PLEASE NOTE:


*

CCNet DIGEST, 17 August 1998
----------------------------

(1) THE VALUE OF THE 1997 XF11 PRECOVERY
    Brian G. Marsden <bmarsden@cfa.harvard.edu>

(2) NEO-GENERATED TSUNAMI & THE EAST COAST OF AUSTARLIA
    Michael Paine <mpaine@tpgi.com.au>

(3) SUGGESTIONS FOR IMPROVING THE CCNet FORMAT
    Iwan Williams <I.P.Williams@qmw.ac.uk>

(4) METEOR TRAILS ARE BEING USED AS CHEAP ALTERNATIVES TO SATELLITE
    SYSTEMS
    From New Scientist

(5) EVIDENCE OF ABRUPT K/T BOUNDARY IMPACT EVENT IN TUNESIA
    E. Robin & R. Rocchia, CEA, CNRS

(6) MASS EXTINCTION OF PLANCTIC FORAMINIFERA AT THE K/T BOUNDARY
    E. Molina et al., UNIVERSITY OF ZARAGOZA


=============
(1) THE VALUE OF THE 1997 XF11 PRECOVERY

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

One final piece of "unfinished business" in the 1997 XF11 affair is the
question of whether there is (or was) any conceivable danger from this
object once the 1990 observations had become available. At the time, in
the general confusion that occurred when these observations surfaced,
and given the misunderstanding in the press of the difference between
statements that were made before and afterwards, I was incorrectly
quoted as suggesting that there was. Obviously, any possible concerns
there might have been about the 2028 encounter immediately vanished
when the new data appeared. Nevertheless, it is legitimate to ask
whether the 1990 observations completely eliminated the possibility of
any danger from 1997 XF11 during the following decades and
centuries.

I am indebted to Graeme Waddington (Oxford) for bringing up this point.
As the first person to obtain a successful linkage of the observations
of comet 109P/Swift-Tuttle in 69 B.C. and A.D. 188, and one of my
co-authors in the first post-recovery definitive treatment of this
comet (Icarus, vol. 105, pp. 420-426, 1993), he takes an interest in
the nonlinear orbital problems that arise when the possibility of large
perturbations exists. In late June he fully confirmed my calculation
(June 8 CCNet Digest) that the 1997-1998 data on 1997 XF11 alone
allowed the possibility of an impact in 2037, and he told me he "found
a couple of 2040 shaves" before I had in fact given him my 2040-impact
computation (IAU Colloquium No. 172 and July 27 CCNet Digest).

That "2040" computation required a current (Epoch 1998 July 6) mean
distance of a = 1.4417866 AU.  What was particularly intriguing about
it, however, was the relatively close agreement (2 arcmin) with the
1990 observations and that its 2028 miss distance of 0.0050 AU (2 lunar
distances) was not greatly different from the 0.0064 AU the 1990
observations seemed to demand. In contrast, the "2037" computation, and
most of the other near-impacts I found, involved a substantially
smaller miss distance in 2028. So the question was: "Given the
information available with the publication of IAUC 6839 on March 12,
was there any possibility of a 2040 impact?".

Consider the following orbital elements:

Epoch 1998 July 6.0 TT = JDT 2451000.5                  Marsden
M 210.53744              (2000.0)            P               Q
n   0.56931567     Peri.  102.47969     +0.72513978     +0.68743581
a   1.4417854      Node   214.11724     -0.65626739     +0.67230478
e   0.4837830      Incl.    4.09506     -0.20853158     +0.27466033

These elements would bring 1997 XF11 to 0.005 AU in 2028 and to within
0.001 AU in 2040. I do not doubt that a small refinement could yield a
2040 collision. The important point about these elements is that they
satisfy the Helin-Lawrence observations of 1990 March 22-23 AND the
1997-1998 observations through Feb. 4 within a fully acceptable +/- 2
arcsec! It is true that the contentious Mar. 3-4 observations
(available to those involved in the orbit computations on Mar. 12 but
not formally published until Mar. 13) could not be included without
their showing systematic residuals of 3 arcsec. Since these
observations were quite isolated from the others, individual orbit
computers might judge differently as to whether they should be
considered seriously or not. 

