PLEASE NOTE:
*
CCNet DIGEST, 7 June 1999
-------------------------
(1) BACK FROM THE TORINO IMPACT WORKSHOP
Benny J Peiser <b.j.peiser@livjm.ac.uk>
(2) DEBRIEF ON TORINO IMPACT WORKSHOP
Jonathan TATE <fr77@dial.pipex.com>
(3) LARGEST IMPACT STRUCTURE DISCOVERED IN FRANCE?
Pierre-Alex Vachon <avachon@src-mtl.com>
(4) ELONGATED ASTEROIDS BELIEVED TO BE WEAKER
Andrew Yee <ayee@nova.astro.utoronto.ca>
(5) OCEANIC MEGA-IMPACTS AND CRUSTAL EVOLUTION
Andrew Glikson <geospectral@spirit.com.au>
(6) NEW TUNGUSKA EXPEDITION
Luigi Foschini <foschini@pinocchio.fisbat.bo.cnr.it>
(7) SYPOSIUM ON PLANETARY IMPACT EVENTS & THEIR CONSEQUENCES
ON EARTH
Ron Baalke <baalke@ssd.jpl.nasa.gov>
(8) AUSTRALASIAN TEKTITE AGE PARADOX
Bernd Pauli HD <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>
(9) IMPACT EARTH
Austen Atkinson <ultrazone@easynet.co.uk>
==============
(1) BACK FROM THE TORINO IMPACT WORKSHOP
From Benny J Peiser <b.j.peiser@livjm.ac.uk>
After four days of presentations, deliberations and decisions,
the
IMPACT workshop in Turin ended last Friday on a very positive
note.
Despite a number of minor disagreements, there is a general
perception that international research on the impact hazard and
NEO
searches are gearing up and moving in the same direction. With
additional search programmes planned in a number of countries in
the
next couple of years, the sky coverage is soon approaching
saturation. Obviously, achieving such a comprehensive coverage
would
be a major breakthrough. Yet it remains questionable whether it
would
actually guarantee the Spaceguard Survey's goal of detecting 90%
of
all NEOs >1km within the next 10 years. Other problems will
also have
to be addressed: the search for fainter objects (< 1 km)
requires
access to sufficiently large telescopes; how will we deal in the
event of an undetected (or, indeed, detected/predicted)
Tunguska-type
impact? Follow-up searches will remain important for any
calculation
of potential impact hazards.
In a politically important statement, directed at national
governments
and funding agencies, the participants of the IMPACT workshop
strongly
recommend that governments should establish national Spaceguard
centres
and to support these centres financially in order to facilitate
international collaboration in the global Spaceguard programme.
One of the more practical results of the IMPACT workshop was the
general agreement on a much improved hazard scale in conjunction
with
the question of how to deal with future predictions of possible
impacts by a sizeable near-Earth object. While the exact details
will
be finalized by the IAU in the next four weeks or so, there is
now a
generally accepted tool on which future cases such as XF11 and
AN10
can be handled in a better way. The final results and
recommendations
of the workshop will be published in July/August.
And finally - can I just say that it was a pleasure to meet
almost
20% of CCNet subscribers at Turin - most of whom I had never met
before. Putting a face to a name and meeting individuals on a
one-to-one basis has certainly helped to improve the
communication
and discussion among many participants. I am particularly glad
that
some of the mistakes and misunderstandings regarding the recent
AN10
debate were sorted out in an amicable manner.
I have attached below Jay Tate's workshop debrief which only
highlights some of the issues discussed at Torino. I am sure
that further reports, impressions and comments will follow.
Benny J Peiser
===================
(2) DEBRIEF ON TORINO IMPACT WORKSHOP
From Jonathan TATE <fr77@dial.pipex.com>
A "HOT DEBRIEF" ON THE WORKSHOP ON "INTERNATIONAL
MONITORING PROGRAMS
FOR ASTEROID AND COMET THREAT" (IMPACT), HELD IN TORINO, ON
JUNE 1-4,
1999.
The Sponsors of the workshop were the IAU, ASI, NASA, ESA,
Spaceguard
Foundation, IACG, The Planetary Society, Alenia Aerospazio -
Divisione
Spazio and the Provincia di Torino.
This meeting was a follow up to the IAU WGNEO sponsored workshop
on the
island of Vulcano (Italy) in September 1995, entitled
"Beginning the
Spaceguard Survey". The aim of that workshop was to
emphasise the need
for a co-ordinated effort, and to establish the basis for
effective
international co-operation on the subject.
