[meteorite-list] Planet V (for Five)

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue May 2 12:00:59 2006
Message-ID: <000e01c66cac$ca4bd560$a757e146_at_ATARIENGINE>

Hi, David, List,

    Not unexpectedly, I agree that HED-Mesosiderites are all
out of one connected origin. This is not a new notion. Digging
around, I found this quote from the early 70's. "It is a reasonable
working hypothesis that there is a close genetic relationship
among the eucrites, howardites and mesosiderites." (John
S. Lewis)
    The use of oxygen isotope ratio slopes is pretty definite,
but listening to the occasional oxygen isotope spat that happens
on this List, it seems to me that people may take them for more
definite than they are.
    With all the other elements, we are dealing with isotopes present
only in solid phases -- they ain't going anywhere. But in early system
formation times, oxygen is present both in the solid phases of various
minerals AND in possible gaseous phases which can (and often do)
undergo exchanges with solid material. So, it's always possible
that the oxygen now present in one rock had two sources, each
from differing times and conditions.
    There's no way to distinguish dual sources. We have to regard
O-ratios as reliable but tricky, like somebody who's usually completely
honest but once in a while will tell you a totally unbelievable whopper
with a perfectly straight face. Maybe the E chondrites are one of those
tall tales. They're certainly not Earthly in any other way, and very
depleted in volatiles, while the Earth is volatile-rich, some of which
are suspected of having been added to the mix from a separate
source. (I guess I have my metaphors mixed; perhaps the E chondrites
are honest and the Earth is fibbing.) Maybe that's it.
    It's funny the way the pieces of one argument tie in to another.
If the solar nebula was very sharply zoned because there was
little mixing, why, the O-isotope data would be like a street address
or a file location on a hard drive. If you belong to the super high
mass density school (more mixed), the O-isotope data would be
more like random gossip. The fact that O-isotopes are as reliable
as they are puts a constraint on how much or little mixing there
could have been.
    Planet V is just one hypothesis to fit the (now) pretty well proven
fact of the Late Bombardment. When the evidence for the LHB
showed up in the 1970's, there were a fair number of people
convinced that it must be a mistake or a wrong number. But since
it seems to have really happened, the only explanation is that
something big got loose and went on a collision rampage. Whether
it was this particular object (Planet V) or some other object with
a different origin and characteristics remains to be seen.
    I was just impressed with how many other things fit with
Chambers' Planet V notion. Chambers' field is celestial mechanics;
he just searched for a solar orbit in the area that seemed stable
(no obvious resonances or other problems) but became unstable
after 600 million years, at the time we need something to come
loose. He found one. I suspect it's up to others to fill in its physical
characteristics.
    The Dawn mission is wonderful, and its ion engines are wonderful,
blah, blah, but... so slow. I have to wait until 2011 to see Ceres?
    I'm a mental primitive; I want to LOOK at it. I had to Google deep
to find out how sharp a resolution the camera on the Dawn mission is:
http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=DAWN&ex=1
    The camera field of view is 5.5 x 5.5 degrees with a resolution of
9.3 m/pixel (175 pixels per mile) at a distance of 100 km. (Nine meters
per pixel is about what the MRO test images got from high orbit,
remarkably detailed.) There are two identical cameras aboard.
    They will be busy. I calculate the surface area of Ceres as
1,153,700 square miles! That's 35 GigaPixels. (The land area
of the US is 3,537,438 square miles counting Alaska and Hawaii;
Ceres is about a third of a US.) Vesta is "only" about 880,000
square miles! (27 GigaPixels) I said "about" because it's a tri-axial
oblate spheroid. (Anybody got the area formula for that?)
    It'll be worth waiting for!


Sterling K. Webb
------------------------------------------------------------------------------------
----- Original Message -----
From: "David Weir" <dgweir_at_earthlink.net>
To: "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>
Cc: "Meteorite List" <meteorite-list_at_meteoritecentral.com>
Sent: Friday, April 28, 2006 12:28 PM
Subject: Re: [meteorite-list] Planet V (for Five)


> Sterling K. Webb wrote:
>
>> Maybe it hit Planet V-for-Five. Maybe it WAS
>> Planet V-for-Five or a good chunk of it. Or a satellite of Planet
>> V-for-Five dragged along for the ride when its
>> orbit became unstable. Or... I look at my little chunks of mesosiderite
>> with new respect. I sidle up to them at the bar and buy them a drink in
>> the hope that they will tell me their life story...
>
> Sterling,
>
> It may be just another one of those O-isotope coincidences, like the fact
> that E chondrites have O-isotopic values that are indistinguishable from
> those of the Earth, or that brachinites have values that are identical to
> the HEDs, but a new O-isotope study by Greenwood et al.
> (http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1768.pdf) of numerous
> mesosiderites demonstrates that their oxygen isotopic values are almost
> identical to those of the HED clan, which suggests that there may be a
> genetic link between them. The results suggest that both HEDs and
> mesosiderites may be derived from Vesta; or, if you want to speculate like
> me - I think the arrival of Dawn (in Sept. 2011) will reveal that HED and
> MES meteorites were derived from a separate, significantly disrupted,
> Vesta-like PB. This latter possibility may leave the door open for a
> possible Planet V origin for these two groups.
>
> David
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Received on Sun 30 Apr 2006 07:21:19 PM PDT