PLEASE NOTE:


*

CCNet DIGEST 19 June 1998
-------------------------

(1) YOU CAN'T HAVE DEEP IMPACT WITHOUT INTERNATIONAL COOPERATION
    Alain Maury <maury@ocar01.obs-azur.fr>

(2) FRENCH QUESTION METHODS USED TO CALCULATE PROBABILITY OF ENGLISH
    IMPACT
    Alain Maury <maury@ocar01.obs-azur.fr> &
    Jean-Marc Mari <jmari@ti.com>

(3) NEW CONTROVERSY LOOMS IN NEO COMMUNITY
    A tormented list moderator 

(4) TUNGUSKA + 90
    Sir Arthur C Clarke

(5) REPORTS OF NEW METEORITE FALLS
    Phil Burns <pib@nwu.edu>

(6) LEONID MISSION HOMEPAGE
    Peter Jenniskens <peter@max.arc.nasa.gov>

(7) METEORITE DELIVERY VIA YARKOVSKY ORBITAL DRIFT
    P. Farinella et al., UNIVERSITY OF PISA

(8) SATURN'S RING AND METEOROID BOMBARDEMENT
    J.N. Cuzzi & P.R. Estrada, NASA, AMES RESEARCH CENTER

(9) MINOR PLANET 1996 PW
    J.K. Davies et al., JOINT ASTRONOMY CENTER

(10) POSSIBLE TRIGGERING OF HEINRICH EVENTS BY ICE-LOAD-INDUCED
     EARTHQUAKES
     A.G. Hunt & P.E. Malin, DUKE UNIVERSITY

==========================
(1) YOU CAN'T HAVE DEEP IMPACT WITHOUT INTERNATIONAL COOPERATION

From Alain Maury <maury@ocar01.obs-azur.fr>

A bit later than everybody else, I went to see Deep Impact last week.
Had to do it fast, for it is certainly not going to stay on screens in
France for long. The only interview I gave concerning impacts on the
occasion of Deep Impact was on Swiss radio. :-)

As everybody will agree, it is certainly the best impact film ever made
as far as special effects go. But all in all it has not been received
as a glorious movie here. Not much of a plot, the US saves the world as
usual, and as far as non-Americans are concerned, nobody feels
concerned, we have seen that in "Independence Day" and in many other US
productions before.

I am pretty sure the question in most people minds was "what next", not
"could this ever happen on Earth for real?". We have had tornados, 
volcanos, asteroids, and everybody is _eagerly_ awaiting the next
catastrophic subject.

Of course a black president in a movie shows that the American movie
industry has made a lot of progress since the McCarthy era. Still,
Hollywood hasn't fully completed its evolution, and hasn't realised
that we live on a 6 billions or more humans (and potential spectators)
planet, and is still doing movies for the home market, while trying to
sell them abroad. I don't know what will be needed for this US lone
ranger attitude to decrease. Maybe the next generation, raised on Japanese
cartoons will do better in that respect.

We have to give excuse to the people who wrote the film script, since
they give the impression to have never seen a real asteroid in their
life, nor do they know anything about the IAU, the international
collaboration of observers, amateurs and professionals, around the
world. The astronomical part in the movie is downright stupid, as is
the "secret" construction of a spacecraft which is about ten times
larger than the Mir station, and is like this second magnitude comet
not seen by anybody else...

To conclude on another subject, I do not feel really at ease with the 
devlopment of the post XF11 situation in the US either.

The recent statement issued by a group of self appointed gurus, with
only one person in the list involved in observations, is part of the
things which makes me very uncomfortable. There seems to be (a minimum
of) two communities, one involved in trying to observe asteroids with
more or less success, and dealing on a daily/nightly basis with the
MPC, and happily so. And another one who does not know what it
takes to publish a single line of astrometric position, but still has
very authoritative ways of condemning the same MPC, and great plans for
the future.

