PLEASE NOTE:
*
CCNet DIGEST, 15 October 1998
-----------------------------
(1) CHAOTIC ORBITS, NON-GRAVITATIONAL FORCES & AND THE
LIMITATIONS OF
IMPACT COMPUTATION
Duncan Steel <dis@a011.aone.net.au>
(2) PREDICTIONS, GOOD AND BAD
THE NEW YORK TIMES, Science Times, page D3,
Tuesday, Oct. 13
(3) EUROPEAN GEOPHYSICAL SOCIETY MEETING 1999
Detlef Koschny <dkoschny@estec.esa.nl>
(4) STILL NO LIMITS TO SCIENCE
THE TIMES, 15 October 1998
http://www.sunday-times.co.uk:80/news/pages/Times/frontpage.html?1617548
(5) THE PROBLEM OF CONFIRMING THE IMPACT ORIGIN OF SMALL CRATERS
C. Koeberl et al., UNIVERSITY OF VIENNA
(6) SCALING ANALYSIS OF METEORITE SHOWER MASS DISTRIBUTION
L. Oddershede et al., TECHNICAL UNIVERSITY OF
DENMARK
(7) MICROMETEORITES FROM ANTARCTICA
C. Engrand & M. Maurette, UCLA
(8) SHOCK-INDUCED EFFECTS OF METEORITE IMPACT CRATERS ON EARTH
I. Martinez*) & P. Agrinier, IPGP, PARIS
(9) JUPITER'S GREAT INEQUALITY & ASTEROID ORBIT EVOLUTION
S. Ferraz Mello et al., UNIVERSITY OF SAO
PAULO
(10) LIFE FLOURISHED WHEN EARTH WAS WARMER
Andrew Yee <ayee@nova.astro.utoronto.ca>
===========================
(1) CHAOTIC ORBITS, NON-GRAVITATIONAL FORCES & AND THE
LIMITATIONS OF
IMPACT COMPUTATION
From Duncan Steel <dis@a011.aone.net.au>
Dear Benny,
I found the item:
>G. Sitarski: Motion of the minor planet 4179 Toutatis: Can we
predict
>its collision with the Earth? ACTA ASTRONOMICA, 1998, Vol.48,
No.3,
>pp..547-561
to be extremely interesting. Lest anyone start bickering about
personalities and whether the people involved know what they are
doing, let me suggest that they immediately remove to a library,
look out Astronomy & Astrophysics Abstracts, and discover for
themselves what epic work Sitarski has done over the years in the
area of dynamics of asteroids and comets, in particular
considering
orbital solutions accommodating non-gravitational forces.
Now let me say why I find this paper very significant, given
events
of the past seven months. Sitarski, having available
astrometry of
(4179) Toutatis stretching over an arc of 63 years, identifies a
clear but small non-gravitational force. One presumes that
he has
accommodated relativistic effects so that this is not a
computational
artifact. The asteroid is therefore, it seems, outgassing:
perhaps
an almost extinct comet (or maybe it will spring back into life
and
follow an even more chaotic path)? A ramification Sitarski
identifies
is the impossibility of predicting the path of this object over
the
next few centuries.
The punchline is so clear that I hardly need to state it. All
solutions
for the anticipated orbital evolution of 1997 XF11 are based upon
a
presumption that only gravitational influences apply. The
observed
arc is (I imagine) too short to allow the identification of
non-gravitional forces of the order identified by Sitarski in the
case
of Toutatis. So how sure are we now about the path that 1997 XF11
will
take?
Duncan Steel
==============
(2) PREDICTIONS, GOOD AND BAD
From THE NEW YORK TIMES, Science Times, page D3, Tuesday, Oct. 13
To the Editor:
William K. Stevens makes valid points about scientific
predictions
("When Scientific Predictions Are So Good They're Bad",
Sept. 29), but
his reference to the stir last March about the possibility of an
asteroid strike in 30 years beautifully illustrates that much of
the
problem lies in how scientific information is presented. My
prediction
was merely that the asteroid in question would come close,
possibly
uncomfortably close. The statement that there was a
"one-tenth of 1
percent" chance of a hit came from another scientist who
misinterpreted
what I had said.