Participation at the Turin workshop included a high proportion of
the
world expertise in NEO studies, and high ranking members of NASA,
the
IAU and other sponsoring organisations.
The objectives of the workshop were:
* To encourage scientists in all nations and their sponsoring
agencies to increase NEO search and follow-up efforts.
* To improve communications among observers worldwide and to use
these improved communications to foster co-ordination of
search and
follow-up activities.
* To assess the actual potential and limitations of ground-based
observing facilities, and to discuss the possible role of
space-based
segments in NEO search.
* To develop procedures for assuring a rapid communication of
accurate information about Extremely Hazardous Objects
which may be
detected in the future.
* To draft and discuss Recommendations to be distributed to the
scientific and political bodies able to support and fund
NEO
researches.
The structure of meeting was to hold an initial plenary session
during
which the conference was briefed on a number of topics, to bring
everyone fully up to date with recent developments. After the
briefings
the conference split up into four sub-groups to discuss specific
issues,
and to produce recommendations to be passed to the IAU. These
recommendations, once agreed by the sub-groups were then
discussed at
another plenary session where they were agreed by the floor, or
not.
While it is not yet possible to detail the recommendations that
will be
passed to the IAU, as they have yet to be
"word-smithed" by the
sub-group chairmen and agreed in their final forms, it is
possible to
list a few of the significant statements made, discussions had
and
recommendations made. So, below are some bullet points, to be
followed
by a full report as soon as the results are published.
* Actual impacts are likely to be preceded by prior close
approaches.
* Comets pose a much smaller risk than asteroids.
* Issues of funding and national interest need to be addressed.
* The issue of whether asteroids are rubble piles or solid bodies
is
still unresolved. This information is very necessary for
any
mitigation strategies. We need 4m-10m class telescopes to
do
compositional studies on NEOs.
* Alan Harris of JPL estimated that about 18% of 1 km and above
sized NEOs have been discovered, but there are large
population
uncertainties. However, we are still discovering asteroids
at too
slow a rate (8-20 times).
* There are currently a number of space missions to asteroids and
comets. This is a "Golden Age" for studying
comets and asteroids
according to Don Yeomans.
* NASA is increasing funds for NEO research, and has set up its
own US JPL program office.
* UK efforts need increased government interest. Recent events
have shown that there is official acceptance of
seriousness of
problem. In the UK we have a wealth of experience, even in
(eg) 4m
class telescopes. VISTA could be a wonderful tool.
* Japan is pressing ahead with its new NEO detection programme..
* There is an urgent need for some follow up programmes, and more
funding (staff) for the MPC. Ted Bowell proposed changes
to the MPC
that were highly controversial, raising questions of
control and IAU
international control. No consensus was reached.
* European possibilities were discussed eg DLR, ODAS, including
the use of ESO facilities.
* The number of inner Earth objects is thought to be similar to
the number of Atens. Both can be easy to find, provided
that you look
at smaller solar elongations.
* Group 1 discussions emphasised the need for S. Hemisphere
telescopes (economic and political).
* Group 2 discussions emphasised the need for research into NEO
physical characteristics.
* In Group 3 the importance of precoveries and plate log searches
was stressed. There was some emphasis on UKST archive..
This would
also be an obvious role for the NSC. There was a strong
recommendation that analysis of PHAs should always be
performed by at
least two independent groups.
* Group 4 developed a protocol, primarily for IAU purposes,
dealing with the announcement of PHOs. In the plenary
session there
was some confused discussion, and eventually a shorter
agreed
document was approved. This emphasised the need for
individual
nations to discuss the issue; what do public, politicians
and
decision makers require? The need for a National
Spaceguard Centre is
obvious.
* R. Binzel discussed his new hazard scale, but J. Tate has
already produced something broadly acceptable for UK
purposes. This
scale is designed for use when talking to the general
public or the
media. D. Morrison observed that "people just don't
understand
probability". S. Isobe reckoned that the index was a
good lecturing
tool, but not good for communicating with the mass media.
Please be aware that this is a far from complete report, but I
hope that
something of the workshop's flavour comes through.
Jay Tate
Spaceguard UK
=================
(3) LARGEST IMPACT STRUCTURE DISCOVERED IN FRANCE?
From Pierre-Alex Vachon <avachon@src-mtl.com>
A friend from France just sent me the June issue of the credible
and
serious "Sciences et Avenir" entitled: The Biggest
Meteorite of the
World.
