PLEASE NOTE:


*

CCNet DIGEST, 26 May 1999
-------------------------


(1) DISCOVERY OF A STREWN CRATER FIELD IN AUSTRALIA POINTS TO MULTIPLE
    COMETARY IMPACTS
    Andrew Glikson <geospectral@spirit.com.au>

(2) PROGRESS REPORT ON NASA'S NEO SEARCH PROGRAM
    David Morrison <dmorrison@arc.nasa.gov>

(3) GAINING INSIGHTS ON SHOOTING STARS
    BERGEN RECORD CORP
    http://www.bergen.com:80/morenews/science24199905248.htm

(4) TEMPERATURE & GAS PRODUCTION ON A MODEL COMET NECLEUS
    A. Enzian et al., CALTECH, JET PROP LAB

(5) OPTICAL PROPERTIES OF COMETARY DUST
    P.A. Yanamandra Fisher & M.S. Hanner, CALTECH,JET PROP LAB


==================
(1) DISCOVERY OF A STREWN CRATER FIELD IN AUSTRALIA POINTS TO MULTIPLE
    COMETARY IMPACTS

From Andrew Glikson <geospectral@spirit.com.au>

Dear Benny,

Discovery of a strewn crater field of late Eocene to pre-Miocene age - a
possible terrestrial analogue of the Shoemaker-Levy-9 Jupiter cometary
event.

NAMED IN HONOUR OF CAROLYN SHOEMAKER - DISCOVERER OF SL9

by John D. Gorter and Andrew Y. Glikson

The late Eugene Shoemaker predicted that the fragmentation of cometary
bodies induced by planetary gravity fields can result in clustered
extraterrestrial bombardment events (Shoemaker and Wolfe, 1994), as
exemplified by the spectacular crash into Jupiter in 1994 of 21 fragments
of the Shoemaker-Levy-9 comet (Levy et al., 1995; Shoemaker, 1998).

Here we report the discovery of a strewn crater field along the late Eocene
to pre-Langhian (37.5-24 Myr) unconformity, north Bonaparte Gulf, Timor Sea
- based on reflection seismic data and drilling. The crater field
consists of a total of 43 structures, the largest being of 5.8 km
diameter, and including (1) an established impact structure (Fohn-1 -
4.8 km diameter) including a PGE-rich breccia lens; (2) several
probable impact craters showing the classic central uplift/rim syncline
structure of impact structures; (3) several likely impact structures
showing near-perfectly circular crater-form or bulge-form; (4) several
possible impact structures whose circularity is not established; (5)
craters associated with probable ejecta rays.

The following is the summary of our paper in preparation:

A terrestrial analogue of the Shoemaker-Levy-9 comet fragmentation event:
the late Eocene - pre-Miocene strewn crater field, Timor Sea, northern
Australia

