PLEASE NOTE:


*
Date sent:        Tue, 27 Jan 1998 10:36:24 -0500 (EST)
From:             Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject:          CC-DIGEST, 27/01/98
To:               cambridge-conference@livjm.ac.uk
Priority:         NORMAL

CAMBRIDGE-CONFERENCE NETWORK
----------------------------

The cambridge-conference e-mail list is a scholarly electronic
network organised by Dr Benny J Peiser at Liverpool John Moores
University, United Kingdom. It is the aim of this network to
disseminate the latest information and research findings related
to i) the geological and  historical neo-catastrophism, ii) NEO
research and the hazards to civilisation due to comets and
asteroids, and iii) the development of a planetary civilisation
capable of protecting itself against cosmic disasters. For further
information about this network and how to subscribe, please
contact b.j.peiser@livjm.ac.uk .

Information circulated on the cambridge-conference network is for
scholarly and educational use only. The attached information may
not be copied or reproduced for any other purposes without prior
permission of the copyright holders.

=========================================
CAMBRIDGE-CONFERENCE DIGEST, 27 January 1998

(1) DON'T WORRY BOB: THE PROBABILITY OF CIVILISATION THREATENING
    IMPACTS IS VERY LOW

(2) LUNAR OBSERVATIONS CAST DOUBT ON FRANK'S SMALL-COMET THEORY

(3) MORE DOUBTS ABOUT SMALL-COMET HYPOTHESIS

(4) EVEN MORE DOUBTS ABOUT SMALL-COMETS

(5) SORRY ABOUT OUR TECHNOLOGY, BUT IMAGES ON FRANK'S FILMS ARE NOT
    REAL OBJECTS BUT DUE TO FAULTY CAMERAS

(6) AN ALTERNATIVE HYPOTHESIS: DO METEORIC IMPACTS IN ATMOSPHERE CAUSE
    'BLACK SPOTS' ON LUIS FRANK'S FILMS?

(7) AND FINALLY: GREEN PROPHETS OF DOOM IN SUDDEN MOOD SWING

==========================

(1) DON'T WORRY BOB: THE PROBABILITY OF CIVILISATION THREATENING
    IMPACTS IS VERY LOW

Commentary on the Remarks of Bob Kobres (Jan. 23, 1998)

From:  Clark R. Chapman, Southwest Research Institute
 cchapman@boulder.swri.edu

I respect the views of people who, like Bob Kobres, believe that
there is great urgency in dealing with the impact hazard because
the *stakes are so high*. But I do not share his views. Other
people, including myself, believe that because the *probability is
so low* (of a *globally* catastrophic event), it subtracts from
such a dramatic sense of urgency as espoused by Kobres.  This is
particularly so because there are so many destructive things that
truly will and do happen frequently that we can devote society's
resources to mitigate. Mounting effective mitigation against
cosmic impacts on the time scale of a decade or a century makes
increasing sense over, say, a crash program in the next year,
because the probability of catastrophe -- though still small --
becomes 10 or 100 times greater on those time scales. That is my
view. On the other hand, in the face of the extreme ultimate
consequences of such an impact, it is difficult for me to
confidently assert that the more alarmist view of Kobres is wrong.

What I respect less in Kobres' essay is the appearance that it is
funding ("green slime") that underlies his desire for us to change how we
speak of the hazard.  If there is anything scientists and knowledgeable
lay-people interested in this topic need to nurture, it is their
credibility. I think it is very important that we be objective in reporting
the scientific facts, including the stakes and the probabilities.  We are
free, as citizens, also to comment on how we personally evaluate these
facts, in the light of our own values, but we should make it clear that
these are just our individual value judgements.  I, for one, think that
Kobres' quote from Duncan Steel is not only "not wrong" but is a fine way to
express the realities of the impact hazard.

I want to add that I think the objective facts are clear that much
smaller impacts, like Tunguska, objectively deserve only modest
attention because -- whatever one believes about the rates and
constancy or inconstancy of their occurrences -- such impacts (a) lack the
finality (with regard to human civilization) of the bigger ones and (b) they
occur *much* less frequently than other natural disasters that have similar
consequences, for which we are doing rather less than we might in cost-
effective mitigation measures.

