[meteorite-list] Angrites - Meteorites from Mercury...

From: Greg Hupe <gmhupe_at_meteoritecentral.com>
Date: Fri, 15 Feb 2008 12:36:49 -0500
Message-ID: <02c301c86ff9$58309d60$0200a8c0_at_Gregor>

Hi Darren and fans of Mercury and/or its likely meteorites,

Three strong candidates come to mind ;-)

NWA 2999
NWA 4590 "Tamassint"
NWA 4801

Best regards,
Greg

====================
Greg Hupe
The Hupe Collection
NaturesVault (eBay)
gmhupe at htn.net
www.LunarRock.com
IMCA 3163
====================
Click here for my current eBay auctions:
http://search.ebay.com/_W0QQsassZnaturesvault



----- Original Message -----
From: "Darren Garrison" <cynapse at charter.net>
To: <Meteorite-list at meteoritecentral.com>
Sent: Friday, February 15, 2008 12:01 PM
Subject: [meteorite-list] Meteorites from Mercury?


Meteorites from Mercury?
February 15, 2008
by Ken Croswell

Meteorites from the Moon and Mars give earthbound scientists free rock
samples
from other worlds. Now Brett Gladman and Jaime Coffey (University of British
Columbia, Vancouver) say we should expect a few meteorites from Mercury too.

Gladman and Coffey conducted computer simulations of what happens after
asteroids and comets slam into the innermost planet and kick debris into
space.
Past studies assumed that rocks knocked off Mercury weren't getting away
with
much more than its escape velocity of 2.6 miles (4.2 km) per second. That's
too
slow to climb away from the Sun and make it out to Earth.

But some previous assumptions were wrong, says Gladman, because the
collisional
circumstances at Mercury are "very different than anywhere else." The Sun's
innermost planet speeds through space with a mean velocity of 30 miles (48
km)
per second. Furthermore, asteroids and comets crossing Mercury's orbit also
travel fast. So impactors strike the planet at speeds 5 to 15 times its
escape
velocity, and ejecta can rocket off the surface traveling much faster than
had
been assumed.

The new study, which has been submitted to Meteoritics and Planetary
Science,
concludes that up to 5% of this high-speed debris from Mercury reaches
Earth - a
third to a half of the delivery rate of meteorites from Mars. Gladman notes
that
roughly a half dozen samples of Mercury should already be sitting in
meteorite
collections worldwide.

But how would an interplanetary prospector recognize that a stone really is
from
the innermost planet? Some planetary geologists think a rare class of
meteorites
called angrites might be good candidates, though others disagree. Gladman
cautions, "Until you have some kind of ground truth, it's very difficult to
make
those claims." He says scientists need more information about the
composition of
Mercury's surface to find matches with suspicious meteorites.

Fortunately, the Messenger spacecraft has begun exploring the planet.
Messenger
flew past Mercury in January and will go into orbit in 2011. It should
provide
the data that will confirm or refute candidate meteorites from Mercury.

Ken Croswell is the author of Ten Worlds: Everything That Orbits the Sun
(Boyds
Mills Press, 2006).

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Received on Fri 15 Feb 2008 12:36:49 PM PST