PLEASE NOTE:


*

CCNet DIGEST 5 August 1998
--------------------------

(1) HOW TO STAY COOL IN FACE OF COSMIC IMPACTS
    Oliver Morton <abq72@pop.dial.pipex.com>

(2) VERY SEXY ...
    Duncan Steel <dis@a011.aone.net.au>

(3) ... YES, INDEED
    Steven J. Ostro <ostro@echo.Jpl.Nasa.Gov>

(4) METEORITE DEBATE HITS TWO-YEAR MARK
    Life on Mars? Scientists still see no definitive answer in rock
    MSNBC SPACE NEWS
    http://www.msnbc.com/news/185351.asp#BODY

(5) METEOROIDS 1998
    Mark Davis <MeteorObs@Charleston.Net>

(6) DECODING SATELLITE IMPACT DATA
    J..A.M. McDonnell & D.J. Gardner, UNIVERSITY OF KENT

(7) UNUSUAL SPECTRA OF 15 NEAR-EARTH ASTEROIDS & EXTINCT COMETS
    M.D. Hicks et al., CALTECH

(8) LOW-COST MISSIONS TO ASTEROIDS
    J.A. Sims et al., PURDUE UNIVERSITY

(9) TECHNICAL & ECONOMIC FEASIBILITY OF MINING NEAR-EARTH ASTEROIDS
    M.J. Sonter, MARK SONTER CONSULTING PTY LTD

(10) THE MASS OF CERES
    B. Viateau & M. Rapaport, BORDEAUX OBSERVATORY


====================
(1) HOW TO STAY COOL IN FACE OF COSMIC IMPACTS

From Oliver Morton <abq72@pop.dial.pipex.com>

Benny -- The Ostro/Sagan paper you forwarded serves in part as a
challenge to imagine high technology civilisations with a laissez faire
attitude towards planetary impacts. Here are a few possibilities, with
science fiction illustrations. Their likelihoods are, obviously, purely
conjectural.
 
Civilisations which live in highly isolated regions of their planet --
eg the abyssal plains. There are various reasonably well rehearsed
arguments against high technology civilisations developing in entirely
marine settings, but none of them mean that a land-living or amphibious
intelligent species cannot choose to move back to the sea and its
deeps. The idea of life in the Marianas trench may not excite us, but
who is to say that profoundly alien cultures might not think it a swell
idea. My impression is that a civilisation living in structures
tethered a few hundred metres above an abyssal plain and powered by
fusion or easily repaired geothermal systems could persist for 100s of
millions of years. Unless something big happened to hit directly on a
centre of population you would be just fine. Abyssal plains seem safer
than space as a place to live -- no risk from nearby gamma ray bursts.
You don't have to stop at the abyss, either; if memory serves, there
are aliens who have chosen to live in the mantle of a planet in David
Brin's "Startide Rising"..
 
Civilisations that don't live on planets but have no interest in
further developing space flight. Any civilisation that lived in a
plethora of somewhat steerable orbital habitats would be effectively
immune to impact extinction and would not necessarily need to develop
astronomical radar (or interstellar interests, for that matter). Their
founding planetary civilisation might have disappeared due to war, 
environmental collapse or, for that matter, an impact; whatever it was,
it doesn't necessarily mean they should have any interest in predicting
future impacts (except so as to get a good view). For an extreme
example of this line of thought, John Varley wrote some stories about
bio-engineered, solar-powered, rad-hardened individuals capable of
spinning their own solar sails living as free-flyers in space. These
people would have had only academic interest in planetary impacts.
 
Civilisations that don't live in biological systems at all. If you
believe in the possibility of downloadable personalities "living" in
computers at all, then it's a fair bet you believe that we will develop
the technology to make such a thing possible well before the next big
impact. These computer habitats, requiring no ecosysytem support and
subsisting purely on energy and information, could be made reasonably
impervious to anything except a direct hit. They could also be
regularly backed up in multiple locations, so that even the complete
destruction of one of them would not end the continuity of memory of
its occupants. If this is how intelligent life ends up, most of it
probably doesn't need to worry about planetary impacts.
 
This sort of scenario is described in fascinating detail in Greg Egan's
most recent novel, "Diaspora". His software based protagonists do, as
it happens, indulge in SETI and interstellar travel -- but he has to
work quite hard to find reasons for them to do so.
 
