[meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 3 Feb 2007 14:26:28 -0600
Message-ID: <00ce01c747d1$960845d0$904ae146_at_ATARIENGINE>

Hi,

    This speculation that 2003 EL61 could become an
inner system Giant Comet is a very, very strange one.
I find it extremely puzzling. But, if 2003 EL61 did, it
would just be the capper on this strangest of all strange
worlds in the solar system! I posted some information
about EL61 last year if you're looking for more:
<http://www.mail-archive.com/meteorite-list at meteoritecentral.com/msg48060.html>

    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).
But 2003 EL61 is not a squashed ball, round and flattened.
No, it's much longer one way across than the other way across.

    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. It has to be VERY stiff stuff.
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.

    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...

    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, EL61
is like Enceledus, the moon of Saturn, with water geysers
which must be driven by internal heat.

    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. So, how much material
is there to be warmed by the Sun if EL61 got shuttled into the
inner solar system?

    Let's compare it to Comet Hale/Bopp, which more people
saw as a naked eye object than any recent comet (McNaught has
been sneaky). Hale/Bopp was 40 kilometers across and we don't
know how much of it was volatiles or how much of its surface
was volatilized by the Sun, but certainly not more than a small
percentage of the comet's bulk. If ALL of Hale/Bopp had been
volatilized, it would have been a hundred times (or more) brighter
and a thousand times more spectacular!

    If the water ice on the surface of 2003 EL61 were a mile deep,
it would have the volume of 136,460 Hale/Bopps! In fact, the
top one foot of 2003 EL61's icy surface contains 2.6 times the
volume of Comet Hale/Bopp!

    Since it seems likely that the freshness of the surface ice on
EL61 is because it is supplied by deep water geysers, there
would seem to be some depth of ice on EL61. If it were 5 miles
deep, the ice volume would be equivalent to the total volume of
682,300 Hale/Bopps. And if the layer were 20 miles deep, the
ice volume would be the equivalent to the total volume of
2,729,200 Hale/Bopps!

    Incidentally, my Ice Unit, 1.0 Hale/Bopp Unit, is exactly
268,082.57 cubic kilometers, or 2.6808257 x 10^14 cubic
meters of ice, weighing 2.6808257 x 10^17 kilograms!
This amount of ice, One Hale/Bopp Unit, is 7.5 times
the mass of ALL the interplanetary dust presently in the
solar system, that which causes the visible reflection
which we can see with our naked eye, the Zodiacal Light.

    The crucial question would be how deeply into the solar
system a perturbed 2003 EL61 would travel in its new,
perturbed orbit? If its perihelion were in Saturn Country,
it would simply become the Big Cheese of the Centaur
Group (of which there a 100 or so) and the Super Comet
might show traces of coma in a telescope. If its perihelion
were near to Jupiter (what an unstable orbit that would be!),
it would be both bright and visually comet-like.

    If its perihelion were any closer, there is another factor
to consider: Danger. Brown treats this (at least as quoted
in this press story) as an almost "touristy" event: "When it
becomes a comet, it will be the brightest we will ever see."

    But if its perihelion were INSIDE Jupiter's orbit, it would
pass through (and thus perturb) the Asteroid Belt! Hey now!
Wait a minute! Perturb the Asteroids? That doesn't sound
so great. No, definitely not a Great Idea. Lively, but not prudent.

    Anybody have a lot of enthusiasm for a Rain of Ice and
Iron like we haven't seem in Eons? No? I don't have much...
That's not "a good thing" (to quote Martha Stewart). Having
a planet-sized body traversing the Asteroid Belt can only
spell Big Trouble.

    Well, what if it didn't pass through the Asteroid Belt?
No way of knowing what the inclination of a perturbed
2003 EL61 would be, after all. What if its perihelion was
closer in than the Asteroids?

    It certainly would have a vaster and more extensive coma
then, wouldn't it? If it came in as far as Mars or even the Earth,
it would be incredibly bright, visible both day and night, with
a tail many millions of kilometers long, and a coma 10 or 20
thousand kilometers across, perhaps 100,000 kilometers
across if it got warm enough. That certainly qualifies as a
celestial "tourist event"!