Malcolm Browne's March 12 front-page story ("Asteroid Is
Expected to
Make a Pass Close to Earth in 2028") correctly said that
there was "no
immediate cause for alarm", that there was some uncertainty
in the
computation of the object's distance and that further
observational
data were being sought to narrow down the uncertainty.
Such data became available later that day, something that would
obviously not have happened in the absence of some kind of
announcement. That resulting refined distance of 600,000 miles
for
2028, while safely more than twice the distance of the moon, is
still
the closest for any asteroid of which we have advance knowledge
until
2086.
My prediction was not "erroneous." It was an
appropriate conclusion
from the information available at the time, and it led to the
discovery
of the data from 1990 that showed the asteroid to be
"safe." That
outcome was not only encouraging, but also illustrative of how
the
scientific process works.
DR. BRIAN G. MARSDEN
Cambridge, Mass.
The writer is the associate director for planetary sciences at
the
Harvard-Smithsonian Center for Astrophysics.
=====================
(3) EUROPEAN GEOPHYSICAL SOCIETY MEETING 1999
From Detlef Koschny <dkoschny@estec.esa.nl>
The next meeting of the EGS, the European Geophysical Society,
will
take place in The Hague in the Netherlands from 19-23 April 1999.
Session PS8 will be on "Meteors and meteor swarms",
convener is Klaus
Scherer at the Max-Planck-Institut for Aeronomy in Lindau,
Germany,
Co-Convenor is Peter Jenniskens, NASA. The text in the EGS
newsletter
says:
"The new developments in observations and aerodynamics of
meteors
should be presented. Special empahsis should be put onto the
latest
observations of the Leonid shower during Novemnber 1998 which is
expected to have a huge meteor rate. First results from the
international Leonid observation campaign shall be
available."
Also of interest to you might be PS7, Small bodies and dust,
Convener
G. Schwehm, ESA.
Check the EGS web page for more info,
http://www.mpae.gwdg.de/EGS/egsga/denhaag99/denhaag99.htm
Detlef/Laffy.
===========================
(4) STILL NO LIMITS TO SCIENCE
From THE TIMES, 15 October 1998
http://www.sunday-times.co.uk:80/news/pages/Times/frontpage.html?1617548
Arthur C. Clarke finds there are still many reasons to boldly go
where
no one has gone before
WHAT REMAINS TO BE DISCOVERED
By John Maddox, Macmillan, £20, ISBN 0 333 65008 5
The title of this book is memorable in more ways than one. Drop
the
first word, and we're in Agatha Christie territory. The
association is
not altogether facetious, for John Maddox is concerned with the
biggest
of all whodunnits - the Locked Universe Mystery, and mankind's
never-ending attempts to solve it.
A few years ago, in a television programme which also featured
the late
Carl Sagan, I was privileged to ask Stephen Hawking the question:
does
the sequence of ever-smaller entities - molecule, atom, nucleus,
quark
- continue indefinitely, or is there a limit, when we finally
reach
something as indivisible as the atom was once thought to be? I
was not
sure that I would be able to understand his answer, as I stopped
reading about nuclear physics when what are laughingly called
fundamental particles began to exceed the number of elements.
Dr Hawking answered that there probably is a basic structure to
the
universe, below which nothing exists, and that it obeys a fairly
simple
theory, adding: "I only hope we are smart enough to find
it."
This is the sort of question that John Maddox discusses, and
after more
than 20 years as editor of Nature, the world's premier science
journal,
he is in a unique position to survey the current field of human
knowledge. He has seen scientific fashions come and go, and -
unlike
Stephen Hawking - is quite sceptical about "Theories of
Everything".
