled basins, it is believed that Mercury's
interior shrank as it cooled, cracking and faulting the surface. There are no
lava flows from these fault zones, so the upper surface, at least, was
relatively cool at that time.

Below is the Messenger (Mercury mission) website which talks about the
composition of Mercury.

http://messenger.jhuapl.edu/


Larry


Quoting Michael Fowler <mqfowler_at_mac.com>:

>
>
> Begin forwarded message:
>
> > From: Michael Fowler <mqfowler_at_mac.com>
> > Date: December 20, 2005 3:38:35 PM CST
> > To: David Weir <dgweir_at_earthlink.net>
> > Cc: Michael Fowler <mqfowler_at_mac.com>
> > Subject: Re: [meteorite-list] AD - 86 Auctions - A Case for
> > Mercury? or not?
> >
> > Hi David,
> >
> > Dr. Irving's proposal certainly allows for a more rapid cooling of
> > Mercury, but perhaps not a sufficiently rapid cooling.
> > Even if it allowed cooling 20 times faster, that would only
> > compress a billion year time scale down to 50 million years, not
> > quick enough by far.
> >
> > Another objection is that the depth of an insulating regolith is
> > probably more important than the nearness of the core to the surface.
> > Once the magma ocean (if there was one) crusts over, the
> > insulating properties of a regolith would probably be the limiting
> > factor. Are there any arguments why Mercury would not rapidly
> > develop a regolith similar the the highland areas of the Moon?
> >
> > In addition, there are basins on Mercury that apparently filled
> > with basaltic lava flows similar to the Lunar ones. It is
> > generally believed that the basins are a product of the Late Heavy
> > Bombardment, therefore the lava flows that filled them must be
> > younger than 3.9 BY and therefore Mercury could not have solidified
> > in the blink of an eye at 4.562 BY ago.
> >
> >
> >> Even if Mercury is not the angrite parent body, this same problem
> >> doesn't go away, as long as we are correct in our conclusion that
> >> the APB is/was large.
> >
> > I am intrigued by Dr. Irving's statement about the large size of
> > the Angrite Parent Body. How large is large? In other words, what
> > possible size ranges are needed to model the Angrites formation &
> > cooling histories?
> >
> > Mike Fowler
> > Chicago
> >
> >
> > On Dec 20, 2005, at 3:05 PM, David Weir wrote:
> >
> >> Hi Mike and List,
> >>
> >> The presumed slow cooling of a large parent body such as Mercury
> >> was indeed one of the constraints that I had also seen as a
> >> problem to an angrite/Mercury connection, given the ancient
> >> formation age of the angrites. I asked this question of Dr. Irving
> >> and he replied to me with a workable solution to this problem. I
> >> hope he won't mind if I include the relevant passage here rather
> >> than try to put it in my words.
> >>
> >> Dr. Irving wrote:
> >>
> >> My way out of the early rapid cooling of a substantial body is to
> >> consider the immense core of Mercury that would permit very
> >> efficient conductive heat transfer that even a silicate mantle
> >> could transmit (by convection or even conduction) and radiate into
> >> space. Even if Mercury is not the angrite parent body, this same
> >> problem doesn't go away, as long as we are correct in our
> >> conclusion that the APB is/was large.
> >>
> >> Regards,
> >> David
> >
>
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Received on Tue 20 Dec 2005 06:45:18 PM PST