[meteorite-list] Ceres May Be An Asteroid Impersonator

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue, 22 Jul 2008 18:54:55 -0500
Message-ID: <053a01c8ec56$5801e180$db5de146_at_ATARIENGINE>

Hi, All,

    I note with horror that (at least) one Listoid has responded
to this press release by saying "now that science has decided..."

    Whoa! Back up!

    No, "science" has not decided! One researcher with a Wild
Hare -- I mean, a Wild Speculation -- has proposed it. That's an
entirely different matter. The press release says, "it was a recently
developed model of the early solar system that prompted
McKinnon..."

    You will note that the developer of the computer model
distances himself from the notion: "Bottke says... 'It is indeed
possible that he is correct, but I would not bet for it at this
point.' "

    The problem with the Kuiper Belt and the rest of the outer
Outer System is that the objects that live there cannot have
been born there.

    The solar system starts as a flat protoplanetary disk of
dust and gas. What its temperature, rate of cooling, density
distribution, and physical characteristics were is a matter
for guesses. So we start with guesses, our best guesses,
yes, but they are guesses just the same.

    Dust sticks together and makes particles; particles
bump together and make lumps, and so on until a big
body is formed. That's the general idea. To make a similar
body at a greater distance than another, there must be the
same mass of materials available everywhere in the disk.
But when we look at stars that currently have protoplanetary
disks, that's not what we see. We see a lot of mass in
close and the disk thins out rapidly toward the edges.

    When we started discovering solar systems of other
stars, we saw system after system with super-Jupiters
orbiting closer to their stars than Mercury does to ours.
Astronomers were flabber-ghasted. What happened?

    Well, if your protoplanetary disk has a lot of matter,
as a planet forms it's orbiting through thick dust which
drags its speed down and makes its orbit shrink. You
keep encountering new dust and gas; you get fatter and
fatter but orbit closer and closer until you reach the inner
edge of the protoplanetary disk and run out of dust, but
by then, you're three Jupiters fat and you're sitting on the
doorstep of your star!

    Our solar system was not a mass-rich protoplanetary
disk, because that didn't happen here. So the likelihood
of Kuiper Belt objects (or comets) forming where the
Kuiper Belt is now is very small. There simply wasn't
enough mass out there.

    Somewhere out around 5-10 AU, podner, there's a
place where ice condenses. In from there, rock vapor
condenses. When they get to accreting, icy-rocky bodies
form and shuffle their orbits. If an icy-rocky body gets
big enough, it starts grabbing gas, and you get a Jupiter.
If an ice-only body gets big enough, it starts grabbing
gas, and you get a Saturn.

    Big bodies have an impressive way of winning orbital
disputes with smaller bodies. Ceres and Pluto (density
2.0-2.1) are very much alike and the two of them were
likely born in the same neighborhood. They both moved
out of the 'hood, Ceres in, to the edge of the City, and
Pluto headed for the far Suburbs. Planets grow apart;
you lose touch after so long... There are some others that
stayed, still hang out in the old neighborhood -- Ganymede,
Callisto, Titan (density 1.8-1.9) and Io, Europa (density
~3.0) -- they joined gangs.

    I could do a complete flip-flop on this and suppose
that Pluto and all the Plutinos are a "planet" that never
came together because of the influence of Neptune, all
out at 40 AU. But the same thing could have happened
much further in and they all marched outward as Neptune
moved out. And so on... there are scores of possibilities
and no way to know for sure.

    The current craze for computer simulation resembles
the last century's "Search for Planet X" (which ended
with the discovery of Pluto nowhere near where it was
supposed to be). "Planet X" was searched for by complex
and intricate mathematics, the "method of residuals," the
"computer simulation" of those days. It worked magically
for Neptune and failed miserably for everything else...

    The dumbest statement in the entire press release is
this one: "If... Bill McKinnon's hunch is right, the largest
asteroid in the solar system isn't an asteroid at all."

    Duh. There is no "Regulation Asteroid, One (1)." There
are asteroids that are Rock; there are asteroids that are Iron;
there are asteroids that are Comets hiding out in disguise.
The Asteroid Zone is a junkheap, a rubbish bin, it's your
grandparents' basement -- it's crammed with every kind of
stuff imaginable.

