PLEASE NOTE:


*
Date sent:        Tue, 20 Jan 1998 10:11:28 -0500 (EST)
From:             Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject:          CC DIGEST, 20/01/98
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

CAMBRIDGE-CONFERENCE DIGEST, 20 January 1998
--------------------------------------------

   "Fate will be overcome if thou resist it; if
   thou neglect, it conquereth"
   (Sir Walter Ralegh)
 

(1) ON THE VISIBILITY OF THE NEAR SPACECRAFT

(2) AMERICAN ANTHROPOLOGICAL ASSOCIATION DRAWS ATTENTION TO NEO THREAT

(3) GRIEVE'S LATEST REVIEW OF TERRESTRIAL IMPACT CRATERS AND THE
    PROBLEMS OF DETECTING IMPACTS IN THE GEOLOGICAL RECORD

(4) ATMOSPHERIC ENTRY AND BREAKUP OF IMPACTING METEOROIDS

(5) ANALYSING ATMOSPHERIC BREAKUP OF METEOROIDS AND IMPACT CRATERING

(6) A NEW PERSPECTIVE: SCANNING IMPACT CRATERS IN 3-D

(7) ROADBLOCKS ON THE KILL CURVE: THE PROBLEMS OF LINKING GIANT IMPACT
    CRATERS TO MASS EXTINCTIONS
 

===================================================================
(1) ON THE VISIBILITY OF THE NEAR SPACECRAFT

From: Clark Chapman cchapman@boulder.swri.edu

For information about visibility of the NEAR spacecraft this Thursday
evening, when it will flash as bright as one of the brightest stars
in the sky by orienting its solar panels to reflect sunlight at a
dozen American cities and Tokyo, check out the following Web site and
links from there:

http://www.boulder.swri.edu/clark/finderos.html

Clark Chapman

===============================================================
(2) AMERICAN ANTHROPOLOGICAL ASSOCIATION DRAWS ATTENTION TO NEO THREAT

From: Rolf Sinclair rsinclai@nsf.gov

Anthropology Newsletter, January 1998, p. 19

COSMIC THREAT TO CIVILIZATION

By Benny J Peiser (Liverpool John Moores)

The July 1994 crash of comet Shoemaker-Levy 9 on Jupiter in July of
1994 proved to be a watershed in the development of mankind's cosmic
consciousness. Dramatic changes in the understanding and perception
of our cosmic environment, initially triggered by the
Cretaceous-Tertiary (K/T) boundary controversy during the early
1980s, appear to have gradually shifted from the geological to the
historical time-frame.

During the last decade, most scientists have accepted the idea of
global catastrophes caused by the impact of extraterrestrial bodies.
Until fairly recently, their acceptance depended on the assumption
that cosmic disasters were restricted to primordial times, millions
of years before the origin of Homo sapiens. This picture has changes
significantly over the last couple of years. One of the most
noticeable changes to the 1980s, which focused primarily on the
demise of the dinosaurs and other mass extinctions, is the growing
concern and risk assessment of the celestial threat to civilisation.

Scholars have now started to investigate the implications of
catastrophic events on societal evolution, cultural anthropology,
human social behaviour and the development of religion. Some of
Britain's leading astronomers argue that both the emergence and the
collapse of civilisations might be associated with episodes of
increased meteoric activity, multiple impacts and related climate
change. Such episodes punctuating the evolution of human cultures
are now looked upon as a primary agency determining the rise and
fall of ancient civilisations.

The emerging paradigm of historical catastrophism also stems from
the awareness that the celestial hazard is not limited to the odd
giant asteroid which hits the Earth every 100,000 or 1,000,000 years.
In contrast to the traditional risk assessment - based on a
statistical analysis of the number of known impact craters on the
Moon and Earth in addition to the currently known asteroidal flux -
it has become evident that super-Tunguskas (i.e. multimegaton
atmospheric or oceanic impacts) are also capable of triggering
ecological downturns which, if severe enough, may result in
civilisation collapse.

