PLEASE NOTE:


*

CCNet, 28/2000 - 6 March 2000
-----------------------------


     QUOTES OF THE DAY

     "Eight hundred thousand years ago, a meteorite blasted into what
     is now Vietnam, burning forests, killing off wildlife and probably
     badly frightening the pre-humans who lived there. But eventually,
     the hominids came back, perhaps having survived the explosion in
     limestone caves or perhaps wandering in from neighboring regions
     decades later. They found a freshly exposed outcropping of rock,
     perfect for making stone tools. Archaeologists say they have found
     those tools - the oldest stone axes ever discovered in China."
       -- MSNBC, 2 March 2000


     "It seems counterproductive to indiscriminately discount handed
     down lore when searching for clues of what caused this most recent
     Ice Age transition when we know that our ancestors witnessed the
     change. A change that did not allow the survival of a large number
     of animals, particularly on the North American continent, that had
     endured glacial to interglacial transitions in the past."
         -- Bob Kobres, 6 March 2000


(1) DID 800k IMPACT AFFECT HUMAN CULTURE?
    Bob Kobres <bkobres@uga.edu>

(2) PRE-HISTORIC IMPACTS
    Michael Paine <mpaine@tpgi.com.au>

(3) NOT A BAD STORY, IF YOU AX ME ....
    Alan Boyle <alan.boyle@MSNBC.COM>

(4) ARE MARTIANS ALIVE BUT HIDING?
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(5) RUMOR OF COMET IMPACTING MARS IS FALSE
    Ron Baalke <BAALKE@kelvin.jpl.nasa..gov>

(6) NEW LAB READY TO TEST SUDDEN IMPACTS
    NASA News <NASANews@hq.nasa.gov>

(7) PRODUCTION OF STAR-GRAZING & STAR-IMPACTING PLANETESIMALS
    A.C. Quillen & M. Holman, UNIVERSITY OF ARIZONA

(8) ANALYSIS OF NANOGRAM-SIZED ASTROMATERIALS
    M.E. Zolensky et al., NASA,LYNDON B JOHNSON SPACE CTR

(9) PLANET & ASTEROID FORMATION IN THE PRESENCE OF GIANT PLANETS
    S.J. Kortenkamp & G.W. Wetherill, CARNEGIE INST WASHINGTON

(10) LONG-TERM DYNAMICS OF BRIGHT BOLIDES
     L. Foschini et al., UNIVERSITY OF TRIESTE

(11) ELEMENTAL COMPOSITION OF VENUS, EARTH, MARS & CHONDRITES
     Y.T. Chuburkov, JOINT INST NUCL RES,  RUSSIA


===============
(1) DID 800k IMPACT AFFECT HUMAN CULTURE?

From Bob Kobres <bkobres@uga.edu>

The NPR blurb linked below interviews an author (Richard Potts of
the Smithsonian) of a paper in the current issue of Science.  Potts
contends that an impact occurred.

<http://search.npr.org/cf/cmn/cmnpd01fm.cfm?PrgDate=03/03/2000&PrgID=3>

800,000  <http://www.npr.org/ramfiles/me/20000303.me.04.ram> Year
Old Tools -- NPR's Chris Joyce reports on the discovery of
800-thousand year-old stone tools in southern China. It's the
first time stone tools, from that time period, have been found in
East Asia. Anthropologists who found the tools suggest it may have
been a freak catastrophe that inspired early humans to make these
tools. (3:38)

From: http://www.sciencemag.org/content/current/
<http://www.sciencemag.org/content/current/
Mid-Pleistocene Acheulean-like Stone Technology of the Bose Basin, South
China

Hou Yamei, Richard Potts, Yuan Baoyin, Guo Zhengtang, Alan Deino, Wang
Wei, Jennifer Clark, Xie Guangmao, and Huang Weiwen
Science Mar 3 2000: 1622-1626.
[Abstract]
<http://www.sciencemag.org/cgi/content/abstract/287/5458/1622
[Full Text]  
<http://www.sciencemag.org/cgi/content/full/287/5458/1622>

Later.
bobk

=================
(2) PRE-HISTORIC IMPACTS

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

Dear Benny

I have just listened to the Australian ABC radio program The Science
Show. Dr Rick Potts was interviewed and talked of his work in China
were they uncovered stone tools and evidence of a large cosmic impact
800,000 years ago. The work is reported in this week's Science
(subscribers only). Abstract below.

Also, I have put together a selection of abstracts from the forthcoming
Lunar and Planetary Science Conference (the selection is highly biased
towards my interests): http://www1.tpgi.com.au/users/tps-seti/lpsc2000.html

regards
Michael Paine

Science Mar 3 2000 Volume 287 Number 5458

Mid-Pleistocene Acheulean-like Stone Technology of the Bose Basin, South
China

Hou Yamei,1 Richard Potts,2* Yuan Baoyin,3 Guo Zhengtang,3 Alan Deino,4
Wang Wei,5 Jennifer Clark,2 Xie Guangmao,6 Huang Weiwen1

Stone artifacts from the Bose basin, South China, are associated with
tektites dated to 803,000 3000 years ago and represent the oldest
known large cutting tools (LCTs) in East Asia. Bose toolmaking is
compatible with Mode 2 (Acheulean) technologies in Africa in its
targeted manufacture and biased spatial distribution of LCTs,
large-scale flaking, and high flake scar counts. Acheulean-like tools
in the mid-Pleistocene of South China imply that Mode 2 technical
advances were manifested in East Asia contemporaneously with handaxe
technology in Africa and western Eurasia. Bose lithic technology is
associated with a tektite airfall and forest burning.

==============
NOT A BAD STORY, IF YOU AX ME ....

From Alan Boyle <alan.boyle@MSNBC.COM>

Oldest stone axes in China discovered: Meteorite strike may have
played role in tool creation, researchers say
http://www.msnbc.com/news/377002.asp

Best, Alan

------

WASHINGTON, March 2 -  Eight hundred thousand years ago, a meteorite
blasted into what is now Vietnam, burning forests, killing off wildlife
and probably badly frightening the pre-humans who lived there. But
eventually, the hominids came back, perhaps having survived the
explosion in limestone caves or perhaps wandering in from neighboring
regions decades later. They found a freshly exposed outcropping of rock,
perfect for making stone tools. Archaeologists say they have found those
tools - the oldest stone axes ever discovered in China.

