PLEASE NOTE:


*
Date sent:        Thu, 28 Aug 1997 16:29:55 -0400 (EDT)
From:             Benny J Peiser <B.J.PEISER@livjm.ac.uk
Subject:          NEW PUBLICATIONS
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

WAVE OF NEW PUBLICATIONS INDICATES SCIENTIFIC REVOLUTION IS UNDER WAY

You can be certain to be in the midst of a scientific revolution once
you realise that it is no longer possible to keep up with the stream of new
publications on the new paradigm - or when rash scholars start to dream
about a "unified model". This exactly is now the case with the theory of
cosmic catastrophism and the problem of assessing the according impact
hazard.

Four of the earliest contributors to this major intellectual
revolution and the main representatives of the British School of
Neo-Catastrophism, who usually advance in tandems, have now joined
forces and have published the main findings of more than 20 years of
astronomical and neo-catastrophist research as a quartett. Whilst this
intellectual transformation is currently sweaping through research centres
in Britain and the USA, it is no longer restricted to the British or
American academic world. What is more, even historical catastrophism seems
to have become part of the standard paradigm, as can be seen by Dr Izokh's
research on the catastrophe at the Pleistocene-Holocene boundary. The
attached papers, many of which come from the curent issue of the ANNALS OF
THE NEW YORK ACADEMY OF SCIENCES (Vol.822, 1997), document a wide variety of
research topics and will certainly cater for the diverse interest of list
members.
 

Benny J Peiser

P.S. Fred Hoyle and Chandra Wickramasinghe have also published a new
book: LIFE ON MARS? (London, 1997).

---------------------------------------------------------------------

S.V.M. Clube, F. Hoyle, W.M. Napier & N.C.Wickramasinghe: Giant
comets, evolution and civilization. In: ASTROPHYSICS AND SPACE
SCIENCE, 1996, Vol.245, No.1, pp.43-60

Giant comets thrown into short-period, Earth-crossing orbits are a
major source of mass flux into the inner planetary system. Their
disintegration products may give rise to climatic cycles, ice epochs,
periodic mass extinctions and other global disturbances. Comets
greater than or similar to 100 kilometres in diameter, in chaotic
orbits beyond Jupiter, probably constitute a more substantial current
hazard than stray asteroids.

----------------------------------------

E.P Izokh: Australo-Asian tektites and a global disaster of about
10,000 years BP, caused by collision of the Earth with a comet (in
Russian). In: GEOLOGIYA I GEOFIZIKA, 1997, Vol.38, No.3, pp.628-660

About 10,000 years ago, at the Pleistocene-Holocene border, some
important events occurred: the glaciation stopped abruptly; the sea
level elevated, and quick (for 20-50 years) climatic and ecological
changes took place, leading to the extinction of the so-called mammoth fauna
and exerting a direct effect on the mankind's evolution and appearance of
civilizations. These and other disastrous events providing a distinct
boundary between the Pleistocene and the Holocene received no relevant
explanation in the Quaternary geology until now. It is shown in the paper
that the disaster under study was caused by the collision of the Earth with
an eruptive comet, brought various volcanic tektite glasses from a remote
planetary body. This extra-terrestrial source of tektites is proven by the
well-known but not adopted paradox of tektite age, i.e. a difference in
hundreds of thousands and millions of years between the radiogenic age of
tektites (time of formation) and time of their fall onto the Earth. The
volcanic nature of tektites is supported (by analogy with volcanic bombs,
lavas, tufflavas, and extrusive formations taking into account
extraterrestrial conditions) by their long and many-stage formation, by
ordered trends of composition variability inherent only in magmatic
differentiation, etc. Relying on a diversity of forms, structure, and
composition of tektites, we made an attempt to reconstruct various types of
volcanic eruptions. Most likely, the place of volcanic activity was a small
or light planetary body of the type of Io, Callisto, Triton, etc. with ice
crust, acid upper and relatively basic lower mantle, with small gravitation,
without atmosphere, etc., situated somewhere on the periphery of the Solar
System. It is  supposed that a very powerful explosion ejected into space
some part of a stone-ice volcanic construction, i.e. eruptive comet,
according to S. K. Ysekhsvyatsky. The comet hypothesis permits explanation
of main features of distribution of tektites over the Earth's surface,
various forms of their connection with impact craters as well as many other
features of tektites. The common Earth impact hypothesis for tektite origin
is not able to explain all these facts; it is deeply perplexed and is
severely criticized in this paper. The 'mammoth' disaster is comparable with
the so-called 'dinosaur' catastrophe at the Cretaceous-Paleogene border,
which also was accompanied with impact craters and fall of tektites. An
analogy is traced with the collision of the Shoemaker-Levi comet with the
Jupiter. Thus, a special class of eruptive comets, cosmic bodies the most
dangerous for the Earth, which are beyond attention of investigators, is
discussed for the first time.

