Here are two more thought-provoking comments on the 'XF11 Affair'. Both
come from distinguised astronomers who have been actively involved in
NEO search programmes for many years - one in continental Europe, the
other in the Australia.

From the generally friendly and positive feed-back I have received
during the last week or so, I've got the impression that most list
members welcome this open and mostly respectful manner of our debate.

In fact, many people felt it most helpful and enlightening that some
of the main players in this drama were able to address the problems
raised by the XF11 Affair in an open and frank way. This enabled all of
us to learn about the actual difficulties, misunderstandings and
chain of events during a completely unprecedented situation. 

After many of us have voiced their views about who was right, who was
wrong and who was somewhere in between the firing lines, can I suggest
that we now focus our debates to the ideas for improvement which have
emerged and to the   p r a c t i c a l i t i e s  of all suggestions
brought forward.

Can I also wish all of those list members, who will be on holiday
as of Monday, a happy Easter, Passover, or simply a refreshing break
from all the flurry. (The rest of us will just have to keep going on
for another week ...)

Benny J Peiser



    Rob McNaught <RMN@AAOCBN3.AAO.GOV.AU>




I have read most of what has been going on on the 97XF11 affair.
Let me offer my personal perspective.

The few around here who search for Earth Grazing Asteroids are mostly
involved into this not for political, religious or financial reasons,
but because we know night after night, that despite the small search
area we are covering, there are many NEOs out there. There are
certainly much better ways to succeed in a scientific carreer than to
try to support an asteroid search program.

We seem to be out of phase with about everything which makes the rest
of the world: Our astronomer colleagues, who deeply hope to get back to
"normal affairs", and still consider most of us as nuts, the general
public, who has never seen a star, except in the background of
publicities, read astrology magazines, and places the astronomer's sky
(I mean space around us, the real thing ) among other concepts like the
one in which you can see an old man on a sledge every Xmas, or the sky
who has an effect on our daily sexual life, or the one in which we will
certainly go after our death, if we have been good.

There is an enormous amount of public information to be done to convey
a real image of the sky to these persons. For your information, there
are still some religious wars around (ask Mark Bailey), all this in the
inner edge of an arm of a galaxy we call our own, and because some
stupid jerks still think their god is better than the neighbours god.
There are still people who commit suicide because they happen to trust
another jerk who has told them wrong things about what a comet is. We
badly need to tell people what a comet or an asteroid is.

So all and all, I consider the XF11 affair a very good thing. I won't
enter into the why ans hows or the what we should or shouldn't have

Astronomers look like idiots who make mistakes in their calculations:
So what! We must explain to people that astronomy is not a religion, it
is a science. We always make mistakes in our calculations. If not, we
would be out of job. We must explain that this is part of science. Do
we look more stupid than astrophysicists who spend so much money into
the Space Telescope and still find stars which are older than the
Universe seem to be ? This "affair" is a very good way to explain what
science is, and we must follow upon this story to explain how it works.

There are asteroids out there which might collide with the Earth? So
what! This is what we have been saying all along. What a good occasion
to tell people how orbits are determined, and why it is important to
track down NEOs, and how calculations can allow predictions like the
one which was done. Tell the journalists about the web page of the MPC.
Tell them, also, that main stream astronomy still consider that,
despite supernovae explosions, black holes, galaxy collisions and other
very violent events astronomers have been used to, most of them still
consider the solar system a safe place to live, and why current NEO
searches have to rely on US Air Force funds instead of regular research
funds (sorry, Al, but as far as I know, NEAT and LINEAR are using
military telescopes, and Spacewatch, AANEAS and ODAS have received at
least some amount of US Air Force funds. In our case, it has been
determinant in the early stages of the devlopment of ODAS. Our CCD was
paid with US Air Force funds, it is not the 15000 francs/year received
last year as a budget by the OCA who have made ODAS possible. DLR is
helping, but the Air Force (through Pete Worden) has been very helpful
in the early stage).

