PLEASE NOTE:


*

CCNet, 6 December 1999
-----------------------


      QUOTE OF THE DAY

      "First of all, there is recent evidence that the object at the
      centre of the Eta Carina nebula is actually two stars. These two
      stars now have very elliptical orbits and they might have come
      close to each other at a time when one or the other was changing
      its size due to changes in nuclear fuel in its core. Because of
      the gravitational forces between them, one of the stars probably
      lost a huge amount of material, which then formed the torus. That
      event is likely to have caused the explosion seen by Herschel
      last century. It is as if the star got quite upset about its lost
      material".
          -- Pat Morris, University of Amsterdam, 3 December 1999


(1) SOUTH AFRICAN BUSHVELD COMPLEX A MASSIVE IMPACT STRUCTURE?
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(2) NEW VIEWS ON THE 1843 ETA CARINAE EXPLOSION
    ESA NEWS, 6 December 1999

(3) ABRUPT CLIMATE CHANGE & ONGOING SEARCH FOR POSSIBLE 
    MECHANISMS
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(4) LUNAR IMPACTS: REACTIONS & CALCULATIONS
    Joan and David Dunham <dunham@erols.com>

(5) NEWS ON THE LUNAR LEONIDS
    Joan and David Dunham <dunham@erols.com>

(6) LEONIDS ARTICLE - WITH SOME FLAWS
    Daniel Fischer <dfischer@astro.uni-bonn.de>

(7) NATURE OF THE TUNGUSKA IMPACTOR
    Peter Snow <p.snow@xtra.co.nz>

(8) NEW BOOK ON IMPACTS BY JOHN LEWIS
    Michael Paine <mpaine@tpgi.com.au>

(9) STABLE CHAOS IN THE ASTEROID BELT
    M. Sidlichovsky, ASTRONOMICAL INSTITUTE PRAHA

(10) KUIPER BELT EVOLUTION DUE TO DYNAMICAL FRICTION
     A. Del Popolo et al., UNIVERSITY OF CATANIA

(11) SLOW & FAST DIFFUSION IN ASTEROID-BELT RESONANCES
     S. Ferraz Mello, UNIVERSITY OF SAO PAULO

(12) ORIGIN & EVOLUTION OF NEAR EARTH ASTEROIDS
     A. Morbidelli, COTE AZUR OBSERVATORY

(13) ON THE PERTURBING FUNCTION IN ORBITAL ELEMENTS
     I. Tupikova et al., LOHRMANN OBSERVATORY

(14) TROJAN ASTEROIDS IN STABLE CHAOTIC MOTION
     E. Pilat Lohinger et al., UNIVERSITY OF VIENNA

(15) PERIODIC ORBITS AROUND A MASSIVE STRAIGHT SEGMENT
     A. Riaguas et al, EUROPEAN SPACE TECHNOL CTR

(16) A SECULAR THEORY FOR TROJAN-TYPE MOTION
     M.H.M. Morais, UNIVERSITY OF LONDON QUEEN MARY & WESTFIELD COLL

(17) THE OZONE LAYER & COSMIC IMPACTS
     B.A. Klumov, INST DYNAM GEOSPHERES

(18) SURVIVAL OF LIFE ON ASTEROIDS & COMETS
     B. C. Clark et al., LOCKHEED MARTIN ASTRONAUT


==========
(1) SOUTH AFRICAN BUSHVELD COMPLEX A MASSIVE IMPACT STRUCTURE?

From Andrew Yee <ayee@nova.astro.utoronto.ca>

Albuquerque Journal, 2 December 1999
[http://www.abqjournal.com/scitech/1scitech12-02-99.htm]

Thursday, December 2, 1999

Geologist Pursues Asteroid Impact Theory
By John Fleck, Albuquerque Journal Staff Writer

A trail beginning among the old volcanoes of southwestern New Mexico
has led a semi-retired University of New Mexico geologist to southern
Africa, into the midst of what might be one of the largest impact
craters on Earth.

Could an asteroid have slammed into the planet 2 billion years ago,
flattening what is now South Africa?

The question for Wolf Elston: When is a volcano not a volcano?

For much of Elston's 50 years of research, he has been in and out of
the old volcanic fields of the southwestern part of the state, where
massive eruptions 20 million to 40 million years ago created much of
what is now the Gila Wilderness.

You couldn't tell it now by looking for volcanic craters.

But for a geologist like Elston, the rocks tell the story of how they
were melted and then blasted up through Earth, to cool again once they
got to the surface.

It was that expertise that led him to South Africa, where for many
years geologists believed a group of rocks called the Bushveld Complex
was evidence of massive volcanic activity some 2 billion years ago.

Elston has joined a group of geologists who now think they're wrong.

At a meeting of the Geological Society of America last month in Denver,
Elston presented his latest findings -- the rocks formed at
temperatures too hot to have come from a volcano.

While he acknowledges his evidence alone isn't enough to prove that an
asteroid slammed into Earth 2 billion years ago, he said he knows of no
other explanation.

"It's either that or something totally new to science," Elston said in
a recent interview.

Elston's involvement in the question dates to the 1970s, when Rodney
Rhodes, a student who had worked in the area, brought the issue to his
attention, telling Elston he believed the rocks might be the result of
a gigantic impact.

Rhodes died in a traffic accident, but Elston carried on the work,
intrigued by the rocks he was seeing.

