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(meteorobs) Excerpts from "CCNet DIGEST, 15 Oct 1998"


[Sorry this one's late! Note in particular the Notice regarding the
 upcoming "EUROPEAN GEOPHYSICAL SOCIETY MEETING 1999". -Lew]

------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST, 15/10/98
Date: Thu, 15 Oct 1998 10:44:03 -0400 (EDT)


CCNet DIGEST, 15 October 1998
-----------------------------

(1) CHAOTIC ORBITS, NON-GRAVITATIONAL FORCES & AND THE LIMITATIONS OF=20
    IMPACT COMPUTATION
    Duncan Steel <dis@a011.aonedot net.au>=20

(2) PREDICTIONS, GOOD AND BAD
    THE NEW YORK TIMES, Science Times, page D3, Tuesday, Oct. 13

(3) EUROPEAN GEOPHYSICAL SOCIETY MEETING 1999
    Detlef Koschny <dkoschny@estec.esadot nl>=20
...

(6) SCALING ANALYSIS OF METEORITE SHOWER MASS DISTRIBUTION
    L. Oddershede et al., TECHNICAL UNIVERSITY OF DENMARK
...

(9) JUPITER'S GREAT INEQUALITY & ASTEROID ORBIT EVOLUTION
    S. Ferraz Mello et al., UNIVERSITY OF SAO PAULO
...

-------------------------------------------------------
(1) CHAOTIC ORBITS, NON-GRAVITATIONAL FORCES & AND THE LIMITATIONS OF=20
    IMPACT COMPUTATION

>From Duncan Steel <dis@a011.aonedot net.au>=20
=20
Dear Benny,
=20
I found the item:
=20
>G. Sitarski: Motion of the minor planet 4179 Toutatis: Can we predict=20
>its collision with the Earth? ACTA ASTRONOMICA, 1998, Vol.48, No.3,=20
>pp..547-561
=20
to be extremely interesting. Lest anyone start bickering about
personalities and whether the people involved know what they are
doing, let me suggest that they immediately remove to a library,
look out Astronomy & Astrophysics Abstracts, and discover for=20
themselves what epic work Sitarski has done over the years in the
area of dynamics of asteroids and comets, in particular considering
orbital solutions accommodating non-gravitational forces.
=20
Now let me say why I find this paper very significant, given events
of the past seven months.  Sitarski, having available astrometry of
(4179) Toutatis stretching over an arc of 63 years, identifies a=20
clear but small non-gravitational force.  One presumes that he has
accommodated relativistic effects so that this is not a computational
artifact. The asteroid is therefore, it seems, outgassing: perhaps
an almost extinct comet (or maybe it will spring back into life and
follow an even more chaotic path)?  A ramification Sitarski identifies
is the impossibility of predicting the path of this object over the=20
next few centuries.
=20
The punchline is so clear that I hardly need to state it. All solutions
for the anticipated orbital evolution of 1997 XF11 are based upon a
presumption that only gravitational influences apply. The observed
arc is (I imagine) too short to allow the identification of=20
non-gravitional forces of the order identified by Sitarski in the case
of Toutatis. So how sure are we now about the path that 1997 XF11 will
take?

Duncan Steel

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(2) PREDICTIONS, GOOD AND BAD

>From THE NEW YORK TIMES, Science Times, page D3, Tuesday, Oct. 13
=20
To the Editor:
=20
William K. Stevens makes valid points about scientific predictions=20
("When Scientific Predictions Are So Good They're Bad", Sept. 29), but=20
his reference to the stir last March about the possibility of an=20
asteroid strike in 30 years beautifully illustrates that much of the=20
problem lies in how scientific information is presented.  My prediction =

was merely that the asteroid in question would come close, possibly=20
uncomfortably close. The statement that there was a "one-tenth of 1=20
percent" chance of a hit came from another scientist who misinterpreted =

what I had said. =20
=20
Malcolm Browne's March 12 front-page story ("Asteroid Is Expected to 
Make a Pass Close to Earth in 2028") correctly said that there was "no  =

