[meteorite-list] CORRECTIONS TO Dwarf Planet 'Becoming A Comet'

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 3 Feb 2007 18:15:49 -0600
Message-ID: <00ff01c747f1$a030c670$904ae146_at_ATARIENGINE>

Hi,

    Just to clear up a few things: EL61 is a big rock
with a thin layer of "snow." But it's so big and there's
so much "snow" on a surface that size, that it amounts
to all those Hale/Bopps. Some of my arithmetic last
night was wrong (note to self: put on glasses, use
calculator, dummie!), but the correct figures don't
change the picture for the better.

    EL61's surface area is hard to calculate, given its odd
shape, but it's about 9-10 million km^2. How do you
measure the surface of that tri-axial shape? It would be
just under 8 million km^2 if it were an efficient sphere,
or 13 million km^2 if it were a box. EL61's shape has
more surface than a sphere of the same volume, but
less than the box it would fit in. Theories of packing
efficiencies say a "long egg" is about 83% efficient,
which would make EL61 about 10 million km^2.

    A "Hale/Bopp" sized object is about 33,500 km^3,
so every kilometer of depth of ice on EL61 is equal
to 298.5 "Hale/Bopp" sized objects. Every ten feet
of "snow" on EL61 is equal to one Hale/Bopp. And
every 45 cm of depth is a layer of material equivalent
to the entire mass of the interplanetary dust of the
Zodaical Light.

    If the ice on EL61's surface was one kilometer deep,
its total volume would be the equivalent volume of a
270-kilometer diameter "comet," a pure iceball. If the
ice is ten kilometers deep, it would be the equivalent
volume of a 580-kilometer diameter iceball. As huge as
that volume of ice is, it's nothing compared to the total
volume of 2003 EL61, which is 1,760,000,000 km^3.

    Another critical factor is that those volatiles are all
spread out on a vast surface with the maximum ability
to intercept the sun's rays, a surface of a body that is
spinning so fast that every point crosses the "nightside"
in 2 hours, guaranteeing full exposure of most of the
surface and an average exposure of 50% everywhere.

    This is less mass than I calculated (too quickly) last
night, but still more than enough to produce the results
I described. I hate when you're off by more than an
order of magnitude too big, but when you discover and
correct it, the results are just as lousy and discouraging
as before. Really annoying, and just as dangerous.

    Could the ice on EL61 just be very shallow, so that
there's no big deal? The only source of crystalline ice
(snow) on such a world is water geysers which must
be driven by internal heat and pressure, like Enceledus,
the moon of Saturn. This argues for some good depth
of ice to reach or generate that heat and pressure.

    With an albedo of 0.70, the surface of 2003 EL61
is a mixture of "new-fallen" crystalline snow (albedo
0.90) and "older" icy surfaces (albedo 0.67). This
suggests about 20% of 2003 EL61's surface is "new
fallen" snow. Crystalline ice (snow) has destinctive
spectral characteristics that ice (old and solid) does
not. EL61's got it; its moons do not.

    If 20% of EL61 is covered with "new" snow, that
suggests a fair rate of "geological" activity. If we had
an orbiter watching it, it would probably find an active
geyser or two going at any one time...

    Brown is using the term "become a comet" to
describe the appearance, not the character, of 2003
EL61 if it entered the inner solar system. It confuses
the listener, because he doesn't mean it IS a comet.

    What a comet "is," is in flux right now, with all
the recent missions and recoveries going on. They
do not appear to be the traditional "dirty snowball,"
but much more asteroidal. Conversely, we keep
finding asteroids that may be "comets." Ultimately,
I think all the Small Bodies are similar with a range
of volatiles that is not as wide as we thought. Comets
are rockier; asteroids are wetter, than believed. The
difference may be between "hot" and "cold" asteroids,
rather than asteroids and comets.


Sterling K. Webb
-------------------------------------------------------------------
----- Original Message -----
From: "Rob McCafferty" <rob_mccafferty at yahoo.com>
To: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>;
<meteorite-list at meteoritecentral.com>
Sent: Saturday, February 03, 2007 4:25 PM
Subject: Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)


Apologies for taking selected bits. Hope it's not out
of context.

--- "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
wrote:

''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''

Curiously, Halley's comet has an abledo of less than
4%, less than that of coal or black velvet. While
Halley is not necessarily typical of comets, it is
agreed that comets are very dark objects.
Nucleus[nuclei] sizes have been estimated by removing
modelled coma brightnesses from Hubble images and for
nearby comets radar measurements seem to confirm the
low albedo.

Cometary dust may begin as silicate grained materials
mantled with organic matter. To this hundreds of
0.01micron ice particles may form from a protosolar
nebula into .5micron grains. These cluster into loose
agglomerates which end up being part of the coma of
comets. The evidence for this theory is the particles
swept up by high altitude research planes [18km up]
believed to be cometary in nature. This being the case
it explains the brightness of the coma and -might I
suggest- the brightness of EL61. It need not be
covered in ice, just covered in this cometary 'snow'


''Now, we come to the Giant Comet Notion. Obviously,
2003 EL61's ice is a surface feature, a thin layer of
volatiles
over what is essentially a rocky body.''

Comets are generally considered to be a thin layer of
rocky material over a lot of volatites, the complete
opposite. I could well be wrong on this. Virgin comets
are unusually bright on their first perihelion
passage. One theory is that the surface volatiles ar
vapourised away leaving this outer layer of dark
material. This would suggest that if EL61 is indeed,
becoming a comet, this is it's first journey inward
which seems most unlikely. Also, comets sublimating
ices have a temperature of 230K. Virgin comets can
achieve this much farther out than comets on
subsequent passes. This is because the dark silicate
layer protects the icy material, insulating it. Only
when the comet gets much closer does the heat conduct
in to cause the sublimation of the ices. However, I
doubt anyone would suggest EL61 has a surface
temperature of >200K. There has to be an alternative
explanation.


Sorry the reply so lengthy. I just don't think EL61
can be cometary in nature.

One other think caught my attention in this post

   '' A mere 10% decrease would lower the planetary
temperature
by 7 degrees C''

I thought the difference between aphelion and
perihelion in earth's orbit made a 7% difference in
solar intensity. Does anyone have a guess as to how
long a change need apply for to effect earth? I
suspect not

Rob McC






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Received on Sat 03 Feb 2007 07:15:49 PM PST