The current status here is that we are running out of funds in June,
and will lay off 2 persons on a team of 4. The press papers have made
us a lot of good. There will be more XF11, people will get to learn
about asteroids, or there will be more Heavensgate phenomenon later on.
This is why we must take the opportunity to send more informations
about asteroids, orbit calculation and the solar system in which we
really live. They'll get to laugh at first, but the idea of our Earth
as a planet will slowly emerge. A planet on which there is intelligent
life in the form of people who are able to predict collisions with
asteroids in the future and some other who are able to do something
about it. Not a planet where there are people wanting to shut Marsden's
mouth down by creating committees and other things of the same order,
simply because they think it is not decent to think that there are
dangerous asteroids out there, and that it is certainly not decent to
try to do something about it.

1997 XF11 has been a magnificent example of how it all SHOULD work. If
there is such a thing as an Earth colliding asteroid out there, how
much would I love a replay of the 1997 XF11 affair (30 years to do
something) instead of a bright light in full daylight. How much smarter
we look when we are able to predict a possible collision, then reassure
everybody that it will not happen (even if the timing was not perfectly
right, a couple of months between the 2 circulars would have been
better, but this is how it came to be), and how really stupid we would
be if a single unexpected, unpredicted and unobserved Tunguska was to
happen next week even in an unpopulated area.

Don't spend energy on creating committees on what to tell and what not
to tell. Say things as they are. If indeed your calculations show that
95% of the potentially dangerous objects are still undiscovered out
there, stand by your calculations, and explain what it really all means
, use the opportunity to explain what least square fitting is and how
it works. Tell people they can do these calculations using data on the
internet, providing the CBAT would stop behaving as a black hole except
for the priviledged few who pay the extended computer service. I have
this gut feeling that you can't go wrong by saying things as they
really are.

Just a question: How was it possible to be "sure" that XF11 would not
collide with Earth using the 88 days arc ( I suppose 40000 km +/- 33000
km in order to avoid Earth )  when the 7 years arc orbit moved the miss
distance from 40000 or so km to 960000 km. As far as I am concerned,
the 40000km could not be so "sure" than they seem to be afterwards but
had somehow to be 40000 +/- 1000000km. Unless somebody has of course
made another mistake in his/her calculations...

C BAT man was right. and C Robin ( Williams ) as well. :-)



From: Rob McNaught <RMN@AAOCBN3.AAO.GOV.AU>

Clark Chapman urges the necessity of peer review. Was this the case
with the non-acceptance of my precovery of Hale-Bopp when Don Yeomans
made a public statement that the position appeared to be in error? It
wasn't and there was no error. It was Marsden who understood the 
possibility of systematic errors in the Hubble Guide Star Catalogue and
only he (as far as I am aware) who corrected Don's statement in public.

Clark also mentions the nonsense of the impending Icarus collision, but
has he forgotten the suggestion that Icarus' orbit indicated
non-gravitational effects? Was Don's article on the possibility of
non-gravitational effects on Icarus peer reviewed? Of course it was.  A
programming error that failed to include the routine calculating
relativistic effects on the orbit caused these small effects. At a
meeting, Sitarski questioned Don's analysis stating that his own
calculations indicated no trends in the residuals and thus there was no
need for non-gravitational effects. Don strenuously defended his
analysis at the meeting, but later corrected it in print.

I am not Don bashing. I admire Don very much, but everyone can make
mistakes and the peer review process does not always improve the
situation. To adamantly state that a theoretical analysis is the final
statement on a matter when there are possibly unknown systematic
effects (e.g. Hale-Bopp) is naive. What is needed are OBSERVATIONS. 
Opportunities for these to be made are often few and far between and a
general request for observations in the case of 1997 XF11 seemed
perfectly appropriate. It has occasionally happened in the past that
students on the 1.0-m at Siding Spring would read of something on the
IAUCs outside their normal field of study, and attempt observations. 
Presumably this also happens at other observatories. As there is still
no consensus about 1997 XF11, would this still be in the discussion
stage? When would a decision finally be made to request observations.
I am interested in how big 1997 XF11 really is. The "1 mile" estimate
based on a default albedo has been converted in the metric press to 1.6
km with no quoted uncertainty! The range 1 to 4 km is more appropriate.
I would hope that whilst the arguments rage back and forward, someone
has actually gone out and tried to determine the colour/albedo/size of
the object.