FULL STORY at
http://www.msnbc.com/news/377002.asp

==================
(4) ARE MARTIANS ALIVE BUT HIDING?

From Andrew Yee <ayee@nova.astro.utoronto.ca>

[http://helix.nature.com/nsu/000302/000302-9.html]

Thursday 2 March 2000

How to spot a Martian
By PHILIP BALL

Could Martians be alive and well, but just hiding? It is unlikely, but
not impossible, new evidence suggests. Benjamin Weiss and colleagues
from the California Institute of Technology have been looking into the
idea that living bacteria-like organisms might exist hundreds of metres
beneath the Martian 'soil'. (Strictly speaking, since this surface
layer does not contain decomposed vegetable matter like earthly soil,
it is called 'regolith'.)

Living on the surface of Mars would be like living in strong bleach.
Mars has no ozone layer, so its surface is strafed with ultraviolet
rays from the Sun. UV exposure damages the delicate organic molecules
from which all terrestrial life is built. It also converts
oxygen-containing rocks to so-called superoxides, bleach-like oxidants
which burn up any organic material they touch.

The combination of UV radiation and superoxides effectively sterilizes
the Martian surface. But further down in the regolith, both these
baleful influences would no longer hold sway. There is plenty of
earthly precedent for life in deep places: microorganisms have been
discovered several kilometres deep, in the cracks of hot rock at
temperatures of more than 100 C, and in Antarctic ice sheets, well
below freezing point. The amount of subterranean life on Earth may even
exceed that at the surface.

One essential requirement of all known life is liquid water. The
surface of Mars is bone dry (although there is some water ice in the
polar ice caps, which are mostly frozen carbon dioxide). But geologists
are fairly sure that water once flowed over the surface of Mars,
because we can still see the river networks and flood debris that it
apparently left behind. And, though no one yet knows, there might still
be water deep below the Martian surface.

Buried Martian microorganisms would also need fuel. They would need a
source of chemical energy, because there is no light in the regolith to
power photosynthesis, for example. Many bacteria that are thought to be
related to very ancient life forms derive their fuel from molecules
that release energy when converted to other forms. Purple sulphur
bacteria, for instance, power their metabolism by pulling apart
hydrogen sulphide into hydrogen and sulphur.

Weiss and colleagues suggest in the Proceedings of the National Academy
of Sciences[1] that buried Martian life forms could live off hydrogen
and carbon monoxide in the planet's atmosphere. These compounds are
produced when ultraviolet rays blast apart water and carbon dioxide,
two of the main components of Mars's thin atmosphere. Energy is
released in the reactions of hydrogen and carbon monoxide with oxygen,
or of hydrogen with carbon dioxide. Martian microorganisms might
subsist on energy from these sources, as UV-generated hydrogen and
carbon monoxide percolate down through the regolith.

If that is so, these gases will be consumed more quickly than they
would be solely by reactions in the atmosphere. So, say Weiss and
colleagues, deep bacteria on Mars would leave a faint imprint on the
composition of the atmosphere -- something we can see and measure. A
discrepancy between the composition expected if non-living processes
alone are creating and consuming the gases, and that actually observed,
would suggest buried life.

The researchers find that if any such discrepancy exists, it is too
tiny to be clearly detectable in current observations of the Martian
atmosphere. Although absence of evidence is not evidence of absence,
these results show that if organisms do exist deep within the regolith,
they are not using anything like the amount of energy that is actually
available from the UV-generated gases.

Yet Weiss and colleagues point out that the planet-wide averages used
in their calculations might mask local discrepancies caused by isolated
pockets of life. Searching for local imbalances in the production and
removal processes for hydrogen and carbon monoxide might therefore be
an indirect way to sniff out hidden life.

James Farquhar and colleagues at the University of California at San
Diego fuel the debate further with evidence that sulphur in the Martian
atmosphere can find its way into the regolith. They have studied
compounds of sulphur found in meteorites thought to have come from
Mars, as they report in Nature[2]. These rare meteorites -- barely more
than a dozen have been found -- represent samples of the Martian
regolith.

Farquhar's group says that the sulphur most probably became
incorporated into the rock when hydrogen sulphide and sulphur dioxide
gases in the Martian atmosphere were split by ultraviolet light.
Differences in the amounts of various sulphur compounds in the regolith
could provide a source of energy, rather as differences in water levels
in a river can generate power, they suggest. Energy that might just
sustain life in the regolith.

[1] Weiss, B.P., Yung, Y.L. & Nealson, K.H. Atmospheric energy for
subsurface life on Mars? PNAS 97, 1395-1399 (2000).

[2] Farquhar, J., Savarino, J., Jackson, T. & Thiemens, M.H. Evidence
of atmospheric sulphur in the martian regolith from sulphur isotopes in
meteorites. Nature 404, 50 (2000).

Macmillan Magazines Ltd 2000 - NATURE NEWS SERVICE

==================
(5) RUMOR OF COMET IMPACTING MARS IS FALSE

From Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

There has been some rumors floating around on the Internet that a
Comet West-Kahoutek-Ikemura is going to impact Mars on May 28-29.
This rumor is incorrect. For starters, a Comet West-Kahoutek-Ikemura
does not exist, though it is obvious the reference is to Comet
West-Kohoutek-Ikemura. The closest Comet West-Kohoutek-Ikemura gets
to Mars is about 6.5 million kilometers (0.04308 AU to be exact) on
June 5, and is not going to hit Mars.

Nothing to write home about.

Ron Baalke

==================
(6) NEW LAB READY TO TEST SUDDEN IMPACTS

From NASA News <NASANews@hq.nasa.gov>

Michael Braukus
Headquarters, Washington,                    March 3, 2000
(Phone:  202/358-1979)

Pamelia Caswell
Glenn Research Center, Cleveland, OH
(Phone:  216/433-5795)

RELEASE: 00-34

NEW LAB READY TO TEST SUDDEN IMPACTS

The last time government cannon boomed across the shores of Lake Erie
was during the War of 1812, but a new laboratory at NASA's Glenn
Research Center, Cleveland, OH, is now experimenting with ballistics of
a different kind.

Building 49 houses Glenn's new ballistic impact facility.  Its main
features are a 40-foot-long gas gun that can eject projectiles at
speeds up to 1,500 feet per second, or over 1,000 mph, and a high-speed
camera that can capture 2.5 million images per second. 

