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
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