------------------------------------

D. K. Yeomans: Comet and asteroid ephemerides for spacecraft
encounters. In: CELESTIAL MECHANICS & DYNAMICAL ASTRONOMY, 1997,
Vol.66, No.1, pp.1-12

To a significant degree, the success of spacecraft missions to comets
and asteroids depends upon the accuracy of the target body
ephemerides. In turn, accurate ephemerides depend upon the quality of
the astrometric data set used in determining the object's orbit and
the accuracy with which the target body's motion can be modelled.
Using error analyses studies of the target bodies for the NEAR,
Muses-C, Clementine 2, Stardust, and Rosetta missions, conclusions are drawn
as to how to minimize target body position uncertainties at the times of
encounter. In general, these uncertainties will be minimised when the object
has a good number of optical observations spread over several orbital
periods. If a target body lacks a lengthy data interval, its ephemeris
uncertainties can be dramatically reduced with the use of radar Doppler and
delay data taken when the body is relatively close to the Earth. The
combination of radar and optical angle data taken at close Earth distances
just before a spacecraft encounter can result in surprisingly small target
body ephemeris uncertainties.

------------------------------------------------

S. J. Weidenschilling: The origin of comets in the solar nebula: A
unified model. In: ICARUS, 1997, Vol.127, No.2, pp.290-306

Comets originated as icy planetesimals in the outer Solar System, as
shown by dynamical studies and direct observation of objects in the
Kuiper disk, Their nuclei have low strength consistent with ''rubble
pile'' structure and inhomogeneities on scales of tens to hundreds of
meters. These properties can be explained by their formation process
in the solar nebula, I present results of numerical simulation of the
growth of cometesimals, beginning with a uniform mixture of
microscopic grains in the nebular gas. Coagulation and settling yield
a thin, dense layer of small aggregates in the central plane of the
nebula, Shear between this layer and the pressure-supported gas
produces turbulence that initially inhibits gravitational instability,
Particles grow by collisional coagulation; relative velocities are dominated
by radial motion due to orbital decay induced by gas drag, The radial
velocity dispersion further delays gravitational instability until the mean
particle size reaches tens of meters, Lack of damping in the swarm of
macroscopic particles limits gravitational instability to large scales that
do not allow collapse to solid bodies, Collisional coagulation is
responsible for growth even after instability occurs, The size distribution
of cometesimals growing by drag-induced collisions develops a narrow peak in
the range tens to hundreds of meters. This occurs because drag-induced
velocities decrease with size in this range, while gravitational focusing is
negligible, Impact velocities have a minimum at the transition from
drag-driven to gravitational accretion at approximately kilometer sizes,
Bodies accreted in this manner should have low mechanical strength and
macroscopic voids in addition to small-scale porosity, They will be composed
of structural elements hating a variety of scales, but with some tendency
for preferential sizes in the range similar to 10-800 m, These properties
are in good agreement with inferred properties of comets, which may preserve
a physical record of their accretion.