Many South African geologists had thought what they were seeing was the
remains of an ancient "ring complex," a group of volcanoes more than
200 miles in diameter.

Elston had studied similar volcanoes in New Mexico, and the rocks he
saw in South Africa didn't look the same.

There are bound to be similarities between volcanic rocks and those
formed when an impact melts rocks. But the characteristics of the rocks
suggested temperatures higher than those of a volcano, Elston told
colleagues at the Denver meeting.

Elston and supporters of the asteroid impact hypothesis haven't won
over all their colleagues.

Last year two geologists, P.C. Buchanan and W.U. Reimold of the
University of Witwatersrand in Johannesburg, published a paper arguing
that there is no evidence in the rocks of a giant impact.

Elston doesn't agree, but he's philosophical, noting that he wouldn't
mind being proven wrong.

Copyright © 1999 Albuquerque Journal

===========
(2) NEW VIEWS ON THE 1843 ETA CARINAE EXPLOSION

From ESA NEWS, 6 December 1999
http://sci.esa.int/missions/newsitem.cfm?TypeID=18&ContentID=8091

Eta Carinae' - ISO tells the true story

03 Dec 1999 In 1843 the stellar system Eta Carinae suffered a violent
explosion which Caused it to become, in just a few decades, an
amazingly beautiful nebula with two huge round blobs of material
symmetrically distributed. For years astronomers have been looking for
the cause of the explosion, and to explain the strange hourglass shape.
A team of astronomers using ESA's infrared space telescope, ISO, have
now succeeded, putting the blame firmly on a previously undetected very
massive 'donut' of dust which squeezes the nebula at its centre. They
publish their discovery in the current issue of the journal Nature (2
December).

"Everything seems to fit more clearly now. We certainly can explain the
double-lobe shape of the system, and we may also have a good idea of
the cause of the explosion itself", says main author Pat Morris, of the
University of Amsterdam.

Eta Carinae, in the constellation of the same name in the southern
hemisphere, has puzzled scientists ever since the famous
nineteenth-century British astronomer William Herschel noticed the
enormous change in the object's brightness, marking the explosion. It
could not have been a supernova explosion - which happens when a very
massive star ends its life - because the exploding star survived. (In
fact, Eta Carinae is still unique in this respect because no other
stellar object, apart from a final supernova explosion, has been known
to lose so much mass so quickly and violently).

Modern astronomers have constructed several hypotheses to explain the
event. One of these theories involved the presence of a disk of dust
squeezing the exploded star like a tight belt, and thus pushing the
expelled material into the two famous lateral blobs now seen in Eta
Carinae. However, the problem was that no telescope could find this
disk. Until now.

ESA's infrared space telescope, ISO, has done just that. Eta Carinae is
the brightest object in the infrared - outside the Solar System - and
the Amsterdam team used both spectrometers on board ISO (called SWS
and LWS) to observe it. They clearly found a huge amount of mass that
had gone undetected before. Then, to find how this mass was
distributed, they turned to a ground-based infrared telescope at the La
Silla observatory (Chile, European Southern Observatory). These
additional observations confirmed their suspicions: the material was
concentrated in a central torus, like a 'donut'.

The mass of the huge central torus seen by ISO is equivalent to 15
solar masses and its radius is about 5 light-years. The Amsterdam
group, led by Rens Waters, also analysed the torus' chemical
composition and compared it with that of the symmetric blobs. Now they
can reconstruct the true story of Eta Carinae, as Morris explains:

"First of all, there is recent evidence that the object at the centre
of the Eta Carina nebula is actually two stars. These two stars now
have very elliptical orbits and they might have come close to each
other at a time when one or the other was changing its size due
to changes in nuclear fuel in its core. Because of the gravitational
forces between them, one of the stars probably lost a huge amount of
material, which then formed the torus. That event is likely to have
caused the explosion seen by Herschel last century. It is as if the
star got quite upset about its lost material".

It comes as a surprise that, if this explanation is true, the explosion
in Eta Carinae had its real roots two millennia ago, since that's when
the formation of the massive torus must have taken place. That's what
the group of Amsterdam estimates, and this is supported by the data
about the torus' chemical composition: it is made of material coming
from the outer layers of the star, while the material in the two
symmetric blobs comes from the central layers and must herefore have
been expelled afterwards.

Footnote about ISO

The European Space Agency's infrared space observatory, ISO, operated
from November 1995 to May 1998, almost a year longer than expected. An
unprecedented observatory for infrared astronomy, able to examine cool
and hidden places in the Universe, ISO made nearly 30 000 scientific
observations.

Contacts:

Martin F. Kessler (ISO Project Scientist):
Tel: +34 91 813 1254
mkessler@iso.vilspa.esa.es

Pat Morris,
University of Amsterdam
Tel: +31 (0) 20 5925126
pmorris@astro.uva.nl

==============
(3) ABRUPT CLIMATE CHANGE & ONGOING SEARCH FOR POSSIBLE 
     MECHANISMS

From Andrew Yee <ayee@nova.astro.utoronto.ca>

From NATUR NEWS SERVICE, 2 December 1999
[http://helix.nature.com/nsu/991202/991202-11.html]

An ocean switch for global cooling
By PHILIP BALL

The average temperature of the Earth can change dramatically over just
a few decades. One of the most striking variations of this sort
happened about 12,000 years ago, when the planet was emerging from the
last ice age. The gradual warming across the globe was interrupted in
the North Atlantic by a sudden return to ice-age conditions -- an
episode called the 'Younger Dryas event'.

