[meteorite-list] Vesta and its core.

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 24 Jul 2010 12:53:25 -0500
Message-ID: <36C371A7B1074F5E872AE9881F22FEB6_at_ATARIENGINE2>

I don't disagree with you (or all the authors you quote)
about short-lived isotopes providing the heat needed
to differentiate or at least contributing substantially to
it, in the case of Vesta and any early-formed body at
least 125-150 km or more.

But how much iron accumulates has not much to
do with how big or massy the body is; they don't
attract the iron by gravity. They are limited to the
iron content of the mineral grains that are the
junk that makes up the smaller bodies they will
accrete from. And that depends on the "nebular"
or disc contents at the place where they form.

It's like having a bunch of jars of "Planet Mix." The
iron content varies (mostly) by distance from the
Sun. Whether you mix up a big planet or a little
one, its contents depend on what was in the jar
of Mix originally. (Although volatiles will be lost
in the "cooking.") The absolute size of the core
is beside the point; what tells you about formation
materials is the percentage content, which is what
the authors you cite are talking about.

> I am also at loss with your reasoning of Earths,
> Mars, and Vestas volume to ratio to the core size.

There "should" be more iron content in a planet
the closer to the Sun it formed. That's the point.
Theoretically, Mercury should be a higher pro-
portion of iron core than the other terrestrial
planets (it does), Venus less than that, Earth
less than that and Mars least of all (it does).

But it's complicated by giant impacts "donating"
more iron core materials to the Earth and Mercury.
Venus appears to have the same amount of iron
core as the Earth, although it's hard to tell because
its core seems to still be liquid, not solid.

The Earth was smaller than Venus and its core was
smaller too... until the Moon Maker body hit us,
gave up its iron core to bulk up ours and added to
our rock mantle. The Moon formed from the escaped
debris.

Without that "accident," the Earth would have been
a smaller planet with an even smaller core. The
mantle and crust would have solidified into a single
piece. The small core wouldn't generate enough
heat for convection and tectonics. A smaller planet
wouldn't gather as many volatile-rich late accretors;
we wouldn't have oceans, just lakes. We would have
a much weaker magnetic field. Atmospheric stripping
would become a significant process. Water loss would
be much faster. In a word, we would have been a lot
more like Mars.

A mice place, but not my idea of home. A Mars-like
Earth would ruin my day...

> "estimates of the amount of metal in Vesta
> vary widely between 0 and 50 wt%"

When estimates vary that widely, it's a clue that
we really don't know. However, those same authors
come up with an even bigger iron core size than
the one I quoted. But we will soon know more.

DAWN will not "go by" Vesta next summer; it will
arrive and stay for a year. In that year, we will learn
more about Vesta every week than we already know
by squinting at it for 200 years.

I expect to see a very ancient body, hammered
beyond belief, with incredible surface relief, and
as dry as our Moon. Of course, surprises are good.
I always like it when the Universe surprises me.


Sterling K. Webb
--------------------------------------------------------------------
----- Original Message -----
From: "Shawn Alan" <photophlow at yahoo.com>
To: <sterling_k_webb at sbcglobal.net>
Cc: <meteorite-list at meteoritecentral.com>
Sent: Saturday, July 24, 2010 2:21 AM
Subject: [meteorite-list] Vesta and its core.