"The whole idea is to watch the impact and see how the materials struck
by the projectiles behave," said Dale Hopkins, a structures engineer
and team leader for the design and buildup of the new facility.  "It's
not just whether they survive, but how they deform and fail."

One of the facility's main tasks is testing materials for aircraft
engine housings. During rare in-flight events, if the engine is hit by
hail or birds, the engine housing must contain any fragments and
withstand the severe loads, or forces, that otherwise could cause the
engine to separate from the wing of the airplane. Current engine
housing materials, usually high-strength metal alloys and non-metal
ballistic fabrics, do this job very well but are very heavy.  The new,
lighter structures being considered for this duty must be evaluated for
their ability to withstand such catastrophic events.

"The new facility allows us to use larger, heavier, irregularly shaped
projectiles that look and behave more like fragments of an engine's
rotating parts.  The testing is much more realistic than before,"
Hopkins said.

The facility is also being used to evaluate flywheel containment
materials.  The disk in a flywheel, a new type of energy storage device
being considered for use in satellites and other advanced applications
rotates at over 50,000 revolutions per minute.  Should the disk fatigue
and rupture, the high-speed particles released would need to be
contained to avoid damaging other equipment or injuring people.

The materials to be tested include intermetallic alloys,
fiber-reinforced composites and cloth-like polymers.  New engine
concepts require materials that can withstand higher temperatures and
higher-speed projectiles than current containment materials.  Similar
work at Glenn over 20 years ago helped prove the worth of the ballistic
materials used in jet engines today, as well as in bullet-proof vests.

The data taken during these impact tests will also be used to verify
and improve the accuracy of computer models that predict material
response to impacts. Manufacturers can use these more accurate models
to shorten the time and reduce the cost of bringing new designs to
market.

Print-quality images are available at:
http://www.grc.nasa.gov/WWW/PAO/pressrel/images/00-xxi1.jpg
http://www.grc.nasa.gov/WWW/PAO/pressrel/images/00-xxi2.jpg

=============
(7) PRODUCTION OF STAR-GRAZING & STAR-IMPACTING PLANETESIMALS

A.C. Quillen*) & M. Holman: Production of star-grazing and
star-impacting planetesimals via orbital migration of extrasolar
planets. ASTRONOMICAL JOURNAL, 2000, Vol.119, No.1, pp.397-402

*) UNIVERSITY OF ARIZONA,STEWARD OBSERV,TUCSON,AZ,85721

During orbital migration of a giant extrasolar planet via ejection of
planetesimals (as studied by Murray et al. in 1998), inner
mean-motion resonances can be strong enough to cause planetesimals to
graze or impact the star. We integrate numerically the motions of
particles which pass through the 3:1 or 4:1 mean-motion resonances of
a migrating Jupiter-mass planet. We find that many particles can be
trapped in the 3:1 or 4:1 resonances and pumped to high enough
eccentricities that they impact the star. This implies that for a
planet migrating a substantial fraction of its semimajor axis, a
fraction of its mass in planetesimals could impact the star. This
process may be capable of enriching the metallicity of the star at a
time when the star is no longer fully convective. Upon close
approaches to the star, the surfaces of these planetesimals will be
sublimated. Orbital migration should cause continuing production of
evaporating bodies, suggesting that this process should be detectable
with searches for transient absorption lines in young stars. The
remainder of the particles will not impact the star but can be
ejected subsequently by the planet as it migrates further inward.
This allows the planet to migrate a substantial fraction of its
initial semimajor axis by ejecting planetesimals. Copyright 2000,
Institute for Scientific Information Inc.

============
(8) ANALYSIS OF NANOGRAM-SIZED ASTROMATERIALS

M.E. Zolensky*), C. Pieters, B. Clark, J.J. Papike: Small is beautiful:
The analysis of nanogram-sized astromaterials. METEORITICS & PLANETARY
SCIENCE, 2000, Vol.35, No.1, pp.9-29

*) NASA,LYNDON B JOHNSON SPACE CTR,PLANETARY SCI   
   BRANCH,HOUSTON,TX,77058

The capability of modem methods to characterize ultra-small samples
is well established from analysis of interplanetary dust particles
(IDPs), interstellar grains recovered from meteorites, and other
materials requiring ultra-sensitive analytical capabilities. Powerful
analytical techniques are available that require, under favorable
circumstances, single particles of only a few nanograms for entire
suites of fairly comprehensive characterizations. A returned sample
of > 1000 particles with total mass of just 1 mu g permits
comprehensive quantitative geochemical measurements that are
impractical to carry out in situ by flight instruments.. The main goal
of this paper is to describe the state-of-the-art in microanalysis of
astromaterials. Given that we can analyze fantastically small
quantities of asteroids and comets, etc., we have to ask ourselves,
how representative are microscopic samples of bodies that measure a
few to many kilometers across? With the Galileo flybys of Gaspra and
Ida, it is now recognized that even very small airless bodies have
indeed developed a particulate regolith. Acquiring a sample of the
bulk regolith, a simple sampling strategy, provides two critical
pieces of information about the body. Regolith samples are excellent
bulk samples because they normally contain all the key components of
the local environment, albeit in particulate form. Furthermore,
because this fine fraction dominates remote measurements, regolith
samples also provide information about surface alteration processes
and are a key link to remote sensing of other bodies. Studies
indicate that a statistically significant number of nanogram-sized
particles should be able to characterize the regolith of a primitive
asteroid, although the presence of larger components (e.g.,
chondrules, calcium-aluminum-rich inclusions, large crystal
fragments, etc.) within even primitive meteorites (e.g., Murchison)
points out the limitations of using data obtained from nanogram-sized
samples to characterize entire primitive asteroids. However, the most
important asteroidal geological processes have left their mark on the
matrix, because this is the finest-grained portion and therefore most
sensitive to chemical and physical changes. Thus, the following
information can be learned from this fine grain size fraction alone:
(1) mineral paragenesis; (2) regolith processes; (3) bulk
composition; (4) conditions of thermal and aqueous alteration (if
any); (5) relationships to planets, comets, meteorites (via isotopic
analyses, including O); (6) abundance of water and hydrated material;
(7) abundance of organics; (8) history of volatile mobility; (9)
presence and origin of presolar and/or interstellar material. Most of
this information can be obtained even from dust samples from bodies
for which nanogram-sized samples are not truly representative. Future
advances in sensitivity and accuracy of laboratory analytical
techniques can be expected to enhance the science value of nano- to
microgram-sized samples even further. This highlights a key advantage
of sample returns-that the most advanced analysis techniques can
always be applied in the laboratory and that well-preserved samples
are available for future investigations. Copyright 2000, Institute
for Scientific Information Inc.