---------------------------------------

J. Powell, G. Maise, H. Ludewig, M. Todosow: High-performance
ultra-light nuclear rockets for near-earth objects interaction missions In:
ANNALS OF THE NEW YORK ACADEMY OF SCIENCES, 1997, Vol.822, pp.447-467

The performance capabilities and technology features of ultra compact
nuclear thermal rockets based on very high power density (30 Megawatts per
liter) fuel elements are described. Nuclear rockets appear particularly
attractive for carrying out missions to investigate or intercept near-Earth
objects (NEOs) that potentially could impact on the Earth. Many of these NEO
threats, whether asteroids or comets, have extremely high closing
velocities, i.e., tens of kilometers per second relative to the Earth.
Nuclear rockets using hydrogen propellant enable flight velocities 2 to 3
times those achievable with chemical rockets, allowing interaction with a
potential NEO threat at a much shorter time, and at much greater range. Two
versions of an ultra compact nuclear rocket based on very high heat transfer
rates are described: the PBR (Particle Bed Reactor), which has undergone
substantial hardware development effort, and MITEE (MIniature ReacTor
EnginE) which is a design derivative of the PBR. Nominal performance
capabilities for the PBR are: thermal power similar or equal to 1000 MW
thrust similar or equal to 45,000 lbsf, and weight similar or equal to 500
kg. For MITEE, nominal capabilities are: thermal power 100 MW; thrust
similar or equal to 4500 lbsf, and weight similar or equal to 50 kg.
Development of operational PBR/MITEE systems would enable spacecraft
launched from LEO (low-Earth orbit) to investigate intercept NEO's at a
range of similar to 100 million kilometers in times of similar to 30 days.

------------------------------

M.R. Rampino, B. M. Haggerty, T.C. Pagano: A unified theory of impact
crises and mass extinctions: Quantitative tests. In: ANNALS OF THE NEW YORK
ACADEMY OF SCIENCES, 1997, Vol.822, pp.403-431

Several quantitative tests of a general hypothesis linking impacts of
large asteroids and comets with mass extinctions of life are possible
based on astronomical data, impact dynamics, and geological
information. The waiting times of large-body impacts on the Earth
derived from the flux of Earth-crossing asteroids and comets, and the
estimated size of impacts capable of causing large-scale environmental
disasters, predict that impacts of objects greater than or equal to 5 km in
diameter (greater than or equal to 10(7) Mt TNT equivalent) could be
sufficient to explain the record of similar to 25 extinction pulses in the
last 540 Myr, with the 5 recorded major mass extinctions related to impacts
of the largest objects of greater than or equal to 10 km in diameter
(greater than or equal to 10(8) Mt events). Smaller impacts (similar to
10(6) Mt), with significant regional environmental effects, could be
responsible for the lesser boundaries in the geologic record. Tests of the
''kill curve'' relationship for impact-induced extinctions based on new data
on extinction intensities, and several well-dated large impact craters, also
suggest that major mass extinctions require large impacts, and that a step
in the kill curve may exist at impacts that produce craters of similar to
100 km diameter, smaller impacts being capable of only relatively weak
extinction pulses. Single impact craters less than similar to 60 km in
diameter should not be associated with detectable global extinction pulses
(although they may explain stage and zone boundaries marked by lesser faunal
turnover), but multiple impacts in that size range may produce significant
stepped extinction pulses. Statistical tests of the last occurrences of
species at mass-extinction boundaries are generally consistent with
predictions for abrupt or stepped extinctions, and several boundaries are
known to show ''catastrophic'' signatures of environmental disasters and
biomass crash, impoverished postextinction fauna and flora dominated by
stress-tolerant and opportunistic species, and gradual ecological recovery
and radiation of new taxa. Isotopic and other geochemical signatures are
also generally consistent with the expected after-effects of catastrophic
impacts. Seven of the recognized extinction pulses seem to be associated
with concurrent (in some cases multiple) stratigraphic impact markers (e.g.,
layers with high iridium, shocked minerals, microtektites), and/or large,
dated impact craters. Other less well-studied crisis intervals show elevated
iridium, but well below that of the K/T spike, which might be explained by
low-Ir impactors, ejecta blowoff, or sedimentary reworking and dilution of
impact signatures. The best explanation for a possible periodic component of
similar to 30 Myr in mass extinctions and clusters of impacts is the
pulselike modulation of the comet flux associated with the solar system's
periodic passage through the plane of the Milky Way Galaxy. The quantitative
agreement between paleontologic and astronomical data suggests an important
underlying unification of the processes involved.