> Ok so if you weren't addressing Angrites in the first place with Vesta
> I am going to change the subject to Vesta and its core
>
> Now you say that Vesta's core volume is roughly 17% and Earth is
> roughly 17% as well. This being said, at 2.35 A.U. Vesta wouldn?t be
> able to attain an iron core at the volume at that distance, concluding
> to you, that Vesta accreted closer to the Sun. Ill refresh your memory
> what you said in your previous post.....
>
> "If there is only enough available iron
> at 1.5 AU for Mars to accumulate a core that is only
> 8% of its volume), how could Vesta, at 2.35 AU, have
> accumulated enough iron for a core 17.5% of its
> volume, or 56% of its original, uncratered diameter?"
>
> Simple.... Vesta is only 300 miles in diameter; Earth?s core is the
> size of the moon. Vestas core has been suggested to be at 130 miles.
> So to obtain iron wouldn?t take much compared to Earth core.
>
> My guess is this:
>
> Abstract:
>
> Geological History of Asteroid 4 Vesta:
> The ?Smallest Terrestrial Planet?
>
> Klaus Keil
>
> Taking
> into account the somewhat uncertain radial heterogeneity
> in 53Mn in the formation regions, these ages can be
> used to translate the 53Mn-53Cr formation intervals of eucrites
> into an absolute age for the differentiation of Vesta.
> Based on measurements of the basaltic eucrite Chervony
> Kut, for example, an age of 4563.6 ? 0.9 Ma is derived, only
> a few million years younger than the formation of CAIs
> (Lugmair and Shukolyukov, 1998). Furthermore, the great
> antiquity of the eucrites and hence the evidence for melting
> and differentiation of Vesta on a timescale of a few million
> years is further supported by the detection of the decay
> products of other extinct radionuclides such as 26Mg from
> the decay of 26Al (half-life 0.73 m.y.) (Srinivasan et al.,
> 1999; Nyquist et al., 2001) and 60Ni from the decay of 60Fe
> (half-life 1.5 m.y.) (see references in Carlson and Lugmair,
> 2000)....
>
> Modeling of the thermal history of Vesta by Ghosh
> and McSween (1998) suggests that heating by 26Al would
> keep the mantle hot for ~100 m.y., consistent with the
> younger ages of cumulate eucrites....
>
> There is convincing geochemical evidence that Vesta
> experienced a high degree of (or possibly complete) melting
> that resulted in the formation of a metal core. For example,
> the depletion in moderately siderophile incompatible
> elements (e.g., Ni, Co, Mo, W, P) relative to nonsiderophile
> incompatible elements in HED meteorites suggests metal
> segregation and hence core formation (e.g., Hewins and
> Newsom, 1988, and references therein; Righter and Drake,
> 1997). However, estimates of the amount of metal in Vesta
> vary widely between 0 and 50 wt% (see references in
> Ruzicka et al., 1997). For example, Ruzicka et al. (1997)
> estimated the mass of the core by mass balance from the
> density of Vesta and the density of the silicate fraction to
> be between ~0 and 25 wt%, with the best estimate being
> ~5 wt%. They also suggested that the core is <130 km in
> radius, the olivine-rich mantle is ~65?220 km thick, the
> lower crustal diogenite unit is ~12?43 km thick, and the
> upper crustal eucrite unit is ~23?42 km thick. Dreibus et al.
> (1997) estimated the mass of the core from their calculated
> composition of the bulk silicate portion of Vesta (assuming
> CI abundances for Fe and Ni) to be 21.7 wt%. They
> also calculated the density of the mantle to be 3400 kg/m3
> and, with a core density of 7900 kg/m3, calculated the bulk
> density of Vesta to be 3800 kg/m3, in good agreement with
> the astronomically determined values (see above). With a
> radius of 263 km and a core mass of 21.7 wt%, they calculated
> a core radius of 123 km.
>
> http://www.lpi.usra.edu/books/AsteroidsIII/pdf/3034.pdf
>
> 26AI has been brought up in many papers to explain differentiation
> among parent bodys and not to mention, Vesta. I like your take on how
> you think Vesta might have formed, but I find it very odd that you
> have no scientific articles that relate to Vesta and how you think
> Vesta formed in a different part of the solar system. I am also at
> loss with your reasoning of Earths, Mars, and Vestas volume to ratio
> to the core size. Vesta is 300 miles in diameter making the core a
> mere 100 miles in diameter if that and Earths iron core the size of
> the moon. But again the core is speculative and we won?t know till
> Dawn goes by in Aug 2011. But all I know is that 26AI is a great
> candidate for differentiation to take place with Vesta and not to
> mention the scientific research to back up how Vesta came to be.
>
>
>
> Shawn Alan
> IMCA 1633
> eBaystore
> http://shop.ebay.com/photophlow/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p4340
>
>
>
>
> [meteorite-list] Its official! NWA 6291 "The King ofAngrites"forsale -
