[meteorite-list] Comet Holmes

[Sterling K. Webb]

Hi, Chris, List

    We have no way of knowing how long Holmes has
been in its present orbit; it could easily be many millions
of years (or a few scores of thousands). It would make 
a million Zone passages every 3.5 million years, which 
would give a good chance of a million-to-one collision
event.

    I am only suggesting an initial impact with a Zone 
body (or any other body) "just once" to create streams 
of co-orbiting debris, which would then grow by the 
Kessler process, i.e., rubble makes more rubble.

    Whatever has caused Holmes' "condition" MUST
have been an unfrequent or unlikely event, as there
seem to be no other comets around that behave in this 
oddball way.

    This is equally true of some unique compositional
feature that may be responsible for these outbursts. (Has 
anybody done spectra for Holmes?! A little IR would
be nice.) 

    Comets, once thought to be compositionally simple 
and essentially similar, even near-identical, are proving to
be far more dissimilar and individual than we thought.
Perhaps Holmes, instead of being around for millions 
of years, is relatively fresh from the outer system and 
contains vast deposits of a volatile that gets very touchy 
when it gets exposed within 2 AU of the Sun. (Spectra 
again come to mind.)

    There are a lot of possibilities.


Sterling K. Webb
-------------------------------------------------------------------
----- Original Message ----- 
From: "Chris Peterson" <clp at alumni.caltech.edu>
To: <meteorite-list at meteoritecentral.com>
Sent: Monday, October 29, 2007 6:08 PM
Subject: Re: [meteorite-list] Comet Holmes


I don't disregard the possibility of collisions with co-orbiting 
material. But the probability of colliding with something while passing 
through the asteroid belt is still exceedingly small. That zone is still 
basically empty space- very little material spread out in a massive 
volume.

Chris

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


----- Original Message ----- 
From: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
To: "Chris Peterson" <clp at alumni.caltech.edu>; 
<meteorite-list at meteoritecentral.com>
Sent: Monday, October 29, 2007 4:07 PM
Subject: Re: [meteorite-list] Comet Holmes


> 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?

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