Best, oliver
 
======================
(2) VERY SEXY ...

From Duncan Steel <dis@a011.aone.net.au>
 
Dear Benny & Steve,
 
I note that Benny's scanner mis-read quite a few characters from the
splendid Ostro & Sagan A&G article; but one error right at the end was
a doozy:
 
> One way or another, interplanetary collisions constitute a unique,
> erogenous environmental factor in the natural selection of long-lived
> civilizations.

I take it that was meant to be 'exogenous' ?!
 
Duncan
=============
(3) ... YES, INDEED

From Steven J. Ostro <ostro@echo.Jpl.Nasa.Gov>

Duncan, yes.
 
Steve

===================
(4) METEORITE DEBATE HITS TWO-YEAR MARK
    Life on Mars? Scientists still see no definitive answer in rock
 
From MSNBC SPACE NEWS
http://www.msnbc.com/news/185351.asp#BODY
  
By Paul Recer
ASSOCIATED PRESS
  
WASHINGTON, Aug. 4 —It’s been two years since scientists announced that
they saw signs of ancient life in a Martian meteorite. At the time,
they were confident that others would quickly confirm their results.
Instead, the claims appear to be fading into the gray zone between
proof and disproof.
 
THE ANNOUNCEMENT stunned the world: Scientists had found evidence of
life on Mars. Inside a meteorite from Mars, NASA researchers said,
they had discovered the fossilized remains of tiny, bacteria-like
animals that may have once thrived on the Red Planet.

The idea seized global attention and gave sudden popular legitimacy to
the possibility of extraterrestrial life. President Clinton called for
a space summit. Famed scientist Carl Sagan called it “a possible
turning point in human history.”

“We’ll know for sure in two years or so,” said NASA researcher Everett
Gibson. Now that two years have passed, excitement and applause have
faded to doubt and skepticism.

Hundreds of scientists have poked, probed, crushed, dissolved and
broken parts of the Mars rock known as Allen Hills 84001. So far, no
one has found absolute, incontrovertible evidence that the potato-sized
chunk ever contained life. Then again, nobody has proven that the team
led by Gibson and David McKay was wrong.

“Everyone was hopeful that it would just take a short period of time to
prove,” said Richard Zare of Stanford University, a key member of the
McKay-Gibson team. “We’ve seen two years go by. I don’t know of anyone
who has changed their opinion.”

Ralph Harvey of Case Western Reserve University, an expert on
meteorites, was excited and skeptical when the McKay group made its
announcement. Now he is just skeptical and believes most other
scientists are, too. “People in the field either aren’t able to confirm
the work or don’t seem favorable to it,” said Harvey.

John Bradley, a professor at Georgia Institute of Technology, is even
blunter: “Early skepticism has evolved into international consensus ...
that this rock does not contain Martian fossils. I do not know of a
single other individual who believes it at this point.”

McKay, Gibson, Zare and others on the Mars rock team, however, still
believe that the presence of ancient microscopic life best explains
what they found inside.
                                
COLD, HARD FACTS

No one disputes the basic facts about the 4.2-pound rock: that it
formed on Mars some 4.5 billion years ago and was catapulted into space
about 16 million years ago after a comet or asteroid smashed into Mars.

The rock floated around for millions of years before it came scorching
through the Earth’s atmosphere about 13,000 years ago and smashed into
Antarctica. It was found by meteorite hunters in 1984. Chemistry tests
later proved the rock came from Mars. What’s inside has caused the
controversy.

McKay’s team, using powerful microscopes, found polycylic aromatic
hydrocarbons, the first organic molecules ever seen inside a Martian
rock. The researchers also found a crystal structure called carbonate,
shaped like extremely tiny worms.

The team concluded the most likely explanation was that about 3 billion
years ago, Martian microbes had crawled into the rock, thrived and then
died. The wormlike structures might be their fossilized remains.
                                
QUESTIONS REMAIN

Rival researchers have attacked the theory on several fronts:

* The organic compounds can be formed in a
  number of ways that do not involve biology.
  
* The wormlike structures are crystals
  that formed with adjacent material when the rock cooled.
              
* Some minerals were formed in the rock at very
  high temperatures — well above the 248 degrees
  Fahrenheit that the critics considered the maximum for life
  formation.
  