    And if the perihelion were even closer to the Sun , the
volume of material pouring off the new "comet" would be
many millions of tons per second. The solar wind pushes
against dispersed material, dust, gas, ice; that's what forms
a comet's tail. But if the volume were great enough, the inner
solar system would fill up with, and become clouded with,
a fog of highly reflective particles, despite the best efforts of
the solar wind.

    The Sun's light would be scattered, diffused and dispersed.
The skies would be brighter at night and dimmer in the daytime.
Eventually, they would look the same both night and day as
the volume of cometary "fog" increased. There would be no
more night. The amount of solar energy reaching the inner
planets would be drastically reduced.

    The situation would be exactly like passing through a GMC
(Giant Molecular Complex) or interstellar cloud, only much worse.
This amount of volatiles released in the inner solar system would
"cocoon" the Sun in a gas and dust envelope.

    If the Earth's solar input dropped by 1%, the planet's mean
temperature would drop by less than 1 degree C. No problemo!
We'd get rid of that pesky Global Warming, you know.

    A mere 10% decrease would lower the planetary temperature
by 7 degrees C. That's not so pleasant. That's less than what
the global temperature was during the last Ice Age (6 degrees
cooler). We don't want the Ice Age back, do we? No, I don't
think so...

    A 20% decrease would lower the planetary temperature by 15
degrees C! You might be saying that a 15 degree drop doesn't
sound all that bad, but we're talking about the planetary mean
temperature. It hasn't been that low in the entire geological history
of the Earth, including the era when there was sea ice at the equator!
At this temperature, the entire planet would be covered by ice
from Pole to Pole, frozen solid!

    That's from a 20% decrease, but the gas production of a truly
planet-sized "comet" could easily produce a 30% to 50% reduction
in solar incidence, which would drop mean temperatures by up
to 50 degrees C. The equatorial temperature of the Earth would be
about what the temperature of Antarctica is now. Mars would fall
to the temperature range of Saturn (or Pluto). Even Venus, the solar
system's Hellball, could become too cool for comfort. Everything
from the Asteroids on out would be at the temperature the Kuiper
Belt is now.

    So, you see, it's not exactly a tourist bonanza nor a celestial
event to be anticipated with bouncy enthusiasm. No, this is not
good at all. This is worse than being bombarded with big asteroidal
impactors and other assorted cosmic disasters. It would not only
make our own planet uninhabitable, but also all the other worlds
where we might conceivably, with herculean effort, attempt to take
refuge, mucking up the entire solar system. (You got any relatives
at Alpha Centauri?) Actually, there's a name for this sort of event...

    I believe it's called The End of The World.

    So, I have to ask myself: how likely is this? Is this going to
happen? Ever?

> Brown has calculated that the object could be due [for] a close
> encounter with the planet Neptune. If so, Neptune's gravity could
> catapult it into the inner Solar System as a short-period comet.

    The likelihood of any "close encounter" repeating itself
is easy to calculate. Suppose two bodies with orbital periods
of 2 and 3 years respectively have a "close encounter." Two
years later, when the first body has returned, the slower body
is still a year away from the potential encounter point. Wait
another two years (four years total); the slower body is now
a year past the encounter point. Only after six years will the
encounter repeat. That is the product of the two orbital
periods ( 2 times 3 = 6 ) and is the time between encounters,
or indeed any specific configuration of the two orbits.

    2003 EL61's period of 284.5 years times Neptune's period
of 164.88 years is 46,900.36 years. That means that the two
had an encounter like what is proposed 46,900 years before, and
another such close encounter 46,900 years before that, and...
Well, 21+ such encounters every million years. Since the very
beginning of the solar system, they've had almost 96,000 such
encounters, and in exactly NONE of them has 2003 EL61 gone
off to visit the inner solar system, not even once.

    How likely is it that next close encounter will have that
result? Or even the next 100 close encounters? How has EL61
managed to hang onto its moons through all these "close"
encounters? Why, after the solar system has held together
for more than four billion years, should it decide to unravel
right now? Is the solar system just coming apart?

