PLEASE NOTE:


*

CCNet DEBATES, 3 June 1998
--------------------------

PLAYING DOWN THE IMPACT RISKS: BOB KOBRES CRITICISES CLARK CHAPMAN'S
STATEMENT BEFORE THE US CONGRESSIONAL SUBCOMMITTEE

From Bob Kobres <bkobres@uga.edu>

There are some statements that Clark Chapman made to a US congressional
subcommittee recently (http://www.boulder.swri.edu/clark/hr.html), which
I view as somewhat misleading and presumptuous. 

The following paragraph is one good example to deconstruct.

“I wish to talk with you not about the probability of impacts millions
of years from now, but about the slight possibility that an asteroid or
comet might strike Earth in our lifetimes, perhaps destroying
civilization as we know it. It takes a truly huge object like Eros, or
like the comet in the movie "Deep Impact," to threaten mass extinctions
[sic] of species. Fortunately, Eros cannot strike Earth in the near
future. And impacts of such magnitude occur extremely rarely, once in
perhaps 100 million years. That's only one chance in a million of
happening during the 21st century: really unlikely! It is an
appropriate topic for science fiction, but nothing to worry about. Such
a body is so large, there's little we could do about an Extinction
Level Event, anyway ("Deep Impact" notwithstanding).”

Because we have very limited knowledge of what size or how many comets
will visit our region of the Solar System during the next century, no
one can say with any REAL authority that an object large enough to
produce an extinction level event is something too unlikely to be
concerned with.  Fifty years ago it could certainly be said that such a
possibility was not worth worrying about because we had no means of
preventing this type of situation--THIS IS WHAT HAS CHANGED.  However,
I expect that even if we started to hone our skills today it will
likely be another fifty years until we are proficient enough with PHO
moving technology to confidently deal with a large threatening comet. 
This required learning time is why we need to start developing capable
technology as soon as possible. 

The last utterance in the quoted paragraph above is a real doozy.  What
is being conveyed here? There may be a dangerous situation that we
can’t mitigate but it is much more apt to arise from too little time,
not too much mass. This is one of the reasons I loathe the
wait-and-see approach to our current situation. Large things that
orbit the Sun do occasionally join our planet violently--this is
established.  The only meaningful question that additional astronomical
fact gathering can answer is: When, in the absence of human
intervention, will the next accretion event occur?  Frequency of
occurrence has been recorded and--given time and resources--can be dug
up at our leisure. Guesses about how often this or that size object
smacks us are meaningless and, I think, irresponsible when our future
success or failure in limiting the geological impact record to past
history could be decided by whether we elect to commit resources to
developing effective PHO moving equipment now, a year from now, or ten
years hence. What does waiting buy us? Lower taxes? For MANY OTHER
REASONS Space development is our best hope for survival!  With the PHO
threat as incentive, the process of learning to thrive in Space can be
accelerated. 

Chapman again: "Such civilization-threatening impacts happen hundreds
of times more often than Extinction Level Events, perhaps once every
few hundred thousand years...or one chance in a few hundred thousand
that one will impact next year...or one chance in a few thousand during
the next century -- during the lives of our grandchildren. Those
chances are so small that they are difficult to comprehend."  …

Chapman obviously gives little credence to the views of Clube and
Napier, who have produced evidence of a recent influx of debris from
the breakup of a large comet, and so ignores the possibility that
current risks may not be as slight as a long term statistical average
would suggest. As far as I’m concerned we have not yet adduced just
what is required for an extinction level event. I argue that it is
quite likely that the abrupt Mega-fauna Extinction, around 11,500 years
ago, was the result of coming a bit too close to a large disintegrating
comet. See: (http://abob.libs.uga.edu/bobk/comfever.html).  This comet
was very probably the progenitor of Comet Encke and other less
flamboyant fragments that Clube and Napier have associated by the
similar orbits of these objects.  With the dependency much of our
species has on remotely obtained foods and the mono-crop farming that
caters to this demand, I doubt that it would take much of a pop to
bring us to the effective end of our line. Finding what it would
really require to threaten civilization or bring us to the brink of
extinction is not an experiment we should allow! The recently reported
evidence of a comet shower terminating the Eocene ~36M years ago should
also give us pause with regard to probabilities that are calculated
with the assumption of a relatively constant population of PHOs at all
times.  See:
(http://www.planetary.org/articlearchive/headlines/1998/headln-052198.html).

