PLEASE NOTE:


*

CCNet DIGEST, 9 June 1998
-------------------------

(1) NEW CALCULATIONS LEAVE CRITICS SPEECHLESS
    Benny J Peiser <b.j.peiser@livjm.ac.uk>

(2) 1997 XF11 WAS NOT DANGEROUS AT ANY TIME
    Clark Chapman <cchapman@boulder.swri.edu>

(3) USAF NEWS RELEASE ON THE GREENLAND METEOROID IMPACT
    Duncan Steel <dis@a011.aone.net.au>

(4) A CLIMATE OF SECRECY IS THE GREATER EVIL
    Jens Kieffer-Olsen <dstdba@post4.tele.dk>

(5) STRANGE NATURAL EVENTS IN LATE ANTIQUITY
    Alfonso López Borgoñoz <borgonoz@mx2.redestb.es>

(6) THE AD 540 EVENT
    Mike Baillie <m.baillie@qub.ac.uk>


===============
(1) NEW CALCULATIONS LEAVE CRITICS SPEECHLESS

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

In yesterday's CCNet Digest, Brian Marsden presented astronomical data
which show that, prior to Helin's and Lawrence's discovery of the 1990
films of asteroid 1997 XF11, there was "a small, but real" possibility
that this PHO could have collided with earth in the next century. I am
in no position to comment on whether or not Brian's sums add up. But
one thing seems obvious to me: Should Brian's data and calculations be
verified, this new twist in the XF11 controversy would prove his rather
outspoken "zero-risk" critics wrong.

Now, Brian has offered his opponents to "peer review" his data. So far,
however, no one seems prepared to come forward with an attempt to
falsify his calculations. Only Clark Chapman has responded to Brian's
challenge. But his reaction is somewhat contradictory and often
difficult to follow. As far as I understand, Clark's main objection is
that orbital calculations (even if they show the possibility of an
actual impact) are simply worthless since "background probability" as
such would rule out an impact in the first place. I don't know whether
I got this right, but this line of argument sounds exactly like the one
I was concerned about in the last question of my interview with Alan
Harris six weeks ago (see CNet Debates 28 April). If Clark is now
confirming that statistical "background probability" will become the
battle cry against actual orbit calculations, one wonders why we should
continue with the search for PHOs and calculate earth-crossing orbits
at all.

What is more, Clark's response to Brian's hard data provides an
impressive example of the enormous difficulties we still have - are are
prone to have in the future - in dealing with the uncertainties of NEO
research. Just imagine we wouldn't have the 1990 films of XF11. On 11
March 1998, Brian Marsden would send out to a dozen of astronomers
yesterday's calculations, showing a small, but probable impact scenario
in 2037. After consultations with his colleagues, seven of them agree
that the public should be informed about this data and the very small,
but possible risk this object might - due to future perturbations -
pose in 40 years time. Three other colleagues, however, argue that
"background probability" would rule out any risk and that no "scary"
statement should be issued before the year 2028. Since no 'consensus'
can be reached among the group of NEO experts, NASA officials veto the
submitted statement by the MPC and instead issue their own "zero-risk"
statement which follows the argumentation of the minority group. As a
response to NASA's decision, three of the seven scientists issue a
personal statement in which they present their own research findings
and calculations.

Now, you may think that this is a highly unlikely scenario. But I would
argue that this is how science has always been working, at least in
since the end of official censorship in England the 1640s. As far as I
can see, it is neither possible nor desirable to force scientists into
a 'consensus' on an issue so pervaded by uncertainties as the nature,
number and hazards of Near-Earth Objects.

Benny J Peiser

P.S. I should add that Brian Marsden provided the heading for his
statement in yesterdays's CCNet Digest. The heading for Clark's
statement below, however, is mine.