immediate cause for alarm", that there was some uncertainty in the=20
computation of the object's distance and that further observational=20
data were being sought to narrow down the uncertainty. =20
=20
Such data became available later that day, something that would=20
obviously not have happened in the absence of some kind of=20
announcement. That resulting refined distance of 600,000 miles for=20
2028, while safely more than twice the distance of the moon, is still=20
the closest for any asteroid of which we have advance knowledge until=20
2086. =20
=20
My prediction was not "erroneous."  It was an appropriate conclusion =20
from the information available at the time, and it led to the discovery =

of the data from 1990 that showed the asteroid to be "safe."  That=20
outcome was not only encouraging, but also illustrative of how the=20
scientific process works.
=20
DR. BRIAN G. MARSDEN
Cambridge, Mass.
=20
The writer is the associate director for planetary sciences at the
Harvard-Smithsonian Center for Astrophysics.

-------------------------------------------------------
(3) EUROPEAN GEOPHYSICAL SOCIETY MEETING 1999

>From Detlef Koschny <dkoschny@estec.esadot nl>=20

The next meeting of the EGS, the European Geophysical Society, will
take place in The Hague in the Netherlands from 19-23 April 1999.
Session PS8 will be on "Meteors and meteor swarms", convener is Klaus
Scherer at the Max-Planck-Institut for Aeronomy in Lindau, Germany,
Co-Convenor is Peter Jenniskens, NASA. The text in the EGS newsletter
says:

"The new developments in observations and aerodynamics of meteors
should be presented. Special empahsis should be put onto the latest
observations of the Leonid shower during Novemnber 1998 which is
expected to have a huge meteor rate. First results from the
international Leonid observation campaign shall be available."

Also of interest to you might be PS7, Small bodies and dust,
Convener G. Schwehm, ESA.

Check the EGS web page for more info,

  http://www.mpae.gwdgdot de/EGS/egsga/denhaag99/denhaag99.htm

Detlef/Laffy.

-------------------------------------------------------
(6) SCALING ANALYSIS OF METEORITE SHOWER MASS DISTRIBUTION

L. Oddershede*), A. Meibom, J. Bohr: Scaling analysis of meteorite=20
shower mass distributions. EUROPHYSICS LETTERS, 1998, Vol.43, No.5,=20
pp.598-604

*) TECHNICAL UNIVERSITY OF DENMARK,DEPT PHYS 307,DK-2800 LYNGBY,DENMARK

Meteorite showers are the remains of extraterrestrial objects which are =

captivated by the gravitational field of the Earth. We have analyzed=20
the mass distribution of fragments from 16 meteorite showers for=20
scaling. The distributions exhibit distinct scaling behavior over=20
several orders of magnitude; the observed scaling exponents vary from=20
shower to shower. Half of the analyzed showers show a single scaling=20
region while the other half show multiple scaling regimes. Such an=20
analysis can provide knowledge about the fragmentation process and=20
about the original meteoroid. We also suggest to compare the observed=20
scaling exponents to exponents observed in laboratory experiments and=20
discuss the possibility that one can derive insight into the original=20
shapes of the meteoroids. Copyright 1998, Institute for Scientific=20
Information Inc.

-------------------------------------------------------
(9) JUPITER'S GREAT INEQUALITY & ASTEROID ORBIT EVOLUTION

S. Ferraz Mello*), T.A. Michtchenko, F. Roig: The determinant role of=20
Jupiter's Great Inequality in the depletion of the Hecuba gap.=20
ASTRONOMICAL JOURNAL, 1998, Vol.116, No.3, pp.1491-1500

*) UNIVERSITY OF SAO PAULO,INST ASTRON & GEOFIS,CP 3386,AVE MIGUEL=20
   ESTEFANO 4200,BR-04301904 SAO PAULO,BRAZIL

This paper deals with the influence of Jupiter's ''Great Inequality''=20
(GI) on the orbital evolution of 2:1 resonant asteroids. This=20
perturbation of Jupiter's motion enhances the chaotic diffusion of=20
orbits and the depletion of asteroids in the Hecuba gap. The failure of =

models that adopt for Jupiter an elliptic motion with only secular=20
perturbations is explained. We also show the dependence of the=20
diffusion rates on the GI period, and the maximum diffusion rates that=20
would take place if the GI period were closer to the libration period.=20
Significant similar effects are absent in the 3:2 asteroidal resonance.
Copyright 1998, Institute for Scientific Information Inc.

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