PLEASE NOTE:


*

CCNet 97/2000 - 28 September 2000
---------------------------------


     "Ah well, without 1997 XF11, where would we be today? Would NASA have
established its NEO Office and increased its NEO funding? Would we have LINEAR and
Spaceguard initiatives around the world? And finally, and more to home, would both
Houses of Parliament have debated the impact hazard and would the UK Government,
subsequently, have set up the NEO Task Force; indeed, would we have the NEO Task
Force Report without the XF11 Affair? I somehow doubt it.
       -- Benny J Peiser



(1) LIFE-ON-MARS HOPES DENTED BY METEORITE CONTAMINATION
    SpaceDaily, 27 September 2000

(2) WORSENING URBAN AIR POLLUTION WON'T INCREASE GLOBAL TEMPERATURE OVER
NEXT 100 YEARS
    Ketrina Jackson <kjackson@nsf.gov>

(3) A GLOBAL TSUNAMI IN 200 AD?
    D.J. Lowe & W.P. de Lange

(4) NATURE AND DESTRUCTION OF THE TUNGUSKA COSMICAL BODY
    V.A. Bronshten

(5) RE-EVALUATION OF THE CAUSE & LOCALIZATION OF THE LATE LUNAR BOMBARDMENT
    G. Arrhenius & A. Lepland

(6) NEW 2.5 KM IMPACT STRUCTURE DISCOVERED IN NW AUSTRALIA?
    J.D. Gorter & S.W. Bayford

(7) CAN SELF-ORGANISED TUNGUSKAS PREVENT THE BIG ROCK?
    B.D. Malamud & D.L. Turcotte

(8) NATURAL HAZARDS: SOCIOPOLITICAL AND HUMANITARIAN CONSIDERATIONS
   J.V. Smith
 
(9) MICKEY MOUSE SCIENCE:
    HOW WALT DISNEY'S ACCOUNT OF THE XF11 AFFAIR IS FOSTERING AN URBAN MYTH
    Benny J Peiser <b.j.peiser@livjm.ac.uk>

(10) 1946 TSUNAMI
     Michael Paine <mpaine@tpgi.com.au>

(11) MEA CULPA!
     Phil Plait <badastro@badastronomy.com>

(12) INVENTION OF IMPACT CRATERING
     Duncan Steel <D.I.Steel@salford.ac.uk>

(13) MOON HAS SQUARE CRATERS TOO
     Ian Tresman <ian@knowledge.co.uk>

=================
(1) LIFE-ON-MARS HOPES DENTED BY METEORITE CONTAMINATION

From SpaceDaily, 27 September 2000

PARIS (AFP) - September 27th, 2000 - Suggestions that life, or the potential
for it, existed on Mars have been dealt a blow by a new question mark that has been
placed over one of the main pieces of evidence -- Martian meteorites found in
Antarctica. Of the 15 Martian meteorites so far retrieved on Earth, six have been found in the dry
valleys of Antarctica.

The most famous one, ALH-84001, found in 1984 in the Allan Hills, sparked
worldwide headlines in 1996 when a NASA team declared its microscopic grooves had been
gouged by microorganisms on the Red Planet 3.6 billion years earlier.

That theory has since been repeatedly attacked by other scientists who
suggested the grooves could have been simply caused by a chemical process or by Earth
bacteria.

Another argument for the meteorites was that they hold high sulphur ratios
and atmospheric gases -- including an isotope of oxygen that, it was suggested,
became trapped in magma billions of years ago when the Martian atmosphere reacted
with water.

But, say a team led by Huiming Bao of the University of California at San
Diego, the meteorites may have been contaminated by the peculiarly salty soils of
dry-valley Antarctica.

An analysis of those soils shows them to have extremely high levels of the
same oxygen isotope, the researchers say.

The isotope was derived from a reaction long ago between the atmosphere and
local gaseous sulphur compounds, they believe. The isotope was then deposited by
precipitation onto surface rock.