=========================
(2) 1997 XF11 WAS NOT DANGEROUS AT ANY TIME

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

Dear Benny,
 
It is a shame that Brian Marsden can't say, in simple English, in your
Digest: "I am sorry. We are overworked and underfunded here. In my
excitement on March 11th, I failed to make an elliptical error analysis
of 1997 XF11 that would have proven that the asteroid could not hit the
Earth in 2028. I furthermore mistook the one-dimensional error that I
did calculate to be a 3-sigma error when it was actually a 1-sigma
error, and therefore said things that weren't correct (e.g. that XF11
almost certainly would come within the lunar distance). Most
regrettably, I failed to check with my other colleagues around the
world who could have shown me my errors before I went public, and
people got confused and scared. Finally I regret waiting more than 5
weeks, until April 18th, to acknowledge that data were available months
earlier that would have showed, had I or anyone else chosen to examine
them, that 1997 XF11 had no realistic possibility of hitting the Earth
in 2028. I've learned my lesson from Comet Swift-Tuttle and now again
from 1997 XF11, and I promise not to make these errors again."
 
It would be so wonderful to hear that from Brian. Instead, he continues
to obfuscate matters. And he succeeds. A few days ago, on National
Public Radio's "Morning Edition," it was reported -- in a piece dealing
with the role of scientists interacting with journalists -- that
Brian's "initial calculation [was] based on that single sighting...and
then all the other scientists started saying, 'hey, have we seen that,
have we seen that?' and they came up with other sightings, and they
instantly went back out into the mass media world and said, 'we need to
correct this.'"
 
Now, that piece does ill credit to National Public Radio. "Single
sighting," indeed!  But it carries the essence of Brian's continuing
tale (repeated numerous times in news stories referenced in this
Digest) about the role of the 1990 observations in proving 1997 XF11
"safe". To be sure, those data may have helped educate *Brian* about
the impossibility of 1997 XF11 striking the Earth in 2028, but as the
CNN story (item #2 in today's CCDigest) says, Paul Chodas had found an
effectively zero threat the previous evening, "15 minutes after he had
the XF11 data in hand." Even when informed about Chodas' result, Brian
wouldn't admit his errors to the media (so some reporters told me on
March 12th).
 
In CCDigest, you have printed Brian's remarks under the heading, "I'm
Sorry, Clark, but 1997 XF11 Was Dangerous." I don't know if those are
Brian's words, or yours, Benny, but the heading should have ended with
the first two words. That's because the last four words are *false*. 
1997 XF11 was *not* dangerous at any time from its discovery by Jim
Scotti through today, if one uses anything resembling a common-sense
definition of the word "dangerous" [dictionary: "able to or likely to 
do harm"]. A particular asteroid is "dangerous" and potentially worthy
of the interest of the broader astronomical world and the news media
if, after it has been observed, it is found to present a significant
fraction of that tiny, but potentially devastating, risk we live with
all the time: namely, that one of those 1,750 km-wide asteroids that
have *not* (yet) been found will strike without warning.
 
I don't quibble with Brian's fascination with the calculating games he
describes in today's Digest. No doubt, there may be some tiny little
place(s) in that original extremely elongated error ellipse of 1997
XF11 which -- if it happened to pass through that place (extremely
unlikely!) -- would have resulted in subsequent evolution of its orbit
that might have been interesting, or even dangerous. But the chances
that it would have passed through that exact place and that all the
subsequent evolution would happen, so that 1997 XF11 could actually
strike the Earth in the next century were always extraordinarily tiny. 
Why don't you just say that, Brian, instead of once again saying that
the asteroid was actually "dangerous" and that we live in "peril"
[dictionary: "imminent danger"] unless every remote contingency isn't
checked out?
 
Brian continues to be confused by the concept of "exactly zero." 
Experts in risk management long ago concluded that you can never reduce
the risk of any hazard to "exactly zero".  Just because Brian can tweak
the numbers and find *some* way to have gotten 1997 XF11 to hit next
century, based on the data available last December or March, does not
mean that the asteroid was *ever* "dangerous" or newsworthy. No
credible person claims that something is "dangerous" just because the
probability of it happening isn't "exactly" zero.  Otherwise, we would
all cower in fear throughout our lives about countless near-zero
dangers.
 
Readers who have been following the 1997 XF11 saga will recall that I
was, also, highly critical of Don Yeomans for his "that's zero folks"
description of Paul Chodas's result.  Brian's example of an impact in
2037 surely illustrates why a claim of "exactly zero" misrepresents the
larger reality. It is perhaps as confusing to non-technical people as
Brian's claim that an extraordinarily improbable contingency is evidence
of "danger". 
 