Now, evidence in Nature[1] suggests that changes in ocean circulation
were responsible. The findings hint that environmental changes that
alter circulation in the North Atlantic -- a possible corollary of
global warming caused by greenhouse gases -- can have a rapid and
profound impact on climate.

The last ice age began to thaw about 15,000 years ago. Five thousand
years later the great ice sheets that had covered much of North America
and northern Europe had retreated towards the North Pole, and the Earth
was about as warm as it is today. But this escape from the deep freeze
was rudely interrupted by the Younger Dryas event, which began about
12,900 years ago.

Changes in the shape, tilt and wobble of the Earth's orbit around the
Sun are thought to have brought about the ice ages. But these orbital
changes happen slowly -- over thousands of years -- whereas some
climate records suggest that the Younger Dryas event was in full swing
in under a century. Understanding the causes of such rapid climate
change is crucial for calculating the possible ramifications of the
human-induced greenhouse effect.

Greenhouse gases come from natural sources too. Might some change in
the processes responsible for this natural greenhouse effect have
triggered the Younger Dryas? This is one possibility; another is that
the cooling was due to a change in ocean circulation.

The deep waters of the world's oceans circulate, carrying warm water
from the tropics to the poles, and cold, dense water back towards the
tropics. This is driven by the fact that water is denser when it is
colder and saltier. Warm water from the tropical Atlantic, for example,
sinks as it flows north and cools, and as it becomes saltier by the
formation of salt-free sea ice. This process is therefore called
thermohaline -- literally 'heat-salt' -- circulation.

If thermohaline circulation were to shut down, the oceans would cease
to bring heat from the tropics to the poles, and the North Atlantic
region would become much colder. Is this what happened during the
Younger Dryas event as the ice sheets melted, injecting fresh water
into the North Atlantic, rendering its waters less dense and so less
inclined to sink?

Carsten Rühlemann from the University of Bremen, Germany, and
colleagues have analysed ocean sediments in the western tropical North
Atlantic Ocean for evidence of the temperature of the surface waters at
the time that the organic matter fell to the seabed. The researchers
find that these waters were relatively warm when the North Atlantic was
cold during the Younger Dryas (and also during an earlier cold
episode).

This suggests that the thermohaline circulation had shut down, so that
the tropical oceans were retaining their heat. If greenhouse gases were
responsible, such cooling would show up everywhere on the planet more
or less at the same time.

Could such changes happen again, for example if the deep ocean currents
were to shift in a warmer world? Perhaps the words of Wallace Broecker,
the US scientist who first proposed the circulation explanation in the
1980s, provide the best answer. "I published a full account of [my
theory] as a popularized article in 1987. Unbeknownst to me, the
editors added the [question] 'Could it happen again?' At the time, this
statement greatly annoyed me because I had carefully avoided any
mention of the future in the article itself. But now in retrospect,
perhaps I should forgive them."

[1] Rühlemann, C., Mulitza, S., Müller, P.J., Wefer, G. & Zahn, R.
Warming of the tropical Atlantic Ocean and slowdown of thermohaline
circulation during the last deglaciation Nature 402, 511 (1999)

© Macmillan Magazines Ltd 1999 - NATURE NEWS SERVICE

==============
(4) LUNAR IMPACTS: REACTIONS & CALCULATIONS

From Joan and David Dunham <dunham@erols.com>

Yesterday, Ray Sterner added a view of the Moon showing the impact
locations to our Web site on lunar impacts at http://iota.jhuapl.edu
Next week, we will be able to improve some of the impact locations and
will also measure the magnitudes relative to stars that were also
imaged that night - so far, the magnitudes are just eyeball estimates.
The PC-23C cameras that we all used is red-sensitive, so the magnitudes
we obtain may be closer to R than to V.  We will also clean up the Web
site, providing a menu to access different topics.

There continues to be some disagreement about the size of the
impacting objects and the craters that they would leave.  Two
messages below give some details on the subject.  It appears that
the fraction of Leonid kinetic energy that is converted to
luminous energy during a lunar impact is quite low, implying rather
large (kilogram-range) objects that would leave craters some tens
of meters in diameter.  But not everyone agrees with that.

David Dunham, IOTA, 1999 Dec. 4
===================================================================

Date: Fri, 3 Dec 1999 14:52:44 -0700
To: Joan and David Dunham <dunham@erols.com>
From: Jay Melosh <jmelosh@LPL.Arizona.EDU>
Subject: Re: News on the lunar Leonids

Dear Joan and David:

I have been following your reports of flashes observed on the moon with
great interest.  I have been curious about the amount of visible light
emitted by an impact for some years now (as well as the infrared signal,
which is much stronger at 2 to 3 microns).  I published an LPSC abstract on
this topic for LPSC XXIV, pp. 975-976 (1993).  Since that time my Russian
collaborators did a much more detailed job of the calculation using the
resources of the FSU nuclear fireball experts.  This work is published in
Solar System Research, vol. 32, pp. 99-114 as "Light flashes caused by
meteoroid impacts on the lunar surface" by I. V. Nemtchinov and a large
number of collaborators.  After all the song and dance they conclude (as we
did in our back-of-the-envelope calculation in LPSC!) that the luminous
efficiency is quite low, not more than .0003 to .00003 of the kinetic
energy of the impactor.  However, since the Leonids are so fast, perhaps
this would be enough to see through a telescope, as you report.