============
(9) PLANET & ASTEROID FORMATION IN THE PRESENCE OF GIANT PLANETS

S.J. Kortenkamp*) & G.W. Wetherill: Terrestrial planet and asteroid
formation in the presence of giant planets - I. Relative velocities
of planetesimals subject to Jupiter and Saturn perturbations. ICARUS,
2000, Vol.143, No.1, pp.60-73

*) CARNEGIE INST WASHINGTON,DEPT TERR MAGNETISM,5241 BROAD BRANCH
   RD,WASHINGTON,DC,20015

We investigate the orbital evolution of 10(13)- to 10(25)-g
planetesimals near 1 AU and in the asteroid belt (near 2.6 AU) prior
to the stage of evolution when the mutual perturbations between the
planetesimals become important. We include nebular gas drag and the
effects of Jupiter and Saturn at their present masses and in their
present orbits. Gas drag introduces a size-dependent phasing of the
secular perturbations, which leads to a pronounced dip in encounter
velocities (V-enc) between bodies of similar mass. Planetesimals of
identical mass have V-enc similar to 1 and similar to 10 m s(-1)
(near 1 and 2.6 AU, respectively) while bodies differing by similar
to 10 in mass have V-enc similar to 10 and similar to 100 m s(-1)
(near 1 and 2.6 AU, respectively). Under these conditions, growth,
rather than erosion, will occur only by collisions of bodies of
nearly the same mass. There will be essentially no gravitational
focusing between bodies less than 10(22) to 10(25) g, allowing growth
of planetary embryos in the terrestrial planet region to proceed in a
slower nonrunaway fashion. The environment in the asteroid belt will
be even more forbidding and it is uncertain whether even the severely
depleted present asteroid belt could form under these conditions.
The perturbations of Jupiter acid Saturn are quite sensitive to
their semi-major axes and decrease when the planets' heliocentric
distances are increased to allow for protoplanet migration. It is
possible, though not clearly demonstrated, that this could produce a
depleted asteroid belt but permit formation of a system of
terrestrial planet embryos on a similar to 10(6)-year timescale,
initially by nonrunaway growth and transitioning to runaway growth
after similar to 10(5) years. The calculations reported here are
valid under the condition that the relative velocities of the bodies
are determined only by Jupiter and Saturn perturbations and by gas
drag, with no mutual perturbations between planetesimals. If, while
subject to these conditions, the bodies become large enough for their
mutual perturbations to influence their velocity and size evolution
significantly, the problem becomes much more complex. This problem is
under investigation. (C) 2000 Academic Press.

===========
(10) LONG-TERM DYNAMICS OF BRIGHT BOLIDES

L. Foschini*), P. Farinella, C. Froeschle, R. Gonczi, T.J.Jopek,
P. Michel: Long-term dynamics of bright bolides. ASTRONOMY AND
ASTROPHYSICS, 2000, Vol.353, No.2, pp.797-812

*) UNIVERSITY OF TRIESTE,DIPARTIMENTO ASTRON,VIA TIEPOLO 11,I-34131
   TRIESTE,ITALY

We have integrated backward and forward in time the orbits of 20 very
bright bolides (with visual magnitude brighter than -10) over a time
span of 5 Myr or more. The sample was mainly selected among events
observed during the period between 1993 and 1996, but we have
included also three older, particularly interesting events (Abee,
1952; Glanerbrug, 1990; and EN220991, 1991). For a large part of the
sample, the orbit is known with sufficient accuracy from the
reduction and analysis of photographic data. However, there are also
some cases in which lower-accuracy orbital data were derived from
other techniques, such as visual, seismic, and radar observation. For
these events we have used two or three alternative initial orbits,
consistent with the existing uncertainty. The results of our
integrations show a great diversity of orbital evolution patterns,
consistent with the behaviour of larger near-Earth objects. The most
frequent fate (42% of the cases) is solar collision, followed by
hyperbolic ejection (17%), and the average dynamical lifetime is of
the order of 10 Myr. Three bolides either have initially or achieve
later Aten-type or Q <1 AU orbits, similar to the fraction of such
objects in the near-Earth asteroid population. Only 2 bolides have a
clear comet-like dynamical behaviour dominated by Jovian encounters,
although ablation properties indicate that the fraction of very weak
bolides is probably higher. Copyright 2000, Institute for Scientific
Information Inc.

============
(11) ELEMENTAL COMPOSITION OF VENUS, EARTH, MARS & CHONDRITES

Y.T. Chuburkov: Comparison of elemental composition of Venus, Earth,
Mars, and chondrites in the light of the Mendeleev periodic law.
RADIOCHEMISTRY, 1999, Vol.41, No.5, pp.434-440

*) JOINT INST NUCL RES,FLEROV LAB NUCL REACT,DUBNA 141980,RUSSIA

The fraction of free neutral atoms No for all elements in the
protoplanet nebula was determined with the account of their abundance
and physicochemical properties. A linear dependence of the ratio of
nonvolatile and volatile elements in chondrites and igneous rocks of
the Earth on No was obtained. The Mendeleev periodic law was used to
prove the occurrence of magnetic separation of elements in the
protoplanet nebula. To this end the concentration ratios of analogous
elements with different No in the matters of Venus, Earth, Mars, and
chondrites were compared. The data obtained demonstrate the
occurrence of magnetic separation of elements in the protoplanet
nebula and show that the Shergotty and Tunguska meteorites by their
relative elemental composition are genetically related to Mars and
asteroids, respectively. Copyright 2000, Institute for Scientific
Information Inc.

