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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