The results were found among samples far inland, which ruled out airborne
particles of sea salt as the source for the sulphur compound.

The data "suggests a possibility that anomalous isotopic signatures detected
on meteorites could come from terrestrial contamination," the scientists say, publishing
their work in Thursday's issue of Nature.

ALH-84001, about the size of a potato, landed in Antarctica around 13,000
years ago, presumably after it had been knocked off Mars by a colliding space wanderer
such as an asteroid. Martian meteorites have been identified as such because their
chemical profile matches that of rocks analysed by US space probes.

NASA announced on June 22 it had found photographic evidence of the recent
presence of water on Mars, a discovery said to have resounding implications for the
prospect of life on the planet.

All rights reserved. © 2000 Agence France-Presse.

==================
(2) WORSENING URBAN AIR POLLUTION WON'T INCREASE GLOBAL TEMPERATURE OVER
NEXT 100 YEARS

From Ketrina Jackson <kjackson@nsf.gov>

Media Contact:
September 27, 2000
Cheryl Dybas
NSF PR 00-66
(703) 292-8070/cdybas@nsf.gov

Program Contact:
Anne-Marie Schmoltner
(703) 292-8522/aschmolt@nsf.gov


          WORSENING URBAN AIR POLLUTION WON'T INCREASE
             GLOBAL TEMPERATURE OVER NEXT 100 YEARS
                               
       Researchers funded in part by the National Science
Foundation (NSF) and affiliated with the Massachusetts
Institute of Technology have found that although urban air
pollution is expected to increase significantly in the coming
century, it will not have a big effect on global temperature
change.

     While there may be temperature increases in certain regions,
global mean surface temperature will not go up significantly
because of urban air pollution, researchers at MIT's Joint
Program on the Science and Policy of Global Change wrote in a
paper to be published in the September 27 issue of the Journal of
Geophysical Research--Atmospheres.

     "It is very important to understand the interplay between
air quality and climate, and recent advances in coupled chemistry
climate models make that possible," says Anne-Marie Schmoltner,
program director in NSF's division of atmospheric sciences.
"Changes in air quality could affect global climate, and
conversely, climate change could affect air quality.  The results
presented by the MIT group provide insight into these complex
interactions."

     Using a method that allows global coupled-chemistry climate
models to take urban air pollution into account in a new way, MIT
researchers found that compared to a reference run excluding
urban air pollution, the average tropospheric ozone concentration
decreases while high concentrations of ozone are projected in the
urban areas. As a consequence of the change
in the chemical composition of the troposphere, the lifetime
of methane increases. This leads to higher ambient methane
concentrations, even if emissions are unaltered.

     "People thought things would go in this direction, but
they couldn't quantify it before," said Monika Mayer,
research scientist at MIT and lead author on the paper,
"Linking local air pollution to global chemistry and climate."
                               
    While scientists agree that urban air pollution can alter
concentrations of greenhouse gases such as ozone in the
troposphere, they have left the complicated chemistry of
urban air pollution out of global climate models.
"Global-scale models that do not take into account urban
areas' highly nonlinear atmospheric chemistry most likely
overestimate tropospheric ozone production due to
unreasonably high background nitric oxide concentrations,"
the authors write.
                               
    Yet, "high-resolution climate models don't have chemistry
coupled to them," said Mayer. "It takes months just to run a
global climate model without the chemistry."

     Population projections show that in the next 100 years,
the concentration of people in urban areas will increase
dramatically. While 30-40 percent of air pollution currently
comes from urban areas, as much as 70 percent may originate
from cities in the future. The researchers carried out three
simulations of 100year projections that factored in the
effects of increased urban air pollution tied to population
increases and economic development in these areas. They found
that even with significant increases in air pollution, global
mean temperature should not change much, although there may be
more pronounced regional effects.

=================
(3) A GLOBAL TSUNAMI IN 200 AD?

