[meteorite-list] 2003 EL61, IN PERSON

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Tue Sep 19 10:23:59 2006
Message-ID: <20060919142356.5359.qmail_at_web36903.mail.mud.yahoo.com>

Hi Sterling, list -

"but core-forming planetesimals all the way out in
Kuiper Belt?!"

Yes, cometissimals - about 75 meters or so, which
themselves can then accrete chaotically over time,
with the heavy elements always gravitationally
precipitating towards the center - the lighter
volatiles always on the outside - and you have
delivery to the surfaces of larger bodies -

Given the problems this presents us for dealing with
cometary impactors, it would be real nice to get some
good spectra of 2003 EL61 right now, but as always,
this kind of study recieves a low priority from the
failed nuclear physicists who control the telescopes
and observing budgets -

by the way, the 64 fragments of SW3 should be in the
Earth's vicinity in 2022, though I don't have any dead
on forecasts yet - as a matter of fact, I wonder where
they are, and how this is being handled, so if anyone
hears anything, please pass it on -

good hunting,
Ed





--- "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>
wrote:

> Hi,
>
>
> Here we've been wasting time talking about who
> found
> 2003 EL61 with not one word about the strangest
> planet in
> the solar system (dwarf or not) itself! This is an
> utterly
> fascinating place!
>
> First of all, there's its shape... Is it round?
> No, Is it irregular?
> No. Is it squished? Well, sort of. Its dimensions
> are 1960 km
> one way, 1518 km the other, and 996 km through the
> axis of
> rotation. Hmm, can you picture that? Neither can I.
> So, here's
> a picture of the shape of 2003 EL61:
>
http://hepwww.physics.yale.edu/quest/sedna/2003_el61.html
>
> Now, if you spin something fast enough (and EL61
> spins
> in under 4 hours per dizzy) and it's stretchy, you
> end up with
> a shape like a squashed ball, or an oblate spheroid
> (or ellipsoid).
> The Earth is so slightly squashed that it looks
> round, but Jupiter
> appears squashed to the human eye.
>
> But 2003 EL61 is not a squashed ball, round and
> flattened.
> No, it's much longer one way across than the other
> way across.
> If it were made of ice or any substance that would
> move, even
> very slowly, when force is applied to it, it
> couldn't maintain
> this shape; it would even out over time. Likewise,
> if it was a
> giant pile of rubble, it would adjust to the forces
> and be round
> and flattened. And, there is an upper size limit to
> a rubble-loid,
> where the energy needed to create rubble is so great
> it scatters
> everything, so no rubble nor planet is left.
>
> Whatever 2003 EL61 is made of, it has to be
> stiff enough
> to hold this shape as it whirls around every 3.9154
> hours. That
> creates a huge amount of force. 2003 EL61 is almost
> as big as
> Pluto, the long way. If it was just round ("Why
> can't you be like
> all the OTHER planets?"), it would be 1500
> kilometers across,
> bigger than Ceres, bigger than Charon. It has to be
> VERY stiff.
>
> We can calculate just how stiff it has to be to
> hold on its
> elliptical midriff bulge while spinning, figure out
> its modulus of
> rigidity and then look to see what materials are
> that stiff. The
> answer is ROCK, rock of a high density. The
> estimates run from
> a density of 2.6 to 3.4 gm/cm^3. For comparison, our
> Moon
> has a density of about 3.3 gm/cm^3. Forget the
> "iceball" notion.
> There can't be more than a smidge of volatiles in
> its composition
> (like the Earth). The actual value is likely to be
> the highest or
> a higher density, otherwise the planet would be
> right on the
> borderline of being able to hold together and any of
> the ordinary
> moderately big impacts you expect every billion
> years or so
> would have shattered it.
>
> The currently favored explanation for the rapid
> rotation is
> a giant impact. Likewise, the existence of two moons
> circling
> 2003 EL61 is attributed to a giant impact, like our
> Moon, like
> Pluto and Charon; it's the moon-maker of choice
> these days...
> But, the force of an impact great enough to spin
> 2003 EL 61