What I criticize most is Chapman's tendency to downplay the fact that:
NO MATTER WHAT ACTUAL RISK WE ARE TAKING, THE GREATEST CHANCE FOR AN
ENVIRONMENTALLY DESTRUCTIVE IMPACT EVENT IS FROM NOW UNTIL WE CONSTRUCT
A PROVEN TO BE EFFECTIVE DEFENSE SYSTEM.  Why the reluctance to say:
Yes, we need to take this threat seriously and we should commit enough
resources to allow the development and deployment of a working defense
system as soon as safely possible! 

When I started to promote this Earth Defense idea there was afoot the
meant-to-be-ominous-sounding phrase: "a window of vulnerability."  This
opening ostensibly justified the expenditure of huge amounts of
resources to close--$60 million for toilet seats alone! ;^)  I suppose
some committee was convinced by arguments that there was a chance that
the Soviets might possibly gain the upper hand in the game of nuclear
brinksmanship. I wonder if that chance was ever quantified?  See:
(http://eee.uci.edu/97y/50070/doc/socpeace/holdren.htm).

Presently we are living beneath a sky of vulnerability, as Life has
been for millions of years. FOR THE FIRST TIME THE POSSIBILITY EXISTS
TO PREVENT AN EVIL STAR (DIS ASTER) FROM OVERTURNING THE EXISTING
ORDER. We shouldn't get too exited though--it might be awfully
expensive to ACTUALLY do this. Not to worry--according to Clark
Chapman:

"Astronomical programs are comparatively cheap. The really large
expenses involve implementing mitigation hardware -- rockets and bombs.
Fortunately that won't be necessary until a threatening, mile-wide
object is found to be headed toward Earth... and then, surely, there
will be no debate [particularly if there is but a few days warning 8^(]
about using nuclear weapons in space -- just once -- to save
civilization from catastrophe. The chances, however, are truly
excellent that Spaceguard will find no threatening asteroid headed our
way, and we can all feel a little more secure about our lives on what
Carl Sagan called this "pale blue dot" -- planet Earth."

What about the Hubble project Clark?  Even the next generation Space
telescope of this ilk is projected to cost about $500-million and
Hubble was quadruple that price--over 2-billion dollars.  I would think
that it might be prudent to have some Space based instruments devoted
to more quickly mapping our local situation and detecting long period
comets earlier, but heck--we might get out of this cheap! Clark thinks
it's a good bet--just keep your fingers crossed a bit longer and
everything will PROBABLY work out. With enough luck we can avoid
investing any of our hard to come by resources into this expensive
Space-based PHO tracking and moving technology. Shoot, if we really
find something headed our way we can just strap some nukes on a few
rockets and let um rip--no problem.  See:
(http://lubbockonline.com/news/021197/hubble.htm) and
(http://ngst.gsfc.nasa.gov/FAQ/FAQAnswers.html#anchor4579961).

Well I’ve probably railed enough but I’ve grown quite weary and wary of
the political influence that academic authority has conveyed on this
subject during the last two decades. The varied opinions and often
dated ‘facts’ that have been put forth (frequently in too definitive of
a tone) have produced a great deal of confusion about this issue. 
There is ultimately much for the academic community to contribute in
better understanding the past influence of impact events however our
future actions should certainly err on the side of caution and be
decided by a broader association as a very serious global defense
determination. If you would like to read an illustrative example of
how on top of things, accurate and hopeful a typical academic
astronomer was on this topic and our future a decade ago see:
(http://abob.libs.uga.edu/bobk/rbarti.html).

Somewhat miffed.
bobk

PS: I don't really know what the Pentagon spent on toilet seats at
$640.00 each but the notion that we can deal with this situation for
practically nothing reinforces the perception that this is a low
priority issue. I think James Oberg had a more realistic assessment of
adequate funding over a decade ago.  See:
(http://abob.libs.uga.edu/bobk/rma.html) and
(http://www.clw.org/pub/clw/ef/msbook.html).