----------------------------------------
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----------------------------------------
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please contact the moderator Benny J Peiser <b.j.peiser@livjm.ac.uk>.
Information circulated on this network is for scholarly and
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*

LETTERS TO THE MODERATOR, 6 March 2000
--------------------------------------


(1) NEO IMPACT SIMULATIONS: THE RISK IN PERSPECTIVE
    Alan Harris

(2) 100,000 YEAR IMPACT SIMULATION
    Michael Paine <mpaine@tpgi.com.au>

(3) FLYING IN AN AIRPLANE ....
    Konrad Ebisch <kebisch@zycor.lgc.com>

(4) WHAT TERMINATED THE LAST ICE AGE?
    Doug Keenan <Doug.Keenan@virgin.net>

(5) MUM TREES?
    Bob Kobres <bkobres@uga.edu>

(6) QUICK-FROZEN MAMMOTHS
    Clark Whelton <cwhelton@mindspring.com>

(7) DID A LUNAR ERUPTION CAUSE A MAJOR MASS EXTINCTION?
    Benjamin D Comings <bcomings@earthlink.net>

(8) NEOS, PLANETARY DEFENSE, AND GOVERNMENT--
    A VIEW FROM ONE HOMEFRONT
    Jeff Kargel

===============
(1) NEO IMPACT SIMULATIONS: THE RISK IN PERSPECTIVE

Comments by Alan Harris [as posted on Dave Morrison's NEO News (3/3/00)

The essential numbers in Paine's first table are the following:

Size range     Number of impacts Average number of
meters         with fatalities     fatalities
------------------------------------------------------------
  13- 99       949              43 000
100-199       124             280 000
200-499        29             700 000
500-999            3          13 000 000

These numbers are copied from his table, with a bit of editing. Note
that the number of fatalities per event excludes events for which
there are no fatalities, so to get total fatalities you need to
multiply the "fatalities per event" by the number with any fatalities,
not the total number of events. Doing that multiplication, and then
dividing by the 100,000-year interval, I get:

Size range  Fatalities in  Fatalities
Meters 100,000 years  per year
-----------------------------------------------------------
  13- 99            41 M         410
100-199            35 M         350
200-499            20 M         200
500-999            39 M         390
   >1 KM             5 B      50,000

I have added back the one big impact in the last line, which Paine
chose to throw out because it was "a matter of bad luck" in his
particular run. That is true to a degree, but only marginally.
According to previous estimates of the "kill curve", there is about a
30% chance of an event occurring in 100,000 years with global
consequences resulting in >1.5B deaths, which means the average
"bottom line" in the above table should be about 20,000 deaths per
year. This is higher than the number quoted in, for example, the NASA
Spaceguard Report, but the distribution of casualties with respect to
the size of impactors is not so different. The biggest impacts still
dominate, causing most of the casualties.

Paine's results are consistent with the Chapman-Morrison estimates of
fatalities as a function of size (a bit inflated upward by high
estimates of impact rate and tsunami effects, but within range). But
a problem in interpretation arises from Paine's selected time
interval (100,000 years), which is short enough that the real action
is improbable and thus doesn't show up. When Paine looks at a typical
millennium, of course he concludes that the action is all at the very
small end (Tunguska-class events), which is to be expected because
those are the largest events that occur in a typical 1,000-year
period. Carrying this approach to its (il)logical extreme, in a
typical decade the worst that happens is Michelle Knapp's car gets
killed. Does that mean we should concentrate on making cars
meteorite-proof? As near as I can see, Lewis' and Paine's simulations
do not indicate a greater importance of small impacts over a long
time period, they just illustrate the illusions of perception that
can occur by limiting the interval of time considered.

Alan Harris
Feb 28 2000

==================
(2) 100,000 YEAR IMPACT SIMULATION

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

Here is a response to comments by Al Harris, as circulated on NEO News.

The time increment chosen for impact simulations is important for
assessing the contribution of small impactors. John Lewis's program
randomly generates the characteristics of the worst event occurring
during the increment period. The longer this period the greater the
chance that a large impact will take place. This is evident when
comparing my 100,000 year simulation in decade increments
( http://www1.tpgi.com.au/users/tps-seti/sta1047.htm )
with the one million year simulation in century increments
( http://www1.tpgi.com.au/users/tps-seti/sta1046.htm )
For impactors with a diameter up to 99m the average fatalities per year
works out at 410 for decade increments but only 240 for century
increments.

You may wonder why I didn't perform all calculations using decade (or
even better, yearly, increments). John's program outputs data in CSV
format which I have to convert to my database package for subsequent
analysis. With the conversion tools that I have available I am limited
to about 10,000 records! Hence I planned each of my simulations to
generate 10,000 events.

Now Al Harris is quite correct in pointing out that, in terms of average
fatalities per year, the large impacts overwhelm the small impacts over
the long term. However, the point that strikes me from John Lewis's work
is that unusual small impacts (<100m diameter) that result in fatalities
can be expected to occur much more frequently than earlier estimates had
suggested - an average of one FATAL event per century instead of one per
millennium. Although the average fatalities from such events worked out
at 43,000 the worst case involved 4.5 million fatalities and there were
a further 7 events with over 1 million fatalities. These deserve to be
taken seriously.

The Spaceguard proposal is quite rightly targetting the
civilisation-threatening objects but it should be made clear that small
objects could 'slip through the net' and cause grave local devastation.
The estimated frequency of these 'local' deadly impacts is also
important for historians - little or no physical evidence would be left
but the events could have severely disrupted society (a theme covered by
Benny Peiser). Complicating the issue is the possibility that impacts
come in clusters - this is not covered in the simulation.

Finally, I encourage as many people as possible to buy the book and try
out the software (no I am not on a commission!). I have started an
informal software users webpage
( http://www1.tpgi.com.au/users/tps-seti/hazards.html ) to document
modifications that people have tried. In particular note my crude
estimate of fatalities from global climatic effects (John's program, as
distributed, didn't cover such large impacts) - I would welcome
suggestions for improving these estimates. I am fairly confident,
however, that a 23 million megaton land impact (the 5km object in my
simulation) would have virtually wiped out the human race.

regards
Michael Paine

=============
(3) FLYING IN AN AIRPLANE ....

From Konrad Ebisch <kebisch@zycor.lgc.com>

John Lewis.... The danger of dying from an impact, he says, is
"comparable to flying an airplane, it's about the same risk."'

How much do we spend on investigations to improve air travel safety? 
How does this compare to what we spend to improve planetary safety? 

Konrad Ebisch

==============
(4) WHAT TERMINATED THE LAST ICE AGE?

From Doug Keenan <Doug.Keenan@virgin.net>

Benny,

Regarding your March 2nd post, the Michigan trees do not record the
Pleistocene-Holocene transition: rather, the trees began growing
after the glaciers started to retreat. I don't believe that the trees
lived during a rapid climate change -- which would explain why they
don't record such a change.