> up to this speed is great enough to melt a rock
> body, and if
> it had melted, the spin would have evened it out to
> a round but
> flattened ball. Even if it hadn't melted, the rock
> would have
> been soft enough to "creep" into a uniform oblate
> spheroid.
>
> The problem is, even though we can figure out
> how stiff
> 2003 EL61 has to be to hold onto its odd shape, that
> doesn't
> explain how it got that shape in the first place...
>
> There are two ways out of this dilemma:
>
> 1.) Since resolution is poor at this distance, it
> could be that
> 2003 EL61 is a body that has been roughly chipped
> away by
> multiple impacts into its present odd tri-axial
> shape, just as
> Vesta seems to have been partially shaped by impacts
> (the
> south pole crater). Is 2003 EL 61 a Super Vesta?
> But a "chipped" shape formed by multiple impacts
> into
> a form so very extreme, with a ratio 4:3:2 for its
> axes, and a
> "chipped" shape that size, 1000 to 2000 km, would
> likely be
> shattered by multiple impacts strong enough to give
> it this
> extreme shape, if it were only a "rockball."
>
> This leaves us with the other alternative:
>
> 2.) 2003 EL 61 IS a Super Vesta! That is, 2003 EL61
> is a
> fully differentiated planetary body, with a rocky
> mantle and
> a iron-nickel core. Their densities are almost the
> same
> (3.4 for 2003 EL61 vs. 3.4 for Vesta).
> As far as we know, the only way you can get an
> extreme
> tri-axial shape is in bodies whose density is far so
> from
> being uniform that the mass distribution distorts a
> two-axis
> ellipsoid of revolution (ellipses having only two
> axes) into
> that tri-axial shape -- in other words, it seems
> inevitable that
> one would have to conclude EL61 is a differentiated
> body.
>
> Look at that picture at that URL above. Imagine
> it as a
> composite of a round but flattened center section
> that is a
> 1000 km by 1500 km oblate spheroid with two "waves"
> on
> opposite sides of the globe, "waves" that rise 250
> kilometers
> high from the oblate surface, like the (very much
> smaller!)
> tidal bulges the Moon raises in the Earth's oceans.
>
> We pretty well have to assume that the spin-up
> impact and
> the moon-forming impact are one and the same impact.
> These
> Moon-forming impacts are relatively infrequent
> (Earth-Moon,
> Pluto-Charon), else every planet would have a giant
> satellite
> just like we do. Two huge impacts of that magnitude
> for
> one small planet is asking a lot! So, one impact did
> it.
>
> Back when we thought the Earth's Moon was "spun
> off"
> the early molten Earth and earnest mathematicians
> modeled
> the process, their biggest problem, and the biggest
> objection
> to the theory, was that the models always produced
> TWO
> bulges ready to be spun off into satellites, and we
> only had
> the one Moon, you see.
>
> So, it would appear that 2003 EL61's Big Whack
> caused
> its molten core and soft lower mantle to merely
> distort into an
> oblate spheroid, while its crust and asthenosphere
> became
> completely fluid. It's possible the initial spin was
> even faster
> than it is today and that the tidal interaction of
> its odd shape
> with its Moon(s) has braked the rotation while
> moving the
> moon(s) outward, just as with the Earth and its
> Moon.
>
> Moon One is 1/18 as bright as 2003 EL61. If we
> assume
> that Moon One is as reflective as 2003 EL61 itself
> (a dubious
> assumption, but what are you gonna do?), it would be
> about
> 350 km in diameter, mass about 1% of its primary
> (like the
> Earth's Moon), and orbits at about 30-35 planetary
> radii (like
> the Earth's Moon). Moon Two is smaller (about 1/4 as
> bright
> as Moon One) at 170 km and closer (at 40,000 km
> instead of
> Moon One's 50,000 km).
>
> Why do I say that its dubious that the Moons are
> as brightly
> reflective as 2003 EL61? First, 2003 EL61 is a very
> bright body,
> reflecting 70% of the light that falls on it, and it
> is indeed, as you
> would suspect from this brightness, covered with
> water ice. BUT,
> it's not old water ice, but new, freshly fallen
> crystalline ice,
> otherwise known on our planet as snow. Apparently,
> it's like