D.J. Lowe & W.P. de Lange: Volcano-meteorological tsunamis, the c. AD 200
Taupo eruption (New Zealand) and the possibility of a global tsunami.
HOLOCENE 10: (3) 401-407 MAY 2000

Meteorological tsunamis are long-period waves that result from
meteorologically driven disturbances. They are also generated by phase
coupling with atmospheric gravity waves
arising through powerful volcanic activity. The AD 1883 Krakatau eruption
generated volcano-meteorological tsunamis that were recorded globally. Because of its
extreme violence and energy release (greater than or equal to 150 +/- 50 megatons explosive
yield), and by analogy with the Krakatau event, it is highly possible that the
ignimbrite-emplacement phase of the c. AD 200 Taupo eruption of North Island, New Zealand,
generated a similar volcano-meteorological tsunami that may have reached coastal areas
worldwide. Tsunami deposits of identical age to the Taupo eruption occur in
central coastal New Zealand and probably
relate to that event; definitive evidence elsewhere has not yet been found.
In theory, volcano-meteorological tsunamis are likely to be produced during comparable
eruptive events at other explosive volcanoes, and thus represent an additional
volcanic hazard at coastal sites far from source. We suggest that evidence for such tsunamis,
both for marine and lacustrine environments, may be preserved in geological records, and
that further work searching for this evidence using a facies approach is
timely.

Addresses:
Lowe DJ, Univ Waikato, Dept Earth Sci, Private Bag 3105, Hamilton 2001, New
Zealand.
Univ Waikato, Dept Earth Sci, Hamilton 2001, New Zealand.

Copyright © 2000 Institute for Scientific Information

===============
(4) NATURE AND DESTRUCTION OF THE TUNGUSKA COSMICAL BODY

V.A. Bronshten: Nature and destruction of the Tunguska cosmical body
PLANETARY AND SPACE SCIENCE 48: (9) 855-870 AUG 2000

The problem of the nature of the Tunguska Cosmical Body (TCB) is closely
related to the mechanism of its disintegration which ended with an explosive disburse. The
only hypothesis capable of explaining such a process is the idea that TCB
was a fragment of a comet. Three alternative hypotheses are considered here.
They assume the TCB to be: (i) a fragment of a
stony asteroid; (ii) a porous snowball; and (iii) a plasmoid. It is shown
that the first of them is not plausible because the fragmentation and explosion of an asteroid
should result in the scattering of numerous fragments over the ground. They, however, have
not been found on the terrain for many years by many tens of explorers who
have carried out a cartful analysis of the soil and peat. Bodies like a
porous snowball or a plasmoid cannot exist in the Solar
system (they should be unstable). The history of the cometary hypothesis is
followed in the article, starting from its original formulation in a book by
the well-known astrophysicist H. Shapley (1930. Flights from Chaos. A Survey
of Material Systems from Atoms to Galaxies. N.Y.: McGraw-Hill, p. 57-58.
Russian translation: From Atoms to Milky Ways. Moscow: ONTI, 1934),
who has priority over F. J. W. Whipple [the latter having put this
hypothesis 4 years later (Whipple, 1934. On phenomena related to the Great
Siberian meteor. Quart. Journ. of the Roy. Meteorol. Sec. 60, 505-513)].
Simultaneously with the evolution of this hypothesis our ideas
of the structure of cometary nuclei have also varied. Estimates of the main
parameters of the TCB - its initial mass m, initial velocity v and energy of explosion E-e -
are examined. The following quantities are assured to be the most plobable:
m = 2 x 10(6) t, v = 31 km/s, E-e = 5 x 10(23) erg. The mentioned value of v corresponds to the
Zotkin-Kresak hypothesis that the TCB was a fragment of the Encke comet. Sekanina's criticism against
this hypothesis is examined. During recent years, three analytical theor ies of the
sequential disintegration of large bodies in the atmosphere have bern put forward by Grigoryan (1979:
Motion and disintegration of meteorites in the planetary atmospheres. Cosmic
Res. 17(6), 875-893), Hills and Goda (1993. The fragmentation of small asteroids in the atmosphere.
Astron. J. 105(3) 1114-1144) (their theory is physically equivalent to
Grigoryan's theory), and by Chyba et al. (1993. The Tunguska 1908 explosion:
atmospheric disruption of a stony asteroid. Nature, 36 (1) 40-44.). The
comparison of all the three theories is presented. It is shown that the
theory of Chyba et al. overestimates the altitudes of disruption of the
meteoroid compared to other theories. The results of the numerical
simulations of the process in the free-Lagrangian and the Eulerian
approximation (Svettsov V.V., Nemchinov I.V., Teterev A.V., 1995.
Disintegration of large meteoroids in Earth's atmosphere: theoretical
models. Icarus 116, 131-153) are also analysed.
The results of numerous studies examined either do not contradict the
cometary hypothesis of the TCB nature or the discrepancies (e.g. in the case of Chyba et al., 1993)
can simply be explained. An interpretation is presented fur the anomalous
sky glow observed after the TCB fall, west of the treefall epicenter, in Russia and in West Europe. It was
first put forward by the author (Bronshten, 1991. Nature of the anomalous illumination of the
sky related to the Tuuguska event. Solar System Res. 25(4), 490 504) and considers the
secondary scattering of solar light by the dust of the head of the comet that entered the Earth's
atmosphere simultaneously with the TCB. (C) 2000 Elsevier Science Ltd. All
rights reserved.

