PLEASE NOTE:


*

CAMBRIDGE-CONFERENCE DEBATE, 2 April 1998
----------------------------------------

(1) DON'T COUNT YOUR CHICKENS BEFORE THEY HATCH, PARTICULARLY NOT ON
    APRIL 1st
    Benny J Peiser <b.j.peiser@livjm.ac.uk>

(2) JUST WHEN YOU THOUGHT 1997 XF11 HAD GONE AWAY
    Brian G. Marsden <bmarsden@cfa.harvard.edu>

(3) ON ADOPTING A NEO HAZARD INDEX
    Gerrit Verschuur <GVERSCHR@MSUVX1.MEMPHIS.EDU>

(4) AXIOM ON PUBLIC ANNOUNCEMENTS SHOULD BE APPLIED INTERNATIONALLY
    Richard Binzel <rpb@astron.mit.edu>

(5) A COMMENT ON DUNCAN STEEL'S "PANDORA'S BOX"
    Clark Chapman <cchapman@boulder.swri.edu>

=====================
(1) DON'T COUNT YOUR CHICKENS BEFORE THEY HATCH, PARTICULARLY NOT ON
    APRIL 1st

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

Can you imagine how much I shrieked with laughter when an American
colleague was so kind to tell me that one of our honourable members
almost swallowed yesterday's message by Coffee Anan? 

> Tom, Bob, Jim, and Dan:
>
> I received a message via the CC Digest saying the UN is going to spend
> $500,000,000 to build a "global system of NEO detection and R&D in NEO
> deflection for the next 10 years."  This is, however, released on 1 April
> 1998, so its authenticity is suspect.  Do you have any independent
> verification that such a committment has been made?

While this reaction certainly made my day, I was even more pleased when
I was informed by a reliable source that yesterday's UN "committment"
was - guess what - actually forwarded to the Secretary General, Kofi
Anan, by one of his acquaintances. And that's no joke!

The rest of today's debate on the CCNet is, I'm afraid to say, of a
more serious nature. It is the start of a critical re-assessment of the
events surrounding asteroid 1997 XF11 and the main lessons the
astronomical community in general and NEO researchers in particular
have to learn for similar events in the future. With more than
1,000,000 amateur astronomers world-wide and numbers growing
continuously, the discovery of new asteroids and comets on an orbit
with close approch to Earth is inevitable and just a question of time.
Thus this discussion is of great concern to all who are either directly
involved or simply interested in NEO research and, more importantly,
the fundamental implications of the NEO threat on human, social and
scientific conduct in the free world.

Benny J Peiser

==================
(2) JUST WHEN YOU THOUGHT 1997 XF11 HAD GONE AWAY

From: Brian G. Marsden <bmarsden@cfa.harvard.edu>

My article in the March 29 Boston Sunday Globe, as well as the extended
version that appeared in the March 30 CC DIGEST, was obviously a
popularized account of my view of the 1997 XF11 affair. It had been my
intention, at some stage, to address the more complex issues in more
detail, and Clark Chapman's "case study", which appeared in the
otherwise delightful April 1 issue of the CC DIGEST, provides an
appropriate impetus. Since, in his capacity as new chairman of the IAU
Working Group on Near-Earth Objects, Dave Morrison was gratuitous
enough to send Chapman's item and my extended Globe article to much of
the IAU leadership, I shall trust that my response here receives the
same treatment. Note that I shall basically refer to the particular
version of Chapman's remarks that actually appears in the CC DIGEST,
although DIGEST readers will be aware of the reference there to
Chapman's 2500-line Web manifesto, parts of which are being construed
by many as libelous, and on which I might touch.  If, as Chapman notes
in his introductory paragraph to the DIGEST (but not the distributed)
version, "the detailed technical analysis ... is still not fully
understood" by him, one rather wonders how he can so confidently
describe what happened.