Sincerely,  Jay Melosh
####################################################################
Jay Melosh                              Tel:   (520) 621-2806
Professor of Planetary Science          Fax:   (520) 621-4933
Lunar and Planetary Lab                 email: jmelosh@lpl.arizona.edu
University of Arizona
Tucson AZ 85721-0092

===================================================================

Return-Path: <mazur@geo.ucalgary.ca>
Date: Sat, 04 Dec 1999 08:20:10 -0800
From: Mike Mazur <mazur@geo.ucalgary.ca>
X-Accept-Language: en
To: Joan and David Dunham <dunham@erols.com>, mazur@geo.ucalgary.ca
Subject: Re: 2 messages about lunar meteor & crater sizes

David,

With regards to the first note, the easiest way to calculate the crater
diameter is to use Lampson's scaling law for explosive craters as given
in Melosh (1989) eqn. 7.2.1. Martin's calculations use a yield scaling
relation that is not necessary for this sort of hand-wavy argument.
Also, he must have made an error somewhere in his math. Using eq. 7.8.1
which is for craters up to 10m on the moon,

D_at=0.015*rho_p^0.16666*rho_t^-0.5*W^0.37*(sin(i))^0.66666

where rho_p is the projectile density (~800kg/m^3 is what Martin
uses... 600kg/m^3 would be closer to Shoemaker's and others' results),
rho_t is the target density (3000 kg/m^3), W is the excavation energy
(probably about 90% of the total actually goes into the excavation),
and i is the angle of impact (90deg being vertical.

A 5g projectile moving at 71km/s has a KE of about 1.26e7 J. If 90% of
this goes into excavation then,

D_at~0.35m

Martin's table should thus be,

Mass (g)    Diameter of crater (m)

5                       0..35
10                      0.46
50                      0.83
100                     1.07

Intuitively, this seems more correct as well. In my original note to
you I think that I gave you a value of 1/2 kg for the projectile. This
I suspect is way too large and I think that misread my calculator.
Let's work through what I did.

If we are using the standard stellar magnitude system then,
m=-2.5log(F*/F_0), where F* is the flux of the star (or object in this
case) being measured, and F_0 is the flux of a 0 mag. star such as
Vega. Recall that F=L/(4*pi*r^2) where L is the luminosity of the
object and r is the distance. Inserting the luminosity equation
(because we ultimately require L) into the eq. for m gives,

m=-2.5log[(L_obj(r_vega*r_vega)/(L_vega*r_obj*r_obj)]
m=-2.5log(L_obj)-2.5log[(r_vega*r_vega)/(L_vega*r_obj*r_obj)]

r_vega=8.1pc=2.498e17 m, L_vega=2.7295e28 J/s, r_obj= dist to impact site ~
d_moon - R_moon - R_earth = 3.7586e8m

Now we can solve for L_obj,

log(L_obj)=[(m+2.5(log[((2.498e17m)^2)/((2.7295e28J/s)*(3.7586e8m)^2)]))/-2.5]

L_obj=10^[(m-26.98)/-2.5] J/s

for an m=3 impact,

L~3.9e9 J/s

So if this luminosity was maintained over a period of 1/30th of a
second (probably much smaller in actuality as I recall someone working
out millisecond durations based on expected plume size) an upper limit
for the energy that went into producing light is about 1.3e8 J. If 10%
of the total energy goes into light production (probably reasonable
based on terrestrial fireball data) then the total energy of an m=3
event is about 1.3e9 J. At 71 km/s the mass would therefore be about
0.5 kg. So it looks like my mass was what I expected and the diameter
must have been in error (I think I said about 0.4 m using Snowball test
data and Lamson's eq.). Using Gault's eq. as given at the start of this
note, the crater diameter for a 0.5 kg leonid is about 1.9 m.

visual mag.    tot. energy (J)   mass (g)   crater size (m)
    3                    1.3e9       500            1.9
    4                    5.2e8       205            1.3
    5                    2.1e8        82            0.96
    7                    3.3e7        13            0.50

At least that's what I get. It all seems reasonable but I would rather
use 600 kg/m^3 for rho_p. Originally when I performed this calculation
I used Lamson's equation which simply relates crater diameter to energy
using known data (I used Snowball) as a comparison. I neglected to
include a factor for lunar gravity, however. Anyway, these are likely
upper limits for reasons mentioned above.

Have fun,

Mike Mazur

p.s. I'm hoping that I didn't miss anything in the above equations when
I typed them out. It is possible.