While the remote possibility of a 2040 impact could thus perhaps not be
completely excluded on March 12, it is important to note that the
observations made later show systematic residuals up to 6 arcsec. 
Although these observations extended only to March 23, this extension
was clearly important (and it would probably not have existed without
the request on IAUC 6837). Furthermore, measurements from 1990 were
also subsequently reported by Bowell from the Shoemaker program.  These
observations were in both March and April, and those on the single
night of 1990 Apr. 23 yield residuals in excess of 15 arcsec from the
above "2040" solution.

We can conclude that the information currently available precludes the 
possibility of an impact by 1997 XF11 during the next half-century. 
The 2040 miss distance will rather clearly be about 0.18 AU. It was
certainly not possible to make that statement on March 11, however, and
it might even have been presumptuous to make it on March 12. So while
we might be inclined to breathe more easily when observations of a
troublesome PHA exist at multiple oppositions, it is still necessary to
be aware of possible orbital uncertainties.

Of course, this also works the other way. Much has been made of the
thought that if there is a good program of search and follow-up
observations, we are likely to become aware of an "actual" danger
decades (or more) before it is due. What if the 1990-1998 data had
yielded a fair probability of a 2040 impact for 1997 XF11?  How much
planning should then go into considering a "mitigation" of the danger? 
Yes, we should surely wait until after observations are made in 2002. 
O.K.: what if, even after 2002, a 2040 impact remains in the cards? 
Could we be sufficiently confident that we actually know what the
effect of the 2028 approach would be on the situation in 2040?  Put
another way, do we attempt our mitigation before or after 2028? If we
wait until after 2028, will there be enough time to guarantee that the
surgery is performed successfully?  If we do it before 2028, might not
the post-2028 situation differ from what we would expect--perhaps in a
way that would reduce the chance of success of another mitigation
attempt after 2028? Interesting questions...

What about danger from 1997 XF11 after the next half-century? In
connection with this, I felt that the summary statement by Morrison
(reproduced in the June 12 CCNet Digest) with its implication that we
really couldn't say anything about it beyond a century from now was
quite startling. It misses the whole point of what made 1997 XF11 so
interesting. Sure, we know that there will be modest encounters with
this object (to distances of 0.01-0.02 AU) in 2095 and 2172 (and in
addition to the lists we maintain at
http://cfa-www.harvard.edu/iau/lists/PHACloseApp.html , I draw
attention to http://www.brera.mi.astro.it/sormano/mbpl.html , the
useful webpage of the Sormano Astronomical Observatory: see the May 12
CCNet Digest). But the fact is that, after 1997 XF11's descending node
actually crosses the earth around the late 2030s, that node continues
to move inexorably away from the earth at a rate of something like
0.014 AU per century. This recession won't keep increasing for ever, of
course, but it will surely be many millennia before the earth crosses
either orbital node again.

No, don't get me wrong. I continue to believe that to search for
precovery observations is a very important integral part of any
worldwide NEO search program. We are still suffering from the 1996
termination of the Australian search program, which, of all such
programs, surely most recognized the value of precoveries. 
Furthermore, it is great to see that automation is now being applied to
find such observations more routinely in the Palomar film archives of
the Helin program. The first such automated success, involving 1993
observations of the recent PHA discovery 1998 OH, was just announced on
MPEC 1998-P23.

