PLEASE NOTE:
*
CAMBRIDGE-CONFERENCE DEBATE, 3 April 1998
-----------------------------------------
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
============================
(1) ALL IN ALL, I CONSIDER THE XF11 AFFAIR A VERY GOOD THING
ALAIN MAURY <maury@ocar01.obs-azur.fr>
(2) LOTS OF WORDS, FEW OBSERVATIONS
Rob McNaught <RMN@AAOCBN3.AAO.GOV.AU>
================================
(1) ALL IN ALL, I CONSIDER THE XF11 AFFAIR A VERY GOOD THING
From: ALAIN MAURY <maury@ocar01.obs-azur.fr>
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
done.
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. :-)
Alain
======================
(2) LOTS OF WORDS, FEW OBSERVATIONS
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
(rmn@aaocbn.aao.gov.au)
*
CAMBRIDGE-CONFERENCE DIGEST, 3 April 1998
-----------------------------------------
(1) OLDEST ASTRONOMICAL MONUMENT RIVALS STONEHENGE
Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
(2) NEW PAPER BY ALVAREZ TEAM ON CHICXULUB IMPACT SCAR (in
French)
P. Claeys et al., Natural Science Museum,
Berlin
(3) HOW PIONEER 10 SURVIVED ENCOUNTER WITH ENCOUNTER WITH
DR KUIPER'S BELT
J.D. Anderson et al., Caltech, JPL
(4) COMETARY DUST & THE PICTORIS DISK
A.G. Li & J.M. Greenberg, Leiden
University
=============================
(1) OLDEST ASTRONOMICAL MONUMENT RIVALS STONEHENGE
From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
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
OLDEST ASTRONOMICAL MEGALITH ALIGNMENT DISCOVERED IN SOUTHERN
EGYPT BY
SCIENCE TEAM
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
Nabta.
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
http://www.colorado.edu/PublicRelations/Egypt.html.
===================================
(2) NEW PAPER BY ALVAREZ TEAM ON CHICXULUB IMPACT SCAR (in
French)
P. Claeys, J. Smit, A. Montanari and W. Alvarez: The Chicxulub
impact
crater and the Cretaceous-Tertiary boundary in the Gulf of Mexico
region, BULLETIN DE LA SOCIETE GEOLOGIQUE DE FRANCE, 1998,
Vol.169,
No.1, pp.3-9
*) NATURAL SCIENCE MUSEUM, INSTITUTE OF MINERALOGY, INVALIDENSTR
43, D-10115 BERLIN,GERMANY
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.
=====================
(3) HOW PIONEER 10 SURVIVED ENCOUNTER WITH ENCOUNTER WITH
DR KUIPER'S BELT
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,
pp.167-170
*) CALTECH, JPL, 4800 OAK GROVE DR, PASADENA,CA,91109
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
Press.
===========================
(4) COMETARY DUST & THE PICTORIS DISK
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
*) LEIDEN UNIVERSITY, ASTROPHYSICS LAB, POSTBUS 9504, NL-2300 RA
LEIDEN, NETHERLANDS
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.
--------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK
--------------------------------
The Cambridge-Conference List is a scholarly electronic network
moderated by Benny J Peiser at Liverpool John Moores University,
United Kingdom. It is the aim of this network to disseminate
information and research findings related to i) geological and
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civilisation due to comets, asteroids and meteor streams, and
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<b.j.peiser@livjm.ac.uk>.
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