[meteorite-list] Comet Holmes

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Mon, 29 Oct 2007 20:35:28 -0500
Message-ID: <014201c81a95$274d0f30$c944e146_at_ATARIENGINE>

Larry, Chris, List

> It crosses the plane... at 4.8 AU.

    Here's a list of 2278 objects which orbit in the
plane of the ecliptic, almost all of which have their
perihelion at or around a median figure of 4.8 AU
http://cfa-www.harvard.edu/iau/lists/JupiterTrojans.html

    You're right; I didn't go and look at the ecliptical
crossing points, but this is even better! The Jupiter
Trojans are clustered at Jupiter's L4 and L5 points in
elongated "bananas." Additionally, there are no doubt
even more of them than these 2278 objects presently
catalogued (being discovered by Listmembers, even).
Thousands more.

    They make a fine "dangerous crossing" for a 3.4 km
comet with no working brakes, them dawdling around that
intersection without ever really getting out of the way,
like a crowd of teenagers. And poor 17P's orbit goes
through them once every 81.834 years. That's for both
the Greek camp and the Trojan camp, so 17P runs
the gaunlet every 40 years.

    Of course, the Trojans are not AT perihelion all at
the same time; their aphelia are an AU or so further out.
But Trojans are the only numerous class of bodies that
stay "herded" into one general area all the time (one area
in Jupiter's rotating frame of reference).

    Larry, I realize that you only wanted to get the
Asteroids off the hook, but I think you pointed a
finger at the ones who did it.


Sterling K. Webb
---------------------------------------------------------------
----- Original Message -----
From: <lebofsky at lpl.arizona.edu>
To: "Chris Peterson" <clp at alumni.caltech.edu>
Cc: <meteorite-list at meteoritecentral.com>
Sent: Monday, October 29, 2007 7:49 PM
Subject: Re: [meteorite-list] Comet Holmes


Hi All:

Another thing against an asteroid impact. If you go to the comet orbit
site at JPL for Holmes, because of its inclination relative to the
ecliptic, it crosses near Mars and Near Jupiter, not in the "middle of the
asteroid belt. It passed through the plane of the Solar System back in
February (before closest approach to the Sun in May) and is now well above
the plane of the Solar System. It crosses the plane at 2.1 AU (near the
inner edge of the asteroid belt) and at 4.8 AU well beyond the asteroid
belt. Granted, there are lots of asteroids with inclinations that put them
well above the plane of the solar system, but I would not say that Holmes
goes "through the center" of the belt.

On another note, it has been years since I have done any thermal modeling
of asteroids, but, even with rocky material, it takes some time for the
interior to "notice" that the asteroid has been near the Sun (thanks to
thermal inertia). It should take even longer for the thermal wave to
penetrate into the surface of a "fluffy" comet.

Also, when it will be warmest will also depend on the direction of it
polar axis. I do not remember the numbers, but even 10 or 15 years after
Pluto's closest approach to the Sun, it is still getting warmer and its
atmosphere getting thicker (at least as of 3 or 4 years ago).

Larry

On Mon, October 29, 2007 4:08 pm, Chris Peterson wrote:
> 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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Received on Mon 29 Oct 2007 09:35:28 PM PDT