It's all well and good that Helin and Lawrence found the earlier data
that tie down XF11's orbit. But it's a red herring to say that *those
observations* were responsible for proving XF11 was not dangerous. 
There *never was* a correctly calculated error probability (including
Brian's "what-if?" examples in today's Digest) of 1997 XF11 colliding
with the Earth at any time during the next century that remotely
approaches the "background" probability that we live with all the time.
 
It's time to admit it, Brian, and move on to more constructive
endeavors. I, for one, am working today on my response to the request
from Congress that I provide it with an "action plan" on how to get
NASA (and other national and international entities) working on an
adequate Spaceguard Survey. Certainly (and this is for Mr. Kobres) it
will include a recommendation for much enhanced funding for the MPC (or
some equivalent entity) to hire the people to analyze all of these data
comprehensively, and to double-check the results before going public
with scary mistakes.
 
Clark R. Chapman
8 June 1998

===============
(4) USAF NEWS RELEASE ON THE GREENLAND METEOROID IMPACT

From Duncan Steel <dis@a011.aone.net.au>

USAF NEWS RELEASE

From:   Headquarters Air Force Technical Applications Center  
        Office of Public Affairs           
        Patrick AFB, Fl.,
        32925-3002
        (407)-494-9915

Date: June 8, 1998

****************************************************************************
On 9 December 1997 at approximately 08:15:55.2 UT, sensors aboard a
U.S. Department of Defense satellite recorded the bright flash of an
apparent meteoroid disintegrating in the atmosphere over Greenland. The
peak radiated intensity recorded on this event  was 9.5E10 watts/sr
(using a 6000K blackbody model for the radiation). Correspondingly, the
total radiated energy of the event was 2.7E11 Joules.

If you have questions call MSgt Rene Uzee, Air Force Technical
Applications Center Public Affairs at, (407) 494-4403.)

*****************************************************************************
PLEASE NOTE: THIS USAF BOLIDE INFORMATION RELEASE AND ALL PREVIOUS
RELEASES CAN BE FOUND ON THE WWW AT
http://phobos.astro.uwo.ca/~pbrown/usaf.html
*****************************************************************************

Individuals interested in obtaining graphical lightcurve information
for this event should send an email with their names, fax numbers and
a description of their intended use of this information to 
peter@danlon.physics.uwo.ca

===========================
(4) ANOTHER COSMIC IMPACT MOVIE

From Steve Koppes <SKoppes@aol.com>

Another new made-for-TV impact movie, titled "Meteorites!" aired last
Wednesday evening (June 3) on the USA network. There were no big names
in this movie, which helps account for the dismal acting.

The plot involved a fictional Arizona town menaced by a deadly shower
of meteorites during a UFO festival (picture the meteorite shower of
Holbrook, Arizona, in 1912, only with many fatalities, crossed with the
celebration of aliens in Roswell, New Mexico, last summer). The movie
made reference to other parts of the country also sustaining damage
from the meteorite shower over several days, but the movie focused on
the little town in Arizona.

The movie did address the difference between a meteor and a meteorite,
and the fact that even small objects can leave relatively large holes
in the ground. There were the inevitable mistakes, however, probably
even more numerous than I am able to point out.

One of the actors -- I think it was the man portraying the director of
the Flandrau Planetarium -- said "the comet" had unexpectedly changed
course. He was actually referring not to a comet but to cometary
debris, which was being tracked by radar. I don't know much about
orbital mechanics, but is it really possible for a stream of meteors to
change course unexpectedly?

Another part that was rather hard to swallow was how so many of the
meteorites -- especially the earliest ones in the stream -- had such an
amazing propensity for landing on people. Nearly an entire family was
destroyed in one early scene. In another scene, a group of outdoorsmen
had the misfortune of experiencing their campsite turned into a crater.

I couldn't help but laugh out loud when an arrogant newspaper reporter
suffered a direct hit by a meteorite at the UFO festival. He was
vaporized, leaving behind only the smoke billowing from his shoes (is
that snickering I hear out there?).

Regards.
Steve Koppes

=======================
(5) A CLIMATE OF SECRECY IS THE GREATER EVIL

From Jens Kieffer-Olsen <dstdba@post4.tele.dk>

Re: AT LONG LAST: US SCIENTISTS REJECT NASA'S INTERIM PROCEDURES ON
    REPORTING PHOs

>"You can't control the flow of news but you can be as truthful as
>possible up front," said Allan Lindh of the U.S. Geological Survey.
>"The press, public and public officials seem to deal well with
>uncertainty, but they don't deal well with the suggestion you might
>hold out on them."

