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
-----------------
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