As he demonstrates, scepticism - or at least caution - is
advisable
even in areas where science seems to have said the last word. For
example, Wegener's theory that the continents might once have all
been
joined together was regarded for decades as total nonsense.
"The only
time," one scientist wrote in his memoirs, "I have ever
seen a man
literally foaming at the mouth, is when I mentioned continental
drift
to a distinguished geologist." Yet through its modern
incarnation as
plate tectonics, this heresy has become a key to our
understanding of
Earth's early history.
It has been said that any new and revolutionary idea goes through
four
stages: (1) "It's crazy"; (2) "It may be true, but
it's not important";
(3) "I said it was a good idea all along"; and finally,
(4) "I thought
of it first". Unfortunately for Wegener, who compounded his
felony by
being a meteorologist and not a geologist, he never lived to
enjoy
even stage three.
What Remains to be Discovered opens with a lengthy introduction -
"The
River of Discovery" - which makes the point that
"modern" science is
only 500 years old, and at the close of every century it seemed
to many
philosophers that their world picture was essentially complete,
apart
from minor details that would soon be filled in. At least, there
would
be no more surprises.
It has been famously said that we learn nothing from history, and
this
is amply demonstrated by the fact that voices are now being heard
echoing this same point of view. But John Maddox cautions:
"Despite
assertions to the contrary, the lode of discovery is far from
worked
out. This book provides an agenda for several decades, even
centuries,
of constructive discovery that will undoubtedly change our view
of our
place in the world as radically as it has been changed since the
time
of Copernicus."
Although centuries are arbitrary divisions, based on the
evolutionary
accident that we happen to have ten fingers, it does seem
remarkable
that it was almost exactly 100 years ago that the bottom fell out
of
Victorian physics with the discovery of X-rays ("A
hoax!" - Lord
Kelvin) and the electron.
The next few years may see a repeat performance: as I read
reports of
mysterious astronomical objects and anomalous energy production
(aka
"cold fusion" - though often it is clearly nothing of
the sort) I have
a distinct "this is where we came in" feeling. And I am
reminded of the
legendary Superintendent of the U.S. Patent Office, who near the
end of
the last century suggested that his department should be closed
because
"there was nothing important left to invent". I say
"legendary",
because the story is self-evidently untrue: whoever heard of a
bureaucrat proposing the dissolution of his own fiefdom?
Maddox divides his book into three: "Matter" ("in
which the origins of
the universe and matter are explored"); "Life"
("in which the origin of
life is considered as well as biological machinery, the riddle of
the
selfish gene, and the next human genome projects"); and
"Our World"
("in which the nature of our brain is explained, as well as
our
greatest invention, mathematics").
As a comprehensive account of the current world view (and its
deficiencies), this book could hardly be bettered, and makes a
convincing point that any limits to discovery - if indeed they
exist -
still lie far in the future. But the haunting question remains:
are
there limits to human understanding? In almost any field of
science, it
now takes most of a lifetime to reach the frontier of knowledge.
The
inevitable result will be extreme specialisation, when countless
experts will know everything about nothing. This may be the final
century of the polymath; perhaps the last specimen of that once
flourishing species may have been J. B. S. Haldane, who died in
1964.
No self-respecting reviewer can sign off without picking some
nits, and
there is a major understatement in footnote four - repeated,
though
with typos which might baffle non-mathematical readers, in
footnote 22.
The Pythagoras equation a + b = c does not have merely
"several"
integral solutions: it has what is known in the profession as a
countably infinite number.
Trust me . . .
Arthur C. Clarke's latest book, 3001, is published by Voyager,
priced £5.99.
Copyright 1998, Times Newspapers Ltd.