by John D. Gorter and Andrew Y. Glikson

The discovery of Fohn-1 - a late Eocene to pre-Langhian (37.5-24 Myr)
impact structure, north Bonaparte Basin, Timor Sea, allows tests of the
origin of an ENE-striking 120x25 km-large swathe of 43 analogous and
smaller circular features excavated in the pre-Langhian erosional surface.
Fohn-1 forms a 4.8 km-diameter ring structure including an upfaulted
central uplift, a circular rim syncline and a poorly defined raised outer
rim. The rim syncline contains lower Miocene infill overlying a 350
meter-thick lens of melt breccia, showing high gamma counts and
near-chondritic PGE anomalies and metal element ratios. The presence in the
breccia of redeposited Campanian and Maastrichtian microfossils suggests
rebound of strata from levels deeper than 1250 m below the pre-Langhian
unconformity and places an upper limit of about 350 m on post-impact
erosion. Larger craters of the strewn field are structurally similar to
Fohn-1. Smaller circular features (Dc<2.0 km) include crater-form and
bulge-form structures, and are interpreted as both original and eroded
remnants of larger craters. Morphometric analysis of crater diameter-depth
and diameter-central uplift relations indicate poor seismic definition of
the crater floors and strong faulting of central structural uplifts. We
suggest the north Bonaparte Basin strewn crater field represents either a
high impact flux of 3.8*10^-10 km^2.yr^-1 during 37.5-24 Ma or,
alternatively, a cometary fragmentation event, possibly contemporaneous
with the late Eocene global bombardment episode. The minimum
pre-disintegration diameter of the projectile is estimated as 760 meters.
PGE and trace metal ratios in breccia samples suggest a chondritic
composition of the parent body. An analogy with the Shoemaker-Levy-9 comet
is militated by the extensive fragmentation, the sub-linear to backscatter
craters array, and the chondritic composition. This
bombardment/fragmentation event was possibly contemporaneous with the
late Eocene impact events recorded by craters such as Popigai (100
km-diameter; 35.7+/-0.8 Myr), Chesapeake Bay (90 km-diameter;
35.2+/-0.3 Myr), Wanapitei and other craters, by the 35.4 Myr North
American tektite strewn field, and by occurrences of shocked quartz,
iridium anomalies, nickel spinel-bearing condensate spherules, and
3He/4He geochemical anomalies in sediments.

References:

(1) Shoemaker, E.M. & Wolfe, R.F., 1994. Mass extinctions, crater ages
and comet showers. In: Smoluchowski, R., Bahcall, J.N. & Matthews, M.S.
(editors), The Galaxy and the Solar System. The University of Arizona
Press, 338–386; (2) Levy, D.H., Shoemaker, E.M. & Shoemaker, C.S.,
Scientific American 273, 69-75 (1995);  (3) Shoemaker, E.M., 1998
(based on the Northcott Lecture, 30 June, 1997). Impact cratering
through geologic time. Journal of the Royal Astronomical Society of
Canada, 92:297-309.

26 May, 1999
Reported by Andrew Glikson
Research School of Earth Science
Australian National University
Canberra, A.C.T. 0200
andrew.glikson@anu.edu.au

===================
(2) PROGRESS REPORT ON NASA'S NEO SEARCH PROGRAM

From David Morrison <dmorrison@arc.nasa.gov>

NEO News (5/25/99): NASA NEO Search Program

Dear Friends and students of NEOs:

NASA, in collaboration with the US Air Force, is moving to implement a
search program to meet the objectives of the Spaceguard Survey, as set down
in the NASA Spaceguard reports of 1992 and 1995.  About a year ago I
reported on the testimony of NASA planetary exploration Theme Director Carl
Pilcher concerning the NASA commitment to the Spaceguard goal of
discovering 90% of NEAs (D > 1 km) within the next decade. NASA has been
working jointly with the US Air Force Space Command (AFSPC) and the
National Reconnaissance Office (NRO) of the US government to further
develop plans to meet this requirement.  At a May 11, 1999, meeting of the
Steering Group for the NASA NEO Program Office, additional details were
reported.

A presentation by Lt. Col. Lindley Johnson (AFSPC liaison officer to the
NRO) stated the joint agency search goal as "To the extent practicable, the
National Aeronautics and Space Administration, in coordination with the
Department of Defense and the space agencies of other countries, shall
identify and catalog within 10 years the orbital characteristics of all
comets and asteroids that are greater than 1 km in diameter and are in an
orbit around the Sun that crosses the orbit of the Earth."

In November 1998, the joint agency Partnership Council directed the NEO
Task Team to staff its recommendations through their respective
headquarters to include specific costs, schedule, and trade space of
options and their ability to meet the stated goal.  These studies concluded
that the NEO detection goal can be accomplished with current hardware and
funding, meeting the goal by the end of 2009.