The public has been accustomed to sensationalism to such a degree that
the XF11 scare was treated as a lark by the layman. I therefore agree
with Allan Lindh that a climate of secrecy is the greater evil.

Illogical as it may seem, I suspect that a genuine scare could result
from a report by astronomers of an object due to pass safely at GEO
distance. Despite such an event being treated as a lark by scientists!

Jens Kieffer-Olsen

=======================
(5) STRANGE NATURAL EVENTS IN LATE ANTIQUITY

From Alfonso López Borgoñoz <borgonoz@mx2.redestb.es>

Dear Benny,

I have received this, do you know something about this?

----------------
Date:         Sat, 30 May 1998 18:11:11 +0300
Sender:       Late Antiquity Discussion Forum <LT-ANTIQ@VM.SC.EDU>
From:         korgianitis Dimitris <trim@OTENET.GR>
Subject:      Fw: Strange natural phenomens during Late Ant.

It is well known from several resources that strange natural phenomena
took place during the 5th and 6th. One of the most anusual is that
about the dissappearence of the sun. This is connected with 
earthquales, fires falling from the sky into the sea and floods that
has caused major damages all over the world. Does anyone know about any
possible cross-checking that maybe has been done by scientists? 
Thinking that if that`s true it could had a major effect to the
mentality of his age.

---------------
From:         Morten Axboe <m_axboe@IMAGE.DK>
Subject:      Strange natural phenomens during Late Ant.: AD 536

One such phenomenon was the 'dust-veil' or 'dry fog', which in 536
dimmed the sun for almost a year, leading to severe colds and failure
of crops. It is mentioned by Procopius, Cassiodorus and other
mediterranean writers, but also by Chinese sources, and can be
demonstrated dendrochronologically both in Europe and in Northern
America. The reason for this phaenomenon is disputed, but in itself it
seems beyond doubt and must have been serious on the whole Northern
hemisphere. The quotes I have found (see below) mention nothing about,
how Christian people actually reacted to this ominious 'dust-veil';
only that 'there was distress.. among men.. from the evil things.' But
what did they actually do to ward off the anger of God? Burn candles?
built new churches? Walk in processions? I am very interested if
anybody has any hints or references on this!

Some references:

Stothers & Rampino: Volcanic Eruptions in the Mediterranean Before A.D.
630 From Written and Archaeological Sources. Journal of Geophysical
Research Vol. 88, No. B6, pp. 6357-6371, Aug. 1983

M.G.L. Baillie: Marking in marker dates: towards an archaeology with
historical precision. World Archaeology Vol. 23 No. 2, pp. 233-243,
1991

M.G.L. Baillie: Dendrochronology raises questions about the nature of
the AD 536 dust-veil event. The Holocene 4,2, pp.  212-217, 1994

M.G.L. Baillie: A Slice Through Time. Dedrochronology and precision
dating. London 1995.

-------------
From:         Ralph Mathisen <N330009@UNIVSCVM.SC.EDU>
Subject:      Strange Natural Phenomena....

OK, for fires in the sky and volcanos, try :) R. Mathisen, "Nature or
Nurture - What Caused the Famines of Late ROman Gaul?", The Ancient
World 24(1993) 91-105.
-------------

From:         Matthias Bode <Bode@STUD-MAILER.UNI-MARBURG.DE>
Subject:      AW: Strange natural phenomens during Late Ant.: AD 536

One such phenomenon was the 'dust-veil' or 'dry fog', which in 536
dimmed the sun for almost a year, leading to severe colds and failure
of crops. It is mentioned by Procopius, Cassiodorus and other
mediterranean writers, but also by Chinese sources, and can be
demonstrated dendrochronologically both in Europe and in Northern
America.