> AD
> Sterling K. Webb sterling_k_webb at sbcglobal.net
> Sat Jul 24 01:28:51 EDT 2010
>
> Previous message: [meteorite-list] Its official! NWA 6291 "The King
> ofAngrites"for sale - AD
> Next message: [meteorite-list] highpoint comet YD cause debate Sat,
> Aug 14, U Wyoming, Laramie: Rich Murray 2010.07.23
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>
> --------------------------------------------------------------------------------
> Actually, I was not addressing the specific question
> of the origin of this angrite (or any angrite), but the
> more general problem of the "universal assumption
> that every sizeable body in the solar system currently
> resides at the same address where it accreted originally."
> If things move around, it complicates the picture
> considerably.
>
> I used Vesta as an example of a body that can't have
> accreted in place. If there is only enough available iron
> at 1.5 AU for Mars to accumulate a core that is only
> 8% of its volume), how could Vesta, at 2.35 AU, have
> accumulated enough iron for a core 17.5% of its
> volume, or 56% of its original, uncratered diameter?
> The Earth has a core of 17% of its volume, or just a
> hair less than Vesta. Mercury has a core that's 43%
> of its volume. Both the Earth and Mercury have
> acquired part-corers from encounters with impactors
> though.
>
> Iron is a moderately refractory element. It will be
> vaporized in the solar nebula only relatively close
> to the Sun. The temperature will drop by the square
> of the distance out in the protoplanetary disc and
> iron will soon condense into the materials from
> which grains will form, get sticky, form particles,
> accrete, etc.
>
> How you gonna get that much iron vaporized out at
> 2.35 AU? The answer to that question is the same one
> I gave before: No Way. And for the same reason.
>
> If you want to know what should accrete out there,
> you can compare Vesta to Ceres. Ceres is in essentially
> the same region as Vesta, at 2.7 AU compared to
> Vesta's 2.35. AU. Ceres seems to have no core at all,
> although Ceres is certainly large enough to have
> differentiated. Ceres likely did accrete in place from
> rock and ice, as it is the largest body in the asteroid
> zone, six times the volume of the original, uncratered
> Vesta.
>
> We can identify Lunar and Martian meteorites only
> because we have composition data gathered by humans
> and robots. That's the only reason. Without a sample
> or a set of readings from Mercury, or Venus, or anywhere,
> the means of reasonable proof are absent.
>
> When the Dawn mission gets to Vesta, we will likely
> be able to nail down the HED identification with that
> body. I quote the mission parameters: "This mission
> was designed to verify the basaltic nature of Vesta
> inferred both from its reflectance spectrum and from
> the composition of the howardite, eucrite and diogenite
> meteorites believed to have originated on Vesta."
>
> Failure to find the expected HED terrain on Vesta would
> be.... interesting. Dawn will be the first test of the entire
> effort to "reason out" parent bodies. It will provide evidence
> where they has mostly been speculation.
>
> The paper you cite (by Chambers) is a good summary
> of the problems in planetary formation theory. There
> are lots of those. I used Vesta as an example because
> it's an obvious example of the sort of thing he discusses
> in the section on "planetary embryos." Vesta would be
> at the smallest end of their size range -- not too hard
> to toss around.
>
> Until there is evidence enough to settle the question, it
> remains speculation. we've had definitions of Science and
> of Faith on the List recently. Let me add another one more:
> Speculation. Speculation is what you do while you're
> waiting for evidence, because there isn't enough evidence
> yet for proof.
>
>
> Sterling K. Webb
> -------------------------------------------------------------------------------
> ----- Original Message -----
> From: "Shawn Alan" <photophlow at yahoo.com>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Friday, July 23, 2010 10:33 PM
> Subject: [meteorite-list] Its official! NWA 6291 "The King
> ofAngrites"forsale - AD
>
>
> Hello Sterling and Listers,
>
> Sterling, thank you for your input about Angrites "might" have a
> connection with Mercury by saying Vesta quote un quote......
>
> "Vesta did not .....form where it is. No Way."
>
> Know I am kinda confused with Vesta and your connection or lack of
> connection to this topic, but I am going to make an educated guess of
> why you might have suggested Vesta in the first place.
>
> This whole topic pulls from Angrites and the possible connections they
> might have with Mercury. I am going to zero in on one meteorite, NWA
> 2999 because it seems that there has been more research done on this