Addresses:
Bronshten VA, 16-130 Varshavskoye Shosse, Moscow 113105, Russia.
Russian Acad Sci, Comm Meteorites, Moscow 117975, Russia.

Copyright © 2000 Institute for Scientific Information

================
(5) RE-EVALUATION OF THE CAUSE & LOCALIZATION OF THE LATE LUNAR BOMBARDMENT

G. Arrhenius & A. Lepland: Accretion of Moon and Earth and the emergence of
life
CHEMICAL GEOLOGY 169: (1-2) 69-82 AUG 15 2000

The discrepancy between the impact records on the Earth and Moon in the time
period, 4.0-3.5 Ga calls for a re-evaluation of the cause and localization of the
late lunar bombardment. As one possible explanation, we propose that the time coverage
in the ancient rock record is sufficiently fragmentary, so that the effects of giant,
sterilizing impacts throughout the inner solar system, caused by marauding
asteroids, could have escaped detection
in terrestrial and Martian records. Alternatively, the lunar impact record
may reflect collisions of the receding Moon with a series of small, original satellites
of the Earth and their debris in the time period about 4.0-3.5 Ga. The effects on Earth
of such encounters could have been comparatively small. The location of
these tellurian moonlets has been estimated to have been in the region around 40 Earth radii. Calculations
presented here, indicate that this is the region that the Moon would traverse at 4.0-3.5 Ga,
when the heavy and declining lunar bombardment took place. The ultimate time limit for the
emergence of life on Earth is determined by the effects of planetary accretion - existing
models offer a variety of scenarios, ranging from low average surface temperature at slow accretion
of the mantle, to complete melting of the planet followed by protracted
cooling. The choice of accretion model affects the habitability of the
planet by dictating the early evolution of the atmosphere and hydrosphere.
Further exploration of the sedimentary record on Earth and Mars, and of the
chemical composition of impact-generated ejecta on the Moon, may determine
the choice between the different interpretations of the late lunar bombardment and cast
additional light on the time and conditions for the emergence of life. (C) 2000 Elsevier Science
B.V. All rights reserved.

Addresses:
Arrhenius G, Univ Calif San Diego, Scripps Inst Oceanog, San Diego, CA 92093
USA.
Univ Calif San Diego, Scripps Inst Oceanog, San Diego, CA 92093 USA.
Tallinn Tech Univ, Inst Geol, EE-0001 Tallinn, Estonia.

Copyright © 2000 Institute for Scientific Information

================
(6) NEW 2.5 KM IMPACT STRUCTURE DISCOVERED IN NW AUSTRALIA?

