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(meteorobs) Excerpts from "CCNet 5/2002 - 8 January 2002"
What an intriguing 'CCNet Digest' issue, for folks with an interest in the
theory of meteor shower creation and evolution... But for anyone who lacks
a taste for this kind of theory, please go ahead and hit "Delete" now. ;>
Here's an exciting exchange between the DMS' Marco Langbroek and Dr. Duncan
Steel, regarding the Quadrantid *meteor shower*, and the particular *debris
trail(s)* which result in its extraordinarily sharp peak. Unfortunately, Dr.
Steel's response fell short of being clear, to this inexpert reader? One of
its main points in particular, that regarding the distinction between "new
meteor shower" and "new meteoroid stream", was hard for me to relate to the
discussion?? I am quite sure I'm missing something, and hope Dr. Steel can
correct me. But I interpreted Marco's primary point (and I hope Marco will
correct me if I misattribute him!), to be that the particular "streamlet",
(or "dust trail" in more modern nomenclature??), associated with the QUAs'
PEAK, is just very unlikely to be as old as Dr. Steel's references suggest.
Dr. Steel then discounts this argument, as being based on one questionable
assumption: Namely, that *older* "trails" are statistically likely to be
observed to produce *more diffuse* activity... But based on this amateur's
limited understanding, both of the dizzying variety of forces which act on
a meteoroid stream, and of how such forces may impact the evolution of the
stream, I'm not clear what alternative interpretation(s) Dr. Steel would
suggest be applied to what is obviously very compact activity? Dr. Steel,
are you suggesting that some form of shepherding (similar to the posited
cause of the 1998 "Leonid fireball shower", but affecting a more diverse
range of particle masses), can explain how such a compact peak could be
reconciled with such an old (>1000 year) ejection time? Or is your asser-
tion that there is no DEMONSTRATED link between the "time compactness" of
a meteor shower feature (like the QUA peak), and "time since ejection" of
the particles which are assumed to produce that meteor shower feature??
In any case, your points very much stimulated my curiosity as an amateur,
Dr. Steel: and in particular, in reading the reference you cite (Jones &
Jones 1993), I was intrigued by the complexity and seemingly magisterial
nature of the ejection/evolution model which the authors used to "create"
a wide array of different observed showers, all from this one parent. If
there have been any follow-up papers published on this particular model,
they'd be very interesting to read. (My ADS search did not seem to turn
up any particular citations to the actual model used by Jones & Jones.)
--
An additional comment, in re the limited usefulness of meteor observing
to get the "whole picture" of a particle stream's structure & evolution:
>There are other parts to every stream that are separated from us in
>space and time which may not be sampled through meteor techniques.
Dr. Steel, I'm surely (again) missing something, but doesn't this point
assume that we are only discussing meteor observations within some very
limited time horizon? Presumably, observations taken throughout a shower
activity period, over many years (and recall there are more or less re-
liable meteor observations going back well over a Century) may gradually
reduce, though admittedly never eliminate, any "sampling bias" produced
by using our home planet and its atmosphere as an observing instrument?
But leaving that aside, I was again confused as to how this point could
be related to the main discussion: In particular, how can one particular
feature, namely the QUA peak, which clearly is amenable to observations
from Earth, somehow be explained by reference to some other structure of
the meteoroid stream which is presumably less readily observed? If this
is in fact the essence of this argument, then how can a test be designed,
for the hypothesis that such "hidden" stream features do in fact exist?
And last but not least (I promise!):
>Here I simply mention that rejection of the hypothesis that
>96P/Machholz 1 is the parent for the Quadrantids implies that
>its fitting against not only the Quadrantids but also the other
>showers that the stream produces is a matter of chance, the
>likelihood of which is very slim.
Apologies, but why is it necessary, in order to disprove the association
of a body with one meteoroid stream, to first also disprove its associa-
tion with any given list of other streams? Forgive my naive question: if
I had to guess, based on my limited knowledge, I'd have to assume that
there is some clear evidence suggesting that all these streams MUST be a
result of ejections from the same parent body? What is this evidence?
--
By the way, in researching this editorial comment, I came on references
to a paper by Jenniskens et al (1997), which is said to clearly imply a
conclusion that the Quadrantids must be comprised of meteoroids ejected
some time in the last 500 years, and no longer. (See one such reference,
below.) Might Doctor J. be willing to comment on this question as well?
Thanks to you both for an enjoyable exchange via CCNet, as well as any
further clarification anyone may choose to provide us on 'meteorobs'...
(And thanks for a new word, Marco! "Sensu lato"="in a broad sense". ;>)
And apologies ahead of time, if my comments have missed the point! :)
Clear skies to all,
Lew Gramer
ref: Williams, Iwan P., Collander-Brown, S.J., 1998MNRAS.294..127W.
[This paper cites among many other sources, Dr. Steel's work on meteor-
oid stream creation and evolution, and then goes on to suggest a THIRD
possibility for the parent body of the QUAs, Asteroid 5496 (1973 NA).]