================   
(2) NEO-GENERATED TSUNAMI & THE EAST COAST OF AUSTARLIA

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

16 August 1998

Thanks to the subscribers who have given me suggestions about the
proposal to revive the Australian Spaceguard program
(http://www1.tpgi.com.au/users/tps-seti/sg_prop.html )

I am developing the section on tsunami effects further because I think
that the possible effects on the east coast of Australia could make the
politicians take notice (unfortunately they are currently going into
election frenzy). I have been involved in town planning issues in my
local government area of Warringah, which is probably one of the most
vulnerable spots along the coast (and also in the electorate of the
Federal Minister for Defence Science, Bronwyn Bishop). I also have a
good knowledge of the topography of the east coast - I knew my surfing
holidays along this coast would come in useful one day! I would
appreciate some feedback on the following text (for the derivation of
factors and links see
(http://www1.tpgi.com.au/users/tps-seti/spacegd7.html)

"Recent computer simulations have shed light on the consequences of
ocean impacts of asteroids or comets. Tsunami and hurricanes resulting
from the impact of even a relatively small NEO can cause fatalities and
damage equivalent to a large NEO striking land. For example a stony NEO
100m in diameter impacting the atmosphere above the ocean can cause an
80 metre tsunami 1,000 kilometres from the point of impact - there is 
a 1 in 20 chance of such an impact occurring in the next 50 years"
(Verschuur, "Impact!", 1996).

Even a 50m NEO can cause a 32m tsunami some 1,000 km from the impact
and there is  a 1 in 2 chance of such an impact somewhere above the
Earth's oceans in the next 50 years. With stony objects this size there
is unlikely to be an actual "impact" with the water - as it plunged
into the atmosphere at 90,000km/h the object would probably
disintegrate in massive explosion several kilometres above the ocean
and this would produce the tsunami.

The possible threat to locations on the shore of deep oceans

For an  indication of the possible threat to a given location, such as
Sydney, on the coastline of a deep ocean, assume that an above-ocean
impact of a 50m diameter NEO within a 3,000km radius constitutes a
threat (energy flux and therefore wave height is inversely proportional
to distance so the estimated tsunami height at 3,000km is 10m -  
similar to the recent New Guinea tsunami). This semi-circle constitutes
some 4% of the total surface area of the ocean and indicates that the
chances of such an impact in the next 50 years are about 1 in 50 or an
average interval between impacts of  2,500 years. Research by the
University of Wollongong suggests that the New South Wales South Coast
has been struck by at least six large tsunami within the last 10,000
years or an average interval of 1,700 years. The causes of the NSW
tsunami have not been identified. It could be giant underwater
"landslides" on the edge of the continental shelf but NEO ocean impacts
may have caused some (or all) of these tsunami.

Vulnerability the East Coast of Australia

The south east coast of Australia makes an sobering case study. This
coastline covers about 1,500 km from the Sunshine Coast in Queensland to
Eden in New South Wales. Many low lying coastal areas along the south
east coast of Australia have been intensively developed. Excluding the
non-coastal suburbs of Sydney and Brisbane, the total population along
this coastline is about 1.2 million. At this stage there does not
appear to have been any modelling of the build up of tsunami over the
east coast continental shelf and so this analysis is speculative but,
from the work by the University of Wollongong, it is evident that large
tsunami do reach the coast from time to time.

Consider the effects of a 10m tsunami like the one which hit northern
New Guinea in July 1998. Based the topography of coastal developments 
along the south east coast of Australia it is conservatively estimated
that about 50,000 dwellings, containing about 140,000 people (about 12%
of the population), are in areas which could be inundated by a 10m
tsunami. If it is assumed that these people are in or near their
dwellings (or similar vulnerable areas) for 50% of the time and that
the death rate from people caught in such a tsunami is 50% then it is
expected that 25% of the population would be killed. The predicted
death toll from one event which caused a 10m tsunami along the south
east coast of Australia is therefore 35,000 (25% of 140,000). This
could easily double during peak summer periods. The chances of such an
event being caused by a 50m asteroid are estimated to be about 1 in
2,500 in any one year therefore the annual expectancy is about 14
deaths per year (35,000/2,500). This is similar to number of deaths
expected from road crashes for a population of 140,000 in Australia.

It is stressed that this analysis is speculative but is probably very
conservative.

We really need to learn more about the risk of this type of event!"

=======================
(3) SUGGESTIONS FOR IMPROVING THE CCNet FORMAT

From Iwan Williams <I.P.Williams@qmw.ac.uk>

Dear Benny,

I enjoy reading all the communications that come from you under the
broad headings of CCdebates and CCdigest. However, in terms of what one
does with them afterwards could i suggest a different divison provided
this does not involve you in too much extra work.