Is it more important to make probability estimates of impacts on the
basis of limited observational data or to try and secure additional
data? This is an interesting question, and your answer may well depend
on whether you are a theoretician or an observer.  Chapman takes the
view that only the former is important, the additional 1990 data being
just "icing on the cake". (But why stop there?  If the 1990 data were
mere icing, why not also the Shelus data from 1998 March 3 and 4 that
he so chided me for withholding?). The fact is that 1997 XF11 is one of
the largest objects that CAN come very close to the earth, and that it
WOULD come particularly close in 2028 was already evident from the data
in the February MPCs, and even from those in the January MPCs. The
worrisome thing is that nobody became interested in the object earlier:
Shelus' observations were the first ones in a whole month, and those
interested in such things seem not to have made any effort to obtain
physical data that could establish an albedo and size. It should not in
fact have been necessary for there to be an urgent scramble on March 12
to search for old images. As soon as objects are added to the list of
PHAs (as 1997 XF11 was in December), they should (if reasonably bright)
surely become prime candidates for physical studies; and as soon as
there is a halfway decent orbit determination (January, certainly
February, for XF11), mechanisms should be established for searching for
old images. Such activities must be considered part of the NEO
enterprise, and they (and follow-up astrometry generally) are every bit
as deserving of funding as are searches for new objects.  After all,
examination of old plates, and CCD recovery attempts for faint objects,
were the principal modi operandi of the late and very much lamented NEO
program at Siding Spring.

So, considering that we were dealing with a computation, from available
data, that even amateur astronomers could do (as Duncan Steel also
aptly pointed out in the April 1 CC DIGEST), there was every reason to
issue IAUC 6837, with a call for further observations, even physical
observations. The possibility of finding past observations was handled
in the accompanying "press information sheet" (or whatever it should be
called) in the WWW, this sheet also being designed to answer questions
readers (including, but not restricted to, the press) of the admittedly
terse IAU Circulars may have.

But, accepting that some people might just be interested in whether
there might be an earth impact prior to the availability of further
data, I used, on IAUC 6837, the perhaps unfortunate but deliberately
not wholly quantitative phrase "Error estimates suggest that passage
within 0.002 AU is virtually certain". Note in particular the word
"suggest". Is that a word one uses when he is absolutely convinced of
something? Sure, this was perhaps a "1 sigma" when it might have been
better to consider a "3 sigma", but is that the end of the world (pun
intended, I suppose)--given that Karri Muinonen estimated the
probability of passage within 0.002 AU to be as high as 90 percent? 
No, Clark, my calculations were not "faulty". I did not even
misinterpret them.  Whether I used "ill-chosen" words is a subjective
judgment--especially if you want to consider that I am writing this
whole document on April 1.

"The chance of an actual collision is small, but one is not entirely
out of the question."  Given that the press information sheet was put
together more hastily than the IAU Circular, this statement is perhaps
also somewhat unfortunate. I have agreed that it is VERY DIFFICULT to
bring the object within 0.00019-0.00021 AU of the earth in 2028--on the
basis of the 88-day arc. But as recently as March 28, Muinonen and
Chodas were STILL arguing about whether an actual collision was
POSSIBLE.  Until this argument is resolved, it is impossible to say
whether the probability of impact was precisely zero or not.

Don Yeomans' e-mailed request for observations of 1997 XF11 reached my
computer at 17:45 EST on March 11.  That was after "normal office
hours" (whatever they are!), but I did in fact send them as soon as was
practical, together with a friendly note to both him and Paul Chodas,
at 19:32 EST (hardly a terrible delay under the circumstances, surely),
saying I "shall be interested to hear what you find, [but] the whole
point is to get ... possible images from old plates".  Chodas had
already indicated to me that he wished "to compute a formal probability
of impact".  Sure, I could be "interested" in this result, but it
obviously would not be the last word. In any case, when Yeomans, in a
message that was widely distributed (I received it at 20:15 EST), gave
the "close approach distance" as "0.00058 +/- 0.00897 (3-sigma) AU", it
immediately occurred to me that this was a decidedly odd way of
expressing an uncertainty that just had to be much more "+" than "-"! 