------- Forwarded Message
From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 5/2002 - 8 January 2002
Date: Tue, 8 Jan 2002 12:52:17 -0000
CCNet 5/2002 - 8 January 2002
-----------------------------
[...]
(12) QUANDRANTID PARENT
Marco Langbroek <m.langbroek@rulpre.leidenunivdot nl>
(13) QUANDRANTID PARENT: A RESPONSE
Duncan Steel <D.I.Steel@salford.acdot uk>
(14) ASTEROID 2001 YB5
Larry Robinson <lrobinsn@ixdot netcom.com>
[...]
============================
* LETTERS TO THE MODERATOR *
============================
(12) QUANDRANTID PARENT
>From Marco Langbroek <m.langbroek@rulpre.leidenunivdot nl>
Dear Benny,
CCNet's issue of January 3 had a news item on the Quadrantid meteor shower,
which stated that the parent comet of the Quadrantids is unknown. In CCNet 4
of 7 January, Duncan Steel reponded to this with:
"This is not true. Periodic Comet Machholz 1 is rather firmly
established as the parent of the Quadrantid meteor shower,
along with seven other showers (such as the N & S Delta Aquarids)"
I disagree with Duncan Steel however, about the "firmness" of this proposed
connection between Machholz 1 and the Quadrantids. This connection demands
that the stream should be old, because the models which generate the
connection base this on modelling of the cometary orbit back to 5000 years
ago, when the comet should have shed the dust that now is visible as
Quadrantid meteors.
However, the Quadrantids definitely are a very young stream, not an old
stream. In our 1997 Astronomy & Astrophysics paper (ref. below), we reported
that the spread in the high accuracy multistation photographic and video
orbits of the Quadrantids (35 photographic and 29 video orbits) which our
Dutch Meteor Society gathered, precludes that this stream is caused by 'old'
dust. The dispersion in orbital elements among our meteor sample is just too
small for that. We estimated that the dust that creates the sharp main
activity peak of this stream should not be much older than 500 years (the
wider low level background activity upon which the main peak is superposed
could be older dust though but is too ill sampled to allow definite
statements on that). This precludes the hypothesis that the stream is
connected to dust shed by comet 96P/Machholz 1 as much as 5000 years ago.
This in turn rules out comet 96P/Machholz 1 as the parent for the
Quadrantids, contrary to Steel's assertion that this is "rather firmly
established".
Given that the parent so far has not been found, it is likely that it is
dormant. The Quadrantids are in a high inclination orbit, and so must be
their parent, so chances that one of the current NEA programms might
discover it are perhaps smaller than for objects with orbits closer to the
ecliptic plane. So this is a case of a NEA (sensu lato, it being a dormant
comet rather than an asteroid) that must be there, but apparently masters
the skill of hiding itself well.
Kind regards,
- Marco Langbroek
Dutch Meteor Society (DMS - www.dmsweb.org)
ref: Jenniskens P., Betlem H., De Lignie M., Langbroek M. and Van Vliet M.:
Meteor stream activity V. The Quadrantids, a very young stream. Astronomy &
Astrophysics 327 (1997), 1242-1252
Marco Langbroek
Faculty of Archaeology
Leiden University
P.O. Box 9515
NL-2300 RA Leiden
the Netherlands
building 1176, room 021
tel. +31 (0)71 5272926
fax +31 (0)71 5272429
e-mail: m.langbroek@arch.leidenunivdot nl
http://home.wanadoodot nl/marco.langbroek/
=============
(13) QUANDRANTID PARENT: A RESPONSE
>From Duncan Steel <D.I.Steel@salford.acdot uk>
Dear Benny,
There are several points on which I disagree with Marco Langbroek in his
discussion of the origin of the Quadrantid meteor shower. Here just a few
will be highlighted.
(a) Marco wrote:
>I disagree with Duncan Steel however, about the "firmness" of this proposed
>connection between Machholz 1 and the Quadrantids. This connection demands
>that the stream should be old, because the models which generate the
>connection base this on modelling of the cometary orbit back to 5000 years
>ago, when the comet should have shed the dust that now is visible as
>Quadrantid meteors.
This statement is incorrect with regard to the age of the stream. For
example, numerical studies published by J.Jones and W.Jones (MNRAS, 261,
605-611, 1993) indicate that P/Machholz 1 may have been captured by Jupiter
about 2,200 years ago, and they found that "there has been sufficient time
for the resulting stream to produce most of the features of the presently
observed Quadrantid/Arietid/Southern delta-Aquarid complex."
(b) Marco wrote:
>However, the Quadrantids definitely are a very young stream, not an old
>stream.
This is an example of why I have in the past been pedantic over the confused
usage of the terms "meteoroid stream" and "meteor shower." The "Quadrantids"
is a meteor shower; it results from the intersection of the Earth with a
particular meteoroid stream. One might say that the Geminids is a young
meteor shower, in that it was not observed until the mid-19th century, but
the stream producing the Geminids is clearly much older. Similarly the
profile of the Quadrantids does not necessarily tell us much about the
age of the responsible stream.