Rob McNaught



    Ron Baalke <>

    P. Claeys et al., Natural Science Museum, Berlin

    J.D. Anderson et al., Caltech, JPL

    A.G. Li & J.M. Greenberg, Leiden University


From: Ron Baalke <>

Office of Public Relations
University of Colorado-Boulder
354 Willard Administrative Center
Campus Box 9
Boulder, Colorado 80309-0009
(303) 492-6431

Contact: J. McKim Malville, (303) 492-8766
Jim Scott, 492-3114

March 31, 1998


An assembly of huge stone slabs found in Egypt's Sahara Desert that date
from about 6,500 years to 6,000 years ago has been confirmed by scientists
to be the oldest known astronomical alignment of megaliths in the world.

Known as Nabta, the site consists of a stone circle, a series of flat,
tomb-like stone structures and five lines of standing and toppled megaliths.
Located west of the Nile River in southern Egypt, Nabta predates Stonehenge
and similar prehistoric sites around the world by about 1,000 years, said
University of Colorado at Boulder astronomy Professor J. McKim Malville.
The Nabta site was discovered several years ago by a team led by Southern
Methodist University anthropology Professor Fred Wendorf. A 1997 GPS
satellite survey by Malville, Wendorf, Ali A Mazar of the Egyptian
Geological Survey and Romauld Schild of the Polish Academy of Sciences
confirmed one of the megalith lines was oriented in an east-west direction.

A paper on the subject by the four researchers will appear April 2 in the
weekly British science journal, Nature.

This is the oldest documented astronomical alignment of megaliths in the
world, said Malville. A lot of effort went into the construction of a purely
symbolic and ceremonial site The stone slabs, some of which are nine feet
high, were dragged to the site from a mile or more distant, he said.

The ruins lie on the shoreline of an ancient lake that began filling with
water about 11,000 years ago when the African summer monsoon shifted north.
It was used by nomads until about 4,800 years ago, when the monsoon moved
southwest and the area again became hyperarid and uninhabitable.

Five megalithic alignments at Nabta radiate outward from a central
collection of megalithic structures. Beneath one structure was a sculptured
rock resembling a cow standing upright, Malville said. The team also
excavated several cattle burials at Nabta, including an articulated skeleton
buried in a roofed, clay-lined chamber.

Neolithic herders that began coming to Nabta about 10,000 years ago --
probably from central Africa -- used cattle in their rituals just as the
African Massai do today, he said. No human remains have yet been found at

The 12-foot-in-diameter stone circle contains four sets of upright slabs.
Two sets were aligned in a north-south direction while the second pair of
slabs provides a line of sight toward the summer solstice horizon.

Because of Nabta=EDs proximity to the Tropic of Cancer, the noon sun is at its
zenith about three weeks before and three weeks after the summer solstice,
preventing upright objects from casting shadows. These vertical sighting
stones in the circle correspond to the zenith sun during the summer solstice
said Malville, an archeoastronomer. For many cultures in the tropics, the
zenith sun has been a major event for millennia.

An east-west alignment also is present between one megalithic structure and
two stone megaliths about a mile distant. There also are two other geometric
lines involving about a dozen additional stone monuments that lead both
northeast and southeast from the same megalith. We still don't understand
the significance of these lines Malville said.

During summer and fall, the individual stone monoliths would have been
partially submerged in the lake and may have been ritual markers for the
onset of the rainy season. The organization of these objects suggest a
symbolic geometry that integrated death, water and the sun Malville said.

Although some believe the high culture of subsequent Egyptian dynasties was
borrowed from Mesopotamia and Syria, Malville and others believe the complex
and symbolic Nabta culture may have stimulated the growth of the society
that eventually constructed the first pyramids along the Nile about 4,500
years ago.

The Nabta culture may have been a trigger for the development of social
complexity in Egypt that later led to the Pharaonic dynasty he said. The
Nabta project was funded primarily by the National Science Foundation.

The site also contains a wealth of cultural debris, including small,
fire-blackened stones from ancient hearths built along the ancient lakeshore
as well as manos, metates and carved and decorated ostrich eggshells.