J.D. Gorter & S.W. Bayford: Possible impact origin for the Middle Miocene
(Serravallian)
Puffin Structure, Ashmore Platform, Northwest Australia. AUSTRALIAN JOURNAL
OF
EARTH SCIENCES 47: (4) 707-714 AUG 2000

The Puffin Structure is interpreted from high-quality 3D seismic data as a
small multiringed impact structure formed by collision of a meteorite or
small asteroid with unconsolidated, water-saturated shallow-marine shelf carbonates during the Middle Miocene
(mid to late Serravallian). The impact created a dish-shaped structure about
2.5 km in diameter with annular rings and no central uplift.

Addresses:
Gorter JD, British Borneo Australia Ltd, POB 1265, W Perth, WA 6872,
Australia.
British Borneo Australia Ltd, W Perth, WA 6872, Australia.

Copyright © 2000 Institute for Scientific Information

===============
(7) CAN SELF-ORGANISED TUNGUSKAS PREVENT THE BIG ROCK?

B.D. Malamud & D.L. Turcotte: Self-organized criticality applied to natural
hazards
NATURAL HAZARDS 20: (2-3) 93-116 NOV 1999

The concept of self-organized criticality evolved from studies of three
simple cellular-automata models: the sand-pile, slider-block, and forest-fire
models.
In each case, there is a steady "input'' and the "loss'' is associated with
a fractal (power-law) distribution of "avalanches.'' Each of the three
models can be associated with an important natural hazard: the sand-pile model with
landslides, the slider-block model with earthquakes, and the forest-fire model with
forest fires.
We show that each of the three natural hazards have frequency-size
statistics that are well approximated by power-law distributions. The model behavior suggests
that the recurrence interval for a severe event can be estimated by extrapolating the
observed frequency-size distribution of small and medium events. For example, the
recurrence interval for a magnitude seven earthquake can be obtained directly from the
observed frequency of occurrence of magnitude four earthquakes. This concept leads to
the definition of a seismic intensity factor. Both global and regional maps of
this seismic intensity factor are given. In addition, the behavior of the models
suggests that the risk of occurrence of large events can be substantially reduced if
small events are encouraged. For example, if small forest fires are allowed to
burn, the risk of a large forest fire is substantially reduced.

Addresses:
Malamud BD, Cornell Univ, Dept Geol Sci, Ithaca, NY 14853 USA.
Cornell Univ, Dept Geol Sci, Ithaca, NY 14853 USA.

Copyright © 2000 Institute for Scientific Information

=============
(8) NATURAL HAZARDS: SOCIOPOLITICAL AND HUMANITARIAN CONSIDERATIONS

J.V. Smith: Natural hazards: Geology, engineering, agriculture, and
sociopolitical/humanitarian  considerations for the twenty-first century.
INTERNATIONAL GEOLOGY REVIEW 42: (7) 617-656 JUL 2000

Dangers from natural hazards have been characterized quantitatively by
national and international  committees of geoscientists based on technical advances in
geochemistry and geophysics (sensu lato). The current status of knowledge on
natural hazards is reviewed with particular emphasis on comet/asteroid impact, earthquakes, and
volcanoes. All these hazards are survivable by the world's population if appropriate measures are
taken over the next century and millennium. Ideas for mitigation include: general use of
weathered volcanic ash and power-station fly ash to make pozzolana cement for strengthening
buildings, and stabilizing weak ground and hillsides prone to slumping;
long-term storage of grains under nitrogen, together with other techniques
for maintaining viability of stored food; drilling
of tunnels under major cities to facilitate traffic flow, and for protection
against impact of bolides and bombs; design of sea and lake fronts to guard against
tsunamis from earthquakes and asteroid impact. The food-storage proposals
could be tailored to help farmers obtain a regular income while producing a
higher crop yield than needed for current food supply. The
land modification plans would provide technical challenges and new business
activities for civil engineers, lawyers, real-estate professionals, and city planners. It
is truly tragic that genuine ideas for mitigation of natural hazards are being implemented
at a snail's pace while funding for weapons nourishes around much of the
world. The early development of my thinking on hazards is an example of the
typical disconnection between "scientific expertise"
and actual day-to-day planning decisions. As a farmer's boy interested in
civil engineering and land planning in an ecological context, I summarize old and new ideas in
an effort to bridge this disconnection, and facilitate the planned transfer of funding
from weapons to actions that enhance human well being. Because the actions are international
in their basic nature and ecological in character, I hope that they will
help to generate a feeling of "One world that must be loved, not abused." We
belong to one biological species, Homo supposedly sapiens sapiens. We must
progress beyond tribal, ethnic, and other divisive matters
associated with wars and civilian conflicts. The rich must help the poor.
Geology and civil engineering can provide important worldwide cooperative
connections.

