[meteorite-list] Comet Holmes

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Mon, 29 Oct 2007 17:07:21 -0500
Message-ID: <00ec01c81a78$148b2480$c944e146_at_ATARIENGINE>

Hi, Chris, List

> The best argument against a collision is the absurd
> improbability of TWO collisions in the last century,
> since this comet has a history of outbursts.

    The problem with probability is the probability of the
assumptions that are applied. If 17P is an isolated object
and any impactor must come from another unrelated orbit,
the likelihood of any collision, ever, is very, very low.

    Like all short period periodic comets, it is assumed
that 17P was perturbed into its present orbit, probably
by Jupiter. Since its orbit ranges from Jupiter to Mars
and is inclined to the solar system plane, 17P must transit
the Asteroid Zone twice every orbit (i.e., every 3.5 years).
One might pass harmlessly through the Zone at many
locations; at other places, you might not be so lucky.

    If 17P is undergoing an on-going disintegration (from
a past major impact, perhaps very long ago), it may well
share its orbit with many smaller, darker (harder) fragments,
millennia-worth of its own "space-junk," a debris stream,
possibly arising from this ancient impact or partial breakup.
This would raise the probability of future "trouble" from
near zero to near 1.0. There may be more than one debris
stream accompanying it, braided around the principal orbit,
with objects distributed along the stream. Such streams
would be quite invisible to us. In the case of Holmes, the
odds of an outburst per orbit seem to be 12 to 1 against.

    Collisions with co-orbiting objects occur at very small
velocity differentials (from the speed of a man walking
briskly up to that of a fast runner). Such collisions are not
catastrophic but damaging: gouging, ripping, crushing,
crust-breaking, volatile churning affairs. Once a century
is not that unlikely for such glancing impacts if there enough
co-orbiting fragments (especially the more silicate ones).

    On the other hand, there may be no external impact event
responsible; it may be the result of some endogenous process
we do not understand. Whipple began the creation of models
that explain comet behavior and self-modification of their orbits,
the effects of thermal exposure, and so forth, and these models
have been greatly elaborated over the years, yet we cannot
explain much of comet behavior. Whipple suggested that Holmes
had been a "double" comet in which the pairs collided.

    Holmes is a prime example of this. We think that it never gets
close enough to the Sun to explain the outbursts, but both the
discovery outburst and the present one occured after perihelion
passage with some delay. In both the discovery brightening and
the present one, the delay was five months! (June 16, 1892 to
November 6, 1892 -- 143 days; with a second outburst of equal
brilliance 60 days later. May 4, 2007 to October 24, 2007 --
173 days. A 60-day second outburst would make Holmes
a Christmas Comet.)

    Does perihelion warming trigger some internal mechanism
that takes about five months to "boil up"? Or does Holmes catch
up with a stream of significant debris (a collisional association)
about five months after perihelion and sometimes interact
collisionally with it?



Sterling K. Webb
----------------------------------------------------------------------------------
----- Original Message -----
From: "Chris Peterson" <clp at alumni.caltech.edu>
To: <meteorite-list at meteoritecentral.com>
Sent: Monday, October 29, 2007 1:49 PM
Subject: Re: [meteorite-list] Comet Holmes


In fact, the coma is not entirely symmetric. There is clearly a denser
region which is offset from the nucleus. This may be a product of
whatever caused the outburst, or it may be tail structure seen through
the coma- that remains to be seen.

Our imagination is perhaps contaminated by visions of Armageddon (the
movie) like geysers bursting from the surface, but in reality the escape
of gas may be much less violent. It isn't unreasonable to expect it to
obey the rules of diffusion, and produce a substantially spherical zone
of expanding material. It is likely that the nucleus is spinning.

The best argument against a collision is the absurd improbability of TWO
collisions in the last century, since this comet has a history of
outbursts.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Francis Graham" <francisgraham at rocketmail.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Monday, October 29, 2007 12:34 PM
Subject: [meteorite-list] Comet Holmes


> Dear List,
> Yes, the clouds finnnallly cleared in the Ohio
> Valley. After a week of hearing the pitter patter of
> rain on the observatory roof, it cleared and I
> screamed aloud: "Now I can see Comet Homes!!!" I
> eagerly and excitedly rolled off the roof to the
> roll-off-roof observatory and paced the floor, waiting
> for darkness. 11:15 AM... 11:20 AM...11:25
> AM...Noon...12:05 PM....it seemed like an eternity.
> Finally, the terminator swept across me as if it were
> a great liberation from the oppressive rule of some
> garish solar dictator. I long already had the
> telescope circles set, locked, and tracking.
> Wowwweee Zoweee! I was not disappointed. What a
> beautiful totally symmetric outburst! What a wonderful
> comet!
> Sterling Webb's post is food for thought. Old
> periodic comets evaporate and their crusts get covered
> with a silicate carbonaceous crust, like melting ice
> on a roadside in spring. When pressure builds up and
> vapor-dust eruptions occur, it should fountain, like
> the wonderful beautiful megafountains of Hale-Bopp.
> But Comet Holmes?!? Noooooo. Something very bizarre
> is at work. There was no specific locality, the coma
> was symmetric.Is it an impact? Even a Carnacas-sized
> whallop on a small crusty periodic comet nucleus would
> do for a brightening; I suspect this (if an impact)
> was a bit larger. Which, renders it improbable. It's
> like a meteor hitting an area the size of Washington
> DC.
> But maybe that's what it is. After all, the
> fictional detective Charlie Chan once said, "Strange
> events often permit themselves the luxury of having
> occurred." Which sums up this outburst to a T.
> I toyed with the idea of the intervening Earth-Moon
> system acting as a gravitational focuser, from 1 AU to
> 1.3 AU, from sun-directed meteors, but the flux would
> not be much higher than the sporadic background.
>
> Francis Graham

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Received on Mon 29 Oct 2007 06:07:21 PM PDT