The near-term actions to implement this goal are the expansion of the
Lincoln Lab (MIT) LINEAR program to use a second 1-m telescope in New
Mexico, so that LINEAR will operate 2 telescopes each at 18 nights/month.
An effort will also be made to extend operations of the NEAT (JPL) detector
on the 1-m USAF GEODSS telescope in Hawaii from 6 to 18 nights/month.
Farther in the future, the agencies will transition the NEAT search to a
1.2-m telescope at Hawaii, and the possibility will be investigated for
expanding the search to use additional AFSPC telescopes.  The general plan
in all these observing programs is for AFSPC to provide the telescopes and
NASA to support the operations associated with NEO searches.

A more detailed statement of the search strategy and requirements is
contained in a letter from NASA Administrator Daniel Goldin to General
Richard B. Meyers, Commander in Chief of the Space Command, dated April 6,
1999.  In part, Mr. Goldin wrote:  "Succinctly stated, the requirement is
to search 20,000 square degrees of sky each month and to detect all moving
objects in that search space to an apparent visual magnitude of 20.5.
Analysis, to date, on the characteristics of the small but significant
population of NEOs observed, indicate this depth in magnitude and monthly
sky coverage will enable us to inventory at least 90 percent of the entire
population of large NEOs (>1 km) within 10 years of the start of the
survey, a goal established by the congressional direction given us.

"Currently, there are two search projects that are funded by NASA but which
rely heavily on Air Force support.  We believe these projects together,
when they reach their full potential, will provide the primary means for
achieving the above goal.  The first is the Lincoln Near Earth Asteroid
Research (LINEAR) project, funded by NASA, but which uses both
state-of-the-art detector systems developed for the Air Force and two Air
Force telescopes at the Experimental Test Site (ETS) at Socorro, New
Mexico.  The second is the Near Earth Asteroid Tracking (NEAT) project
which is currently being supported on one of the operational Maui Ground
Electro-Optical Deep Space Surveillance telescopes.

"Cooperative discussions with the Air Force Space Command have led to the
identification of an Air Force Research Laboratory 1.2 meter telescope at
the Maui site for use by NEAT.  If the NEAT camera can be accommodated on
this telescope, it will enable the NEAT project to continue making an
important contribution to the search effort at the dimmer magnitudes, while
allowing the heavily used GEODSS telescope (now used part-time to support
NEAT) to be returned to full time space surveillance operations.

"We believe that the two LINEAR telescopes (one currently operating and a
second scheduled for future operation) at the ETS and the NEAT camera on
the 1.2m at Maui, if operated in close coordination, will be able to search
20,000 square degrees of sky per month for all NEOs brighter than magnitude
20.5. This year our funding for all phases of NEO survey work, including
discovery, follow-up, ground-based characterization, support of the Minor
Planet Center, and our new program office at the Jet Propulsion Laboratory
(JPL) in Pasadena, California, is $3.5M.  NASA is committed to sustaining a
vigorous search effort until the stated goal is reached.  We solicit your
continued support to these two projects so important to the success of the
NEO survey effort.

"We briefly note that our ground-based survey work on NEOs is but a small
part of NASA's total program of studying the comets and asteroids that
comprise the NEO population.  Space-based efforts include NASA's Near Earth
Asteroid Rendezvous (NEAR) mission, which will spend a year closely
studying the near-Earth asteroid Eros.  The Deep Space-1 spacecraft, an
exciting technology mission, will study the asteroid 1992 KD.  The recently
launched STARDUST spacecraft will return cometary dust samples to the Earth
in early 2006.  NASA has selected another mission, the Comet Nucleus Tour
(CONTOUR) mission, to investigate three diverse cometary nuclei.  In
addition, NASA is a partner on two non-US missions, the ROSETTA mission
which will perform a landing on a cometary nucleus and the Japanese MUSES-C
mission which will return a sample from a near Earth asteroid.  The data
returned from these missions on the physical and chemical nature of the
target bodies will be absolutely vital if we are presented with a future
need to modify the orbit of an Earth-threatening NEO."