Apparently, geologists who were re-analyzing Landsat 2 pictures
of
Rochechouart and Bizeneuille, two adjacent areas of south-western
France, discovered that the two already known 20 km-wide craters
were
in fact 200 to 300 km wide! There shock waves actually
touched each
other, as their impats were 140 km apart, 200 million years ago.
The Rochechouart impact is said to be the biggest meteorite that
has
crashed on Earth! It is taken for granted that the two
impact
structures came from the same asteroid, and only a few seconds
separated them. Further research has revealed that other 200
million
year old impacts have the same latitude: Manicouagan
(Québec) and
Saint-Martin (Canada). Red Wing (USA) and Obolon (Ukraine) are
also
located on the same path that can be traced between Manicouagan
and
Rochechouart. Remember the multiple impacts on Jupiter? Same
phenomenon
here, they say.
This chain of impact is thought to be one of the five most
important
catastrophes that have happened on Earth. They estimate the
Rochechouart meteorite measured 15km and the Bizeneuille one
perhaps
even bigger. The suggest that the impacts were the equivalent of
40
million Hiroshimas (yes 40 million), affecting thousands of
square km
in the Northern hemisphere. They would also explain the presence
of the
purest quartz found on Earth. It is used by Nasa and other
aerospace
manufacturers.
As for the origin of these two meteorites, the article mentions
the
theory of the tenth planet, an outsider-kind of a planet, at the
limit
of our solar system. It could be responsible for "fishing
out" comets
from the Oort Cloud where they are thought to be circulating in
great
numbers. Apparently, this theory is controversial.
The article ends on a question mark: will an even bigger
meteoritic
impact be found on Earth? They seem to point to Manicouagan in
Northern
Québec, where they found a 70 km-wide core. The further study of
satellite images will tell us, it concludes.
If anyone is interested, I could scan and put the entire article
on the
list. It is in French. Let me know.
A la prochaine!
--
Pierre-Alex Vachon - avachon@src-mtl.com
Réalisateur - Director
Emission Branché - http://radio-canada.ca/branche/
=================
(4) ELONGATED ASTEROIDS BELIEVED TO BE WEAKER
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Public Affairs Office
Lawrence Livermore National Laboratory
Contact: Stephen Wampler
Phone: (925) 423-3107
E-mail: wampler1@llnl.gov
FOR IMMEDIATE RELEASE: June 1, 1999
NR-99-05-03
ELONGATED ASTEROIDS BELIEVED TO BE WEAKER
LIVERMORE, Calif. -- Elongated or stretched asteroids in space
are apparently
weaker than spherical asteroids, a scientist at the Department of
Energy's
Lawrence Livermore National Laboratory will report today. Mark
Hammergren,
a planetary scientist at Livermore's Institute of Geophysics and
Planetary
Physics, came to this conclusion after studying nearly 850
asteroid
observations by dozens of astronomers.
Hammergren will present his results during the opening day of the
Centennial
meeting of the American Astronomical Society in Chicago, Ill.
During his
study of asteroid observations, Hammergren found that very
elongated
asteroids are never seen to be rotating faster than once every
four hours. In
contrast, more spherical asteroids can rotate as fast as once
every 2.3 hours.
Such evidence, Hammergren said, provides strong support for the
theory that
most asteroids are not tightly-bonded solid chunks of rock, but
rather are
loose aggregates of material, sometimes called "rubble
piles.."
"Solid asteroids can rotate as fast as they want and still
hold together, but
if rubble piles rotate too fast, they'll fly to pieces,"
Hammergren said. "It
makes sense that more elongated asteroids, which have weaker
gravity on
their ends, would be even more prone to break up."
Based on his research, Hammergren theorizes that "rubble
pile" asteroids
in space are governed by the same processes that lend stability
to piles of
sand on Earth.
"In effect, loose and weak materials in rubble piles have
the ability to
support large surface features on asteroids, just as loose sand
and weak
dirt can support huge mountains on Earth," he said.
Hammergren also offered two other findings based on his theory of
rubble
pile stability.
One is that changes in a rubble-pile asteroid's shape would
probably not
occur gradually, but would instead happen cataclysmically, as a
series of
massive landslides.
The other is that if such landslides occur on the surfaces of
rapidly-
rotating asteroids, parts of the asteroids' surfaces may be
thrown off
into space.
Such break-ups provide a possible explanation for the formation
of
asteroid moons, which orbit the original asteroid similar to the
way the
moon orbits the Earth.