    The variety is great. There are 83 classes of iron asteroids
and 100 uniques; there are stone asteroids that are more kinds
of rock bodies than there are letters of the alphabet (counting
subgroups); there is probably stuff we don't even know about;
and you're going to tell Ceres it doesn't belong because it's
a "little Pluto"? Because it's "not like" the other Asteroids?
Because it's the fat round kid on the block?

    Stupid.

    Standard Disclaimer Again: This story is a Press Release,
so there's no way to know what the heck McKinnon actually
said. Did Pluto form in the Asteroid Zone and go out? Did
Ceres form at 40 AU and spiral in? Did they both start at 5-10
AU and go their separate ways?

    Can't tell what he meant from the Press Release. So, Hire
a Press Agent who speaks Hype; have him write punchy
Crap; then, Publish it. That's how you do Science... Isn't it?


Sterling K. Webb
----------------------------------------------------------------------------------
----- Original Message -----
From: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Thursday, July 17, 2008 6:25 PM
Subject: [meteorite-list] Ceres May Be An Asteroid Impersonator



http://www.sciencenews.org/view/generic/id/34157/title/Ceres_may_be_an_asteroid_impersonator

Ceres may be an asteroid impersonator
By Ron Cowen
Science News
July 15, 2008

The largest member of the asteroid belt could have emigrated from the
solar system's fringe

If planetary scientist Bill McKinnon's hunch is right, the largest
asteroid in the solar system isn't an asteroid at all. Ceres, as the
470-kilometer-wide object is called, may be a relative of Pluto that
formed at the solar system's fringes but came in from the cold several
billion years ago.

McKinnon, based at Washington University in St. Louis, said he was first
struck by Ceres' unusually low density - more similar to icy comets from
the outer solar system than the rocky bodies found in the asteroid belt
that lies between the orbits of Mars and Jupiter. The density of Ceres,
referred to as a dwarf planet, is only slightly higher than that of
Pluto. Models suggest Ceres "looks remarkably Pluto-like," McKinnon says.

But it was a recently developed model of the early solar system that
prompted McKinnon to formally propose that Ceres might be an escapee
from the Kuiper belt, an outer solar system reservoir of frozen bodies
that includes Pluto. He presented his proposal July 15 in Baltimore at
the Asteroids, Comets, Meteors conference.

According to the model, developed by researchers including Hal Levison
and Bill Bottke of the Southwest Research Institute in Boulder, Colo.,
and Alessandro Morbidelli of Observatory of the C??te d'Azur in Nice,
France, the orbits of the outer four planets - Jupiter, Saturn, Uranus
and Neptune - were initially packed much closer together than they are
today.

Beyond these planets resided a band of dust, ice and gas particles. Over
time, as some of these particles leaked inward, their gravitational tug
lengthened the distance between the orbs. For instance, Jupiter migrated
inward, while Saturn moved outward.

At some point, according to the theory, Saturn reached a gravitational
sweet spot: The time it took to go around the sun became exactly twice
that of Jupiter's. That interplay strengthened the planets' mutual tug,
and ultimately hurled Uranus and Neptune into the outlying band of dust,
ice and gas. The entry of Uranus and Neptune scattered debris from the
chilly band, sending some of its denizens into the inner solar system.

That's how Ceres might have migrated from the outer solar system into
the asteroid belt, McKinnon suggests.

"We are saying that many objects from the outer solar system - what we
call the primordial disk of comets that went on to produce the Kuiper
belt - are captured in the outer part of the asteroid belt as a
byproduct of the model," Bottke says. He and Levison presented updated
versions of the theory at the meeting just before McKinnon's presentation.

"I consider McKinnon's idea as something of a thought balloon to
stimulate thinking," Bottke says. "It is indeed possible that he is
correct, but I would not bet for it at this point."

Additional information on Ceres' composition, to be gathered by NASA's
Dawn spacecraft when it visits Ceres in 2015, could clarify the body's
origin. But proof may require measuring the ratio of hydrogen to its
heavier isotope, deuterium, in the ices or water vapor venting from the
body, which would require a mission beyond Dawn, McKinnon says. If the
ratio matches that observed in comets, "the case is closed" for Ceres
being an emigre to the asteroid belt, he says.
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Received on Tue 22 Jul 2008 07:54:55 PM PDT