The above statements by Lt. Col. Johnson and NASA Administrator Goldin
provide a clear and highly specific statement of the NASA and USAF goals
and their strategy for meeting these goals.  Probably the most difficult
task is to achieve NEA detection at V = 20.5 with the 1-m USAF telescopes,
which have previously been used for more rapid surveys that do not extend
this deep. To achieve the Spaceguard goals, the three NASA-AFSPC
telescopes, as well as others supported by NASA (such as Spacewatch,
LONEOS, and the Catalina Survey) will need to be coordinated to work
together as a team. LONEOS and Catalina are both still in their test
phases, and improvements are expected in each over the coming months. In
addition, if the anticipated discovery rate is achieved, it will be
necessary to enhance the follow-up capability on other telescopes,
primarily through international agreements.  In this coordinated search, it
will not be possible for the discovery telescopes to do their own
follow-up, a topic discussed extensively by NASA's Shoemaker Committee in
its 1995 report on the Spaceguard Survey.

Meanwhile, following is a snapshot of current discovery performance
prepared by Al Harris of JPL.  The values in the table are the numbers of
NEOs brighter than absolute magnitude 18.0 (i.e., D > 1 km) discovered in
successive 6-month periods.

NEA DISCOVERY SUMMARY (D > 1 km) JULY 97 THRU JUN* 99

Discoverer 97(2) 98(1) 98(2) 99(1)
------------------------------------------------------------------------
LINEAR 2 10 26 21
NEAT 3 5 2   0
Spacewatch 1 2 1   5
LONEOS 0 0 4   3
Catalina 0 0 0    3
Other 2 2 2   2
------------------------------------------------------------------------
Total 8 19 35 34

* Scaled from actual discoveries Jan-Apr 1999.

We have so far discovered about 18% of the NEAs larger than 1 km.  The
current discovery rate is approximately 70/yr, dominated by the LINEAR
program (using one telescope). The current performance of the survey is
roughly a factor of 5 below that required to meet the Spaceguard goals
using the criteria that Harris has applied in the past.  In a recent
re-evaluation of these criteria, Harris now suggests that at this point in
the survey, we should be discovering about 500/year, or a factor of 7 more
than at present.  However, Harris also notes that there is considerable
uncertainly in this figure, and additional modeling would be useful.  He
will be speaking on this subject at the IMPACT workshop in Torino in June
1999.

The expansion of LINEAR to two telescopes and the increased performance
anticipated from NEAT could bring this system performance to within a
factor of 2-3 of that required if the 1-m telescopes can achieve detections
at magnitude 20.5.  Additional modeling of the total performance of these
instruments used in a coordinated manner will have to be done, as well as
actual experience to determine if performance at V = 20.5 is realized.
Clearly, however, we have made tremendous strides in the past year, and
NASA with its USAF partners has a goal to complete the survey (to 90%) by
2009.

* * * * * * *

For your information, following is the membership of NASA's NEO Program
Office Steering Group (where IAU = International Astronomical Union):

Michael A'Hearn, President of the Solar System Division of the IAU
Andrea Carusi, President of the Spaceguard Foundation
Paula Cleggett, Deputy Associate Administrator, NASA Public Affairs Office
Timothy Ferris, University of California, author
Lindley Johnson, Lt. Col., US Air Force Space Command
David Morrison, President of the IAU Working Group on NEOs
Hans Rickman, Assistant Executive Secretary of the IAU
Irwin Shapiro, Director of the Harvard-Smithsonian Observatories

Also:

Donald Yeomans, NASA NEO Program Manager, JPL
Carl Pilcher, NASA Solar System Exploration Theme Director
Tom Morgan, NASA Planetary Astronomy Discipline Scientist

* * * * * * *

In a separate news item, the Authorization Committee of the US House of
Representatives has passed a 3-year bill for NASA that authorizes
expenditure of up to $10.5M for NEO searches for each of the next three
fiscal years.  This represents an increase of $7M per year over the current
and anticipated NASA rate of expenditure for this purpose.  This
authorization is a clear statement of interest from Congress in pursuing
the Spaceguard Survey.  However, to actually be translated into additional
funds for NASA, this House authorization would have to be supported by
similar action in the Senate Authorization Committee, plus be voted by the
full House and Senate, plus be supported by the respective House and Senate
appropriation committees, plus be passed as an appropriation by both House
and Senate, plus be approved by the President.  Sorry folks, but that is
the process for appropriation of funds in the United States!