In spite of mankind's rude awakening, there is no need for
desperation or apocalyptic fatalism. Terrestrial life has now, for
the first time ever, developed the intelligence and technology to
discern the mortal dangers from space. It has also evolved to such
a level that effective strategies of planetary defense can be
devised and implemented. By turning away Near Earth Objects (NEOs)
and the threat they pose to civilisation, humans have acquired the
capability to change the course of nature and halt the vicious cycle
of cosmic cataclysms. Scientists have the responsibility to take this
challenge head-on and to ensure that humankind takes its fate into
its own hands. This would certainly mark the start of a new turning
point in the development of cosmic consciousness and autoevolution.
    ****
[Benny J Peiser is a historian and anthropologist with particular
research interest in neocatastrophism and its implications for
human and societal evolution. He is a senior lecturer at Liverpool
John Moores University (UK). As a Fellow of the Royal Anthropological
Society and a member of Spaceguard UK, he has published numerous
papers on the historical, cultural and religious implications of
neocatastrophism. He recently organized a conference at Cambridge U
on "Natural Catastrophes during Bronze Age Civilizations:
Archaeological, Geological and Astronomical Perspectives"; full
information is at http://www.knowledge.co.uk/xxx/sis/camconf.htm]

======================================================================
(3) GRIEVE'S LATEST REVIEW OF TERRESTRIAL IMPACT CRATERS AND THE
    PROBLEMS OF DETECTING IMPACTS IN THE GEOLOGICAL RECORD

R. A. F. Grieve: Extraterrestrial impact events: the record in the
rocks and the stratigraphic column. PALAEOGEOGRAPHY PALAEOCLIMATOLOGY
PALAEOECOLOGY, 1997, Vol.132, No.1-4, pp.5-23

GEOLOGICAL SURVEY OF CANADA, OTTAWA, ON K1A 0Y3, CANADA

The known terrestrial impact record is a biased sample of a much larger
population of impact events. The biases are due to the modifying effects of
terrestrial geologic processes, coupled with incomplete searches for impact
structures and impact-related materials, Terrestrial impact structures have
the same basic forms as impact craters on the other planets of the inner
solar system but, because of post-impact modification by terrestrial
geologic process, are recognised by the occurrence of shock metamorphic
effects. In some cases; siderophile anomalies have been identified in impact
lithologies and have been used to estimate the composition of the impacting
body, Similar shock metamorphic effects and a siderophile anomaly in K-T
boundary materials are indicative of a major impact event, which has been
correlated with the formation of the Chicxulub structure: Mexico. Evidence
of a small number of other impacts occur in the stratigraphic record, most
commonly as tektite or microtektite horizons. In some cases they are known
to be accompanied by geochemical anomalies, In other cases a number of Ir
anomalies have been reported in the stratigraphic record but there is no
confirmatory evidence that they are due to impact. The majority of known
impact events in the stratigraphic record are from relatively recent
geologic time. Logic dictates, however, that many more impacts must be
recorded in terrestrial sediments and model calculations indicate that
relatively small impacts (D greater than or equal to 20 km) have the
potential to cause atmospheric blow-out and, thus, global dispersion of some
of the impact products. Geochemical detection, however, of such events may
not be easy; in some cases because of relatively small absolute signals
against the background of the daily infall of cosmic material. In addition,
non-chondritic bodies may result in no appreciable geochemical anomaly. In
view of this, any claim to a geochemical signature of impact in the
stratigraphic record should be accompanied by a physical search for impact
materials; although, in the case of impacts into oceanic crust, this too
will be difficult. Given the K-T experience, however, and the fact that
large-scale impact on Earth is a natural consequence of the character of the
solar system, the potential of impacts to provide local and global marker
horizons can not be ignored. Similarly, the fact that impacts may have the
potential to result in shortterm biologic or climatic excursions can not be
dismissed arbitrarily, when considering the causes of such phenomena as
stable isotope anomalies in the stratigraphic record.