===============
(5) THE PROBLEM OF CONFIRMING THE IMPACT ORIGIN OF SMALL CRATERS
C. Koeberl*), W.U. Reimold, S.B. Shirey: The Aouelloul crater,
Mauritania: On the problem of confirming the impact origin of a
small
crater. METEORITICS & PLANETARY SCIENCE, 1998, Vol.33, No.3,
pp.513-517
*) UNIVERSITY OF VIENNA,INST GEOCHEM,ALTHANSTR 14,A-1090
VIENNA,AUSTRIA
The impact origin of small craters in sedimentary rocks is often
difficult to confirm because of the lack of characteristic shock
metamorphic features. A case in point is the 3.1 Ma Aouelloul
crater
(Mauritania), 390 m in diameter, which is exposed in an area of
Ordovician Oujeft and Zli sandstone. We studied several fractured
sandstone samples from the crater rim for the possible presence
of
shock metamorphic effects. In thin section, a large fraction of
the
quartz grains show abundant subplanar and planar fractures. Many
of the
fractures are healed and are evident only as fluid inclusion
trails. A
few grains showed sets of narrow and densely spaced fluid
inclusions
trails in one (rarely two) orientations per grain, which could be
possible remnants of planar deformation features (PDFs), although
such
an interpretation is not unambiguous. In contrast, an impact
origin of
the crater is confirmed by Re-Os isotope studies of the target
sandstone and glass found around the crater rim, which show the
presence of a distinct extraterrestrial component in the glass.
Copyright 1998, Institute for Scientific Information Inc.
============
(6) SCALING ANALYSIS OF METEORITE SHOWER MASS DISTRIBUTION
L. Oddershede*), A. Meibom, J. Bohr: Scaling analysis of
meteorite
shower mass distributions. EUROPHYSICS LETTERS, 1998, Vol.43,
No.5,
pp.598-604
*) TECHNICAL UNIVERSITY OF DENMARK,DEPT PHYS 307,DK-2800
LYNGBY,DENMARK
Meteorite showers are the remains of extraterrestrial objects
which are
captivated by the gravitational field of the Earth. We have
analyzed
the mass distribution of fragments from 16 meteorite showers for
scaling. The distributions exhibit distinct scaling behavior over
several orders of magnitude; the observed scaling exponents vary
from
shower to shower. Half of the analyzed showers show a single
scaling
region while the other half show multiple scaling regimes. Such
an
analysis can provide knowledge about the fragmentation process
and
about the original meteoroid. We also suggest to compare the
observed
scaling exponents to exponents observed in laboratory experiments
and
discuss the possibility that one can derive insight into the
original
shapes of the meteoroids. Copyright 1998, Institute for
Scientific
Information Inc.
=================
(7) MICROMETEORITES FROM ANTARCTICA
C. Engrand*) & M. Maurette: Carbonaceous micrometeorites from
Antarctica. METEORITICS & PLANETARY SCIENCE, 1998, Vol.33,
No.4,
pp.565-580
*) UCLA,DEPT EARTH & SPACE SCI,LOS ANGELES,CA,90095
Over 100 000 large interplanetary dust particles in the 50-500 mu
m
size range have been recovered in clean conditions from similar
to 600
tons of Antarctic melt ice water as both unmelted and partially
melted/dehydrated micrometeorites and cosmic spherules. Flux
measurements in both the Greenland and Antarctica ice sheets
indicate
that the micrometeorites deliver to the Earth's surface similar
to
2000x more extraterrestrial material than brought by meteorites.
Mineralogical and chemical studies of Antarctic micrometeorites
indicate that they are only related to the relatively rare CM and
CR
carbonaceous chondrite groups, being mostly chondritic
carbonaceous
objects composed of highly unequilibrated assemblages of
anhydrous and
hydrous minerals. However, there are also marked differences
between
these two families of solar system objects, including higher C/O
ratios
and a very marked depletion of chondrules in micrometeorite
matter;
hence, they are ''chondrites-without-chondrules.'' Thus, the
parent
meteoroids of micrometeorites represent a dominant and new
population
of solar system objects, probably formed in the outer solar
system and
delivered to the inner solar system by the most appropriate
vehicles,
comets. One of the major purposes of this paper is to discuss
applications of micrometeorite studies that have been previously
presented to exobiologists but deal with the synthesis of
prebiotic
molecules on the early Earth, and more recently, with the early
history
of the solar system. Copyright 1998, Institute for Scientific
Information Inc.