* The rock contains very few minerals
  formed in the presence of water. Since water is thought to be
  essential to life, it’s unlikely the dry rock ever contained life,
  critics said.
  
* Organics found in the rock are of Earth origin. The
  molecules got into ALH84001 while it sat in Antarctic ice.
 
McKay, Gibson, Zare and other members of the original team have
countered each argument, doing lab experiments to reinforce their
findings. Gibson has debated scientists in open meetings.

The debate may never be settled, says NASA’s Ed Weiler, “until we go
there (to Mars) and get some samples.” No matter how or when the
question is answered, notes Zare, science has been the winner.
“Prior to this study, if you talked about searching for life on another
planet, you were considered a nut,” he said. “It has now become a huge
topic that is attracting the best scientists.”
                                
1998 Associated Press.

===========
(5) METEOROIDS 1998

From Mark Davis <MeteorObs@Charleston.Net>

A meeting to be held in Tatranska Lomnica, Astronomical Institute, Slovak
Academy of Sciences August 16-22, 1998

The topics include:

- Structure and evolution of meteoroid streams, the sporadic background
- Associations with meteoroid parent bodies
- Physics and chemistry of meteors / meteoroids / meteorites
- Interplanetary particles and cosmic dust, proporties and dynamics
- Leonid meteor stream
- Observational programs (optical, radar, onboard)

Scientific Organizing Committee:
W.J. Baggaley (Chairman), P.B. Babadzhanov, O.I. Belkovich, Z.
Zeplecha, G. Cevolani, B.A.S. Gustafson, A. Hajduk, I. Hasegawa, R.L.
Hawkes, I. Mann, J. Jones, B.A. Lindblad, V. Porubcan, M. Simek, I.P.
Williams

To receive additional information, contact Vladimir Porubcan at:

Astronomical Institute SAV
Dubravska 9
84228 Bratislava
Slovakia

tel.:421-7-375157 fax:421-7-375157 e-mail: astropor@savba.savba.sk

=================
(6) DECODING SATELLITE IMPACT DATA

J.A.M. McDonnell & D.J. Gardner: Meteoroid morphology and densities:
Decoding satellite impact data. ICARUS, 1998, Vol.133, No.1, pp.25-35

UNIVERSITY OF KENT, PHYS LAB, UNIT SPACE SCI & ASTROPHYS, CANTERBURY
CT2 7NR, KENT, ENGLAND

The densities of interplanetary micrometeoroids have been inferred by
various techniques in the past; a valuable (albeit indirect) technique
has been the study of the deceleration profile of radar meteor trails,
for example. Impacts on the thin foils of the Micro-Abrasion Package on
NASA's LDEF satellite and the Timeband Capture Cell Experiment on ESA's
Eureca satellite now provide direct in situ measurement of the
cross-sections diameters of impacting micrometeoroids and also of space
debris particles. Combining these data with impact data from
thick-target impact craters, where the damage is mass-dependent, and
where such targets have experienced a statistically identical flux,
leads to a measure of the impactor density which is only weakly
affected by the assumed impact velocity. Comparing the space result
with those from simulations shows that the density distribution of
interplanetary particles in space has a more significant low density
component than the distributions obtained by most other recent methods
and that the mean density is in the range 2.0 to 2.4 g cm(-3) for
masses of 10(-15) to 10(-9) kg. The characteristic density - namely,
the single value which would characterize the impact behavior of the
distribution-is 1.58 cm(-3). Perforation profiles reveal that a large
fraction of the largest particles impacting the satellites are
nonspherical but that typical aspect ratios are mostly in the range
1.0-1.5. Flux distributions of the meteoroid population incident on the
Earth at satellite altitudes are derived in terms of mass and mean
diameter. (C) 1998 Academic Press.

