[meteorite-list] NWA 2999 - A Case for Mercury? or not?
From: Michael Fowler <mqfowler_at_meteoritecentral.com>
Date: Tue Dec 20 16:57:05 2005 Message-ID: <C86283CB-7A4F-4488-BC87-162402C51A40_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 > Received on Tue 20 Dec 2005 04:56:54 PM PST |
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