--------------------------------------

J.M. Greenberg & J.L.Remo: Comets as porous aggregates of interstellar dust.
In: ANNALS OF THE NEW YORK ACADEMY OF SCIENCES, 1997, Vol.822, pp.96-117

A comet model is derived based on the interstellar dust chemical
composition in dense molecular and diffuse clouds resulting from their
subsequent chemical interactions and UV photoprocessing. The collapsing
presolar nebula leads to a porous aggregate model for comet nuclei, from
which is derived certain physical properties that include thermal
conductivity and tensile strength. The porous morphological structure is
also shown to imply anomalous (expansion rather than contraction) behavior
when subjected to strong shock waves, which is supported by recent shock
experiments on (porous) carbonaceous chondrite material.

-----------------------------------------------------------

P.R. Weissman: Long-period comets and the oort cloud. In: ANNALS OF
THE NEW YORK ACADEMY OF SCIENCES, 1997, Vol.822, pp.67-95

The long-period comets pose a unique problem for the impact hazard
problem. Because of their very long orbital periods and generally
large distances from the Sun, they cannot be surveyed and catalogued
in the same manner as the near-Earth asteroids and short-period
comets. They appear at random, uniformly distributed on the celestial
sphere. Current technologies can detect long-period comets at
distances of similar to 5 AU, giving somewhat less than a one year
warning time for potential Earth impactors. The mean impact
probability for a long-period comet crossing the Earth's orbit is 2.2
to 2.5 x 10(-9) per perihelion passage. The mean impact velocity is
similar to 52 km sec(-1), but the most probable impact energy is
characterized by a velocity of 56 to 58 km sec(-1). The estimated
current impact rate for cometary nuclei large enough to create 10 km
diameter (or larger) craters on the Earth is between 5 x 10(-7) and
2.8 x 10(-6) per year, with a best estimated value of 1.0 x 10(-6) per year.
Nuclei large enough to initiate global climatic disturbances strike the
Earth, on average, every 16 Myr. The impact frequency may be increased
substantially for brief periods of time during cometary showers, initiated
by major perturbations of the Oort cloud. Improved technologies are needed
to detect approaching long-period comets at large heliocentric distances so
as to increase the warning time for potential impactors.

---------------------------------------------------

B.G. Marsden: Overview of orbits. In: ANNALS OF THE NEW YORK ACADEMY
OF SCIENCES, 1997, Vol.822, pp.52-66

After a brief summary of the distribution of both large and small
bodies in the solar system, there follows a categorization of the
various hazards from comets and asteroids, the concept of PHA, or
''potentially hazardous asteroid,'' being introduced to include one
that is large enough and can pass close enough to the Earth's orbit
that it might conceivably yield a globally-damaging impact in the
forseeable furture. Future search stragtegies are discussed, as they
involve increasing both sky coverage and faintness limit, arguments
being given for ensuring much fainter detections in the general
opposition region than at much smaller elongations. It is concluded
that a proposed ''impact hazard scale'' is generally less useful than
recognition of the PHA status. The current situation with regard to
follow-up astrometric activity, particularly by amateur astronomers,
is viewed favorably, but professional search activity is at a
depressingly low level.

-----------------------------------------------------

D. Steel: Meteoroid orbits: Implications for near-earth object search
programs. In: ANNALS OF THE NEW YORK ACADEMY OF SCIENCES, 1997,
Vol.822, pp.31-51

The available orbital database on macroscopic potential impactors of
our planet (asteroids and comets, collectively near-Earth objects or
NEOs) numbers less than one thousand, whereas there have been some
hundreds of thousands of orbits of Earth-impacting meteoroids
determined in various surveys, mostly using meteor radars. If one
assumes that NEOs have orbital characteristics broadly similar to
meteoroids, then the orbits of the latter can give important
indications concerning the conduct of search programs designed to
discover large NEOs well ahead of any catastrophic impact, allowing
ameliorative action to be taken. For smaller NEOs that cannot be
telescopically detected until the day or so before impact, the radiant
distribution of observed meteors shows the regions of the sky from which
impactors are most likely to emanate. It is shown that the vast majority of
meteoroids striking the Earth have geocentric (apparent) radiants within two
near-ecliptic regions a few tens of degrees wide and centered on longitudes
+/- 90 degrees from the apex of the Earth's way (the so-called helion and
anti-helion sources). These are bodies with low inclinations, large
eccentricities (e = 0.7 - 0.9) and quite small semimajor axes (mostly a =
1.3 - 2.5 AU). After allowing for the terrestrial motion about the Sun
(conversion to the true radiant), the longitudes are around +/- 120 degrees
from the apex. For a ground-based search on the nightside, the best search
region is that within similar to 20 degrees of the are joining the
geocentric and true radiants (longitudes 90 degrees and 120 degrees). On the
dayside, proximity to the solar direction argues for a space-based
surveillance program, if small NEOs are to be found just prior to impact.