David Morrison

+++++++++++++++++++++++++++++++++++++++++++

David Morrison, NASA Ames Research Center
Tel 650 604 5094; Fax 650 604 1165
david.morrison@arc.nasa.gov or dmorrison@mail.arc.nasa.gov
website: http://space.arc.nasa.gov
website: http://astrobiology.arc.nasa.gov
website: http://impact.arc.nasa.gov

=====================
(3) GAINING INSIGHTS ON SHOOTING STARS

From BERGEN RECORD CORP
http://www.bergen.com:80/morenews/science24199905248.htm

Gaining insights on shooting stars

Monday, May 24, 1999

By ALEXANDRA WITZE
Special from The Dallas Morning News

Halfway between the two most anticipated meteor showers of the decade,
astronomers are finding that the more they learn about shooting stars,
the less they seem to understand.

Last November, scientists locked their collective gaze on the Leonid
meteors. Using specially outfitted instruments on airplanes and on
Earth, researchers gathered the most data ever on a single meteor
shower.

"It really was the Leonids up close and personal," says Peter
Jenniskens, an astronomer at the NASA Ames Research Center and the
Search for Extraterrestrial Intelligence Institute, both in
Northern California.

Round two will come this November, when the Leonids are expected to put
on a particularly good show, as they did in 1998. Scientists are glad
for this second chance; the data they gathered last year seem to raise
more questions than answers.

The 1998 Leonids campaign revealed details about the temperature,
speed, and chemical makeup of meteors as they streak through Earth's
atmosphere, scientists reported at the Ames center last month. But they
didn't detect organic material within the meteors or debris trailing
after them as expected, Jenniskens says.

Like all meteor showers, the Leonids happen annually when Earth passes
through a trail of debris left by a passing comet. The dust particles,
no bigger than a Rice Krispie, burn up in the atmosphere as blazing
light streaks. The Leonids occur every Nov. 17 and are named because
they appear to shoot outward from the constellation Leo.

The Leonids are pieces of Comet Tempel-Tuttle, which sheds debris as it
swings through the solar system every 33 years or so. So roughly every
33 years, skywatchers expect a particularly good Leonids show. Comet
Tempel-Tuttle last visited in February 1998; it may create good Leonid
displays through 2001, some astronomers think.

But other astronomers have found that it wasn't the 1998 visit of the
comet -- but rather one six centuries ago -- that made last year's
shower so vivid. A team of Irish and Russian astronomers has calculated
that the 1998 show was caused by debris left by Tempel-Tuttle in 1333.

The peak of the 1998 shower came more than half a day earlier than
expected -- which suggested it wasn't that year's comet debris burning
up.

"We thought if we searched through all the possibilities for the last
1,400 years, we'd find one in particular that gave the timing just
right," says David Asher of the Armagh Observatory in Northern Ireland.

Asher and colleagues calculated that debris from the 1333 passage would
have been in just the right place to create last year's display.

For a different perspective, other astronomers took to the skies last
November. Jenniskens, for instance, led a NASA effort that flew two
airplanes in parallel paths to photograph and study the meteors.

Surprisingly, he discovered that most of the Leonids burned up at
roughly the same temperature, regardless of their size or speed.
Meteors were also detected at higher altitudes than ever before -- 120
miles above Earth's surface.

"It's very hard to understand why the meteors light up at that high
altitude," he says, where there is little atmosphere to create
friction. Possibly the Leonid particles contain volatile chemical
components, which burn up more easily than expected.