Now to the events of March 12.  I was up early because I had to be at a
local television studio for a live program at 7:00 EST. I quickly
checked the overnight e-mail an hour earlier, noted the requests to
publish a "correction", to the effect that there could be "no
collision", and I responded to them at 6:10 EST to the effect that that
"unmodeled effects surely make [the probability] nonzero.  We need more
data." Back from the studio and--like everyone else--in the thick of
further press enquiries and interviews, I received from Muinonen (to
whom I had also sent the March 3-4 observations, as he had requested)
his assessment of the situation, which was that he obtained a nominal
miss distance of 0.00033 AU (when I had 0.00031 AU) and was "in
agreement with" me "that collision with the Earth cannot be ruled out
at the moment".  This was in flat contradiction to Yeomans and Chodas! 
In any case, since I had not even mentioned on the IAU Circular that a
collision with the earth was a possibility (however remote), what,
indeed, was the point of publishing a new remark against or in favor of
this proposition?

Then, around 12:15 EST, I received word that Eleanor Helin and Ken
Lawrence had images from 1990!  It would take a few hours to get
measurements, of course. On the interview for the CBS Evening News I
taped at 12:30 I in fact MENTIONED this important new development, but
I don't know if it were used in the broadcast. It was also around this
time that I received a phone call from Chapman "ordering" me to discuss
probability analysis with Chodas and Yeomans. I may or may not have
mentioned the forthcoming 1990 observations to Chapman: they were
obviously not of relevance to him anyway, although I knew they would be
of relevance to Chodas and Yeomans, who would obviously agree with me
that these solved the problem completely. 

We received the March 23 measurements from Helin at 14:00 EST, whilst I
was again in the midst of an interview, and Gareth Williams had
computed an orbit showing the 0.006-AU miss distance by the time I was
driven off again to the television studio at 14:20.  Since Paul Chodas
wrote that he had computed this at 14:49 EST, Williams was clearly the
first to get this result. But single-night measurements can be
problematic, and the MPC standards require the data from the second
night that we knew would be forthcoming. The March 22 measurements
arrived around 17:00, about the time I got back to my office, and
Williams had completed the definitive computation, again with the
0.006-AU miss distance, within minutes. Amidst further interruptions
for phone calls and e-mail messages, I then prepared the IAUC 6839,
finally managing to complete it around 19:30 EST. It was put into the
CBAT/MPC Computer Service five minutes later, e-mailed to subscribers
over the course of the next 15 minutes and was  available for FREE
viewing on the WWW at 19:55.

At 20:00 I participated in two more television interviews, including
one for the next morning's NBC "Today Show", here in the office. The
crews left shortly after 21:00, and I received notification of the JPL
orbit computations, obviously identical with ours, at 21:20.  On
arrival home at 22:15 I did yet one more radio interview, for CBS news,
while eating the dinner my wife had prepared for me hours earlier (how
did we manage before microwaves?), this then signaling for me the end
of what had been--and obviously not just for me--a rather strenuous
day... This feeling is compounded if one realizes that the combined
scientific expertise for the IAUCs and the MPCs is contained in just
three people, one of whom was on sick leave for part of March 12.  Our
part-time secretary stayed late to field calls. Our administrator was
on vacation for the week. The head of the Smithsonian Astrophysical
Observatory's public affairs office was also out of town, and this is
one of the complications that led to the unfortunate circumstance that
the Press Officer of the American Astronomical Society distributed our
press information sheet as a full-blown press release on behalf of the
IAU.

To suggest that the IAU Circulars should be "peer reviewed" and to
imply that this requires that "all data from the international
astronomical community should be disseminated as rapidly as is
technically possible" is a red herring. A formal review process simply
takes too long. Nevertheless, the editors do frequently consult with
experts in particular areas, and as a result the number of outright
errors on the IAU Circulars is actually surprisingly small.  Speed will
often tend to spawn errors, but to produce in a slow and plodding
manner is not a guarantee that they will be eliminated.

At the NASA policy discussion in Houston on March 17, a couple of
participants insisted that they needed to have all the astrometric data
immediately they were received by the MPC, without the need for
checking.  As I pointed out, this is a complete impracticality, in that
most contributors of data EXPECT that we shall do what we can to verify
their data.  To send out masses of unchecked data, not related to
specific objects, would cause both mass confusion as well as mass
embarrassment.  For example, just during the past couple of weeks, we
received an extensive batch of near-equatorial observations that
omitted the sign of the declination, whether that was in the range 0 to
+1 degree or in the range -1 to 0 deg.  While we were able to sort this
out before any observations were actually published, this could have
been a very damaging situation that would also have involved our
receiving e-mails enquiring about specific problems for months to come.
In any case, since the interest is in NEOs, to make available 4000 or
more observations every day would quickly overwhelm the most ardent MPC
subscriber. Nobody should be under the illusion that our checking of
the data is a "pet research project of ours".  Believe me, we get far
fewer interesting and publishable results out of it than one might
think, considering the effort we put into it.  Some might instead be
tempted to regard this activity, carried out by Williams over the
course of many hours seven days per week, as a thankless task--although
it is in fact clearly appreciated by essentially all of the observers.

