[meteorite-list] Mercury Fragments on earth (not)

From: Michael Fowler <mqfowler_at_meteoritecentral.com>
Date: Thu, 04 Aug 2011 19:44:43 -0500
Message-ID: <4D86420C-BF09-436D-9350-27160F1554E0_at_mac.com>

We should always keep an eye out for meteorites that have unusual characteristics.

That said, I believe there is one fatal flaw in the calculations of the poster paper.

"it is the only planet where impact speeds routinely range from 5?20 times the planet's escape speed; this causes impact ejecta to leave its surface moving many times faster than needed to escape its gravitational pull. Thus, a large fraction of mercurian ejecta may reach heliocentric orbit with speeds sufficiently high for Earth? crossing orbits to exist immediately after impact, resulting in larger fractions of the ejecta reaching Earth as meteorites."

Read carefully, the fatal flaw is that for impact speeds that high, nearly everything is vaporized, or turned to dust. The conundrum, is that the impactor must shock, or transfer energy to the Mercurian rocks fast enough to eject them, but not so fast as to vaporize or crush them.

I think that brings us back to square one. ie, Mercurian meteorites are very unlikely, but not impossible.

Mike Fowler
Chicago


> At 11:07 AM 8/4/2011, Edwin Thompson wrote:
>
>
>> A very compelling poster was presented at a Met Soc meeting back in
>
>> the 90's showing a very plausible scenario that might have produced
>
>> meteorites on Earth having come from the surface of Mercury.
>
>
> Brett Gladman and Jaime Coffey from the University of British
> Columbia discussed the possibility of meteorites originating from
> Mercury in a 2009 paper from Meteoritics and Planetary Science. A
> prepublication copy is available online:
>
> http://arxiv.org/ftp/arxiv/papers/0801/0801.4038.pdf
>
> They concluded that there should be a number of meteorites of
> Mercurian origin already here -- around 1/3 to 1/2 the number which
> originated from Mars.
>
> The Messenger spacecraft should provide better information about the
> possible composition of Mercurian meteorites.
>
> David Weir offers a useful summary of the subject of Mercurian meteorites at:
>
> http://www.meteoritestudies.com/protected_MERCURY.HTM
>
>
> -- Philip R. "Pib" Burns
> pib at pibburns.com
> http://www.pibburns.com/
Received on Thu 04 Aug 2011 08:44:43 PM PDT