Images of the project can be downloaded from the World Wide Web at


P. Claeys, J. Smit, A. Montanari and W. Alvarez: The Chicxulub impact
crater and the Cretaceous-Tertiary boundary in the Gulf of Mexico
No.1, pp.3-9


Geophysical anomalies clearly indicate a vast circular structure buried
under similar to 1 000 m of Cenozoic sediments of the Yucatan platform
(SE Mexico). Cores drilled in the structure indicate the presence of
suevite-like impact breccia, with abundant shocked minerals, and of a
melt-breccia dated by Ar-40/Ar-39 at similar to 65 Ma. The lithology
and age show that the Yucatan structure is thus the long sought
Cretaceous-Tertiary (KT) impact crater. The suevite and melt-breccia
are derived from the fracture and fusion of the lithologies present
under the Yucatan platform at the time of impact, a succession of
approximately 3 km of carbonate and evaporite sediments overlying a Pan
African age (550 Ma) silicate rich basement. The Chicxulub melts are
chemically similar to the fragments of impact glasses found at the KT
boundary all around the Gulf of Mexico. Impact glasses and shocked
quartz form the base of a 2 and 4 metres thick coarse clastic sequence
which marks the KT boundary from Alabama to Guatemala. These sands and
silts were probably deposited, over a short period of time (a few days)
by the gigantic tsunami waves triggered by the Chicxulub impact.
Because of the target lithology, the Chicxulub event must have almost
instantaneously released into the atmosphere huge quantities of water
vapor, CO2 and SO2. These components must have played a key role in the
perturbation of the global Earth system and mass extinction taking
place at the KT boundary. Copyright 1998, Institute for Scientific
Information Inc.


J.D. Anderson*), E.L. Lau, K. Scherer, D.C. Rosenbaum and V.L. Teplitz:
Kuiper belt constraint from Pioneer 10, ICARUS, 1998, Vol.131, No.1,


We extract information from the failure of small objects to cause
detectable damage to Pioneer 10, which has been inside the Kuiper Belt
for a decade, Belt objects too small for telescope detection and too
large for IR emission visibility are addressed. This is a size range
with few other potential techniques, short of a new space mission, for
direct detection. Results, based on an 8-inch radius propellant tank,
are bounds of about 1/10th of an Earth mass on low-mass, low-density
objects. Implications of Poynting-Robertson drag and ISM erosion, and
potential improvements to the bounds, are discussed. (C) 1998 Academic


A.G. Li & J.M. Greenberg: A comet dust model for the beta Pictoris
disk, ASTRONOMY AND ASTROPHYSICS, 1998, Vol.331, No.1, pp.291-313


The 10 mu m silicate emission feature and the continuum emission from
near infrared to millimeter of the dust in the disk of beta Pictoris
may be derived by assuming that the dust is continually replenished by
comets orbiting close to the star. The basic, initial dust shed by the
comets is taken to be the fluffy aggregates of interstellar silicate
core-organic refractory mantle dust grains (with an additional ice
mantle in the outer region of the disk). The heating of the dust is
primarily provided by the organic refractory mantle absorption of the
stellar radiation. The temperature of some of the particles close to
the star is sufficient to crystallize the initially amorphous
silicates. The dust grains are then distributed throughout the disk by
radiation pressure. The steady state dust distribution of the disk then
consists of a mixture of crystalline silicate aggregates and aggregates
of amorphous silicate core-organic refractory mantle particles
(without/with ice mantles) with variable ratios of organic refractory
to silicate mass. The whole disk which extends inward to similar to 1
AU and outward to similar to 2200 AU is divided into three components
which are primarily responsible respectively, for the silicate
emission, the mid-infrared emission and the far infrared/millimeter
emission. As a starting point, the grain size distribution is assumed
to be like that observed for comet Halley dust while in the inner
regions the distribution of small particles is relatively enhanced
which may be attributed to the evaporation and/or fragmentation of
large fluffy particles. The dust grains which best reproduce the
observations are highly porous, with a porosity around 0.95 or as high
as 0.975. The temperature distribution of a radial distribution of such
particles provides an excellent match to the silicate 10 mu m (plus
11.2 mu m) spectral emission as well as the excess continuum flux from
the disk over a wide range of wavelengths. These models result in a
total mass of dust in the whole disk similar to 2 x 10(27) g of which
only 10(-5) - 10(-4) is hot enough to give the silicate excess
emission. The specific mineralogy of crystalline silicates has been
discussed. Copyright 1998, Institute for Scientific Information Inc.

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