My compromise was that we should be able to make available, generally
on a daily basis, all new observations of unnumbered NEOs. Such a move
would have allowed others to keep fully on top of the 1997 XF11
situation, right from the start. Whether they would actually have DONE
so is quite a different matter.

BGM, 1998 Apr. 1

=====================
(3) ON ADOPTING A NEO HAZARD INDEX

From: Gerrit Verschuur <GVERSCHR@MSUVX1.MEMPHIS.EDU>

Late last year Sky & Telescope commissioned me to write an article
related to NEOs for their June 1998 edition, timed to coincide with
the release of a couple of Hollywood movies on the subject of impacts.
I completed the article by the mid-February deadline, a week or so
before the 1997 XF11 furor hit the headlines. Sky & Tel had defined a
theme for the article: how should the public be informed in the case of
an impending impact? They specifically asked me to discuss Richard
Binzel's Hazard Index, something he has written and talked about for
several years. A Hazard Index could be used to indicate the probability
of an impact as well as the magnitude of the likely event. If you see
the Sky & Tel article bear in mind that at the time of writing
1997 XF11 was a complete unknown to me. I like odd coincidences, but
this one was too close for comfort. 

The moral of the story is that the NEO community might do well to
consider the implementation (on an international level) of some form of
Hazard Index to be used in all future reporting of close passes and
potential strikes. I fully appreciate that probabilities mean little to
most lay people, and that is why the use of some numerical scale makes
sense. Consider the Richter Scale for earthquakes. Most lay people
appreciate that a magnitude 7 quake is very bad whereas a 5 is usually
not so significant and that a 3 is not worth writing about. But they
don't actually have a clue as to what the 3, 5 or the 7 mean in terms
of absolute energies, say. If some form of Hazard Index for NEOs was to
be adopted the public might begin to appreciate that near misses are
common, that misses inside the moon's orbit are less common, that
strikes by small objects occur from time to time, and that civilization
destroying impacts are infrequent. The use of a cleverly constructed
scale may prevent false alarms while also serving to realistically
communicate a warning taking into account uncertainties in orbital
predictions at any given time. As Binzel notes, an Index value will
change over time as the predictions improve with new data.

The International Spacegaurd Foundation or the IAU may wish to take the
lead in deciding whether a Hazard Index is worth considering, how to
define such an index, and how toimplement its use in the future.

Gerrit L. Verschuur

PS. Thanks to all those who responded to me survey last year. I used
some of your input in the above-mentioned article.

====================
(4) AXIOM ON PUBLIC ANNOUNCEMENTS SHOULD BE APPLIED INTERNATIONALLY

From: Richard Binzel <rpb@astron.mit.edu>

Dear Benny,

I am a bit surprised by Duncan Steel's response to my proposed axiom
regarding public announcements pertaining to Earth approaching objects
for which a collision cannot be ruled out, which I repeat below.

There is nothing in this axiom regarding nationality, control over NEO
researchers, or censorship. It is an axiom describing a responsible
code of scientific conduct which can be followed by either professional
or amateur researchers regardless of nationality.

Sincerely,
Richard P. Binzel
Associate Professor of Planetary Science
M.I.T.

--------------------------------------------------------------------
"A public statement regarding an Earth approaching object for which
a collision cannot be ruled out should not be issued without:

     a) Giving a quantitative value for the probability;
     b) Having independent verification on this probability;
     c) Placing this probability into the context of the
        collision probability with the background population
        of similar-sized objects."

