[meteorite-list] Outside planets?

From: S.Singletary <jumper_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:10 2004
Message-ID: <5.0.2.1.2.20020726020524.00adaa30_at_hesiod>

>We have strong
>evidence suggesting that wandering, planet-like objects, have come from
>outside
>our solar system and have hit at least two of our planets. We believe that
>Earth's encounter with a Mars-sized planet liberated our Moon some 4 or so
>billion years ago.


I would challenge this statement (or maybe I just misunderstood it) but I
was under the impression that Theia* must have been formed in much the same
region as the proto-Earth. The oxygen isotopes from the Moon and Earth are
identical. They are also close to those of Mars and the HED parent
body. If Theia had come from outside of the solar system, I would expect
both the Earth's and Moon's oxygen isotopic composition to be vastly
different. I'm also guessing that there are also a whole host of other
geochemical/isotopic arguments that could be made but I don't have my books
with me at the moment.

*Theia was the mother of the moon goddess Selene and hence the name has
been proposed for the name of the impactor that formed the moon (I think
I'm spelling it right but there are a lot of vowels in there and I'm
usually vowel challenged).

Steven

Steven Singletary
54-1224
Dept. Earth, Atmospheric and Planetary Sciences
M.I.T.
Cambridge, MA 02139
Tel - 617.253.6398
Fax - 617.253.7102
Received on Fri 26 Jul 2002 02:16:37 AM PDT