====================
(8) SHOCK-INDUCED EFFECTS OF METEORITE IMPACT CRATERS ON EARTH
I. Martinez*) & P. Agrinier: Meteorite impact craters on
Earth: major
shock-induced effects in rocks and minerals. COMPTES RENDUS DE L
ACADEMIE DES SCIENCES SERIE II FASCICULE A-SCIENCES DE LA TERRE
ET DES
PLANETES, 1998, Vol.327, No.2, pp.75-86
*) IPGP,4 PL JUSSIEU,F-75252 PARIS 05,FRANCE
The basic principles of the physics of shock waves are
summarised,
showing how shock pressures, shock and post-shock temperatures,
and
shock durations can be estimated in the case of large meteorite
impacts
on Earth. In a second part, the pertinence of laboratory
high-pressure
dynamic experiments for simulating large meteroite impact events
and
for calibrating their physical conditions is discussed. It is
concluded
that most shock features are common to natural and laboratory
shocks,
although the lifetime of experimental shocked states is shorter
by
several orders of magnitude. Then, a review is made of the major
shock
effects observed in minerals and rocks. Quartz has been by far,
the
most extensively studied shock mineral. particularly, planar
deformation features (PDFs), interpreted as resulting from
relaxations
at the shock front, are unambiguous shock indicators, for shock
pressures approximately between 15 and 35 GPa. At higher
pressures, the
formation of high-pressure polymorphs of SiO2 in shocked quartz
is also
discussed. Shock effects in some other selected minerals,
although less
extensively studied, are also reviewed, with special emphasis on
the
discovery of diamonds at impact sites and of all the
high-pressure
polymorphs of olivines an pyroxenes, including silicate
perovskite, in
shocked meteorites. Finally, the controversial links between
large
impacts and major environmental effects are discussed in a
fourth part. ((C) Academie des sciences/Elsevier, Paris).
=============
(9) JUPITER'S GREAT INEQUALITY & ASTEROID ORBIT EVOLUTION
S. Ferraz Mello*), T.A. Michtchenko, F. Roig: The determinant
role of
Jupiter's Great Inequality in the depletion of the Hecuba gap.
ASTRONOMICAL JOURNAL, 1998, Vol.116, No.3, pp.1491-1500
*) UNIVERSITY OF SAO PAULO,INST ASTRON & GEOFIS,CP 3386,AVE
MIGUEL
ESTEFANO 4200,BR-04301904 SAO PAULO,BRAZIL
This paper deals with the influence of Jupiter's ''Great
Inequality''
(GI) on the orbital evolution of 2:1 resonant asteroids. This
perturbation of Jupiter's motion enhances the chaotic diffusion
of
orbits and the depletion of asteroids in the Hecuba gap. The
failure of
models that adopt for Jupiter an elliptic motion with only
secular
perturbations is explained. We also show the dependence of the
diffusion rates on the GI period, and the maximum diffusion rates
that
would take place if the GI period were closer to the libration
period.
Significant similar effects are absent in the 3:2 asteroidal
resonance.
Copyright 1998, Institute for Scientific Information Inc.
================
(10) LIFE FLOURISHED WHEN EARTH WAS WARMER
From Andrew Yee <ayee@nova.astro.utoronto.ca>
News Services
University of Arizona
Contact(s): Judith Totman Parrish, 520-621-4595,
parrish@geo.arizona.edu
October 14, 1998
Life flourished when Earth was warmer, scientist says
The threat of a global warming doesn't scare Judith Parrish, a
geologist at the University of Arizona in Tucson and an expert on
ancient climates.