=====================
(5) A COMMENT ON DUNCAN STEEL'S "PANDORA'S BOX"

From: Clark Chapman <cchapman@boulder.swri.edu>

Much of what Duncan Steel (April 1 CC Digest) has said about
the undesirability and impossibility of controlling information is valid.
But he misses an essential point.  The world has long been exposed to
the uncensored "babble" of anyone who wants to say something and has
access to a printing press.  With the advent of the Internet, the babble has
increased to a roar.  Yet society, and the scientific community, have
developed ways to deal with it, to sort out the wheat from the chaff.

Among reputable scientists, that way is to "certify" reputable
scientific results by having them checked, peer-reviewed, and published
in technical journals.  Associated with that, the scientific community has
traditionally regulated itself, by not going to the public media until the
date of publication of the peer-reviewed technical article.  That approach
is *required* by Science and Nature, for example.

Such procedures don't prohibit lay people, amateurs, truthsayers,
fortune-tellers, pseudo-scientists, and professional scientists who don't
care about their reputations from publishing their hasty results immediate-
ly -- on the Internet, or anywhere -- and such stories are frequently
reproduced in the supermarket tabloids.  But serious people, opinion
leaders, policy makers, and the like rely on those media (like the New
York Times, in America, for example) that attempt to abide by society's
self-regulating procedures in order to report stories with a higher degree
of reliability.

No procedures developed in the U.S. or anywhere will prohibit
casual, unchecked results from going out. As many people may not
know, just a few days before the 1997 XF11 affair, there was Internet
chat of a preposterous claim by some "Russian scientists" (not the
reputable experts that I know) that the asteroid Icarus might hit the Earth
in the year 2006. This story, however, did not create banner headlines
around the world. Nor should it have done so.

It is appropriate and necessary that serious astronomers, and the
serious media, adapt to the modern realities of the Internet and establish
effective procedures -- essentially peer-review -- to reduce the chances
that mistakes like 1997 XF11 will happen again.  It is appropriate that
entities like the I.A.U., NASA, the Spaceguard Foundation, and all
manner of amateur and professional astronomical societies, funding
agencies, etc. (national and international) adopt procedures to ensure that
centuries of traditional peer-review procedures are maintained in the
current Information Age.

The Minor Planet Center represents itself to be, should be, and
was taken (by the media) to be a *reliable* source of information,
representing the astronomical community.  All of us, not just the MPC,
lost some credibility a few weeks ago when failures in the peer-review
process at the MPC led to the XF11 scare.  It is wholly appropriate to
mandate procedures of peer-review.  To be sure, as Steel says, the
conspiracy theorists -- like those who believe that NASA is suppressing
information about the "Face on Mars" -- will complain.  But that is a
small price to pay for ensuring that scientists continue to retain the
amazingly high level of credibility that they currently hold in the public's
eye.

Clark Chapman



*

CAMBRIDGE-CONFERENCE DIGEST, 2 April 1998
-----------------------------------------

(1) NEO DISCOVERY AND MISSION OF OPPORTUNITY
    Jim Benson <Jim@SpaceDev.Com>

(2) LATE TRIASSIC MULTIPLE IMPACT EVENT ON EARTH
    J.G. Spray et. al., University of Brunswick

(3) K/T IMPACT SPAWNED GIANT SUBMARINE AVALANCHES
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(4) SORRY ARTHUR, BUT EVIDENCE SUGGESTS CHICAGO FIRE WAS UNRELATED TO
    FIREBALL OBSERVATION
    Mark Bailey <meb@star.arm.ac.uk>

(5) PRE-TELESCOPIC FIREBALL OBSERVATIONS DURING THE LAST 2000 YEARS
    Phil Burns <pib@nwu.edu>

========================
(1) NEO DISCOVERY AND MISSION OF OPPORTUNITY

From: Jim Benson <Jim@SpaceDev.Com>

Greetings.

I wish to draw two possibly important topics to your attention.

First is the "$5,000 Benson Prize for the Amateur Discovery of Near
Earth Asteroids." This was announced at the AAS conference last
spring. More details can be found at:

http://www.skypub.com/benson/prize.html.

So far, two prizes have been earned, and interestingly enough, by
the same person, Roy Tucker of Texas who is the first amateur to
ever discover two NEOs and the only person to win Benson prizes
(ten each at $500).