At any rate, what does this statement serve ? And who? How do you
translate "underfunded astronomer"? For most of us it is a pleonasm,
but in this case I have the impression it is meant to say "stupid
astronomer", unable to calculate, or maybe "doing things _we_ wouldn't
dare doing, and since _we_ are the authority, _we_ have the right to
impose our point of view and analysis to the rest of the world" or
whatever. And this does not correspond to the reality. As a
non-American observer I feel as if some technocrats, who could have
worked on the Space Station, but who happen to be concerned by
asteroids because they have written a book on other's work in the
asteroid field ten years ago were taking over and deciding for
everybody else. I may be a bit rough, but what I have read in the past
has made me jump of my chair several times. By the way, is Spaceguard
any kind of a NASA trademark ?

To make things short, reread my analysis of Deep Impact, and replace
Hollywood by NASA and "film" by "US Spaceguard Survey". Some of the
phrases match almost too good to be true.

Alain Maury.

=====================
(2) FRENCH QUESTION METHODS USED TO CALCULATE PROBABILITY OF ENGLISH
    IMPACT

From Alain Maury <maury@ocar01.obs-azur.fr> &
     Jean-Marc Mari <jmari@ti.com>

You like coincidences, so what do you make of this one? Here is
something to think about... or not !

    Abraham Lincoln was elected to Congress in 1846.
    John F. Kennedy was elected to Congress in 1946.

    Abraham Lincoln was elected President in 1860.
    John F. Kennedy was elected President in 1960.

    The names Lincoln and Kennedy each contain seven letters.

    Both were particularly concerned with civil rights.
    Both wives lost their children while living in the White House.

    Both Presidents were shot on a Friday.
    Both were shot in the head.

    Here is an interesting one:
    Lincoln's secretary was named Kennedy.
    Kennedy's secretary was named Lincoln.

    Both were assassinated by Southerners.
    Both were succeeded by Southerners.

    Both successors were named Johnson.
    Andrew Johnson, who succeeded Lincoln, was born in 1808.
    Lyndon Johnson, who succeeded Kennedy, was born in 1908.

    John Wilkes Booth, who assassinated Lincoln was born in 1839.
    Lee Harvey Oswald, who assassinated Kennedy was born in 1939.

    Both assassins were known by their three names.
    Both names comprise fifteen letters.

    Booth ran from the theater and was caught in a warehouse.
    Oswald ran from a warehouse and was caught in a theater.

    Booth and Oswald were assassinated before their trials.

    And here's the kicker:
    A week before Lincoln was shot he was in Monroe, Maryland.
    A week before Kennedy was shot he was in Marilyn Monroe.

Jean-Marc Mari <jmari@ti.com>

=====================
(3) NEW CONTROVERSY LOOMS IN NEO COMMUNITY

From a tormented list moderator  

Yesterday's CCNet scare about a possible English impact on 12 July 1998
(at 22.00 GMT!) has come under fire from different quarters of the
globe. Some list members have openly accused the moderator of "crying
Rule Brittania" and of frightening the living daylight out of people.
French critics in particular (see above) seem unconvinced by the
complex mathematical methods applied in the calculations. Others have
demanded further evidence for the dire prediction. I have attached
below an alternative method for calculating the odds which basically
confirms yesterday's findings. Despite repeated calls not to inform the
public, it would appear that the chances of an English impact, while
being small (I repeat: small!), cannot be ruled out altogether. Here is
the data to prove the case:


                                 1982 Italy
                       1978 Argentina   Argentina 1986
                    1974 Germany            Germany 1990
                  1970 Brazil                  Brazil 1994
               1966 England                        ?    1998

====================
(4) TUNGUSKA + 90

From Sir Arthur C Clarke

Do you all know about this conference 27-30 June in Krasnoyarsk - inc
trip to the epicentre? Fax 7 3912 296 995,
e-mail root@n-angara.krasnoyarsk.su, or andrei@olkhov.msk.ru
WEB: http://www.tm.ru/tunguska

More info in Astro & Geophysics, June - inside back page.

            Sir Arthur   19 Jun 98

======================
(5) REPORTS OF NEW METEORITE FALLS

From Phil Burns <pib@nwu.edu>

Several news outlets are reporting that a meteorite crashed through
a house in Nashville and another struck a barn in New Mexico.  See

     http://www.msnbc.com/local/wsmv/7345.asp
     http://cnn.com/TECH/space/9806/18/meteorite.house.ap/index.html

for more information including a photo of one of the fragments and the damaged
ceiling in Nashville. 