(c) Continuing:
>In our 1997 Astronomy & Astrophysics paper (ref. below), we reported that
>the spread in the high accuracy multistation photographic and video
>orbits of the Quadrantids (35 photographic and 29 video orbits) which our
>Dutch Meteor Society gathered, precludes that this stream is caused by 'old'
>dust. The dispersion in orbital elements among our meteor sample is just too
>small for that. We estimated that the dust that creates the sharp main
>activity peak of this stream should not be much older than 500 years (the
>wider low level background activity upon which the main peak is superposed
>could be older dust though but is too ill sampled to allow definite
>statements on that).
This interpretation of observational data is based upon certain assumptions
that may or may not be valid. Broadly-speaking the interpretation is similar
to that of the recent modelling of the Leonid outbursts: lack of dispersion
is assumed to indicate a youthful filament of a stream. The assumption that
this also applies to these Quadrantid observations is just that: an
assumption. In fact, modelling of the spreading of the stream produced by
the comet in question shows the persistence of certain concentrations (e.g.
see Figure 3 in Jones & Jones, cited above). That is, unless the meteoroids
(observed as meteors by this DMS group) had very similar orbital elements,
they would not have intersected the Earth at that time. The low dispersion
under that circumstance is not directly linked to the time since the
meteoroids were released from their parent, and so the underlying assumption
is invalid.
(d) Continuing again:
>This precludes the hypothesis that the stream is
>connected to dust shed by comet 96P/Machholz 1 as much as 5000 years ago.
>This in turn rules out comet 96P/Machholz 1 as the parent for the
>Quadrantids, contrary to Steel's assertion that this is "rather firmly
>established".
Here I simply mention that rejection of the hypothesis that 96P/Machholz 1
is the parent for the Quadrantids implies that its fitting against not only
the Quadrantids but also the other showers that the stream produces is a
matter of chance, the likelihood of which is very slim. This would
offend against William of Ockham (who of course is not infallible).
(e) Marco wrote:
>The Quadrantids are in a high inclination orbit, and so must be
>their parent...
This is simply untrue. The inclinations of the stream producing the
Quadrantids and also (of course) 96P/Machholz 1 vary between about 10
degrees and almost 90 degrees: see Figure 6 of Jones & Jones, or Gonczi,
Rickman & Froeschle, MNRAS, 254, 627-634, 1992. Such a spread is attained
within 1000 years after release.
In all of this, the solution to the "problem", as such, is the way in which
the comet and meteoroids evolve dynamically when very close to the 2:1
jovian mean-motion resonance.
The trouble with trying to jump from meteor shower observations to a general
picture of the whole stream is that showers only occur at certain sets of
orbital elements producing a node at 1 AU. There are other parts to every
stream that are separated from us in space and time which may not be sampled
through meteor techniques.
I will leave it to someone else to stake a claim for Comet 1491 I being the
Quadrantid parent.
Kind regards,
Duncan Steel
==============
(14) ASTEROID 2001 YB5
>From Larry Robinson <lrobinsn@ixdot netcom.com>
Dear Benny:
This is the second time I write to you regarding 2001 YB5. The first time
was on January 1, when this object was still listed on NEODys and the MPC as
a Virtual Impactor.
In CCNet today I see at least two references to 2001 YB5 being discovered in
early December and another saying December 12. I am not sure where these
authors are getting their dates, but the observations of this object are
easily obtained by anyone with a computer and internet access. This object
was discovered on December 27 by 644 Palomar Mountain NEAT and immediately
followed up by other stations. Later it was discovered on previous plates
taken at observing station 608 Haleakala-NEAT/MSSS on December 26 by 118
Modra where observers J. Toth, S. Gajdos got the third night and the impact
solution was announced by Spaceguard Central Node. So we did not have 25
days warning on this one before closest approach or potential impact. We had
only half that time!
Only after further observations by 734 Farpoint, 649 Powell, 413 Siding
Spring, and several others was the all clear sounded on this object. That
occurred at about noon on January 2, EST or 17:00UT on January 2 for the
astronomically inclined. Had it not been cleared, we would have probably
only have had one week's notice before an impact event that would have
changed all of our lives forever.
Many observations have followed these. Here are all of the observations from
the Minor Planet Ephemeris Service at
http://scully.harvarddot edu/~cgi/MPEph2.COM
It is not hard to get the facts on these things. At least right now it is
public knowledge, if you take the time to look.
A few obvious questions occur to anyone, such as what would the procedure
have been, if those follow up observations had confirmed an impact solution?
Who would make the call, to whom, and when? Did anyone notify anybody this
time, even to let them know there was a remote possibility of an impact on
January 7? Is there a formal procedure for notification? What could be done
in a case like this?
Larry Robinson
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