The Ames team plans to repeat the two-airplane approach this November,
perhaps substituting a Boeing plane with an infrared telescope on its
top. Such a telescope could better study the heat given off by the
meteors and any debris they leave behind.

Other researchers bounced light beams off the glowing trails left by
the Leonids, discovering turbulent swirls in the smoke. Knowing how
those trails are structured can help scientists understand how meteors
dissipate their heat into cold space, Jenniskens says.

Copyright 1999 Bergen Record Corp.

==================
(4) TEMPERATURE & GAS PRODUCTION ON A MODEL COMET NECLEUS

A. Enzian*), J. Klinger, G. Schwehm, P.R. Weissman: Temperature and gas
production distributions on the surface of a spherical model comet
nucleus in the orbit of 46P/Wirtanen. ICARUS, 1999, Vol.138, No.1,
pp.74-84

*) CALTECH, JET PROP LAB, DIV EARTH & SPACE SCI, MS 183-601,
   PASADENA,CA,91109

A multidimensional comet nucleus model is used to estimate the
temperature and gas production distributions on the surface of a comet
nucleus in the orbit of of 46P/Wirtanen. The spherical model nucleus is
assumed to be made up of a porous dust-ice (H2O, CO) matrix. Heat and
gas diffusion inside the rotating nucleus are taken into account in
radial and meridional directions. A quasi-3D solution is obtained
through the dependency of the boundary conditions on the local solar
illumination as the nucleus rotates. As a study case, we consider a
homogeneous chemical composition of the surface layer which is assumed
to contain water ice. The model results include the distributions of
temperature and gas production on the surface. For the chosen test case
of a nucleus spin axis perpendicular to the orbital plane we found that
the CO gas production on the surface is quasi-uniformly distributed in
contrast to the nonuniform water outgassing. The mixing ratio at a
specific point on the comet nucleus surface is not representative of
the overall mixing ratio which is observed in the coma. (C) 1999
Academic Press.

=================
(5) OPTICAL PROPERTIES OF COMETARY DUST

P.A. Yanamandra Fisher*), M.S. Hanner: Optical properties of
nonspherical particles of size comparable to the wavelength of light:
Application to comet dust. ICARUS, 1999, Vol.138, No.1, pp.107-128

() CALTECH,JET PROP LAB,4800 OAK GROVE DR,PASADENA,CA,91109

Scattering calculations for nonspherical particles have been carried
out in order to explain observed optical properties of cometary dust.
We focused on two optical properties of cometary dust sensitive to
particle shape: negative linear polarization at phase angles less than
or equal to 21 degrees and the 11.2-mu m silicate emission feature. The
discrete dipole approximation (DDA) method was employed to compute the
scattering matrix for nonspherical silicate and absorbing particles of
size comparable to the wavelength. Silicate particles with a variety of
shapes and size parameter X-eq similar to 2.5, corresponding to a
linear dimension of 0.5-1.0 mu m, can produce negative linear
polarization at small phase angles, whereas carbon particles produce a
strong positive maximum of polarization near phase angles of 90
degrees. Mixtures of silicate and carbonaceous material, on a scale
small compared to the wavelength, eliminate the negative polarization
in this size range; however, macroscopic mixtures of silicate and
carbon could yield the observed negative linear polarization at low
phase angles (less than or equal to 21 degrees) and a maximum positive
polarization at phase angle of 90 degrees. The position of the 11.2-mu
m thermal emission peak observed in comets, attributed to crystalline
olivine, depends strongly on particle shape even for particles much
smaller than the wavelength and can be matched with anisotropic Mg-rich
olivine for our model tetrahedra or moderately elongated bricks.
Spheres and extreme shapes, such as disks or needles, appear to be
ruled out. Approximately 20% crystalline olivine and 80% disordered
olivine reproduces the observed spectra of comets with comparable peaks
at 10 and 11.2 mu m, e.g., P/Halley, Bradfield 1987 XXIX, Mueller, Levy
1990 XX, and C/1995 O1 (Hale-Bopp). This study is an essential first
step toward realistic modeling of comet dust as aggregates composed of
nonspherical monomers having dimensions comparable to the wavelength of
incident radiation. (C) 1999 Academic Press.