Well, sounds quite like the special effects in DEEP IMPACT, doesn't it?
But seriously: Has anybody asked geologists if they have any impact
crater at hand that fits the year? And what about Greenland ice drill
cores? They were quoted on the list just recently in connection with
lead poisoning. A solution could be in the ice layers.
------

From:         Dio <dionysios@EARTHLINK.NET>
Subject:      Re: AW: Strange natural phenomens during Late Ant.: AD 536

Well, this is from memory and not specific, but just a couple of weeks
ago in the USA a television program aired on Discovery channel, I
believe, in concert with the release of Deep Impact, and went into as I
recall fairly scientifically (?) past evidence of real impacts. One was
described for the 6th century and a gentleman from Ireland was
interviewed who had been looking into dendrological evidence there. He
was convinced from it that indeed there was an impact somewhere in the
first halff of that century. Certainly it seemed to be one more than
usually fraught with earthquakes, etc,, unless the ancient sources are
just exaggerating for rhetorical effect, etc.
--------

From:         Matthias Bode <Bode@STUD-MAILER.UNI-MARBURG.DE>
Subject:      AW: Strange Natural Phenomena....

In our department library I found the following book:

D. Justin Schove & Alan Fletcher: Chronology of Eclipses and Comets AD 1 -
1000. The Boydell Press. 1984.

This book does not only list the things mentioned in the title, but
also all sorts of strange things that can be found in written sources.

For 536 they have ample evidence for some sort of dust-veil or dust
clouds blocking sunlight for almost a year. For example in Procopius
[dots already in the book]:

"during this winter Belisarius remained in Syracuse and Solomon in
Carthage. And ... during this year a most dread portent took place. For
the Sun gave forth its light without brightness, like the moon, during
this whole year, and it seemed exceedingly like the sun in eclipse, for
the beams it shed were not clear nor such as it is accustomed to shed. 
... And it was the time when Justinian was in the tenth year of his
reign." (Wars 4 = Vandal War 2, Ch 14.; Loeb 1916: p. 326-329)

The authors also quote a certain Michael the Syrian (12th C) as follows:

"...in the year of the Greeks 848 [AD 536] there was a sign in the sun.
Such a thing had never been seen before and it is nowhere written that
anyting similar had happened in the world ... the sun was dimmed, and
the darkening lasted a year and a half, that is to say, 18 months. Each
day it shone about four hours and even then the light was merely that
of a weak shadow. Everybody declared that its original light would
never return. The fruits did not ripen and wine had the taste of acid
grapes."

They also quote evidence from Greenland ice:

Hammer, C.U., Clausen, H.B. and Dansgaard, W. 1980 "Greenland ice-sheet
evidence of post-glacial volcanism and its climatic impact". NATURE
(288), 230-235. and: R.B. Stothers "Mystery cloud of AD 536" NATURE
(accepted) 1984.

That's all there is in the book by Schove and Fletcher. I haven't been
able to look into the articles in Nature yet. Schove and Fletcher think
the whole phenomenon is volcanic in origin.

==================
(6) THE AD 540 EVENT

From Mike Baillie <m.baillie@qub.ac.uk>

Having lived for some years with the AD 540 event (I call it the AD 540
event because the various effects in tree-ring chronologies centre on
AD 540, although the event itself is better defined as 536-545), and
having tried to find hints in ancient, and other, sources for the most
likely cause, I have found myself drawn away from the original Stothers
and Rampino volcano hypothesis (because of the lack of any clear
dramatic acid signal in the Greenland ice-core records) to what I
believe is the next most likely cause. To account for the environmental
downturn in the trees, and in human food crops, in the later 530s, and
to account for the dust-veil descriptions as picked up by the
volcanologists, the most likely cause has to be "loading of the
atmosphere by cometary debris" either through direct contact with a
comet (though obviously not a direct impact) or through interaction
with one of Clube and Napier's "cosmic swarms" of Tunguska class and
super-Tunguska class impacts. The obvious place to search for evidence
is in the ice core records. However as outlined in "A Slice Through
Time", page 104,(Routledge, London, 1995) there are problems with the
ice-core records in the sixth century AD. The worst problem is the loss
of 14 metres of the American GISP2 ice record between "545-613" on
their dating. I have therefore turned to historical and mythological
sources relevant to the period. In my view, these sources do not rule
out the possibility of a cometary interaction. I have written the story
up in a popular book format which will, with any luck, be published
this summer.  MB

Mike Baillie
Palaeoecology Centre
School of Geosciences, Queen's University, Belfast
(01232) 335147

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