Second, is the Near Earth Asteroid Prospector (NEAP) by my company,
SpaceDev, Inc (www.spacedev.com). Yesterday (March 31), NASA opened the
new round of the Discovery program. NEAP is considered by NASA to be a
"Mission of Opportunity" and therefore instruments and experiments on
NEAP eligible for funding through the Discovery program. SpaceDev is
the world's first commercial space exploration company, and is simply
selling fully insured rides on NEAP for instruments and experiments.

I urge you to think about how the knowledge of NEOs might be advanced
by placing an experiment on NEAP. One idea discussed is the placement
by NEAP of a radio beacon on its target asteroid 1996 XB27 with the
purpose of accurately tracking the beacon (NEO) over a period of years
in order to better understand orbital perturbations and therefore
improve our ability to model future orbital changes.

Letters of intent must be furnished NASA by the end of April and
proposals are due around the end of June. The proposal process should
be relatively easy since you need only describe your experiment and
not an entire mission, which we will do for you. The pre-proposal
conference will be at the LPI in Houston on April 14. I will be there
to assist those wishing to fly an experiment to our NEO. We launch in
October of 2000 and arrive in July of 2001.

Please help us get the word out about this unique and historical
opportunity.

Also, please help us in gathering more information about 1996 XB27 --
its size, type, rotation, refined orbital elements, etc.

Thank you for your help and consideration.

Jim Benson
(Jim@SpaceDev.Com)

           SpaceDev - NEAP (Near Earth Asteroid Prospector)
-o-  Commercial Space Exploration & Development of Space Resources  -o-
              http://www.spacedev.com  -o-  Info@SpaceDev.Com

===============================
(2) LATE TRIASSIC MULTIPLE IMPACT EVENT ON EARTH

J.G. Spray*), S.P. Kelley and D.B. Rowley: Evidence for a late Triassic
multiple impact event on Earth, NATURE, 1998, Vol.392, No.6672,
pp.171-173

*) UNIVERSITY OF NEW BRUNSWICK, DEPARTMENT OF GEOLOGY, FREDERICTON, NB
E3B 5A3, CANADA

Evidence for the collision of fragmented comets or asteroids with some
of the larger (jovian) planets and their moons is now well established
following the dramatic impact of the disrupted comet Shoemaker-Levy 9
with Jupiter in 1994 (ref. 1). Collisions by fragmented objects result
in multiple impacts that can lead to the formation of linear crater
chains, or catenae, on planetary surfaces(2). Here we present evidence
fora multiple impact event that occurred on Earth. Five terrestrial
impact structures have been found to possess comparable ages (similar
to 214 Myr), coincident with the Norian stage of the Triassic period
These craters are Rochechouart (France), Manicouagan and Saint Martin
(Canada), Obolon' (Ukraine) and Red Wing (USA). When these impact
structures are plotted on a tectonic reconstruction of the North
American and Eurasian plates for 214 Myr before present, the three
largest structures (Rochechouart, Manicouagan and Saint Martin) are
co-latitudinal at 22.8 degrees (within 1.2 degrees, similar to 110 km),
and span 43.5 degrees of palaeolongitude, These structures may thus
represent the remains of a crater chain at least 4,462 km long. The
Obolon' and Red Wing craters, on the other hand, lie on great circles
of identical declination with Rochechouart and Saint Martin,
respectively. We therefore suggest that the five impact structures were
formed at the same time (within hours) during a multiple impact event
caused by a fragmented comet or asteroid colliding with Earth.
Copyright 1998, Institute for Scientific Information Inc.

=========================
(3) K/T IMPACT SPAWNED GIANT SUBMARINE AVALANCHES

From: Andrew Yee <ayee@nova.astro.utoronto.ca>

[http://www.unc.edu/news/newsserv/research/bralow2.html]

News Services
University of North Carolina-Chapel Hill

Contact: David Williamson or Bret Johnson, (919) 962-8596

Release No. 281 March 30, 1998

Embargoed until 6 p.m.Tuesday, March 31, 1998

Ancient meteorite collapsed margin, spawned giant submarine avalanches

By DAVID WILLIAMSON, UNC-CH News Services

CHAPEL HILL -- After untold years of streaking across the galaxy, a
giant meteorite smacked the Earth 65 million years ago with the force
of a million atomic bombs.