Joan and David Dunham wrote:

> -----Original Message-----
> From:   beechm@uregina.ca [SMTP:beechm@uregina.ca]
> Sent:   Wednesday, December 01, 1999 1:33 PM
> To:     Dunham, David
> Subject:        Re: Lunar impacts - press release, more flashes, etc.
>
> Hi David,
>
> I have a few comments about the size of crater that might
> be produced by Leonid impacts. They are revised upwards of
> my earlier value of a few meters. Using the experimental
> formula derived by  Gault et al (J. Geophys. Res, 80, 2444,
> 1975 - see also Melosh's book "Impact Cratering" page 120)
> for impacts into a regolith material the following crater
> diameters are predicted for Leonids.
>
> Assumptions:
>
> V = 71 km/s (not really an assumption)
> density of meteoroids = 1000 kg/m^3 - most people use 800 kg/m^3
> but the difference will not be significant as the density
> eneters to the 1/6th power
> density of regolith material = 3000 kg/m^3
>
> Mass(gram)        Dia (meters)
> 5                 18
> 10                22
> 50                35
> 100               42
>
> So, at the upper mass end (more comments later) the crater is
> quite sizeable, but still not visible from Earth.
>
> IF Roger Venable's calculation for the mass is correct (and
> I have to admit I think it is on the very high side), then a
> large ~ 100 m diameter crater will result. It is just possible
> 20 kg and possibly larger mass metoroids exist in the Leonid
> stream (I wrote about this is in a paper in the Astronomical
> Journal 116, 499, 1998), but the observed mass index of visual
> meteors would not support sampling a single such meteor even
> at the very high ZHR's observed. The visual meteor results
> (that is with a mass index of about 2.0) suggest that one 1kg
> meteoroid might strike an area equivalent to the area of
> the Moon's half disk. Hence I am very sceptical about
> associating the impacts with meteoroids any more massive than
> several 100g (but, when it boils down to it, who really knows?)
>
> Ok, I hope this helps.
>
> With best wishes,
>
> Martin
>
> Martin Beech, Campion College, The University of Regina.

Joan and David Dunham
7006 Megan Lane
Greenbelt, MD 20770
(301) 474-4722
dunham@erols.com

===============
(5) NEWS ON THE LUNAR LEONIDS

From Joan and David Dunham <dunham@erols.com>

A summary of the six confirmed lunar impacts is given in the table
below.  This is an ASCII plain text table that must be viewed with a
fixed-space font such as Courier for the columns to line up properly. 
We are naming these with letters in the order of discovery.  The UT
date is 1999 November 18.  In each case, the events were confirmed on
my videotapes made at George Varros' backyard in Mount Airy, Maryland,
and the timings are from my tapes. The previously-reported estimates of
the locations of D and E were rather far off in longitude, according to
measurements of the video images made by Ben Wun and me earlier today.

           Accuracy, Approx. Discovered  Selenographic
Name  UTC     sec. Mag1 Mag2    by       Long. Lat. Description
   h  m   s
F  3:05:44.2   0.6   5   9? David Palmer  69W  44N  50km e of Harding
D  3:49:40.40  0.03  3   7  David Palmer  69W   2N   w. wall of Hevelius
E  4:08:04.1   0.6   5   8  David Palmer  77W  15S 120km SW of Rocca
A  4:46:15.2   0.1   3   8  Brian Cudnik  71W  14N  50km ENE of Cardanus
B  5:14:12.93  0.05  7   8  Pedro Sada    58W  15N 200km WNW of Marius
C  5:15:20.23  0.05  4   7  Pedro Sada    59W  21N  75km S Schiaparelli

Mag1 is the approximate magnitude of the flash estimated from my tape on
the half-frame on which it first appears.  Mag2 is the estimated
magnitude a half-frame, or 1/60th second, later.  In all cases I can't
see any evidence of the flash in the half-frame 1/30th second after the
first one, except for D, where it seems to appear there at about 9th
mag.  The selenographic locations should be accurate to within about 2
deg. or 50 km, but the locations of F and E could be in error more due
to foreshortening near the limb and lack of nearby features in the Moon
images generated with the Occult program used for the location
determination.  Their locations can be improved by using a grid overlay
that we plan to generate.  All of these are in the western part of
Oceanus Procellarum (Ocean of Storms) except D and E, which are in
highlands area a short distance west of the western shore of Oceanus
Procellarum. The times of B and C have been determined by Don
Stockbauer, Victoria, Texas, after creating an accurately time-inserted
copy using an IOTA-Manly video time inserter.  He also determined the
time of A, but for technical reasons to less accuracy; it will be
possible to refine it later. D, E, and F have been timed from the tape
just using a stopwatch.

D seems to be the brightest impact. Besides Palmer's and my videotapes,
it is also in videotapes by Pedro Sada and by Rick Frankenberger in San
Antonio, Texas.  My image for the event also shows three stars, from
north to south (right to left in the image) being 7.6-mag. SAO 146577,
8.2-mag. SAO 146578, and 8.9-mag. SAO 146574, all of whose occultations
were recorded a few minutes later.  The first two stars are also
visible in David Palmer's frame of the D impact.

Sada reports two more events estimated at about 5th magnitude at
4:32:50.8 and 4:34:49.7 UTC, but they have not been found in other
tapes (the field of view of my 5-inch telescope used for the 6 known
events was aimed at a more southern part of the Moon than usual, so
they would have been missed if they occurred a little north of the
equator).  The 2nd event was fairly close to the terminator.  Other
possible unconfirmed events (some chance of their being videotape
defects) were recorded by me at 4:50:15.9 UTC and by David Palmer at
2:42:02.

The images for all six events are at http://iota.jhuapl.edu. That site
also has a link to the article about the impacts that was published on
page 2B of the December 1st Baltimore Sun, and the NASA news Web site
that has an animation of impact A. Some of Palmer's images are on the
IOTA Web site at http://www.lunar-occultations.com/iota

The mass of the impacting meteoroids, and the resulting craters, has
still not been resolved.  Mass estimates range from 50 grams to 20 kg,
and crater sizes from several meters to almost 100 meters, in any case
probably too small to be visible from earth-based observations.

