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

[Michael Fowler]

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
>