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.
----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To subscribe, please
contact the moderator Benny J Peiser at <b.j.peiser@livjm.ac.uk>.
Information circulated on this network is for scholarly and
educational
use only. The attached information may not be copied or
reproduced for
any other purposes without prior permission of the copyright
holders.
The electronic archive of the CCNet can be found at
http://abob.libs.uga.edu/bobk/cccmenu.html