Also, there has been a large amount of research done on how
Milankovitch forcing could have led to the Pleistocene-Holocene
transition on sub-centurial timescales. The key appears to be
the thermohaline conveyor belt in the Atlantic, whose behaviour is
likely extremely sensitive to small changes in climatic conditions. 

On the timescale of the Pleistocene-Holocene transition, see
R. G. Fairbanks [Nature, 362: 495 (1993)], who observes this:

"... Greenland's climate, emerging from the last ice age, ... 
shifted from glacial to inter-glacial conditions over an
astonishingly quick 3-5 years. ... air temperature warmed by
7 C during [this shift]...."

The span of 3-5 years is actually due to the resolution of the
measuring technology.  A more accurate assessment would be "probably
less than 5 years, and perhaps even 1".

I haven't checked subsequent work for refinements.  Cosmic
mechanisms, though, would seem to fit this timescale.

Cheers,
Doug Keenan
http://freespace.virgin.net/doug.keenan

================
(5) MUM TREES?

From Bob Kobres <bkobres@uga.edu>

Hi Benny.

The report on the ancient tree stand in Michigan is in the February 21
issue of Journal of Ecology (which has not reached our library).
See: http://explorezone.com/archives/00_02/23_buried_forest.htm

The ExplorerZone site provides an interesting reference to an earlier
paper (Nature, abstract below) dealing with contemporary tree ring
growth along glacial margins.
http://explorezone.com/archives/99_07/08_siberian_trees.htm

Apparently this paper shows that increased snowfall has worked to keep
annual tree growth about the same although the local temperature has
been recorded as rising for the last thirty years. If this snowfall
growth-governor is universal (perhaps Mike Baillie would comment on
this) then it would certainly reduce the rate-of-climate-change
significance of regular growth found in the Michigan specimens from
10,000 year ago. It would seem that although trees do not lie, they can
be ambivalent in certain circumstances.  ;^)

~~~~~~~~~~~~~~~~~~~~~~
Nature 400, 149 - 151 (1999) Macmillan Publishers Ltd.

Influence of snowfall and melt timing on tree growth in subarctic Eurasia

E. A. VAGANOV, M. K. HUGHES, A. V. KIRDYANOV, F. H. SCHWEINGRUBER &
P. P. SILKIN

The causes of a reduced sensitivity of high-latitude tree growth to
variations in summer temperature for recent decades, compared to
earlier this century, are unknown. This sensitivity change is
problematic, in that relationships between tree-ring properties and
temperature are widely used for reconstructing past climate. Here we
report an analysis of tree-ring and climate data from the forest-tundra
zone, in combination with a mechanistic model of tree-ring growth, to
argue that an increasing trend of winter precipitation over the past
century in many subarctic regions led to delayed snow melt in these
permafrost environments. As a result, the initiation of cambial
activity (necessary for the formation of wood cells) has been delayed
relative to the pre-1960 period in the Siberian subarctic. Since the
early 1960s, less of the growth season has been during what had
previously been the period of maximal growth sensitivity to
temperature. This shift results not only in slower growth, but also in
a reduced correlation between growth and temperature. Our results
suggest that changes in winter precipitation should be considered in
seeking explanations for observed changes in the timing of the 'spring
greening' of high-latitude forests, and should be taken into account in
the study of the role of the Siberian subarctic forest in the global
carbon cycle.
~~~~~~~~~~~~~~~~~~~~~~~~~~

Nevertheless, I suspect the "Does anybody really know what's going on?"
question at the end of the ABC blurb is contemporarily apt.  See:

http://www.nature.com/nature/fow/
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v404/n6773/full/404023a0_fs.html
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v404/n6773/full/404061a0_fs.html
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v399/n6735/full/399429a0_fs.html

There is though the issue of quickly, but gently, burying five acres of
forest. This would seem to require a considerably deep slackwater
deposit!/? Catastrophic floods from melting ice did occur during the
Pleistocene to Holocene transition and it seems reasonable to assume that
learning what lies beneath the sediments deposited by these floods will
eventually provide the clearest picture of what conditions were like
when they occurred.  For example:

http://www.peak.org/csfa/mt14-4.html#part2
http://www.ncdc.noaa.gov/ogp/papers/hirsch.html
http://www.geo.wvu.edu/~kite/Paleoflood2Talk1999EditedForHtml/sld001.htm

An informative student paper on the Scabland flooding:
http://tchgrey.com/Travel/Info/Geo/Channeled_Scablandpaper.html

Also, it seems counterproductive to indiscriminately discount handed
down lore when searching for clues of what caused this most recent
Ice Age transition when we know that our ancestors witnessed the change. 
A change that did not allow the survival of a large number of animals,
particularly on the North American continent, that had endured glacial
to interglacial transitions in the past.

http://abob.libs.uga.edu/bobk/nicd.html
http://abob.libs.uga.edu/bobk/walams.html

Later.
bobk

================
(6) QUICK-FROZEN MAMMOTHS

From Clark Whelton <cwhelton@mindspring.com>

Hi, Benny.

This article discusses the well-known frozen mammoth problem, and
several possible explanations, including changes in the poles and
celestial catastrophe.

Clark

http://atlantisrising.com/pdfs/mammoths.pdf
Number 22 - ATLANTIS RISING - page 23

ANCIENT MYSTERIES

The Mystery of the Quick Frozen Mammoths

New Attention for One of Science's Most Disturbing Puzzles

BY BEVERLY C. JAEGERS

Editor's note: The recent wave of publicity surrounding the discovery
of an intact Mammoth frozen in Siberian permafrost has rekindled debate
over the sudden and mysterious demise of the species. While the
extraction of the beast from the ice and possible plans to clone it
-- a la Jurassic Park -- have fired the imagination of millions, few
have considered the implications of such discoveries in the great
debate between proponents of the "gradualist" school of evolutionary
theory and the "catastrophist" camp. At stake are the theoretical
underpinnings of current orthodoxy, opposed as it is to the notion that
natural -- and for that matter, human -- history on Earth may have been
far more dramatic and tumultuous than we have thus far dared to
properly consider.

FULL STORY at http://atlantisrising.com/pdfs/mammoths.pdf

MODERATOR'S NOTE: see also: Bringing Mammoth back to life, in
The Times, 2 March 2000
http://www.the-times.co.uk/news/pages/tim/2000/03/02/timfeafea02001.html?999

=============
(7) DID A LUNAR ERUPTION CAUSE A MAJOR MASS EXTINCTION?

