[meteorite-list] Vesta is NOT a "protoplanet"

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 23 Jul 2011 01:41:49 -0500
Message-ID: <42A27E9DA452425896ED1494803E20AF_at_ATARIENGINE2>

Hi, Rob, List,

The term I see NASA using most is "planetary embryo"
in the context of "the last surviving planetary embryo."
I suppose you could say that an object can only be a
planetary embryo while planets are accreting, so maybe
"last surviving" should be "the former planetary embryo
known as Vesta" (rather like the star "formerly known as
Prince").

The term comes from the Nebular Hypothesis in which
a forming star is surrounded by a "protoplanetary disk,"
the disk from which ALL its planets will form. Later, there
was a wrinkle of the Nebular Hypothesis in which they
thought that the gas giants and their satellite systems
formed out of a "protoplanetary disk" all their own, inside
the overall protoplanetary disk and at the center of which
was a "protoplanet." That use of protoplanet in this contest
would only apply to a gas giant massed body, not a puny
Earth or Vesta.

The term "planetary embryo" comes from the Accretion
Hypothesis but "protoplanet" seems to be used inter-
changeably with it, as in: "Protoplanets are large planetary
embryos within protoplanetary discs that have undergone
internal melting to produce differentiated interiors." This,
next to a picture of Vesta, which fits that definition (sort
if) by being differentiated, although it not up to 1000
kilometers in size (another criterion):
http://en.wikipedia.org/wiki/Planetary_embryo

It further sets forth: "In the inner Solar System, the three
protoplanets to survive more-or-less intact are the asteroids
1 Ceres, 2 Pallas, and 4 Vesta. Kuiper-belt dwarf planets
have also been referred to as protoplanets. Because iron
meteorites have been found on Earth, it is deemed likely
that there once were other metal-cored protoplanets in
the asteroid belt that since have been disrupted and that
are the source of these meteorites." Under this definition
of protoplanet, Vesta would be a planetesimal still, because
it's smaller than the 1000-kilometer lower limit for a
protoplanet.

Then, planetary embryos would be planetesimals under
1000 kilometers and protoplanets are planetesimals above
1000 kilometers. Presumably, all asteroids would be
planetesimals no matter what size they are or protoplanets
if their big enough no matter what shape they are, and
presumably, all asteroids are either planetesimals or
protoplanets unless they are round or in hydrostatic
equilibrium and would be planets no matter what size
they are unless they are cheating by being squishy to
be round or unless they are broken pieces of something
that once was round...

This is insane.

Rob clearly seems to think you can only BE a
planetesimal or a protoplanet while the system is
forming and if you get left out of the final product,
what are you? I see Vesta sitting there saying, "You
doan unnerstand, I cudda been a contender."

Under this consideration, there are NO planetesimals
or protoplanets at all, accretion being a thing of the
past, so let's just dust our hands and never speak of
this again.

On the other hand, NASA needs all the self-service it
can get, poor baby, got no spacecraft, hafta take Russian
taxis everywhere it goes... Why not humor them?

And while we're complaining, I want to address that
"ancient battered surface" clich?. Nobody doubts the
HED's come from the Vestoids, and nobody doubts that
the Vestoids are the debris of that absolutely gigantic
South Pole Crater hit so often ascribed to the "ancient
battered surface." But all you have to do is examine the
shock-reset ages of Vestoid chunks to date that huge
hit, and it is therefore LESS than a billion years old.
It's not ancient at all.

And since that so-called ancient feature is overlayed
with clear lava flow formations, there must have been
active magmatism on Vesta more recently than that.
The crater size distribution (when the counters finish)
will likely show a youngish surface, so let's ease up
on all that "pristine from the dawn of the solar system"
talk.

This is all tourist talk of Vesta, as the boat pulls into
the harbor and we get a first glance. The real work is
yet to be done on the "former protoplanet (or perhaps
planetesimal or planetary embryo) now known as Vesta."


Sterling K. Webb
--------------------------------------------------------------------------
----- Original Message -----
From: "Rob Matson" <mojave_meteorites at cox.net>
To: "John Lutzon" <jl at hc.fdn.com>; <meteorite-list at meteoritecentral.com>
Sent: Friday, July 22, 2011 11:19 PM
Subject: [meteorite-list] Vesta is NOT a "protoplanet"


> Hi John,
>
> Just a gentle request to resist the urge to parrot NASA's erroneous
> (and mildly self-serving) labeling of Vesta as a "protoplanet". Vesta
> will never evolve into a planet via accretion, so while one might
> have optimistically called it a protoplanet 4+ billion years ago,
> that window of opportunity has long since closed. To label it as
> such is simply an anacronism; it is an asteroid, and nothing more.
>
> Cheers,
> Rob
>
> -----Original Message-----
> From: meteorite-list-bounces at meteoritecentral.com
> [mailto:meteorite-list-bounces at meteoritecentral.com]On Behalf Of John
> Lutzon
> Sent: Friday, July 22, 2011 8:50 PM
> To: brian burrer
> Cc: meteorite-list at meteoritecentral.com
> Subject: Re: [meteorite-list] Is Vesta Mong Nong?
>
> Hello List,
>
> I don't know what i don't know---so:
> The latest photo of Vesta shows about 1/2 of this protoplanet which is
> about
> 350 miles in diameter
> and the largest crater looks approximately 1/10 0f this radius which
> means
> the crater dia. is about 17.5 miles--quite a hit for such a little
> guy.
> I remember seeing a photo of a much smaller asteroid with an impact
> crater
> of
> about 1/3 to 1/2 the size of the whole thing and wonder why it wasn't
> cracked in half or completely obliterated.
>
> So, are impact forces mitigated when an object is not in a tightly
> bound
> orbit confiscation and just gets "pushed" rather than crushed?
>
> John
>
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Received on Sat 23 Jul 2011 02:41:49 AM PDT