====================================================
(2) LUNAR OBSERVATIONS CAST DOUBT ON FRANK'S SMALL-COMET THEORY

J.A. Grier & A.S. McEwen: The small-comet hypothesis: An upper limit to the
current impact rate on the Moon. GEOPHYSICAL RESEARCH LETTERS, 1997, Vol.24,
No.24, pp.3105-3108

UNIVERSITY OF ARIZONA, LUNAR & PLANETARY LAB, TUCSON,AZ,85721

Frank et al. [1986b] and Frank and Sigwarth [1993] hypothesized the
intense bombardment of the terrestrial atmosphere by small comets.
Their model requires that the Moon is impacted by small comets
(10(7)-10(8) g) at a rate of almost one per minute. We calculate that
an object of this mass, even with an exceedingly low density and
relatively low velocity, will nevertheless produce a crater at least 50 m in
diameter. These craters will excavate immature lunar soil and produce a very
bright spot with a diameter df at least 150 m. If low-density comets exist
that might not create deep craters [O'Keefe and Ahrens, 1982], they will
nevertheless disturb the regolith sufficiently to create detectable bright
spots. If the small-comet hypothesis is correct then the near-global lunar
imaging returned by Clementine in 1994 should reveal similar to 10(7) bright
spots in locations where craters are not present in images acquired in the
1960's and early 1970's. We find no new bright limit to the current
cratering rate by small comets is 33/yr, similar to 10(4) below that
expected if the small-comet hypothesis were valid. Copyright 1998, Institute
for Scientific Information Inc.

===================================
(3) MORE DOUBTS ABOUT SMALL-COMET HYPOTHESIS

B. Rizk & A.J. Dessler: Small comets: Naked-eye visibility
GEOPHYSICAL RESEARCH LETTERS, 1997, Vol.24, No.24, pp.3121-3124

UNIVERSITY OF ARIZONA, LUNAR & PLANETARY LAB, TUCSON, AZ, 85721

We investigate an obvious consequence of the small-comet hypothesis. We find
that the 30-ton cloud of water-ice particles formed by a small comet would
survive long enough to be an unmistakably bright object. The visual
magnitude of such clouds would be between that of a bright star and the full
Moon. A whole-Earth small-comet flux of 20/min implies the sudden appearance
of at least two bright patches of light every five minutes. The two-hour
periods after sunset and before sunrise ought to produce the most
spectacular sightings - intermittent punctuations of bright rapidly-moving
points of light. Because such events are not reported, we conclude that this
class of object does not exist in detectable numbers. Copyright 1998,
Institute for Scientific Information Inc.

=================
(4) EVEN MORE DOUBTS ABOUT SMALL-COMETS

T.D. Swindle & D.A. Kring: Implications of small comets for the noble
gas inventories of Earth and Mars. GEOPHYSICAL RESEARCH LETTERS, 1997,
Vol.24, No.24, pp.3113-3116

UNIVERSITY OF ARIZONA, LUNAR & PLANETARY LAB, 1629 E UNIV BLVD, TUCSON, AZ,
85721

Frank et al. [1986a,b] proposed the possibility of large numbers of
small comets impacting the Earth. Using the parameters for the small
comets suggested by Frank and Sigwarth [1993], we find that, over the
lifetime of the solar system, such small comets would deliver far more Ar,
Kr, and Xe to the atmospheres of Earth and Mars than those atmospheres
presently contain if, as Frank and Sigwarth [1993] assumed, the small comets
formed in very cold regions far from the Sun. Comets can be greatly depleted
in noble gases if they form relatively close to the Sun (for example, near
Jupiter), but this source region is inconsistent with other features of the
proposed model. Alternatively, if the comets did form in very cold regions
far from the Sun, the current flux would have to be at least a factor of
30,000 higher than the long-term average. Copyright 1998, Institute for
Scientific Information Inc.

===============================
(5) SORRY ABOUT OUR TECHNOLOGY, BUT IMAGES ON FRANK'S FILMS ARE NOT
    REAL OBJECTS BUT DUE TO FAULTY CAMERAS

G. Parks*), M. Brittnacher, L.J.Chen, R. Elsen, M. McCarthy,
G. Germany & J. Spann: Does the UVI on polar detect cosmic snowballs?
GEOPHYSICAL RESEARCH LETTERS, 1997, Vol.24, No.24, pp.3109-3112