    On the other hand, there's this: we explain 2003 EL61's
extraordinary shape and fantastic spin to a Major Collision
with Something. We also assume it happened in the far distant
past, early in the history of the solar system (mostly because
it was more crowded then and also because we don't want
to think it could happen now). What if the body that "collided"
with 2003 EL61 was a moon of Neptune? What if the collision
was "recent," meaning "only" half a billion years ago (or less)
and that the collision altered EL61's orbit to make a too-close
encounter and a voyage to the inner solar system possible?

    Now, there's a nasty thought...

    Which is why, instead of a news snippet with three sentences
of potential information, there ought to be an actual publication,
however informal, with, you know, real numbers and real
calculations and real information. To modify a great movie line:
Show me the numbers!

    Since EL61 has only been observed for 2-3 years of its 285
year orbit (1%) and the earliest prediscovery photo is 1955 (18%
of an orbit ago), just how accurate are those orbital determinations
and the resultant calculations? Inquiring minds want to know...

    My considered scientific opinion?

    'Tain't happenin', dude!


Sterling K. Webb
-------------------------------------------------------------------------------------------
----- Original Message -----
From: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Wednesday, January 17, 2007 11:32 AM
Subject: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)

http://news.bbc.co.uk/2/hi/science/nature/6268799.stm

Dwarf planet 'becoming a comet'
By Paul Rincon
BBC News
January 17, 2007

An unusual dwarf planet discovered in the outer Solar System could be en
route to becoming the brightest comet ever known.

2003 EL61 is a large, dense, rugby-ball-shaped hunk of rock with a fast
rotation rate.

Professor Mike Brown has calculated that the object could be due a close
encounter with the planet Neptune.

If so, Neptune's gravity could catapult it into the inner Solar System
as a short-period comet.

"If you came back in two million years, EL61 could well be a comet,"
said Professor Brown, from the California Institute of Technology
(Caltech) in Pasadena.

"When it becomes a comet, it will be the brightest we will ever see."

Cosmic oddball

2003 EL61 is a large object; it is as big as Pluto along its longest
dimension. It is one of the largest of a swarm of icy objects that
inhabit a region of the outer Solar System known as the Kuiper Belt.

But it is extremely unusual: spinning on its axis every four hours, it
has developed an elongated shape.

2003 EL61 is apparently composed of rock with just a thin veneer of
water-ice covering its surface. Other Kuiper Belt Objects (KBOs) contain
much more water-ice.

Professor Brown's computer simulations show that the object is on a very
unstable orbit and set for a close encounter with Neptune.

The eighth planet's gravitational force could either sling the icy rock
ball into the inner Solar System as a comet, out into the distant Oort
Cloud region, or even into interstellar space.

Orbits of Kuiper Belt Objects tend to be very stable, but the region is
thought to be a reservoir for short-period comets.

Occasionally, some of these objects must get tossed inward to become the
fizzing lumps of ice and dust that criss-cross our cosmic neighbourhood.

Shedding surface

Mike Brown and his colleagues have come up with a scenario to explain
2003 EL61's physical characteristics and behaviour.

About 4.5 billion years ago, the object that became 2003 EL61 was a
ball, half composed of ice and half of rock - like Pluto - and about the
same size as Pluto.

Some time early in its history, it was smacked, edge on, by another
large KBO. This broke off much of 2003 EL61's icy mantle, which
coalesced to form several satellites.

As expected, the satellites seem to be composed of very pure water-ice.

Professor Brown suggested that some of 2003 EL61's mantle may already
have made it into the inner Solar System as cometary material.

The oblique impact also caused 2003 EL61 to spin rapidly. This rapid
rotation elongated 2003 EL61 into the rugby ball shape we see today.

"It's a bit like the story of Mercury," Professor Brown explained.

"Mercury got hit by a large object early in the Solar System. It left
mostly a big iron core, with a little bit of rock on the outside. This
is mostly a rock core with a little bit of ice on the outside."

Mike Brown outlined details of his work during a plenary lecture at the
recent American Astronomical Society meeting in Seattle.
Received on Sat 03 Feb 2007 03:26:28 PM PST