The collision, which scientists believe led dinosaurs and many other
species to die off within a few years, also caused massive landslides
along the edge of the continent north of Mexico's Yucatan Peninsula,
new evidence suggests. Six miles wide, the rock and metal chunk cut a
hole 120 miles across and devastated an area from northeast Mexico to
what is now the U.S. Gulf Coast.

"Until now, little has been known about the effect of the impact on the
continental margin closest to the crater, which is directly north of
the Yucatan," said Dr. Timothy Bralower, professor of geology at the
University of North Carolina at Chapel Hill. "Because it happened so
long ago, you can't even see the crater from the air or from space."

In a paper published in the April issue of the journal Geology,
Bralower and colleagues report evidence that the impact caused parts of
the Yucatan margin to slide into the deep sea. Co-authors are Drs.
Charles K. Paull, professor of geology at UNC-CH, and R. Mark Leckie of
the University of Massachusetts at Amherst.

"In cores of sediment taken from the base of the margin by the Ocean
Drilling Program, we found fragments of several types of rock and
fossils of various ages matching the strata from different levels on
the margin," Bralower said.

Fragments were mixed with minute, round melted rock beads known as
spherules flung from the impact site, he said. Such beads are direct
evidence of an impact blast.

"The blast shattered large chunks of the edge of the margin, and they
literally slid down to the depths of the ocean," Bralower said.

Collapsing margins triggered giant submarine avalanches that moved at
up to hundreds of miles an hour and spread across the Gulf of Mexico
and into the Caribbean.

"We find the same mixture of fossils, rocks and spherules in Haiti and
in the central part of the Caribbean suggesting that the submarine
avalanches traveled great distances," Bralower said.

Geologists cannot rule out the possibility that other margins collapsed
because of the blast and that avalanches came from a number of sources,
he said. But it's clear that the impact had a huge effect on Gulf of
Mexico topography.

Among the more spectacular results of the margin collapse, which
suddenly displaced billions of gallons of water, were giant tidal waves
that inundated coastlines around the gulf.

Scientists named the event, which was like a cannon ball hitting a duck
pond -- except on a vastly larger scale -- the Chicxulub impact, after
the Yucatan crater site. Bralower and colleagues dubbed the mixture of
microfossils, rock fragments and impact-created materials they studied
the "Cretaceous-Tertiary boundary cocktail."

Core sampling to about 3,000 feet took place aboard the 470-foot JOIDES
Resolution, the world's largest scientific drill ship.

The National Science Foundation and the Texas A&M University-based
Ocean Drilling Program supported the research.

Note: Bralower can be reached at (919) 962-0704.

===================
(4) SORRY ARTHUR, BUT EVIDENCE SUGGESTS CHICAGO FIRE WAS UNRELATED TO
    FIREBALL OBSERVATION

From: Mark Bailey <meb@star.arm.ac.uk>

The suggestion made in the film `Target Earth', that the Great Peshtigo
Fire was started by a meteorite or bolide does not fit with the
evidence in both Father Pernin's (1874) account and that of Robert
Wells (1968) [Refs: P. Pernin 1971, `Wisconsin Stories: the Great
Peshtigo Fire', State Historical Society of Wisconsin; R. W. Wells
1968, `Embers of October', reprinted 1995 Peshtigo Historical Society].
Wells, however, does mention a report by Phineas Eames, one of the
Birch Creek farmers, who describes an event which closely resembles a
bright fireball. This occurs one hour after the devastating Peshtigo
Fire, and so could not have been the cause of the latter even if the
fireball had touched ground.

Mark Bailey
Armagh Observatory
meb@star.arm.ac.uk

=====================
(5) PRE-TELESCOPIC FIREBALL OBSERVATIONS DURING THE LAST 2000 YEARS

From: Phil Burns <pib@nwu.edu>

R. P. Greg's catalog of meteorites and fireballs from A.D. 2 to A.D.
1860 is available online in web page format:

     http://www.mplc.co.uk/eduweb/sites/bookman/meteorites/greg.html

This is a subpage of the UK and Eire Meteorite Page, authored by Eric
Hutton, which includes historical information on falls in these
countries from the 14th century to the present.

-- Phil "Pib" Burns
   Northwestern University, Evanston, IL.  USA
   pib@nwu.edu
   http://pibweb.it.nwu.edu/~pib/

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