Another purported meteorite landed in a backyard in New Mexico.  Scientists
in New Mexico suggest all three meteorites are fragments of the
same object since the three strikes occurred at about the same time
last Saturday morning.  The fragments have been sent to the Smithsonian
for analysis.

-- Phil "Pib" Burns
   Northwestern University, Evanston, IL.  USA
   pib@nwu.edu
   http://pibweb.it.nwu.edu/~pib/

============================
(6) LEONID MISSION HOMEPAGE

From Peter Jenniskens <peter@max.arc.nasa.gov>

For those who live in Europe:

The Leonid Mission Homepage can now also be viewed at the address:
http://strw.leidenuniv.nl/~leonid/ from a server located at Leiden
University, the Netherlands. This is the same site as:
http://www-space.arc.nasa.gov/~leonid/ and both sites will be updated
simultaneously. We hope that the new shadowsite will make it more easy
to keep track of the Leonid airborne mission project and other
activities related to the upcoming returns of the Leonids. We will
follow the number of visitations to see if the site does fulfill a
need.

Sincerely,

Dr. Peter Jenniskens

==================
(7) METEORITE DELIVERY VIA YARKOVSKY ORBITAL DRIFT

P. Farinella, D. Vokrouhlicky, W.K. Hartmann: Meteorite delivery via
Yarkovsky orbital drift. ICARUS, 1998, Vol.132, No.2, pp.378-387

*) UNIVERSITY OF PISA, DIPARTIMENTO MATEMAT, VIA BUONARROTI 2, I-56127
   PISA, ITALY

We provide a unified discussion of the Yarkovsky effect in both the
original, ''diurnal'' variant and also for the ''seasonal'' variant
which has been recently shown by Rubincam (1995) to be important for
meteorite-sized, regolith-free asteroid fragments. After computing the
rate of the corresponding semimajor axis drift as a function of size
and spin rate, and comparing the relevant time scales with those for
collisional disruption and spin reorientation, we discuss some issues
in meteorite science which are put in a new light by the relevance of
the Yarkovsky effect. In particular, this mechanism provides a good
explanation for the fact that meteorite cosmic ray exposure ages (in
particular for irons) are much longer than the dynamical lifetimes of
objects delivered to the Earth-crossing region through resonances.
Thanks to the Yarkovsky effect, small asteroid fragments in the belt
undergo a slow drift in semimajor axis (with a random-walk component
related to their rotational state) and therefore have enough mobility
to reach the resonances after comparatively long times spent in
nonresonant main-belt orbits. Metal-rich fragments have slower
Yarkovsky drift rates than stones, but their much longer collisional
lifetimes may explain why iron meteorites appear to sample a larger
number of asteroid parent bodies compared to ordinary chondrites. (C)
1998 Academic Press.

====================
(8) SATURN'S RING AND METEOROID BOMBARDEMENT

J.N. Cuzzi*), P.R. Estrada: Compositional evolution of Saturn's rings
due to meteoroid bombardment. ICARUS, 1998, Vol.132, No.1, pp.1-35

*) NASA, AMES RES CTR, DIV SPACE SCI, MAIL STOP 245-3, MOFFETT
   FIELD, CA, 94035

In this paper we address the question of compositional evolution in
planetary ring systems subsequent to meteoroid bombardment. The huge
surface area to mass ratio of planetary rings ensures that this is an
important process, even with current uncertainties on the meteoroid
flux. We develop a new model which includes both direct deposition of
extrinsic meteoritic ''pollutants'' and ballistic transport of the
increasingly polluted ring material as impact ejecta. Our study
includes detailed radiative transfer modeling of ring particle spectral
reflectivities based on refractive indices of realistic constituents.
Voyager data have shown that the lower optical depth regions in
Saturn's rings (the C ring and Cassini division) have darker and less
red particles than the optically thicker A and B rings. These coupled
structural-compositional groupings have never been explained; we
present and explore the hypothesis that global scale color and
compositional differences in the main rings of Saturn arise naturally
from extrinsic meteoroid bombardment of a ring system which was
initially composed primarily, but not entirely, of water ice. We find
that the regional color and albedo differences can be understood if all
ring material was initially water ice colored by tiny amounts of
intrinsic reddish, plausibly organic, absorber, which then evolved
entirely by addition and redistribution of extrinsic, nearly neutrally
colored, plausibly carbonaceous material. The regional compositional
differences result from different susceptibilities to pollution of
regions with very different surface mass density. We further
demonstrate that the detailed radial profile of color across the abrupt
B ring-C ring boundary can constrain key unknown parameters in the
model. We carefully reanalyze and revise meteoroid flux estimates by
Cuzzi and Durisen (1990, Icarus 84, 467-501) and estimate the duration
of the exposure to extrinsic meteoroid flux of this part of the rings,
at least, to be on the order of 10(8) years. This conclusion is easily
extended by inference to the Cassini division and its surroundings as
well. This geologically young ''exposure age'' is compatible with time
scales estimated elsewhere based on the evolution of ring structure due
to ballistic transport and also with other ''short time scales''
estimated on the grounds of gravitational torques. However, uncertainty
in the flux of interplanetary debris and in the ejecta yield may
preclude ruling out a ring age as old as the Solar System at this time.
(C) 1998 Academic Press.