Lawrence Livermore National Laboratory is managed by the
University of
California for the U.S. Department of Energy.
================
(5) OCEANIC MEGA-IMPACTS AND CRUSTAL EVOLUTION
From Andrew Glikson <geospectral@spirit.com.au>
Oceanic mega-impacts and crustal evolution
[Geology, 27:337-341 (1999)]
Andrew Y. Glikson
Research School of Earth Science, Australian National University,
Canberra, A.C.T. 0200
ABSTRACT
Lunar mare crater counts, the terrestrial impact flux, and
astronomical
observations of asteroids and comets define a consistent impact
rate of
4-6 * 10^-15 km^-2.yr^-1 within the inner solar system since the
end of
the Late Heavy Bombardment (LHB) ~3.8 Ga ago. Coupled with the
observed
crater size vs cumulative crater size frequency relationship of N
~
Dc^-1.8 (N = cumulative number of craters of diameter > Dc),
these
rates imply formation on Earth of more than 450 Dc ³ 100
km-diameter
craters, more than 50 Dc³ 300 km-diameter craters, and more than
20 Dc³
500 km-diameter craters. Geochemical and isotopic constraints
require
that more than 80% of the projectiles impacted on time-integrated
oceanic crust since the LHB. The injection of shock energies
calculated
at >10^8 megatons TNT-equivalent by a Dp > 10 km-diameter
projectile
may result in propagating fractures and rift networks, thermal
perturbations, and ensuing magmatic activity. Examinations of the
geologic record for correlated impact and magmatic fingerprints
of such
events remain inconclusive in view of isotopic age uncertainties.
Potential but unproven connections may be represented by the (1)
Cretaceous-Tertiary boundary (ca. 65 Ma) impact(s), onset of the
Carlsberg Ridge spreading, Deccan volcanism, and onset of the
mantle
plume of the Emperor-Hawaii chain; (2) Jurassic-Cretaceous
boundary
(ca. 145 Ma) impacts, onset of Gondwana breakup, including
precursors
of the east African rift structures; (3) Permian-Triassic
boundary (ca.
251 Ma) impact(s), Siberian Norilsk traps, and early Triassic
rifting;
and (4) the 3.26 Ga basal Fig Tree Group (east Transvaal) Ir-rich
and
Ni-rich quench spinel-bearing impact spherules and
contemporaneous
igneous-tectonic activity. Tests of the theory require further
identification and isotopic dating of distal ejecta, impact
spherule
condensates, and meteoritic geochemical anomalies.
================
(6) NEW TUNGUSKA EXPEDITION
From Luigi Foschini <foschini@pinocchio.fisbat.bo.cnr.it>
Dear Benny,
I would like to inform you that next July a new scientific
expedition
will go to the Tunguska region in order to improve our knowledge
about that event.
You can find more informations at the web page:
http://www-th.bo.infn.it/tunguska/
The page is continuously updated.
Cheers,
Luigi
===============
(7) SYPOSIUM ON PLANETARY IMPACT EVENTS & THEIR CONSEQUENCES
ON EARTH
From Ron Baalke <baalke@ssd.jpl.nasa.gov>
International Symposium on Planetary Impact Events and their
Consequences to the Earth
- Space and Earth Planetary Circumstances -
Yamaguchi, September 27-30, 1999
Scientific Targets:
This symposium has scientific targets to discuss catastrophic
events on
lunar formation, impact craters, meteorites, meteoritic showers,
geological
boundaries, space debris, new materials, artificial impacts and
life
chemical evolution as analyses of space and terrestrial
circumstances.
http://www.sci.yamaguchi-u.ac.jp/geo/PIECE1.html
================
(8) AUSTRALASIAN TEKTITE AGE PARADOX
From Bernd Pauli HD <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>
TAYLOR S.R. (1999) The Australasian tektite age paradox (MAPS
34-3,
1999, From the Editors, page 311):
Students of tektites possess the interesting property of dividing
themselves into two irreconcilable camps. Even the embers of the
long
dead lunar vs. terrestrial origin debate are still occasionally
rekindled into flame. Another division of longstanding has
concerned the
age of fall of the tektites of the Australasian strewnfield that
covers
about ten percent of the surface of the Earth. Early workers,
including
such astute observers as Charles Fenner, George Baker, and Edmund
Gill,
who picked up pristine tektites on the arid and ancient surface
of
Australia, became convinced that this shower of glass had arrived
very
recently. Ages around 10 000-20 000 years were usually quoted. As
some
early radiometric age determinations of tektites gave spuriously
old
ages, these data fuelled the notion that the age of the fall was
disconnected to the time of formation of tektites. It was then a
short
intellectual leap to bring them from outside the Earth. More
precise
dating eventually yielded ages ca. 770 000 years for the time of
formation of the glass. As the flanges on the famous
button-shaped
australites gave effectively the same result, this also marked
the
time of entry through the atmosphere of these aerodynamically
shaped
forms. Thus the time of formation and fall was close. Then
microtektites were discovered in drill cores from deep-sea
sediments,
close to, but not identical with the Brunhes-Matuyama Boundary.