At present the material sent falls into a number of categories, ie

1. Abstracts or reviews of papers in Refereed journals.
2. Newspaper and popular magazine type articles that (even though
   in some cases written by well respected authors) are not refereed
3. News items and reports (eg the UK Spaceguard report)
4, gossip, opinion, comments on previous contributions etc.

All are interesting and all are of value. However, items in 1, i would
like to keep for at least 2-3 years as a valuable reference source.

Items in 2 I might want to keep, but not for 2-3 years, I might also
want to be selective in what I keep.
3. I want to read but not keep
4. I want to glance through, read interesting bits but not keep.

It would thus help me enormously if these did not come mixed
up semi at random.

Hence:

1 - could go into a file (unread) at the given time.
2 - would go into a different file
3 - I would print out to read
4 - I would read on the screen, saving bits for printing if
    they loked interesting.

Thus i am sugesting four categories rather than the present two, for
example, CCabs, CCdigest, CCnews, CCdebate.

Thanks for the good work

Iwan Williams

-----------

Note: Finding most of Iwan William's suggestions convincing, I would
like to invite other list members to send me their comments and
additional suggestions regarding Iwan's proposals. I am certainly open
to and welcome ideas which would make the CCNet more user-friendly,
that is if it does not involve much additional work. After all, I've
also got a day-job.

Benny J Peiser 

========================
(4) METEOR TRAILS ARE BEING USED AS CHEAP ALTERNATIVES TO SATELLITE
    SYSTEMS

From New Scientist
UK Contact: Claire Bowles
claire.bowles@rbi.co.uk
44 171 331 2751

US Contact: Barbara Thurlow
newscidc@idt.net
(202) 452-1178

Meteor Trails Are Being Used As Cheap Alternative To Satellite Systems

Cold War Legacy Has Ended Up On The Streets Of Seattle

A COMMUNICATIONS system developed to keep the US military talking after
a nuclear war is now helping a private ambulance company monitor the
movements of its vehicles.

During the Cold War, the US military developed a method of sending data
by bouncing radio signals off meteor trails. Every day more than a
million specks of dust enter the Earth's atmosphere from deep space and
burn up, leaving trails of particles. Amateur radio operators had
noticed in the 1920s that they could bounce signals off these trails.
Although the trails last only a few tenths of a second, there are so
many that at any given time there are usually enough for a ground-based
transmitter to work with.

The high cost of developing the "Meteor Burst" system meant that the
project was cancelled when the Cold War ended. The scientists who
worked on the system left to set up a Seattle-based company called
StarCom Technologies, which has developed a civilian version as a cheap
alternative to satellite systems.

StarCom transmitters continually send probe signals to test for
reliable reflections. When a return signal is sensed, the transmitter
sends out a rapid burst of digital data at frequencies between 40 and
50 megahertz that can be picked up over a wide area. The data transfer
rates are low, up to 20 kilobits per second, and transmission time is
limited to a few hundred milliseconds per meteor, but this is
sufficient for uses such as monitoring vehicles' positions.

This is the purpose for which the system has been tested by a private
ambulance company, American Medical Response (AMR), which ferries
patients all over Washington State and Oregon. After successful tests
of prototypes over the past six months, the company this week began
fitting StarCom transceivers to a quarter of the 80 vehicles it uses to
serve Seattle and the surrounding area.

All the ambulances are fitted with a global positioning satellite
receiver as well as a StarCom transceiver, allowing them to continually
report their position back to AMR's Seattle control room. The system
enables the company to keep track of where an ambulance is and whether
it has a patient on board.

"We crosschecked the StarCom data with our own computer mapping and
feel pretty confident that it is hitting the mark," says Greg Sim of
AMR.

StarCom now wants to hide transmitters in vehicles that will
automatically send out a signal if the vehicle is stolen. The system
could also be used to interrogate measuring instruments in remote
areas.