Addresses:
Smith JV, Univ Chicago, Dept Geophys Sci, 5734 S Ellis Ave, Chicago, IL
60637 USA.
Univ Chicago, Dept Geophys Sci, Chicago, IL 60637 USA.
Univ Chicago, Ctr Adv Radiat Sources, Chicago, IL 60637 USA.

Copyright © 2000 Institute for Scientific Information

===================
* LETTERS & OPINION
===================

(9) MICKEY MOUSE SCIENCE:
    HOW WALT DISNEY'S ACCOUNT OF THE XF11 AFFAIR IS FOSTERING AN URBAN MYTH

From Benny J Peiser <b.j.peiser@livjm.ac.uk>

You know that intellectual standards are going down the drain when
scientists start to promote the cartoon versions of populist science. This is certainly
the case with the recent promotion of Walt Disney's account (or should I say:
blunder) of the events surrounding the announcement of asteroid 1997 XF11
way back in March of 1998.

A couple of days ago, Alan Harris (JPL/NASA) re-opened the unfortunate
XF11 affair with another public broadside against Brian Marsden. In a
message to the MPML mailing list on 26 September, Al Harris posted a cutting from
Discover Magazine's list of "Twenty of the Greatest Blunders in Science in the Last
Twenty Years" which included what Al calls "the 1997 XF11 fiasco."

Brian Marsden, Harris continued, "shares company with quite a few other
planetary and space stories: the Challenger disaster, failed Mars missions, the Mars
Rock story and the Iridium satellite constellation. I'm not sure I would make the
same choices, but in any case Marsden is in pretty select company. You can
check it all out at:
http://www.discover.com/oct_00/featblunders.html"

-------------------------------------------------------
Twenty of the Greatest Blunders in Science in the Last Twenty Years
What were they thinking?

By Judith Newman

The Sky Is Falling Again

Um, never mind. On March 12, 1998, on the front page of The New York Times,
a headline read: "Asteroid Is Expected to Make a Pass Close to Earth
in 2028." Brian G. Marsden, director of the Central Bureau for Astronomical
Telegrams at the Smithsonian Astrophysical Observatory, predicted that on
October 26, 2028, an asteroid about a mile in diameter would come within
30,000 miles of Earth. That's within spitting distance, spacewise, which
evoked comparisons to the asteroid that crashed on the Yucatàn peninsula 65
million years ago, allegedly wiping out all the dinosaurs. "When you first
discover a comet, or any kind of body, you start measuring its position,"
notes Robert Park. "From that you extract its trajectory. The more
measurements you make, the more accurate your trajectory gets." Marsden issued his
warnings based on very early trajectory measurements. Now he anticipates
the asteroid will pass Earth at a safe distance of 600,000 miles.

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

So what's wrong with exposing this kind of "scientific blunder" on a mailing
list for NEO observers? For a start, Discover.com, as Victor Noto has
correctly pointed out, is a small Disney Company entertainment website and
not, as Harris seemed to believe, identical to the science journal Discovery.com.

This then raises the question as to whether Walt Disney really understand
what their writing about. After all, if you want to expose a scientific blunder
and wish to take the mickey out of scientists, you'd better get your facts
right.