Also, why do we persist in using phrases such as "nuclear weapons in
space?"  The term "nuclear devices" is more appropriate as it can
convey that the gadgets are to be used as PHO moving tools and they all
might not go BOOM. The advantage of nuclear material is its energy
density. In some instances a near surface explosion should suffice to
redirect a small PHO but if we had to deal with a Deep Impact type
monster we would possibly fare better by landing several suitably
designed nuclear reactors at the most advantageous pole of the PHO and
let them cook. With sufficient advanced warning and knowledge of how
such contraptions would actually behave, an extended duration
comet-fart along the comet's axis of rotation could conceivably be
engineered to provide enough additional velocity to the object, in the
available time, to move its Earth-approach by at least half of our
planet's diameter. The need is to get out there and see what will work
the best while there is time to experiment. Talk of rocketing nuclear
bombs or weapons into Space is frightening to most people and will not
help build popular support for developing dependable PHO deflection
technology. The idea of a last minute gaffer-tape and antacid scenario
sure scares me! PHO handling needs to be conceptualized as an integral
part of future Space development, not as a heroic battle with a deadly
enemy. These poor PHOs just need a little guidance from us--that's
all.  See: (
http://abob.libs.uga.edu/bobk/nucreaim.html) and
(http://abob.libs.uga.edu/bobk/petition.html). 

Now what was the explosive yield of that Tunguska thing and where would
it have hit four hours …no --maybe that was two hours … or was it three
minutes later?  I'm cornfused here.  ;^)

According to Clube and Napier it was Leonid Kulik who first mentioned
that a four-hour later impact would have scorched St. Petersburg.  See:
http://abob.libs.uga.edu/bobk/rma.html 

I think that to some degree this is a wording problem. I used to
express this as, “if Earth had been advanced in its rotation by
71 degrees the object would have come down on top of Leningrad,”
(trying to imply that the Earth was at the same point of its orbit) but
this is not very clear either. Finally I decided that there were so
many variations on this ‘what if’ that it hardly mattered how it was
stated as the main point was that this event could have smashed a major
population center as easily as it flattened a forest. I like Duncan’s
egg-timer example though.  The problem, I think again, would be
explaining why. Also it would be trickier to specify the conditions
for the object to bulls-eye a large city. Many people do not have a
very clear idea how things move about in Space anyway. Often in trying
to clarify the St. Petersburg example, after much hand waving and
finally telling the person to just try to imagine that the Earth
started rotating four and three quarter hours earlier than it actually
did (getting more abstract), I would get hit with a question like: Do
many of these things orbit the Earth? 

Talk can be tricky.
bobk


Bob Kobres
bkobres@uga.edu
http://abob.libs.uga.edu/bobk
706-542-0583
Main Library
University of Georgia
Athens, GA  30602



*

CCNet DIGEST 3 June 1998
------------------------

(1) RE-ASSESSING THE GREAT ASTEROID SCARE OF 1998
    21st Century (The World of Research at Columbia University)
    http://www.21stC.org/

(2) IF THE SKY FALLS, WILL ANYBODY HEAR IT?
    Phil Burns <pib@nwu.edu>

(3) NASA WANTS TO PLAY THE ROLE OF BIG BROTHER
    San Jose Business Journal
    http://www.amcity.com:80/sanjose/stories/060198/editorial1.html

(4) TUNGUSKA YIELD
    Duncan Steel <dis@a011.aone.net.au>

(5) COSMIC DUST TO GET CLOSE EXAMINANTION
    Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

(6) WORLD PREMIERE OF 'ARMAGEDDON' AT KENNEDY SPACE CENTER
    Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>

(7) METEOR ECHOS & ELECTRON DENSITIES FROM GROUNDSCATTER
    D. Andre et al., UNIVERSITY OF SASKATCHEWAN

(8) DETECTION OF METEORIC CONTRAIL AND METEORIC DUST
    M.C. Kelley et al., CORNELL UNIVERSITY

(9) OBSERVING THE GEMINIDS AND QUADRANTIDS
    P. Brown et al., UNIVERSITY OF WESTERN ONTARIO


==================
(1) RE-ASSESSING THE GREAT ASTEROID SCARE OF 1998
 
From: 21st Century (The World of Research at Columbia University)
      http://www.21stC.org/
 
RUN FOR YOUR LIVES! (UH, NEVER MIND.)
 
By Tony Reichhardt
 
It wasn't the first time someone shouted "Asteroid!" and then quickly
had to take it back. In 1989 a badly translated American wire service
story prompted Chinese news telecasts to sound a false alarm about an
imminent impact. Three years later Comet Swift-Tuttle was predicted to
come perilously close to Earth in 2126, until a recalculation showed no
threat after all.
 