From Benjamin D Comings <bcomings@earthlink.net>
Forwarded by Larry Klaes <lklaes@bbn.com

Natural Earth-bound Obsidian is already essentially water-free, so I
assume we are comparing vanishingly small with super-vanishingly
small.
(see http://more.abcnews.go.com/sections/science/DyeHard/dye991117.html)  

I am suspicious of a Lunar origin of Tektites, but the idea is
interesting, perhaps odd enough to be true. Ablation on an ancient
Tektite may be hard to prove. A standard blob of volcanic glass is
already likely to have a pseudo-aerodynamic shape if it was ejected
into the atmosphere from a volcano, and there are a variety of
volcanic processes that we do not understand, and we have likely not
seen in our short human history, or even guesssed at a lot of the
types of volcanism that can occur. It seems likely that interesting
forms of volcanism might occur centuies or millenia after major
impacts, as the earth re-adjusts, melts and ejects things that were
thrust into the mantle.

Another item in the article that seems odd is that they suggest that 
the solar wind or sunshine swept away the ring of tektites within a
million years. Why would a ring around the earth go bye bye in 1
million years, and Saturn have such huge rings still?  Is the solar
pressure so much reduced at the distance of Saturn that rings can be
preserved there?

I had heard it suggested that some Tekties resulted from a very 
intense solar flare heating the earth's surface enough to fuse sand. 
That is an even more outrageous theory.

Tektites are clearly associated with some impact craters, such that
it seems clear that impacts created some or most tektites:
http://www.qadas.com/qadas/nasa/nasa-hm/1182.html

Traditional thought has tektites resulting from material that may
have been shot into space during impact and thus could reasonably
show ablation:
http://geology.about.com/education/geology/library/bl/images/bltektite.htm?rnk=r1&terms=tektites

This site states that Tektites contain (yes a generalism) minerals
indicative of high pressure impacts:
http://www.geocities.com/~dweir/TEKTITES.HTM  I think that the
analysis there is accurate, and so I include it here:

"Lechatelierite, a form of fused quartz, and other relict mineral
inclusions showing evidence of shock metamorphism, are found inside
tektites, consisitent with an impact origin rather than one based on
igneous volcanism. Additionally, the high-pressure polymorph of
quartz known as coesite has been identified in tektites, indicating
pressures greater than 20 kb. Elemental abundance patterns along with
size and shape characteristics of the mineral inclusions suggest that
the parent material was a terrestrial, fine-grained, sedimentary
deposit similar to a graywacke or loess.

One revealing fact in the origin debate is that no tektites have ever
been found in Antarctica, where meteorites from most all classes have
previously been recovered, including many lunar specimens. A major
point of contention held by the lunar-origin theorists has been the
very low content of water in tektites compared to the terrestrial
source rock. A recent study into the physics and chemistry of impact
melting and vaporization explains this lack of water as a natural
outcome of the thermodynamics associated with shock pressures in
excess of 100 GPa and temperatures in excess of 50,000C. Under
these conditions, volatile-containing bubbles would carry all of the
water vapor out of the silicate droplets, along with O2, leading to
reduction of Fe and the formation of the dark green to black colors
associated with tektites. Furthermore, lunar rocks contain still less
water than tektites do."

I would be interested to get a handle on the exact water contents we
are talking about.

  Tx for drawing my attention to this.

Ben

=================
(8) NEOS, PLANETARY DEFENSE, AND GOVERNMENT--
     A VIEW FROM ONE HOMEFRONT

By Jeff Kargel [as posted on NEO News, 3/3/00]

The recent essay by General Worden (U.S. Air Force) and the ensuing
discussion on planetary defense by Louis Friedman (Planetary Society)
and Major Tate (Spaceguard U.K.) is very stimulating and prompts this
further response.  I, too, must first offer a disclaimer.  It is in my
unofficial status as a private citizen that I write.  Nothing written
here has any connection whatsoever with the views and policies of my
day job employer (a U.S. government agency) or of the Foundation for
the International Nongovernmental Development of Space (FINDS), with
which I am affiliated when I wear my space development research hat
some evenings and weekends. My background is in geology and planetary
science.

I have never awakened a single night to ponder impact hazards. I was up
late one night considering this issue, but that was at the theater
watching the movie Armageddon. My sleepfulness is not for any lack of
appreciation for the many ways we could meet our doom by a crashing
rock. I do field research at Meteor Crater, study impact-melted
glass and metal globules from that crater, see impact-stressed
boulders heaved in great piles, and I have walked through millions of
years of sedimentary strata penetrated by a small metallic bolide
that had "Arizona AND bust" written on it.  Meteor Crater is very
near (40 miles east of me), and it is dear to my heart.  The violence
and inevitability of impacts is apparent.  I look at the recent NEAR
images of Eros and note that Meteor Crater is the size of one of the
smaller craters resolvable in those early orbital images of that famous
NEO.

We can debate the statistical chances of meeting our impact doom as
individuals; we can scale up the threat and discuss the odds of
civilization meeting its collective doom by impact -- if we choose to
nitpick the odds of catastrophe, we could argue over no more than one
order of magnitude difference.  So I agree with General Worden's
assumption that NEOs play a major past and ongoing role in the
evolution of life and also that we personally and as a civilization
face a threat from these objects. It's a serious issue worthy of
serious evaluation.

The impact hazard is an issue that fascinates but does not worry me.
Viewed from the homefront I have more immediate personal concerns and
responsibilities and global concerns, as we all do.  I raise my
children; I worry about fascism in Austria; I worry also about the
threat of biological terrorism and nuclear warfare and about the
reality of global warming's impact.  But I don't worry about NEO
impacts. I learn about impact hazard assessments, impact dynamics,
the impact records of the solid bodies in the solar system, and the
role of impacts in biological evolution and planetary geology.  Over
the geologic long term it's hard to overestimate the hazard that NEOs
present.  But there are a huge array of threats as severe and far
more likely to hit us in the next decade or century or millennium;
and some of these problems, as intractable as they may seem at times,
are easier than impacts to partly mitigate.  In terms of potential
for causing mass extinction, humans give NEOs good competition.  One
such human-caused global mass extinction event is occurring even now
as we discuss the NEO threat, and another global mass extinction is
thought to have occurred just 8,000-10,000 years ago with a large
human factor at the root cause.