=================
(7) UNUSUAL SPECTRA OF 15 NEAR-EARTH ASTEROIDS & EXTINCT COMETS

M.D. Hicks*), U. Fink & W.M. Grundy: The unusual spectra of 15
near-Earth asteroids and extinct comet candidates. ICARUS, 1998,
Vol.133, No.1, pp.69-78

*) CALTECH, JET PROP LAB MS 183 501, 4800 OAK GROVE DR, PASADENA, CA,
91109

We present moderate resolution reflectance spectra from 0.55 to 1.0 mu
m for 15 near-Earth asteroids and extinct cometary nuclei candidates
obtained at the Catalina Station 1.54-m telescope near Tucson, Arizona.
Though our limited wavelength coverage often makes firm classification
difficult, an analysis of our measurements reveals that there is an
over-representation of asteroids with unusually deep 0.9-to 1-mu m
absorption features, Several of our objects have spectra consistent
with Q-type asteroids and within the limits of our signal-to-noise
ratio, are compatible with a chondritic composition. It is apparent
that the near-Earth asteroids as a population have an unusual taxonomic
distribution, one that is much closer to that of meteoritic falls than
may have been previously assumed. (C) 1998 Academic Press.

==============
(8) LOW-COST MISSIONS TO ASTEROIDS

J.A. Sims, J.M. Longuski, A.J. Staugler: Trajectory options for
low-cost missions to asteroids. ACTA ASTRONAUTICA, 1997, Vol.41, No.11,
pp.731-737

PURDUE UNIVERSITY, SCH AERONAUT & ASTRONAUT, W LAFAYETTE, IN, 47907

We consider a wide variety of gravity-assist trajectories using Venus,
Earth and Mars to obtain low launch energy trajectories to four large
asteroids in the main belt. These trajectories are constructed by
analytic and numeric search techniques. We optimize promising
trajectories for minimum total Delta V and search for additional
(nontargeted) asteroid flybys. Several optimized opportunities with
multiple asteroid flybys are reported, followed by a discussion of
general characteristics of the various trajectory types. (C) 1998
Elsevier Science Ltd. All rights reserved.

==============
(9) TECHNICAL & ECONOMIC FEASIBILITY OF MINING NEAR-EARTH ASTEROIDS

M.J. Sonter: The technical and economic feasibility of mining the
near-earth asteroids. ACTA ASTRONAUTICA, 1997, Vol.41, No.4-10,
pp.637-647

MARK SONTER CONSULTING PTY LTD, ASTEROID ENTERPRISES PTY LTD, 11
DENELAND DR, HAWTHOMDENE, SA 5051, AUSTRALIA

The Near Earth Asteroids are primary targets for resources to support
space industrialization. Robust technical and economic approaches to
project planning feasibility evaluation are needed to evaluate such
space mining ventures. This paper discusses the technical engineering
and mission-planning choices and shows how the concept of probabilistic
Net Present Value can be used to optimize asteroid mining project
designs. The generic mission reviewed envisages a lightweight (3 or 4
tonnes) remote (teleoperated) regolith miner or drilling rig,
recovering products such as water and other volatiles using solar
thermal power, and subsequently returning approximately 1000 to 2000
tonnes to Low Earth Orbit, using solar thermal rocket propulsion.
Initial estimates of NPV are highly favourable for some targets. (C)
1998 M. J. Sonter. Published by Elsevier Science Ltd.

==========================
(10) THE MASS OF CERES

B. Viateau & M. Rapaport: The mass of (1) Ceres from its gravitational
perturbations on the orbits of 9 asteroids. ASTRONOMY AND ASTROPHYSICS,
1998, Vol.334, No.2, pp.729-735

BORDEAUX OBSERVATORY, CNRS, URA 352, BP 89, F-33270 FLORAC,FRANCE

The mass of (1) Ceres is about half of the total mass 2. Method of the
main asteroid belt, and its long-term perturbations on the orbits of
many solar system objects are important. For this reason, a very good
knowledge of this mass is necessary. Although many determinations of
the mass of Ceres have been made until now, the uncertainty remaining
on its value is yet too high. A determination of the mass of Ceres,
based on its gravitational perturbations on the orbits of 9 asteroids,
is presented. All the available observations of the perturbed asteroids
were used. In particular, for the asteroids observed by Hipparcos, the
very accurate Hipparcos data were added to the ground-based
observations. Other accurate observations, recently made with the CCD
meridian circles of Bordeaux and Valinhos (near Sao Paulo, Brazil)
observatories, were also included. The value obtained for the mass of
Ceres, (4.759 +/- 0.023) 10(-10) M., is in good agreement with most
recent results obtained by the other authors, and is a more precise
value of this mass. In particular, this result shows that the value of
the mass of Ceres recommended by IAU should be decreased by nearly 5%.
Copyright 1998, Institute for Scientific Information Inc.

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