----------------------------------------
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*

LETTERS TO THE MODERATOR, 26 May 1999
-------------------------------------

(1) AMPLIFICATION OF THE CONCEPT FOR ASTEROID-BASED OBSERVATORIES (ABOs)
    Elton L. Jones <jonee@epix.net>

(2) ALL WE NEED ARE APPROPRIATE FIRE EXISTS
    Gerrit Verschuur <GVERSCHR@MOCHA.MEMPHIS.EDU>

(3) EVENTS WITH LOW PROBABILITY SHOULD NEVER BE IGNORED
    Norbert Giesinger <norbert.giesinger@siemens.at>

(4) HOW TO OBSERVE ASTEROID 1999 AN10 IN 2027
    Alain Maury <Alain.Maury@obs-azur.fr>


=============
(1) AMPLIFICATION OF THE CONCEPT FOR ASTEROID-BASED OBSERVATORIES (ABOs)

From Elton L. Jones <jonee@epix.net>

Dear Benny Peiser

I wanted to revise and extend my  informal posing from May 24th. It was
my intention to evaluate the  body of knowledge and effort which may
have already occurred into the advantage of using a NEO which had a
short period and small distance from the earth in order to survey for
other NEOs. Many NEOs, we believe, are scantly detectable from earth
because of their small yet dangerous sizes. Furthermore, if it was
merited, I intended to propose and defend the concept. I had hoped to
stir thinking and discussion about what advantages 1999 AN10 could be
to science at a time when the dialogue seemed fixed on the danger it
could pose. I  mentioned two possible uses, but the primary focus would
be as an instrument platform - - a space craft which would be around
earth for 600 years hence. Long before the hotel, casino, and condo
developments spring up there, it might be worth getting past those
unknown and undiscovered bodies in the path of our future as a planet.

When ideas arrive from whatever segment, a sound approach is to develop
consensus and evaluate apparent merit. All to frequently, there is a
forthright dismissal and stifling of ideas because we tend to look at
why it is not rather then why we can! If "it is not my idea, it is
merit-less" mentality especially if it is suspected of competing with
other agendas. I also admonished readers that before there was a
collection of ideas, to reach a decision or opinion- - either way- -
was imprudent, in my view.

While I understood that it might start a preliminary dialogue- - I did
not wish to start a heated public debate per se ... especially one in
which other agendas are ground-out on my  words. I have read  a single
response to the concept which uses "misguided" as its sole assessment.
It was an advocation for a mining operation on the Trojan's wherever we
may find them, and an escape velocity vs distance point of view. I hope
this was not in academic arrogance that this was stated,  but based in
an unexpressed or unshared rationale as to why a  consideration of the
ABO is unsound. I have no condemnation on the merits of that as a
future direction of any of man's expansion into the solar system.  The
response had many ideas of merit on other issues. However, it addresses
little specifically to the concept of an asteroid-based observatory.

The observatory's primary function could be an advanced guard in the
detection of NEOs and earth orbit crossing bodies. If feasible, is it
desirable? Will it give us a "leap" in detection and avoidance of
unknown, culture disrupting, meteoroids which might be in the 100-500
meter size range. I intuitively believe that having another set of
instruments searching a different area of the solar system is a "leap"
advantage, but welcome comments as to why we do not need such a
capability or as to why it makes sense to consider.