She's seen the ghost of the distant past in fossil leaves from
the mid-
Cretaceous, about 100 million years ago. These long-dead leaves
tell
tales of a warmer climate, when forests grew in the now-barren
polar
regions.
"Life flourished when the climate was warmer," said
Parrish, UA
professor of geosciences. Her book, "Interpreting
Pre-Quaternary
Climate from the Geologic Record," is being released this
month. The
Quaternary represents roughly the last 2 million years, a time of
recurring ice ages when continental glaciers sometimes stretched
as far
south as Illinois.
"The last 2 million years don't have anywhere near the full
range of
climate history," Parrish emphasized. "The lack of ice
during the
Cretaceous is typical. Having the great big ice caps is not
typical."
The Cretaceous describes the period 113 million to 65 million
years
ago, when dinosaurs roamed the planet. Geological evidence
indicates
that during the Cretaceous, as during much of the Earth's
history, the
planet was much warmer than it is today -- and generally warmer
than it
is projected to be in the next few centuries as the result of a
buildup
in greenhouse gases.
Some of that evidence comes from Parrish's own research,
including a
paper she recently wrote with colleagues on the vegetation found
near
the South Pole during the mid-Cretaceous. The team of researchers
traveled to locations in New Zealand to examine sediments and
fossils
deposited during the mid-Cretaceous, using methods they had
developed
for a previous project in Alaska.
When the fossils were deposited in what are now New Zealand and
Alaska,
the land masses under scrutiny were both located at latitudes of
between 70 and 85 degrees -- within the polar circles that are
shrouded
in continuous darkness for several months every year. Latitudinal
lines
run from the middle of the planet to its tip, starting at 0
degrees
around the equator and continuing to 90 degrees North and South
at each
pole.
Yet despite the darkness and polar location, the fossils
indicated that
the lands in question supported a thriving forest during the
mid-Cretaceous. Parrish and her colleagues believe the forests
resembled modern-day forests of western Oregon, with a canopy of
cone-bearing trees shading an understory of ferns and horsetails.
Unlike modern pine trees, though, the Cretaceous conifers
apparently
shed their leaves every year. Present-day Oregon forests thrive
at 45
degrees North but fade into a different forest type by about 50
degrees
North.
"By the time you get up to British Columbia, the diversity
of the
understory has dropped," Parrish said. The boreal forest,
which ranges
up to about 70 degrees North, has much smaller trees and fewer
species,
she noted. "By that time, they're scrawny little things.
It's generous
to call them trees."
The size of local plant life tends to increase with warmer
temperatures, given enough water for ample growth. But the shape
of the
leaves yields even more information for researchers looking for
clues
on past climates. In fact, Jack A. Wolfe, a scientist based at
the UA
Desert Laboratory on Tumamoc Hill in Tucson, developed a
successful
method for estimating annual average temperature of a region by
comparing leaf shapes of local plants.
Parrish and her colleagues applied Wolfe's technique to their
polar
forests. The results? They estimated that the average annual
temperature around the poles during the mid-Cretaceous was about
10
degrees Celsius, or roughly 50 degrees Fahrenheit.
Yet the warmer poles did not necessarily mean hotter tropical
climates,
as Parrish points out. Other researchers have found evidence for
relatively stable temperatures in the lower latitudes around the
equator when comparing the Cretaceous to modern times.
"When you have global change, the action is in the higher
latitudes,"
Parrish explained. Computer models today predict most of the 2 to
7
degree Fahrenheit warming expected over the next century will
also be
centered on the poles rather than tropical regions.
There is at least one consequence of a future warming that could
adversely affect many people, however: Sea level is expected to
rise by
as much as 3 feet over the next century as water trapped in
continental
ice melts into the ocean and inundates coastal cities.
"It's more a social problem than anything else,"
Parrish said of the
perceived threat of global warming. "It's just that 80
percent of the
population has chosen to live near coastal areas."
LINKS:
http://www.geo.arizona.edu/
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