> Enceledus, the moon of Saturn, with water geysers
> which must
> be driven by internal heat. If 2003 EL61 moons are
> water ice
> bodies with internal heat like Enceledus, fine, but
> that's not
> the type of satellite that would be formed by a
> planet-smashing
> make-a-moon giant impact. The impact scenario on a
> rocky
> body produces a rocky moon.
>
> If 2003 EL61's Moon One were as reflective as
> the Earth's Moon
> (a typical rocky body), it would be 1100 kilometers
> across instead
> of 350! If 2003 EL61's Moon One were as reflective
> as the typical
> small TNO, it would be the size of Ceres. If 2003
> EL61's Moon One
> were just half as reflective as 2003 EL61, it would
> be bigger than
> Vesta! (To illustrate the prejudice about outer
> system objects being
> "tiny," if you were to put 2003 EL61's MOON in the
> asteroid zone,
> it would be the fifth biggest asteroid, even at a
> "mere" 350 km!)
> Water ice has been detected spectroscopically on
> Moon One, but
> not the feature that indicates crystalline ice; its
> spectra is more like
> Charon's. Charon is about 55% as reflective as 2003
> EL61 which
> would make Moon One about 680 km. My guess is that
> Moon
> One will turn out to be at least 500 km in diameter.
>
> I'm having a lot of trouble reconciling this
> whole picture
> of 2003 EL61 with the traditional image of a Kuiper
> Belt where
> iceballs accrete by the gentle kisses of a trillion
> snowflakes...
> In fact, to suggest that 2003 EL61 is a
> differentiated planetary
> body like Vesta is enough to cause solar system
> formation
> specialists to run screaming away or start gathering
> sticks and
> branches for the traditional burning-at-the-stake.
> It's really
> hard to explain, if true.
>
> It's bad enough to have all those battered iron
> cores out
> on the asteroid zone when they should have stayed in
> the
> terrestrial planet zone, but core-forming
> planetesimals all
> the way out in Kuiper Belt?! Horrors! It's a mystery
> how
> Enceledus generates water volcanoes; it's an even
> bigger
> mystery how 2003 EL61 does it. Are the internal
> stresses
> in 2003 EL61 so great they heat the whole body? Is
> the
> surface in a continuous state of Richter 2.3?
> Anybody
> want to live on a totally twitchy planet?
>
> I would give a great deal to see a nice sharp
> jpeg of 2003
> EL61 from just a million kilometers away, but
> unfortunately
> neither I nor anyone else on The List is likely to
> live long
> enough for that to happen (nor for a 20-meter scope
> in orbit
> nor anything else that would get us a good look...)
>
> And with ERIS and 2003 EL61 hogging all the
> limelight,
> who pays any attention to the third big body
> announced
> at the same time: 2005 FY9? Since I think its
> nickname of
> "easterbunny" is ridiculous, I suggest a new one:
> the "shy
> sister." The albedo of 2005 FY9 remains unknown,
> meaning
> we have no way to estimate its size. Observations in
> the
> infrared by the Spitzer, combined with similarities
> of spectrum
> with Pluto yield a very conservative estimate of
> 1600 km,
> or slightly bigger than 2003 EL61, which would make
> 2005
> FY9 the largest known Kuiper belt object after Eris
> and Pluto.
> But unlike Pluto's neutral hue, 2005 FY9 is much
> redder
> than it or Eris and redder KBO's have lower
> reflectivities,
> particularly big ones. If the "shy sister" has an
> albedo like
> Quaoar's (10%), for example, the size of 2005 FY9
> could
> be a whopping 3000 km! That would make it the
> biggest of
> them all.
>
> We just can't tell yet. The "shy sister" is
> currently the
> second brightest Kuiper belt object after Pluto
> (despite its
> great distance), with a magnitude of nearly 17. Back
> in 1930,
> it was brighter still, and Clyde Tombaugh probably
> could
> have found it but it was hiding out in the Milky
> Way! The
> "shy sister" is so shy, she doesn't have a satellite
> (that we
> can find). She's content to let everybody watch Eris
> and
> 2003 EL61 ("Elly"?); she's really very shy.
>
>
> Sterling K. Webb
> ----------------------------------------------------
>
>
>
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Received on Tue 19 Sep 2006 10:23:56 AM PDT