======================================================================
(4) ATMOSPHERIC ENTRY AND BREAKUP OF IMPACTING METEOROIDS

B. A. Ivanov*), A. T. Basilevsky & G. Neukum: Atmospheric entry of
large meteoroids: implication to Titan. PLANETARY AND SPACE SCIENCE,
1997, Vol.45, No.8, pp.993-1007

RUSSIAN ACADEMY OF SCIENCE, INSTITUE OF DYNAMICS & GEOSPHERES,
MOSCOW, RUSSIA

The preparation for the Cassini-Huygens mission gives an opportunity to
revise the problem of an atmospheric entry and breakup of cratering
meteoroids. The numerical modeling of the meteoroid's flight through the
atmosphere is presented in comparison with more simple models. The
simulation takes into account the brittle/ductile properties of the
meteoroid material: the Grady-Kipp-Melosh model of tensile failure is
accompanied with a simple model of the shear failure. The main difference
with previously published models consists in the treating of the
post-failure deformation of the damaged material as a flow of a cohesionless
media with a dry friction. Numerical results are used to make a
parameterization of a simple Grigorian-like model, which finally is applied
to predict the atmospheric shielding effect on Titan. For a modern
atmosphere of Titan and mostly ice projectiles the observable deficiency of
impact craters due to atmospheric shielding would be in the range of 6-8 km,
where the number of craters would be two times smaller than for the airless
Titan.

====================================================================== (5)
ANALYSING ATMOSPHERIC BREAKUP OF METEOROIDS AND IMPACT CRATERING

B. A. Ivanov*), D. Deniem & G. Neukum: Implementation of dynamic
strength models into 2D hydrocodes: Applications for atmospheric
breakup and impact cratering. INTERNATIONAL JOURNAL OF IMPACT
ENGINEERING, 1997, Vol.20, No.1-5, pp.411-430

*)INSTITUTE OF DYNAMICS & GEOSPHERES, MOSCOW 117939, RUSSIA

A statistical model of a tensile strength is implemented into the
SALE-2D hydrocode. The well-tested 2D code has been modified to handle
multi-material problems and strength effects. The key element of the model
is the Grady-Kipp-Melosh kinetic model of tensile strength, adopted to
hydrocode calculations. The resulting numerical algorithm allows to estimate
general features of the atmospheric breakup of meteoroids and fracturing
around impact craters.

======================================================================
(6) A NEW PERSPECTIVE: SCANNING IMPACT CRATERS IN 3-D

L. Kay*), A. Podoleanu, M. Seeger & C.J. Solomon: A new approach to the
measurement and analysis of impact craters. INTERNATIONAL JOURNAL OF IMPACT
ENGINEERING, 1997, Vol.19, No.8, pp.739-753

*) UNIVERSITY OF KENT, DEPARTMENT OF PHYSICS, CANTERBURY CT2 7NR,
KENT, ENGLAND

We describe a low-coherence interferometric technique which we have
used for 3-D mapping of impact craters produced in the laboratory. We
also propose an approach to analyse the impact craters in terms of the
Zernike polynomials. Preliminary results suggest that this set may provide a
useful parametric representation, thereby enabling us to relate crater
features to impact parameters.

=========================================================================
(7) ROADBLOCKS ON THE KILL CURVE: THE PROBLEMS OF LINKING GIANT IMPACT
    CRATERS TO MASS EXTINCTIONS

C. W. Poag: Roadblocks on the kill curve: Testing the Raup hypothesis
PALAIOS, 1997, Vol.12, No.6, pp.582-590

US GEOLOGICAL SURVEY, 384 WOODS HOLE RD, WOODS HOLE, MA, 02543

The documented presence of two large (similar to 100-km diameter),
possibly coeval impact craters of late Eocene age, requires
modification of the impact-kill curve proposed by David M. Raup. Though the
estimated meteorite size for each crater alone is large enough to have
produced considerable global environmental stress, no horizons of mass
mortality or pulsed extinction are known to be associated with either crater
or their ejecta deposits. Thus, either there is no fixed relationship
between extinction magnitude and crater diameter, or a meteorite that would
produce a crater of >100-km diameter is required to raise extinction rates
significantly above a similar to 5% background level. Both impacts took
place similar to 1 - 2 m.y. before the 'Terminal Eocene Event' (= early
Oligocene pulsed extinction). Their collective long-term environmental
effects, however, may have either delayed that extinction pulse or produced
threshold conditions necessary for it to take place.



CCCMENU CCC for 1998

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