> meteorite compared to other Angrites.
>
> One observation of why some scientist feel that NWA 2999 "might" be
> from
> Mercury is that NWA 2999 meteorite has gone through a vertical
> tectonics
> process, which occurs on Earth and Mercury. In addition to this
> vertical
> tectonic process.......
>
> Papike et al. [9]
> suggested that angrites might be samples from
> Mercury based on volatile depletion, and systematics
> of plagioclase compositions and Fe/Mn ratios in
> mafic minerals.
>
> http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1344.pdf
>
> Now Sterling, is this the reason why you brought Vesta into this
> equation, because its a differentiated body and the vertical tectonic
> process might have happened on Vesta? Or its because you feel that
> Vesta
> some how moved from one side of the hood to the other side because of
> the iron core being too big for where Vesta is located at?
>
> Lets change the topic and focus on your statement on how you feel
> about
> Vesta, quote un quote ......
>
> "Vesta did not .....form where it is. No Way."
>
>
> Now this would be a perfect example to use this quote Greg
> Lindh.......
>
> This reminds me of a quote by Mark Twain. The quote follows:
>
> "There is something fascinating about science. One gets such wholesale
> returns of conjecture out of such a trifling investment of fact."
>
> Something to think about....
>
>
> Iron meteorites tell their own tale. These meteorites
> come from asteroids that became hot enough to melt
> and differentiate. The most plausible source of heat
> was the decay of short-lived isotopes, especially 26Al.
> Melting must have occurred while was still abundant,
> which means these asteroids took something like 2
> Myr to form [19,20]. Why did some asteroids melt
> when others did not? Presumably, different stages of
> planet and asteroid formation occurred concurrently in
> the same region of the nebula. Some objects formed
> earlier than others, and their subsequent thermal
> evolution was different as a result.
>
> http://groups.csail.mit.edu/mac/users/wisdom/extrasolar/chambers.pdf
>
> I think this pulled abstract could explain your educated guess of why
> you think Vesta had accreted somewhere else besides where it is :) My
> guess is that when differentiation occured, that with some parent body
> the process was more prevalent because there might have been an
> abundant
> amount of 26Al , which this short lived isotope produces alot of heat
> which would be a good environment for differentiation to take place
> aka
> in Vesta :) but thats my suggestion and some science to back it up :)
>
>
>
>
> Shawn Alan
>
>
>
> [meteorite-list] Its official! NWA 6291 "The King ofAngrites"for
> sale -
> ADSterling K. Webb sterling_k_webb at sbcglobal.net
> Thu Jul 22 17:03:44 EDT 2010
>
>
> Previous message: [meteorite-list] Its official! NWA 6291 "The King of
> Angrites"for sale - AD
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> Angrites" for sale - AD
> Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
>
> Martin, Jason, Shawn, &c.,
>
> The fly or flaw in the ointment, the paper, and the
> responses is an unspoken but apparently universal
> assumption that every sizeable body in the solar
> system currently resides at the same address where
> it accreted originally.
>
> What about a body that accretes in the 0.50 AU block,
> then moves 'way up the street and out to the 2.35 AU
> neighborhood? Like say, Vesta. Now, I'm not saying
> Vesta did that, you know, fled from the 'hood and
> moved to the suburbs... I just saying Vesta did not
> form where it is.
>
> No Way.
>
> Models that "fit" Vesta propose a iron core of about
> http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2129.pdf
> 300 kilometers out of an original spherical body of
> 540 km. diameter. Such a body HAS to have accreted
> much, much closer to the Sun. I repeat, No Way.
>
> So, isotopic data that tell you where a body accreted
> MIGHT tell you everything you need to know about the
> place or it MIGHT tell you nothing of any use whatsoever.
>
> Even the old notion about the distribution of iron cores
> in the inner solar system is wrong. Decades ago, we
> assumed bigger iron cores in close, getting smoothly
> smaller as you moved out from the Sun. Then, we
> discovered that Venus' core is proportionally much
> smaller than the Earth's, and that Mars core is puny.
>
> Then, when we moved to the theory of the Moon being
> formed by a giant "impact," or graze, or embrace, all
> the models said we had two cores -- our original core
> and the core captured from the big proto-Moon. Mercury
> too shows evidence of such a collision (although no
> moon resulted).
>
> All of a sudden, Venus and Mars have "normal" cores.
> The Earth is cheating -- it's packing an extra halfcore
> in its hip pocket, and Mercury has two cores-worth of