David Dunham, IOTA, 1999 December 3

Joan and David Dunham
7006 Megan Lane
Greenbelt, MD 20770
(301) 474-4722
dunham@erols.com

===============
(6) LEONIDS ARTICLE - WITH SOME FLAWS

From Daniel Fischer <dfischer@astro.uni-bonn.de>

http://www.sciencenews.org/sn_arc99/12_4_99/fob3.htm - the doubts by
Weissman (last paragraph) seem unfounded as most of the flashes
reported by Dunham were imaged by video cameras in *different*
locations; thus satellite glints can be firmly excluded, right?

Regards, Daniel

From SCIENCE NEWS ONLINE, 4 December 1999,                   
Vol. 156, No. 23

THE BEST LEONID SHOWER IS YET TO COME?

By R. Cowen

The streaks of light came fast and furious. Some raced across the sky
in nearly parallel tracks, leaving behind hazy trails. A few seemed to
dive into the moon.

If last month's Leonid meteor shower proved disappointing in the United
States, it took Europe and the Middle East by storm. And if the 
predictions of two astronomers continue to hold true, Earth will be in
for a really big show in 2001 and another in 2002.

At the shower's peak, on Nov. 17, some observers saw between 3,000 and
5,000 shooting stars, or meteors, in a single hour. Activity reached a
crescendo at 9:05 p.m. EST—just 3 minutes earlier than predicted by
David J. Asher of Armagh Observatory in Northern Ireland and Rob
McNaught of the Australian National University in Weston.

Scenes from the 1999 Leonid shower: Meteor's fireball and its fading
light seen for more than 20 minutes over the Italian Alps. (©Lorenzo
Comolli)

This is the first accurate prediction of a meteor storm, says Brian G.
Marsden of the Smithsonian Astrophysical Observatory in Cambridge,
Mass.

The Leonid meteor shower happens every November, when Earth passes
through a stream of dusty debris, or meteoroids, expelled by Comet
55P/Tempel-Tuttle. Dust grains slam into Earth's atmosphere and burn,
creating the streaks of light known as meteors. About every 33 years,
when the comet passes near, Earth encounters a large amount of debris,
resulting in a heavy shower or storm.

Exactly which years the Leonid dust particles will generate a storm has
been difficult to predict. That's because astronomers hadn't realized
that the debris stream is composed of distinct, narrow strands of
dust, each expelled by the comet during a different passage by the sun,
notes Asher. It's a matter of hit or miss: If Earth plows through the
center of a dense strand, a storm will occur.

By simulating the motion of strands in the solar system, Asher and
McNaught conclude that the dust strand Earth traveled through last
month was shed by the comet in 1899. Although that's the same
material the planet traveled through during the spectacular storm of
1966, last month's event wasn't as dazzling because Earth crossed the
strand's edge rather than its center, Asher says.

Donald K. Yeomans of NASA's Jet Propulsion Laboratory (JPL) in
Pasadena, Calif., says he agrees with the pair's explanation for the
1999 event. "I do take their future predictions more seriously now," he
adds.

Next year, McNaught and Asher calculate, Earth will pass for the first
time through the edge of a band of dust cast off by the comet in 1866,
yielding a puny shower. In 2001, however, Earth will plow sequentially
through no less than three trails—debris expelled in 1767, 1699, and
1866—and the light show should prove more stunning than last month's.
In 2002, when Earth again encounters material from 1866, as well as
from 1933, the Leonids should also put on a great show, McNaught and
Asher say.

Their findings may shed light on a puzzling feature seen just hours
after the Leonid shower reached its 1999 peak. Observers saw flashes of
light near the moon, as if meteoroids had crashed on its surface.
Researchers reported the phenomenon in a Nov. 26 circular of the
International Astronomical Union.

The brilliance of these flashes requires that the meteoroids have as
much mass as a bowling ball—a rare but not extraordinary occurrence,
estimates Alan W. Harris of JPL. Moreover, Asher and McNaught calculate
that the moon intercepted a denser part of the 1899 stream than Earth
did and thus encountered a greater number of large meteoroids at the
time the flashes occurred. However, cautions Paul R. Weissman of JPL,
the flashes could merely have been sunlight glinting off satellites or
space debris.

References and sources for this article at
http://www.sciencenews.org/sn_arc99/12_4_99/fob3ref.htm

From Science News, Vol. 156, No. 23, December 4, 1999, p. 356.
Copyright © 1999, Science Service.

=============
(7) NATURE OF THE TUNGUSKA IMPACTOR

From Peter Snow <p.snow@xtra.co.nz>

With regard to V.A. Bronshten's comments re the Nature of the Tunguska
impactor , i.e cometary versus asteroidal in nature, he states that no
rocks have been found in the area that would suggest asteroidal origin.
I visited the area 1996 specifically to view rocks that were quite
close to the campsite. These rocks were brecciated and were shallowly
embedded in deep peat. The Tungu`s who hunted the area prior to the
Tunguska explosion, it is said, claimed the stones appeared after the
explosion. Smaller fragments of the stones I believe were taken from
the site one was described as being glassy in nature. There is a
Russian physicist who has studied these rocks, his name escapes me at
the moment. I believe his working hypothesis is that they were
extraterrestrial in nature. Thought this may be of interest

Dr Peter Snow

=============
(8) NEW BOOK ON IMPACTS BY JOHN LEWIS

From Michael Paine < mpaine@tpgi.com.au >

Dear Benny,

I have just received a copy of the new book by Planetary Scientist John
Lewis *Comet and asteroid impact hazard on a populated Earth*. It
includes a diskette with a Monte Carlo program to run simulations of
Earth impacts over time. The book is basically a handbook for the
software with a wide range of physical information about NEOs, impacts
and effects on the human population. An excellent resource covering
physics, chemistry and environment. I can recommend it to anyone
studying the possible influence of impacts on civilisation. Over
thousands of years airburst events like Tunguska turn out to be
important sources of fatalities and yet they leave little or no physical
evidence.

