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Cambridge-Conference Digest - January 20, 1998

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 

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 

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.