-------------------------------------------------

E.F. Helin, S.H. Pravdo, D.L. Rabinowitz, K.J. Lawrence: Near-earth
asteroid tracking (NEAT) program. In: ANNALS OF THE NEW YORK ACADEMY
OF SCIENCES, 1997, Vol.822, pp.6-25

The discoveries of near-Earth asteroids (NEAs) and comets have
increased enormously over the last 10-20 years. This is a consequence, in
large part, of the success of programs that have systematically searched for
these objects. These programs have been motivated by the relationships of
NEAs to terrestrial impacts, meteorites, comets, and their relative
accessibility to spacecraft missions. This paper will review the long-term
Palomar Planet-Crossing Asteroid Survey (PCAS), a photographic program, and
the current Near-Earth Asteroid Tracking (NEAT) system, NASA's new
electronic detection program. The primary goal of NEAT is to discover and
inventory near-Earth asteroids and comets, collectively called near-Earth
objects or NEOs, larger than 1 km in size. Details of the NEAT system and
program results are presented and discussed.



*
Date sent:        Thu, 28 Aug 1997 13:27:58 -0400 (EDT)
From:             Benny J Peiser <B.J.PEISER@livjm.ac.uk
Subject:          MOROKWENG IMPACT CRATER
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

NEW STUDY ON MOROKWENG IMPACT CRATER (SOUTH AFRICA)

R. J. Hart, M. A. G. Andreoli, M. Tredoux, D. Moser, L. D.
Ashwal, E. A. Eide, S. J. Webb, D. Brandt: Late Jurassic age for
the Morokweng impact structure, southern Africa. In: EARTH AND
PLANETARY SCIENCE LETTERS, 1997, Vol.147, No.1-4, pp.25-35

A roughly 70 km diameter circular feature buried beneath the
Kalahari sands in South Africa is revealed on regional
aeromagnetic maps. Boreholes drilled into the centre of the
structure intercept a similar to 250 m thick sheet of quartz
norite, interpreted as an impact melt, which overlies
brecciated and shock; metamorphosed basement granite, Zircons
recovered from the quartz norite, yield U-Pb ages of 145 +/-
0.8 Ma, and biotites provide Ar-Ar ages of 144 +/- 4 Ma, These
data provide strong evidence for the occurrence of a Late
Jurassic impact crater (the Morokweng impact structure)
similar to 100 m beneath the surface.



*
Date sent:        Thu, 28 Aug 1997 10:14:20 -0400 (EDT)
From:             Benny J Peiser <B.J.PEISER@livjm.ac.uk
Subject:          Looking for videos
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

from: Mark Davis <MeteorObs@charleston.net

To all you video observers:

I was contacted by the television "network" here in the U.S.
known as The Learning Channel. Thay are producing a 5 part
documentary on manmade and natural disasters that face the
planet. One session will be on the threat posed by asteroids,
comets, etc. Part of the show will discuss fireballs and
meteorites.

They are looking for footage of fireballs to use in addition
to what they have now (the video from 1972 and from
Peekskill). If anyone has some footage that the LC might be
interested in, you can contact me via email and I will pass on
to you their contact point.

Mark Davis, MeteorObs@charleston.net
Mt. Pleasant, South Carolina, USA
Coordinator, North American Meteor Network
Assistant Coordinator, ALPO Meteors Section
===================================================
 Visit the NAMN home page at:
  http://medicine.wustl.edu/~kronkg/namn.html
===================================================



CCCMENU CCC for 1997

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