*) UNIVERSITY OF WASHINGTON, GEOPHYS PROGRAM, BOX 351650,
SEATTLE, WA, 98195

If 20 to 40 ton cosmic snowballs pelt Earth as claimed by Frank and
Sigwarth [1997a], dark pixels will be produced in the 130.4 nm images
of dayglow obtained by the Ultraviolet Imager (UVI) on the Polar
spacecraft. Examination of the UVI images has revealed that dayglow
images are indeed spotted with single and multiple dark pixels. But is a
snowball the only explanation for these dark pixels? To learn more about the
dark pixels, we have examined the calibration images obtained from the same
camera just before the instrument was launched. We find that dark pixels
similar to those in dayglow images also exist in calibration images. This
strongly indicates that the source of the dark pixels is instrumental. For
further verification, a statistical analysis found the dark pixels from
dayglow and calibration images have nearly identically shaped occurrence
patterns. We have also looked for evidence of spacecraft 'wobble' which
demonstrates that the source of a bright or dark feature in the images is
external to the camera, but found none for dark pixels. Finally, we studied
the bright streaks that frequently appear in UVI images, sometimes
comet-like in appearance. These trails are ionization tracks produced by
cosmic rays or other penetrating energetic particles interacting with our
camera. We conclude that the source of the dark pixels in dayglow images is
internal to the camera system and there is no scientific evidence from UVI
that snowballs pelt Earth. Copyright 1998, Institute for Scientific
Information Inc.

==============================
(6) AN ALTERNATIVE HYPOTHESIS: DO METEORIC IMPACTS IN ATMOSPHERE CAUSE
    'BLACK SPOTS' ON LUIS FRANK'S FILMS?

M.B.E. Boslough & G.R. Gladstone: An impact plume model for atmospheric
holes in the FUV dayglow. GEOPHYSICAL RESEARCH LETTERS, 1997, Vol.24, No.24,
pp.3117-3120

SANDIA NATIONAL LABS, MS 0820, POB 5800, ALBUQUERQUE, NM, 87185

A transient decrease in FUV dayglow emission from a similar to 10(3)
km(2) region of Earth's upper atmosphere is one expected outcome of the
collision of a stony meteoroid as small as 50 cm in diameter. Computational
models of the entry of projectiles between 210 and 21,000 kg predict the
ejection of low-density plumes of air from the stratosphere and mesosphere
at velocities of up to 5 km/s. The plumes reach an altitude of over 1000 km,
displacing the atomic O-rich thermosphere, and replacing it with
photoelectron-and O-poor air from beneath 80 km. The FUV dayglow is normally
dominated by O emissions so the plume appears as a dark spot when viewed
from above. FUV dayglow holes are reported at rates similar to 10(4)-10(6)
larger than the impact flux of objects in the sie range modeled here,
suggesting either 1) the observed rate is greatly overestimated, 2) there is
an additional mechanism, or 3) much smaller impactors (which we have not
modeled) can also generate FUV darkening plumes. Copyright 1998, Institute
for Scientific Information Inc.

======================

(7) AND FINALLY: GREEN PROPHETS OF DOOM IN SUDDEN MOOD SWING

From: NEW SCIENTIST, 24 January 1998

THERE MAY BE A FUTURE AFTER ALL

It was about as likely as the US cutting its carbon dioxide emissions
or the world's farmers renouncing pesticides. Lester Brown, president
of the Worldwatch Institute in Washington, DC and one of the
environmental movement's leading doom merchants, has surprised the
world by lightening up.

Each year for the past 14 years, Brown has forecast gloabl disaster as the
demand for natural resources outstripped supply. But the institutes latest
annual audit of the Earth's ecological health, State of the World 1998, he
claims there are signs of hope. Large corporations such as British Petroleum
and Toyota are beginning to adopt strategies for sustainable development,
while countries like China and Denmark are making major advances in energy
efficiency. The world's $2-billion wind power business is growing by 25 per
cent a year, compared with 1 per cent annual increases in the coal and oil
markets. Brown even suggests that the world could be on the brink of an
environmental revolution comparable to the overthrow of state communism in
Europe in 1990.

The new-found optimism, however, does not prevent him from sounding his
usual dire warnings. "If the world economy as it is now structured continues
to expand, it will eventually destroy its natural support system," he says.

Rob Edwards.
------
The permission by the Editor of the NEW SCIENTIST to post this
article for scholarly use on the cambridge-conference network is
greatfully acknowledged.



CCCMENU CCC for 1998

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