Nobody, I am sure, will be surprised to learn that Disney's mini-story about
the XF11 affair has to be taken with a pinch of salt.

The first crucial mistake in the Discover cartoon is at the beginning of
line 5:
The announcement stated that asteroid 1997XF11 could come within 30,000
miles of the earth, not "would." I fear that this difference, which is to scientists
as that between night and day, is very frequently misrepresented (or simply
misunderstood) by journalists. One could venture say that the could/would
confusion is frequently the principal problem from which journalism - even
science journalism - suffers.

Roberta Park's quoted statement is also incorrect. After all, it's not the
number of observations that matters in this respect, but the length of time
they span. And rather than issuing "warnings", Brian Marden, as we know, was
noting the apparent apathy of observers to what was obviously an interesting object
by urging them to make that timespan longer, both by means of continuing new
observations and the search for possible observations on old plates.

It is also interesting that the writer feels that "30,000 miles" is indeed
worrisome - "within spitting distance" - yet the now "anticipated" 600,000
miles is "safe". (remember the 3 million miles of 2000 QW7 that made
global headlines recently as "near miss"?) NEO researchers did not seem to
consider a minimum miss distance of 30,000 miles in any way worrisome, even
if it would have turned out to be correct: to them, clearly, "a miss is as
good as a mile". But it was precisely the possibility that the 2028 miss
distance was about 500,000 miles (allegedly "safe", in the mind of
Discover.com) that an object such as 1997 XF11 could (*not would*) have hit the earth 12
years later.

If there was a scientific blunder at all, it was rather made by Alan Harris
himself when he calculated, on 11 March 1998, that, in 2028, "the probability of
impact [of XF11] is probably greater than 0.1%." That calculation was indeed a
blunder.

I have always wondered why Alan Harris never stopped his camapign against
Marsden's XF11 announcement. He appeares driven and almost obsessed by the
whole affair. Historians of the XF11 affair and its long-term implications on NEO
research and NEO politics may be interested to known that it was Al himself who, on
the day of the MPC release, congratulated Marsden on the tone and format of the
XF11 announcement:

"I think Brian is to be commended for restraint and discretion in the
wording of the announcement below. Let me add a couple more sensational
details that could have been added, but thankfully weren't: [...] For
the first time, we have an object with a significantly non-zero
probability of impacting the Earth."

Ah well, without 1997 XF11, where would we be today? Would NASA have
established its NEO Office and increased its NEO funding? Would we have LINEAR and
Spaceguard initiatives around the world? And finally, and more to home, would both
Houses of Parliament have debated the impact hazard and would the UK Government,
subsequently, have set up the NEO Task Force, indeed, would we have the NEO Task Force
Report without the XF11 Affair? I somehow doubt it.

Benny J Peiser

================
(10) 1946 TSUNAMI

From Michael Paine <mpaine@tpgi.com.au>

Dear Benny,

The article explains the most likely source of the 1946 tsunami 'Fryer
said the earthquake alone doesn't explain the large waves, but it shook
loose a huge submarine landslide into the Aleutian Trench.' The diagram
in the Star-Bulletin article clearly shows a source in that trench.
http://starbulletin.com/2000/09/23/news/story9.html
Submarine landslides can cause tsunami that are much larger than ones
caused by earthquakes alone. It is an interesting event but I suspect it
but has nothing to do with asteroid-generated tsunami, other than
providing a good case study for tsunami modeling.

regards
Michael Paine

=============
(11) MEA CULPA!
           
From Phil Plait <badastro@badastronomy.com>

In the CCNet from 22 September 2000, James Oberg says
about heating meteors:

>Actually, friction has nothing to do with it -- although
>this is a common, careless, misconception. The source of
>heat on an entering object is the shock compression of the
>air piled up in front of it

Mea Culpa!