My own rough estimates of human fatalities may prove too optimistic 
( http://www1.tpgi.com.au/users/tps-seti/spacegd7.html ).

Reading the book this weekend will take my mind off the apparent loss of
the Mars Polar Lander!

Michael Paine

==============
(9) STABLE CHAOS IN THE ASTEROID BELT

M. Sidlichovsky: On stable chaos in the asteroid belt. CELESTIAL
MECHANICS & DYNAMICAL ASTRONOMY, 1999, Vol.73, No.1-4, pp.77-86

ASTRONOMICAL INSTITUTE PRAHA,BOCNI II 1401,PRAGUE 14131 4,CZECH
REPUBLIC

The twenty most chaotic objects found among first hundred of numbered
asteroids are studied. Lyapunov time calculated with and without inner
planets indicates that for eleven of those asteroids the strongest
chaotic effect results from the resonances with Mars. The filtered
semimajor axis displays an abrupt variation only when a close approach
to Mars takes place. The study of the behaviour of the critical
argument for candidate resonances can reveal which is responsible for
the semimajor axis variation. We have determined these resonances for
the asteroids in question. For the asteroids chaotic even without the
inner planets we have determined the most important resonances with
Jupiter, or three-body resonances. Copyright 1999, Institute for
Scientific Information Inc.

=============
(10) KUIPER BELT EVOLUTION DUE TO DYNAMICAL FRICTION

A. Del Popolo*), E. Spedicato, M. Gambera: Kuiper Belt evolution due to
dynamical friction. ASTRONOMY AND ASTROPHYSICS, 1999, Vol.350, No.2,
pp.685-693

*) UNIVERSITY OF CATANIA,IST ASTRON,VIALE A DORIA 6,I-95125
CATANIA,ITALY

In this paper we study the role of dynamical friction on the evolution
of a population of large objects (m > 10(22) g) at heliocentric
distances > 70 AU in the Kuiper Belt. We show that the already flat
distribution of these objects must flatten further due to
non-spherically symmetric distribution of matter in the Kuiper Belt.
Moreover the dynamical drag, produced by dynamical friction, causes
objects of masses greater than or equal to 10(24)g to lose angular
momentum and to fall through more central regions in a timescale
approximate to 10(9)yr. This mechanism is able to transport inwards
objects of the size of Pluto, supposing it was created beyond 50AU,
according to a Stern & Colwell's (1997b) suggestion. Copyright 1999,
Institute for Scientific Information Inc.

============
(11) SLOW & FAST DIFFUSION IN ASTEROID-BELT RESONANCES

S. Ferraz Mello: Slow and fast diffusion in asteroid-belt resonances: A
review. CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY, 1999, Vol.73, No.1-
4, pp.25-37

UNIVERSITY OF SAO PAULO,INST ASTRON & GEOFIS,CAIXA POSTAL 3386,SAO
PAULO,BRAZIL

This paper reviews recent advances in several topics of resonant
asteroidal dynamics as the role of resonances in the transportation of
asteroids and asteroidal debris to the inner and outer solar system;
the explanation of the contrast of a depleted 2/1 resonance (Hecuba
gap) and a high-populated 3/2 resonance (Hilda group); the overall
stochasticity created in the asteroid belt by the short-period
perturbations of Jupiter's orbit, with emphasis in the formation of
significant three-period resonances, the chaotic behaviour of the outer
asteroid belt, and the depletion of the Hecuba gap. Copyright 1999,
Institute for Scientific Information Inc.

================
(12) ORIGIN & EVOLUTION OF NEAR EARTH ASTEROIDS

A. Morbidelli: Origin and evolution of Near Earth Asteroids. CELESTIAL
MECHANICS & DYNAMICAL ASTRONOMY, 1999, Vol.73, No.1-4, pp.39-50

COTE AZUR OBSERVATORY,CNRS,BP 4229,F-06304 NICE 4,FRANCE

The present paper reviews our current understanding of the origin and
evolution of NEAs, at the light of the results of recent quantitative
numerical simulations that have revolutioned the previously accepted
scenario. Copyright 1999, Institute for Scientific Information Inc.

=============
(13) ON THE PERTURBING FUNCTION IN ORBITAL ELEMENTS

I. Tupikova*), M. Soffel, S. Klioner: On the classical expansion of the
perturbing function in individual orbital elements. CELESTIAL MECHANICS
& DYNAMICAL ASTRONOMY, 1999, Vol.74, No.3, pp.147-152

*) LOHRMANN OBSERV,INST PLANETARE GEODAESIE,MOMMSENSTR 13,D-01062  DRESDEN,GERMANY

Starting from the classical expansion of the perturbing function in the
three-body problem, the transformation to individual orbital elements
is performed in principle up to any degree in small parameters. Some
corrections to the results presented in the well-known article by Yuasa
on secular perturbations of asteroids are given. Consequences for the
expansion of the indirect part of the perturbing function are
discussed. Copyright 1999, Institute for Scientific Information Inc.

