[meteorite-list] Comet Holmes

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue, 30 Oct 2007 16:22:14 -0500
Message-ID: <01e301c81b3a$f1b5dd60$c944e146_at_ATARIENGINE>

Hi, Larry, List

Sitting up late at night and being too rusty to do
things the hard way, I used the simulator at
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=17p&orb=1
and am doing just what they say NOT to do,
namely, run it for decades and decades...

If you tilt the view all the way over to a completely flat,
looking-down-from-above view of the solar system,
it's much easier to visualize the state of the 17P orbit.
You can see that Holmes 17P can only go through
the Jupiter Trojan points at its own (17P's) descending
node. (Just in case there's anybody else following this,
here's a really nice map of the gravitational potentials
around the Lagrange Points, using the Earth for illustration:
http://en.wikipedia.org/wiki/Image:Lagrange_points.jpg)

Round and round we go... Yes, Holmes did go through
the trailing (L5, Trojan Camp) Trojans around January,
1989 and during the summer of 1906, roughly 81.6 years
apart. Holmsie went through the leading (L4, Greek Camp)
Trojans about January, 1934 and in July, 1851, roughly
81.5 years apart.

All of this assumes that driving the simulator 'way beyond
its warranty mileage isn't making it crazy. (As soon as I wrote
that, I went and checked known perihelion dates and, yeah,
it wanders off at distant dates, but let's just assume it's a
progressive error that affects dates only, OK? But the dates
I derived could be "off" by many months.)

Then, there's the possibility of "Lagrangian Clouds." The
Earth has'em. They've been photographed, but they seem
to come and go. They were discovered in the 1950's:
http://en.wikipedia.org/wiki/Kordylewski_cloud
by Kordylewski. Given Jupiter's massive GravPotential,
do you suppose dust and small debris accumulate at its
Lagrange points? I mean, if it can accumulate thousands
of masses the size of Jupiter Trojans...

Another Google Chase: the 1200 brightest Jupiter Trojans
are between 85 and 105 km in diameter. Big guys. My guess
is that there's a lot of little junk in the Trojan "Clouds." The
Jupiter Trojans are arranged in "families" like Zone asteroids,
and there are "double" or binary Trojans. The smallest
Trojans being detected by big fat 'scopes are down to 700
meters in diameter, and their distribution is "normal" (with
a power coefficient of 2), meaning that there are lots of
little ones and little stuff awaiting detection.

More stuff to bonk into.

Fascinating to observe a plot of the Jupiter Trojans'
positions; they are scattered along, inside, and outside
Jupiter's orbit, but they never leave... There's a plot in:
http://www.dtm.ciw.edu/sheppard/pub/Sheppard04JupChapter.pdf
(As one who gripes about knowledge being locked up
by academic publishers, Kudo's to Scott S. Sheppard
of the Carnegie Institution, who has all his papers online.)

The Trojans extend along the orbit for many, many degrees,
so the timing of Holmes 17P's passage is not very critical.
In fact, I'd say the comet goes through Trojan territory on
about 25% of its descending node passages.

It's still mostly empty space. All of space is mostly empty
space. But time is long. There's a lot of it, too.

And Larry is right about the heat pulse from perihelion
taking a long time to warm down through the object and
reach some touchy volatile which then goes crazy and
explodes into a coma. Or, it could be a graze by a co-orbiter,
or, a bonk from Trojan debris that exposes it. Or, maybe it
has a natural ice-moderated 235U breeder reactor at its core...

I would be glad to be proven wrong by finding out
what's actually going on; that's why we speculate. What's
happened to that comet? Hey! That's all we want to know.
Monkey sitting in the tree, staring at that big white shining
disc in the sky...


Sterling K. Webb
--------------------------------------------------------------------
----- Original Message -----
From: <lebofsky at lpl.arizona.edu>
To: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
Cc: <lebofsky at lpl.arizona.edu>; "Chris Peterson" <clp at alumni.caltech.edu>;
<meteorite-list at meteoritecentral.com>
Sent: Monday, October 29, 2007 8:49 PM
Subject: Re: [meteorite-list] Comet Holmes


Hi Again Sterling:

Next plane crossing (at 4.8 AU or so) is in 2 years. At that time Jupiter
is on the other side of the Sun, so the Trojans, which ar, on average, 60
degrees fore and aft of Jupiter not not even close this time around.

So, my bias is a thermal burp (belch). I have seen what an expanding gas
can do. From a solid to a gas, things like carbon dioxide can expand
500-fold or more. Can cause quite a bang.

Larry

On Mon, October 29, 2007 6:35 pm, Sterling K. Webb wrote:
> 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?
>>
>> ______________________________________________
>> Meteorite-list mailing list
>> Meteorite-list at meteoritecentral.com
>> http://six.pairlist.net/mailman/listinfo/meteorite-list
>>
>>
>>
>
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
>
Received on Tue 30 Oct 2007 05:22:14 PM PDT