He is correct. The hypersonic passage of the meteoroid compresses the
air tremendously, which heats it. Radiant energy from the shocked air
heats the forward surface of the meteor, melting it. There is a
standoff zone of relatively dead air in front of the meteor, and
friction with that ablates off the melted material.

I would define friction as the force of air moving laterally over a
surface, so the heating is not really friction-induced. References
on the actual heating mechanism of the air in front of a meteor
(at least, the ones I could find) are maddeningly vague, but John Lewis
at the University of Arizona set me straight, and I thank him for it. If
there are any remaining errors in my comments, they are mine and not his.

-Phil

 *    *    *    *    The Bad Astronomer    *    *    *    *

Phil Plait                    badastro@badastronomy.com
The Bad Astronomy Web Page: http://www.badastronomy.com

=============
(12) INVENTION OF IMPACT CRATERING

From Duncan Steel <D.I.Steel@salford.ac.uk>

Dear Benny,

I am not sure about your start dates in:

"...early researchers on impact cratering processes found themselves
between the mid 19th and the  mid 20th centuries.  It should be recalled
that it took more than 100 years before the initial impact hypothesis  for
many lunar and terrestrial craters could be finally verified..."

Although Edmond Halley suggested in the 1690s that comets must hit the
Earth from time to time, and he suggested that the Caspian Sea might be
the scar from such an event, the real beginning of the impact hypothesis
might really be judged to have occurred around 1890 when Daniel Barringer
(in Arizona) and Alexander Bickerton (in New Zealand) mooted ideas that
were thought crazy at the time. If one goes back to the mid-19th century,
one finds people being totally bewildered by the craters of the moon.
For example, Charles Babbage (no idiot he) suggested in the late 1840s
that they were similar in origin to coral atolls, left high and dry
after the lunar seas (maria) had dried up; he was influenced by Charles
Darwin's description of tropical atolls as observed in the 1830s on the
famous voyage of the Beagle. I might point out that in the same discussion
Babbage put forward what might well be regarded as the first description
of the greenhouse effect in the planetary context (that is, he discussed
how different planets might have elevated temperatures due to the effects
of their differing atmospheres trapping more of their re-emitted infra-red
radiation). I discussed this in:

D. Steel, 'Charles Babbage, the craters of the Moon, and the Greenhouse
Effect,' Journal of the British Astronomical Association, 102, 246-247
(1992).

Kind regards,

Duncan Steel

MODERATOR'S NOTE: The invention of the impact cratering idea goes back to
1802 and is mainly a German invention. The idea emerged as a direct consequence
of the discovery of the first two asteroids in 1801 and 1802. Once it was
realised that such small bodies existed in the solar system, it was clear that they
may occassionally collide with the moon or earth. Thus, in 1802, the von
Bieberstein brothers in Germany and again in 1815 K.E. von Moll suggested that the lunar
craters were caused by asteroidal impacts. The idea was picked up and
expanded by F. von Gruithuisen in 1829 but completely overshadowed by the emerging
uniformitarian/anti-catastrophist paradigm which took shape in the 1830s and
1840s.
While Richard Proctor revived the impact hypothesis in his 1878 book on the
Moon, the whole issue was dropped when the second edition was published a couple
of years later. Altogether it took some 160 years for the impact hypothesis to become
a scientific fact, beginning from its original invention in 1801 until its
verification in the early 1960s.

BJP

=============
(13) MOON HAS SQUARE CRATERS TOO

From Ian Tresman <ian@knowledge.co.uk>

RE: HOLY SMOKE: SQUARE CRATERS DETECTED ON EROS

Apparently the moon has square craters too. See

1. http://members.home.net/bill2space/square-craters.html

2. http://www.lunaranomalies.com/double_craters_in_hort.htm


Regards,

Ian Tresman, Compiler, Catastrophism! CD-Rom Disc
9 Ashdown Drive, Borehamwood, Herts. WD6 4LZ. UK.
Fax: 0870 284 8769. Email: ian@knowledge.co.uk
Web: http://www.catastrophism.com

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