============
(9) MINOR PLANET 1996 PW

J.K. Davies*), N. McBride, S.F. Green, S. Mottola, U. Carsenty,
D. Basran, K.A. Hudson, M.J. Foster: The lightcurve and colors of
unusual Minor Planet 1996 PW. ICARUS, 1998, Vol.132, No.2, pp.418-430

*) JOINT ASTRONOMY CTR, 660 N AOHOKU PL, HILO, HI, 96720

Minor Planet 1996 PW is unusual in having the orbital characteristics
of a long period comet but showing no sign of cometary activity around
the time of its discovery. We present optical data which reveals a
double peaked lightcurve (period 35.44 +/- 0.02 hrs and amplitude 0.44
+/- 0.03 magnitudes) and VRIJHK photometry which shows colors (V - R =
0.56 +/- 0.04, V - I = 1.03 +/- 0.06, V - J = 1.80 +/- 0.05, V - H =
2.19 +/- 0.05, and V - K = 2.32 +/- 0.05) typical of D type asteroids
and suspected bare comet nuclei. A low signal to noise reflectance
spectrum in the K band shows a flat continuum with no evidence for
spectral features. Image profiles from coadded frames in the R band
indicate no apparent cometary activity with an implied upper limit to
the dust production rate of 0.03 kg s(-1). (C) 1998 Academic Press.

==============
(10) POSSIBLE TRIGGERING OF HEINRICH EVENTS BY ICE-LOAD-INDUCED
     EARTHQUAKES

A.G. Hunt*), P.E. Malin: Possible triggering of Heinrich events by
ice-load-induced earthquakes. NATURE, 1998, Vol.393, No.6681,
pp.155-158

*) DUKE UNIVERSITY, NICHOLAS SCH ENVIRONM, DIV EARTH & OCEAN SCI, BOX
   90235, DURHAM, NC, 27708

North Atlantic sediments dating from the last ice age contain layers of
rock fragments from northeastern Canada (so-called Heinrich layers).
Like modern iceberg-borne sediments from Greenland, these layers have
been attributed to ice-rafting episodes. Six Heinrich layers have been
documented and correlated with climate changes. The layers, which are
several centimetres thick, contain negligible amounts of foraminifera
(which accumulate at a few millimetres per century), implying that they
were deposited over just a few years. These ice-rafting Heinrich events
are separated by progressively shorter intervals from about 40 to 6
kyr, and it has been suggested that they are related to the
Milankovitch cycles in the Earth's orbital parameters. Alternatively,
they may be generated by forcing mechanisms arising from the internal
dynamics of the Laurentide ice sheet. Here we suggest the possibility
that the Heinrich events were precipitated by ice-load-induced

earthquakes, analogous to those produced by reservoir water loads. We
suggest that near its edge, the Laurentide ice sheet sheared the
Earth's crust, inducing repeated failure that released the ice rafts.
This region (along Canada's northeastern seaboard) shows evidence of
both current and past seismic activity owing to postglacial rebound.
Our model accounts for the intervals between both the Heinrich events
and the evidence of palaeoseismicity, and can be tested, by studying
local sedimentary relationships. Copyright 1998, Institute for
Scientific Information Inc.

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