This
evidence from two separate disciplines convinced most workers
that the
Australasian tektite event had occurred about three quarters of a
million years ago. The stratigraphic evidence was relegated by
most
workers to an uncertain status on account of the difficulties of
dating Pleistocene land surfaces in Australia.
A number of workers familiar with the Australian localities
continued to
insist on a recent fall (e.g., Lovering et al., 1972) relegating
the
awkward deep-sea microtektite data to a separate event. Their
position
was reinforced by fieldwork by Izokh (1993) in Vietnam, clearly
part of
the same strewnfield, where he claimed a 10 000 year age for the
fall.
However work from Vietnam, reported by Fiske et al. (1996), has
shown
that "the tektite-bearing horizon represents a
paleo-erosional surface"
and "because the tektites are not presently in a
chronostratigraphic
horizon, their stratigraphic age is uncertain" (p. 40).
Studies in this
area are aided by the exposures in the myriad bomb craters
resulting
from the Vietnam war. This information is possibly the sole
beneficial
result of that expensive and ultimately futile bombardment.
Robert Fudali (1993) had previously drawn attention to the fact
that
most australites showed signs of weathering and transport and
that
perfect specimens constituted only a very small fraction of
collections.
He noted that at the Port Campbell, Victoria locality, the
australites
appeared to be coming from a deeper sandy horizon rather than the
present surface, all this suggesting that the young age was in
error.
At this stage, GENE SHOEMAKER, long familiar with the tektite
problem,
entered the scene. In conjunction with Ralph Uhlherr and assisted
in the
field by his indefatigable wife, CAROLYN, he began mapping the
Port
Campbell area. Gene was a superb field geologist whereas Ralph,
who had
been collecting tektites in the area for many years, has an
intimate
knowledge of the local geology. Their combined work (Shoemaker
and
Uhlherr, 1999) has pinned down the precise horizon, the Hanson
Plain
Sand, from which the tektites found in younger deposits have been
reworked. The famous stratigraphic paradox has been resolved.
The paper by Gene and Ralph was prepared for press by Carolyn,
following
the tragic accident that has deprived us of the great services of
Gene.
It was typical of GENE that in his final scientific
contribution he
settled a major scientific controversy by m e t i c u l o u
s field
work. This reminds us that his first was to establish, by studies
at
Meteor Crater, that the origin of both terrestrial and lunar
craters was
due to meteorite impact rather than volcanism.
Stuart Ross Taylor - Associate Editor
Copyright property of the Meteoritical Society, 1999.
=================
(9) IMPACT EARTH
From Austen Atkinson <ultrazone@easynet.co.uk>
Benny/CCNET members,
Reaction to Impact Earth has been overwhelmingly positive, thus
far. I
only hope that it helps to spread the word about the impact
threat to
the uninitiated. Certainly the TV and radio interviews that I
have
given over the last two weeks have resulted in a lot of positive
feedback - even from the British governmental elite!
For those who might be interested in meeting me or coming along
to ask
questions/see my talk, there are a number of bookshop events yet
to take
place, following the success of the event at Books Etc
(Whiteley's,
Bayswater) on May 27th. The dates and locations are as follows:
Tuesday 8th June
7.00 - 9.00 pm Waterstones Contact: Nial Duff Tel: 0141 333 1915
Venue: 153 - 157 Sauchiehall Street Glasgow
Thursday 10th June
6.00 - 8.00 pm Dillons Contact: Peter Oakes Tel: 01483 457545
Venue: 50-54 High Street Guildford, Surrey GU1 3ES
If you would like to contact me, send an email to:
Austen Atkinson <ultrazone@easynet.co.uk>
or visit the Impact Earth website at the following URL:
http://easyweb.easynet.co.uk/~ultrazone/book_signing_promo1.html
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