"We are using the satellites which nature provides for free," says Guy
Rosbrook, StarCom's chief executive and a former Meteor Burst
scientist. "There are so many meteors that you can regard the sky
as a wide-area cracked mirror."

Author:Barry Fox
New Scientist issue 15th August 98, page 17

====================
(5) EVIDENCE OF ABRUPT K/T BOUNDARY IMPACT EVENT IN TUNESIA

E. Robin*) & R. Rocchia: Ni-rich spinel at the Cretaceous-Tertiary
boundary of El Kef, Tunisia. BULLETIN DE LA SOCIETE GEOLOGIQUE DE
FRANCE, 1998, Vol.169, No.3, pp.365-372

*) CEA, CNRS, LAB SCI CLIMAT & ENVIRONM, AVE TERRASSE, F-91198 GIF SUR
   YVETTE, FRANCE

Ni-rich spinel, a mineral formed by fusion and oxidation in the
atmosphere of meteoritic material, has been found throughout the world
at the Cretaceous-Tertiary (KIT) boundary, supporting the view that a
cosmic event did occur at the end of the Cretaceous. Here, we report on
the stratigraphic distribution of this mineral in the stratotype for
the K/T boundary at El Kef, Tunisia. This site is appropriate for the
detailed stratigraphical study of the K/T cosmic and biologic
catastrophes as it has a high sedimentation rate did is barely affected
by reworking. We observed that the stratigraphic distribution of spinel
is confined to a 1-3 mm rust colored layer that coincides with a
dramatic decrease of the carbonate fraction. This observation clearly
shows that the cosmic event and the biologic crisis took place abruptly
and developed rapidly, in less than 100 years, consistent with the
hypothesis of a large asteroid or cometary impact triggering the mass
extinction at the end of the Cretaceous. Chemical analyses of spinel
from El Kef reveal that it differs from spinel from other sites, even
close to El Kef, suggesting the accretion of several objects. This
result can be explained by the fragmentation of the bolide, either
before the impact (comet break-up) or upon the impact (oblique impact),
with in both cases, dispersion of the debris all over the Earth.
Copyright 1998, Institute for Scientific Information Inc.

=================
(6) MASS EXTINCTION OF PLANCTIC FORAMINIFERA AT THE K/T BOUNDARY

E. Molina*), I. Arenillas, J.A. Arz: Mass extinction in planktic
foraminifera at the Cretaceous/Tertiary boundary in subtropical and
temperate latitudes. BULLETIN DE LA SOCIETE GEOLOGIQUE DE FRANCE, 1998,
Vol.169, No.3, pp.351-363

*) UNIVERSITY OF ZARAGOZA, DEPT CIENCIAS TIERRA, E-50009 ZARAGOZA,
   SPAIN

The high resolution sampling across the Cretaceous/Tertiary (K/T)
boundary of the most expanded and continuous sections located in Spain
and Tunisia allows us to test and elucidate the extinction model of
Cretaceous planktic foraminifera in subtropical and temperate
latitudes. The planktic foraminiferal extinction occurred over a short
period, with 5% of the species disappearing in the late Maastrichtian,
70% of the species became extinct at the K/T boundary and about 25% of
the species are ranging into the early Danian. The species that became
extinct at the K/T boundary were large, complex tropical and
subtropical forms that dwelled in deep and intermediate water
depths. Their disappearance constitutes the largest and most sudden
extinction event in the history of planktic foraminifera. Nevertheless,
the small cosmopolitan surface dwellers with simple morphologies appear
to have survived and the last of them gradually disappeared in the
early Danian. The planktic foraminiferal extinction model can be
interpreted as a catastrophic mass extinction that was centred at the
K/T boundary, and was superimposed on a less evident and controversial
gradual mass extinction which apparently began in the late
Maastrichtian and continued into the early Danian. The catastrophic
pattern of extinction of 70% of the species at the K/T boundary is very
compatible with the effect of a large asteroid impact. Copyright 1998,
Institute for Scientific Information Inc.

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