> core. Venus and Mars that are normal respectable planets,
> and Earth and Mercury are "core-snatchers."
>
> A simple question like "what should a meteorite from
> Mercury be like?" is not a simple question. First, if
> Mercury suffered a giant impact early on, then its
> present crust (and upper mantle and maybe more)
> is derived from the impacting body. And that Big
> Whacker accreted... where? Nearby? Faraway?
> In-between?
>
> Then, there is the case of a parent body of some
> size blasted off the ORIGINAL primordial crust (and
> mantle) of Mercury by the giant impact, finding a new
> orbit, and providing enigmatic meteorites for the next
> billions of years. That original Mercurian crust could
> have been quite different from the present crust.
>
> As Jason pointed out, there were a gaggle of large
> differentiated bodies in the early system. I go with
> the "hundreds" rather than 30-40; see the work by
> SwRI that suggests 100+ of them from the inner
> solar system ended up in the Asteroid zone. The
> Zone is made up of "natives" and a horde of refugees,
> which could have accreted pretty much anywhere
> and will each have a unique formation history all
> their own.
>
> Present arguments are somewhat simple-minded.
> It's going to take centuries to sort out the life history
> of every body big enough to bother with.
>
> It's going to be fun.
>
>
> Sterling K. Webb
> --------------------------------------------------------------------------------
> ----- Original Message -----
> From: "Martin Altmann" <altmann at meteorite-martin.de>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Thursday, July 22, 2010 6:00 AM
> Subject: Re: [meteorite-list] Its official! NWA 6291 "The King
> ofAngrites"for sale - AD
>
>
> Huh, I found even a paper, which postulates, that the HEDs are from
> Mercury
> and the angrites from Venus....
>
> http://www.lpi.usra.edu/meetings/otp2004/pdf/3012.pdf
>
>
>
> ;-)
> Martin
>
>
>
> -----Urspr?ngliche Nachricht-----
> Von: meteorite-list-bounces at meteoritecentral.com
> [mailto:meteorite-list-bounces at meteoritecentral.com] Im Auftrag von
> Jason
> Utas
> Gesendet: Donnerstag, 22. Juli 2010 11:27
> An: Shawn Alan; Meteorite-list; Adam Hupe
> Betreff: Re: [meteorite-list] Its official! NWA 6291 "The King of
> Angrites"for sale - AD
>
> Shawn,
> Well-said -
> But I can't emphasize enough the fact that such large bodies existed
> in large numbers in the early solar system. That much is obvious from
> the large numbers of ungrouped (and grouped) differentiated
> achondrites that we have in our collections here on earth, as well as
> from all various types of iron meteorites, which represent the cores
> of diffeentiated planetismals. All in all, we have meteorites that
> suggest well over 30-40 such bodies in the early solar system, and
> computer-run models in some cases suggest hundreds of such bodies.
>
> http://www.ucmp.berkeley.edu/education/events/cowen1d.html
>
> http://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System#For
> mation_of_planets
>
> Note that wikipedia suggests 50-100 such bodies. I wouldn't usually
> reference wikipedia for something like this, but see references 35-36
> for the article - that's actually a decent estimate that's been backed
> up by some serious work done by experts -- it's not just a crap
> wikipedia reference.
>
> So, angrites may be from Mercury. If we say that, regardless of their
> composition and history, they just needed to be from a large
> planetismal capable of some metamorphic activity, then we've got a
> 1/50 to 1/100 chance that angrites are, in fact, from Mercury.
>
> The trouble is that their chemistry and age suggest that they're not
> from Mercury.
>
> I agree. They *might* be from Mercury. And yes, some smart people
> have said that they *might* be from Mercury.
> But it seems to me that this article is being deemed credible because
> of its authors, and not because of what it actually says.
>
>
>
>>I do not refute Melinda Hutson's article that was never peer reviewed
>
>
>
>>and
>
>
> contains several errors according to the classifying scientists. I
> asked
> scientists about the article and they stated, it is obvious that she
> didn't
> read
> the original peer reviewed abstract carefully, even mistaking the type
> of
> petrology that was discussed using formulas that simply do not apply
> to
> the
> texture NWA 2999 exhibits.
>
> I'd like to know what these errors were, and how the error might have
> affected her conclusions. Perhaps Adam or someone else would be
> willing to explain her errors and how they suggest that angrites are
> actually from Mercury.
>
> Seems like this is the perfect sort of topic for the list...
>
> Regards,
> Jason
>
>
>
>
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Received on Sat 24 Jul 2010 01:53:25 PM PDT