[meteorite-list] Comet Holmes

From: Chris Peterson <clp_at_meteoritecentral.com>
Date: Mon, 29 Oct 2007 17:08:07 -0600
Message-ID: <01e101c81a80$9b741030$0a01a8c0_at_bellatrix>

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?
Received on Mon 29 Oct 2007 07:08:07 PM PDT