I would ask questions as the the advantages of practicality, logistics,
and effectiveness.... such as:

Assuming that the observatory chassis would be assembled in orbit after
multiple lifts, designers can design a platform for end-use simplicity
and functionality as opposed to designing components for launch vehicle
constraints. Is the size of the transporter a significant driver of
design, given the need to travel the distance and maneuver  to intercept
velocity given the size package we ultimately would like to "install" on
an asteroid?

I was not addressing escape velocity, but addressing the transit times
to other bodies and pointing out the advantage to transit times of days
versus years should we need to maintain the observatory. Why take a
long arduous journey to go to the mountain if the mountain is coming to
us? Return journeys are more accessible from orbit stationed vehicles
for various reasons.

What increase in effectiveness does a returning ABO offer... with
emphasis on surveying the near earth and earth crossing area of
interests.  I believe that our best detectors for these small but
harmful bodies (i.e. Not just visible asteroids) will be, phased array
radars,  scanning lasers, and staring thermal detectors. All of these
are range sensitive/limited.

Low reflectivity of many bodies make viewing from earth with optical
systems a marginal method. In this case distance does mater. The
closer the instrument is to the target the better the resolution. Earth
based radars may survey Venus but can they resolve a transient blip
which may not be detected again for months? Being close to the
transmitter the time for return of an echo is seconds instead of
minutes. The scan rate is faster as well as. The radar may move on to a
new sector with shorter sounding times .

The cowboy in me  would also want to get an idea of how big a rope I
would need to lasso the d$%&  thing and what I am going to hook it to
once I have it "in tow".

Finally, I hope I have at least encouraged readers to look for
unrealized possibilities in the in the  clutter of dismal  happenings--
to look at what everyone else has viewed and see what no one else has
yet seen.

Regards,

Elton Jones

==================
(2) ALL WE NEED ARE APPROPRIATE FIRE EXISTS

From Gerrit Verschuur <GVERSCHR@MOCHA.MEMPHIS.EDU>

Regarding the parallels between the impact threat and a theater fire
raised by Jon Richfield, the sensible option is to design and construct
appropriately marked fire escapes.

Gerrit Verschuur

====================
(3) EVENTS WITH LOW PROBABILITY SHOULD NEVER BE IGNORED

From Norbert Giesinger <norbert.giesinger@siemens.at>

Dear Dr. Peiser,

reading in recent days, and especially today, about the ongoing
developments in the case of 1999 AN10 on the net, I think it can be
learned now that events with low probabilities (poisson-distributed and
others) should never be ignored - and never should the distribution of
knowledge be supressed. Otherwise, there is a low but nonzero
probability that the existing knowledge of a forthcoming event will be
lost. To say it bluntly - the loss of the homepage, the loss of the few
persons with knowlede concerning this event...due to a number of
possible events is possible.

Think of a scenario where the knowledge concerning 1999 AN 10 is
restricted to a few people, forgotten in coming years, 1999 AN10 not
recovered in 2004 or later... the probabilites of such event chains are
low - but not zero and may eventually lead to global consequences.

In some sports, it is quite important not to ignore the the forerunners
of accidents - a number of years ago when I was a bit engaged in
caving, I learned to be alarmed and to be very cautious when stumbling
became too frequent.

Thank you for your efforts !

Very sincerely yours
Dr. Norbert Giesinger FBIS
Viktorgasse 17/22
A-1040 Vienna
norbert.giesinger@siemens.at

=============
(4) HOW TO OBSERVE ASTEROID 1999 AN10 IN 2027

From Alain Maury <Alain.Maury@obs-azur.fr>

AN10 will be about 5 arc seconds wide at closest distance, which means
anybody could be able to see its shape through a small telescope...
With adaptative optics, that means resolving around 20 meters on the
surface of the object (if it is indeed 1km or so diameter).

Alain

-----------------
CCNet-LETTERS is the discussion forum of the Cambridge-Conference
Network. Contributions to the on-going debate about near-Earth objects,
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Benny J Peiser at <b.j.peiser@livjm.ac.uk>. The fully indexed archive
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CCCMENU CCC for 1999

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