I heard an estimate/prediction recently that there is a high
likelihood of a biological weapons attack on the United States within
5 to 10 years. What are the chances that the attack will succeed?  Is
there a 50% chance that it will kill a few people and incite hysteria
among billions of others?  Could such an attack work as much
devastation as the sponsors of the attack may envision? Is there a
10% chance that millions of people will die? Could a bio attack using
genetically engineered organisms be so severe that civilization
itself is threatened?  Is there even a 1% chance that within 5 to 10
years all human life besides those innoculated in advance by evil
people will perish due to bio terrorism?  Could this threat potential
now be as large as that recently posed by nuclear weapons at the
height of the cold war? I have no capacity to estimate these odds
scientifically. However, it seems appropriate that our military
services should be and are
focusing their efforts on military and terrorist threats rather than impacts.

Less sensationalistic, less threatening, but far more certain on the
century time scale than bio terrorism and mega-impacts is global
warming, which does not threaten the existence of Mankind, but it
does threaten our well being, the existence of many nation states and
cities, and global political stability.  Global warming is a threat
that has virtually a 100% chance of occurring in the next century and
will cause trillions of dollars in damage and hundreds of billions of
dollars to partly mitigate and accomodate.

Between paychecks and personal life decisions, I do occasionally
worry about things out of my control.  But not impact hazards.  It's
just a matter of my worries priorities list, which is only a few
worries long. Then again, I don't worry about house fires, or
drive-by shootings, and other things that I probably should worry
about; I pay for professional worriers to deal with things for which
I can't or don't want to devote time or energy.   And so it is with
NEO hazards.  As something I "do" weekends and nights, NEOs can
attract either my pessimism or my optimism; I have time for only one,
and I choose to be optimistic about NEOs.  I carry optimism about
what NEOs have to offer humankind rather than pessimism about any
sort of horrid fate NEOs could impose on our planet's life, including
us.

NEOs are of consuming interest to me because of the riches they offer
Mankind- (1) platinum and palladium for wondrous new technologies;
(2) germanium and arsenic and other substances that will help us
develop space solar power and help solve our energy crisis and global
warming conundrum; (3) organics for interplanetary agriculture; (4)
water to fuel our interplanetary shuttles and to moisten our
extraterrrestrial agricultural fields; and (5) steel and other
construction materials for our extraterrestrial cities.  NEOs offer
the best chance we have to build our space infrastructure beyond low
Earth orbit and expand our civilization to other worlds, eventually
including Mars.   This is a near-term prospect for the first half of
the 21st century.

Leaping ahead a few hundred thousand millennia, Mars will come in
handy when the Sun brightens so formidably that our oceans evaporate
and life on Earth becomes as sustainable as life on Venus.  (Does
that sound too remote to be of concern?  No more so than the
super-Chicxulub life-extinguishing 500-million-year bolide; solar
brighteningm is just more predictable than impacts.)  Long before any
natural event is likely to render our planet sterile, humanity will
have extended our presence to many other planetary systems around
other stars.  We can hope, anyway.  Humanity will then be safe from
NEOs and the maturation of the Sun along the stellar Main Sequence
and all the natural and manmade hazards imagineable short of the
collapse of the Universe or the explosion of a very nearby Supernova.
On the long march of the future, planetary systems' left overs will
continue to strike and devastate planets, but Mankind and what once
was Earth life will have its insurance policy.

The same planetary left overs, including NEOs in our solar system,
will be viewed more as the treasure and stepping stones that they are
than the hazards they pose.  They are like islands in the vast ocean;
each island has its volcanic or cyclonic or malarial hazards, but
each island  offers nesting grounds for sea turtles or harbors for
ships.  Just as the timber
and soil and mineral wealth of America helped make a new world, NEOs
will make possible our interplanetary and interstellar voyaging.  The
chances are very strong, if we can avoid destroying ourselves (the
big uncertainty), that we will be star trekkers long before any
planet-threatening NEO again strikes Earth.  And by that time, we
will surely know where the threatening NEOs are and be able to divert
them.

General Worden would like to have a detection program right now so as
to find and keep tabs on the most threatening and modestly
threatening NEOs. The space development community wants a detection
program right now so as to identify the most promising NEO mineral
sources for our future use. What I find puzzling amidst our common
interests is that the General would prefer not to increase investment
in optical telescopes for NEO search and characterization.  From both
the pessimistic (hazards) and optimistic (resources) perspectives,
characterization of an asteroid's type and physical state is needed
to assess the object's threat magnitude, the best threat mitigation
strategy, and the NEO's resource potential. The "pessimists" and
"optimists" thus have plenty of common ground.  Like the General, the
optimists are interested both in big NEOs (lots of stuff to mine in
situ) and small NEOs (possibility to move or capture them).  A NEO
found and whose orbit is catalogued is virtually useless as a
resource unless we know of what it is made.   Thus, we need a "rapid
reaction force" capable of producing at least a simple R-G-B spectral
classification within hours or days of discovery of as many NEOs as
possible before they get away.  A well organized amateur network of
hundreds of CCD-equipped telescopes wired to a data analysis center
could be very helpful; in addition we need a small number of
dedicated large telescopes.  This would seem to be in everybody's
interests.

With the recent activity of the U.S. and British militaries in moon
missions, asteroid and Mars impact probes, and asteroid detection
programs, one could wonder what's really up with this interest.  But
I'll take stated justifications for military asteroid detection
programs at face value. I have no problem with the military getting
involved in exploration of space beyond geosynchronous orbit, so long
as the military is one that is supportive of democratic values, is
beholden to the public they serve, and contributes to non-classified
scientific understanding of the Cosmos.  It seems the American and
British militaries pass this test.  The new military interests and
long standing civilian scientific and corporate interest in deep
space is forging a stronger alliance for planetary exploration and
space development.  That alliance will be most robust if multiple
complementary means of asteroid detection and characterization are
supported and if the usual interagency turf wars are replaced by
interagency and public-private collaboration.

I say the more the merrier.

Jeff Kargel
25 February 2000

-----------------
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Network. Contributions to the on-going debate about near-Earth objects,
the cosmic environment of our planet and how to deal with it are welcome.
The fully indexed archive of the CCNet, from February 1997 on,
can be found at http://abob.libs.uga.edu/bobk/cccmenu.html



CCCMENU CCC for 2000

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