===============
(14) TROJAN ASTEROIDS IN STABLE CHAOTIC MOTION

E. Pilat Lohinger*), R. Dvorak, C. Burger: Trojans in stable chaotic
motion. CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY, 1999, Vol.73, No.1-
4, pp.117-126

*) UNIVERSITY OF VIENNA,INST ASTRON,TURKENSCHANZSTR 17,A-1180
   VIENNA,AUSTRIA

The orbits of 13 Trojan asteroids have been calculated numerically in
the model of the outer solar system for a time interval of 100 million
years. For these asteroids Milani et al. (1997) determined Lyapunov
times less than 100 000 years and introduced the notion ''asteroids in
stable chaotic motion''. We studied the dynamical behavior of these
Trojan asteroids (except the asteroid Thersites which escaped after 26
million years) within 11 time intervals - i.e. subintervals of the
whole time - by means of: (1) a numerical frequency analysis (2) the
root mean square (r.m.s.) of the orbital elements and (3) the proper
elements. For each time interval we compared the root mean squares of
the orbital elements (a, e and i) with the corresponding proper
element. It turned out that the variations of the proper elements e(p)
in the different time intervals are correlated with the corresponding
r.m.s.(e); this is not the case for sin I-p with r.m.s.(i).
Copyright 1999, Institute for Scientific Information Inc.

=============
(15) PERIODIC ORBITS AROUND A MASSIVE STRAIGHT SEGMENT

A. Riaguas*), A. Elipe, M. Lara: Periodic orbits around a massive
straight segment. CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY, 1999,
Vol.73, No.1-4, pp.169-178
     
*) EUROPEAN SPACE TECHNOL CTR,TERMA,D-64293 DARMSTADT,GERMANY

In this paper, we consider the motion of a particle under the
gravitational field of a massive straight segment. This model is used
as an approximation to the gravitational field of irregular shaped
bodies, such as asteroids, comet nuclei and planets's moons. For this
potential, we find several families of periodic orbits and
bifurcations. Copyright 1999, Institute for Scientific Information Inc.

===========
(16) A SECULAR THEORY FOR TROJAN-TYPE MOTION

M.H.M. Morais: A secular theory for Trojan-type motion. ASTRONOMY AND
ASTROPHYSICS, 1999, Vol.350, No.1, pp.318-326

UNIVERSITY OF LONDON QUEEN MARY & WESTFIELD COLL,ASTRON UNIT,LONDON E1
4ES,ENGLAND

We derive a secular theory for Trojan-type motion in the framework of
the restricted three-body problem, which is valid inside the entire
regular coorbital region. We show that under certain conditions it is
possible to extend the theory to include the secular perturbations from
additional bodies and an oblate central mass. We are then able to
predict the location of linear secular resonances which may play an
important sole in determining the long-term stability of Trojan orbits
associated with planets or satellites. Copyright 1999, Institute for
Scientific Information Inc.

==============
(17) THE OZONE LAYER & COSMIC IMPACTS

B.A. Klumov: Destruction of the ozone layer as a result of a meteoroid
falling into the ocean. JETP LETTERS, 1999, Vol.70, No.5, pp.363-370


INST DYNAM GEOSPHERES,MOSCOW 117334,RUSSIA

The falling of a large celestial body into the ocean causes a large
number of compounds (for example, HCl, Cl, Br, Na, H2O, OH, and NO)
that destroy ozone molecules directly or indirectly to be ejected to
stratospheric altitudes. The bleaching of the atmosphere in the UV
range as a result of such ozone destruction creates negative feedback
that restores the ozone. The characteristic time for such restoration
in the stratosphere decreases sharply with altitude, ranging from
several months at 30 km to several days at 20 km. (C) 1999 American
Institute of Physics. [S0021-3640(99)00917-2].

===========
(18) SURVIVAL OF LIFE ON ASTEROIDS & COMETS

B. C. Clark*), A.L. Baker, A.F. Cheng, S.J. Clemett, D. McKay,
H.Y. McSween, C.M. Pieters, P. Thomas, M. Zolensky: Survival of life on
asteroids, comets and other small bodies. ORIGINS OF LIFE AND EVOLUTION
OF THE BIOSPHERE, 1999, Vol.29, No.5, pp.521-545

*) LOCKHEED MARTIN ASTRONAUT,ADV PLANETARY STUDIES GRP,DENVER,CO

The ability of living organisms to survive on the smaller bodies in our
solar system is examined. The three most significant sterilizing
effects include ionizing radiation, prolonged extreme vacuum, and
relentless thermal inactivation. Each could be effectively lethal, and
even more so in combination, if organisms at some time resided in the
surfaces of airless small bodies located near or in the inner solar
system. Deep within volatile-rich bodies, certain environments
theoretically might provide protection of dormant organisms against
these sterilizing factors. Sterility of surface materials to tens or
hundreds of centimeters of depth appears inevitable, and to greater
depths for bodies which have resided for long periods sunward of about
2 A.U. Copyright 1999, Institute for Scientific Information Inc.

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