Now, in 1998, here was Brian Marsden of the Harvard-affiliated Central
Bureau for Astronomical Telegrams in Cambridge, Mass., astronomy's
record keeper and unofficial town crier warning of a possible smashup
in our lifetime. As it turns out, the mile-wide rock known as 1997 XF11
will miss us by a comfortable 600,000 miles in 2028. We only know that
because Eleanor Helin's asteroid search team at NASA's Jet Propulsion
Laboratory (JPL) went to the team's archive and discovered an
8-year-old image of the object within 24 hours of Marsden's March 11
alert. Using the new data, Marsden and others made a more precise
determination of its orbit. No apocalypse. Sorry, everyone.
 
The first thing asteroid researchers want to know is that they're not a
bunch of bumblers, David Helfand,a Columbia astronomer, agrees. "Nobody
did anything wrong," he says, at least not in a scientific sense. Nor
did the press get the story garbled. True, says Helfand, three out of
seven TV crews that visited his office asked whether this was really a
Hollywood plot to hype two coming asteroid disaster movies. But by and
large, says Benny Peiser, an anthropologist at Liverpool John Moores
University in England, who runs an electronic forum for scientific
discussion of the asteroid threat, the press behaved in a "very
rational and very considered way."
 
So why are scientists who study asteroids for a living so upset? And
why, weeks later, were many of them still sending out acrimonious
e-mail blaming each other for the Great Asteroid Scare of 1998?
 
Reason No. 1: What was normally a private, unhurried scientific process
suddenly became very frantic and public. Marsden's official IAU
Circular 6837 gave his estimate of how close the asteroid would come to
Earth and encouraged other astronomers to make additional observations
to help reduce the uncertainty.. All standard procedure.. But the
circular was followed by a press release that reached a much wider
audience of reporters, virtually ensuring that the story would make
worldwide headlines the next day. Most asteroid researchers, even those
who say Marsden is unfairly blamed for crying wolf, say the press
release, which specifically mentioned the remote possibility of an
Earth collision (the circular hadn't - you would have had to do the
calculation yourself), was a mistake. Marsden, a likeably droll Briton,
admits that the press release part of his strategy "needs rethinking."
 
Leif Robinson, editor-in-chief of the popular astronomy magazine SKY &
TELESCOPE, has known Marsden for nearly 40 years, but chides him and
the rest of the asteroid research community for an "incredible naivete"
when it comes to public relations. Each and every day researchers hunt
for objects that could put an end to the world as we know it. But, says
Robinson, "Nobody thought about what to do if [the search] succeeded."
 
Reason No. 2: Rivalries within the asteroid community made matters
worse. Only a handful of people worldwide do the kinds of calculations
necessary to determine asteroid positions 30 years hence. Before Helin
dug through her old photos in response to Marsden's request, all but
one team headed by Don Yeomans at JPL agreed that the chances of 1997
XF11 hitting the Earth were small, but not zero. When Helin produced
her images, Yeomans cranked out his own press release saying the chance
of a collision was now officially zero. Many reporters were left with
the idea that JPL researchers had somehow corrected Marsden's faulty
calculations even though the Harvard-affiliated group posted its own
revised estimate within 90 minutes of Yeomans'. Marsden is still
bitter, and many in the asteroid community agree that Yeomans' action
gave an erroneous impression of disagreement when none existed.
 
Less then a week later, NASA, which funds the two largest asteroid
searches under way, asked the squabbling scientists to play nicely
together and next time to confer among themselves before sounding an
alarm. But not everyone is convinced that an official party line is a
good idea when it comes to asteroid warnings. For one thing, says
Marsden, it's an international concern, not just NASA's. Peiser agrees:
Even if a false alarm is messy and embarrassing, "the more it happens
in the public, the better."
 
Besides, the public didn't seem all that terrified anyway, and many
editorialists played the episode for laughs. THE NEW YORK POST ran its
usual screaming headline, "KISS YOUR ASTEROID GOODBYE," and asked nine
Ordinary Citizens: "If the asteroid were to hit Earth tomorrow, what
would you do today?" Two-thirds said they would get drunk.
 
If it happens, they may not have the time. David Morrison of NASA's
Ames Research Center, who headed a 1992 NASA study of the asteroid
threat, points out that because 90 percent of dangerous asteroids are
still undiscovered (due in part to stingy government funding for
ground-based searches), the most likely warning we'll get it none. "The
first we would know of the danger," he speculates, "is when we saw the
flash of light and felt the ground shake."
 
Tony Reichhardt

TONY REICHHARDT writes about the space program for NATURE and AIR &
SPACE/Smithonian
 
Copyright 1998, 21st Century, Columbia University

====================
(2) IF THE SKY FALLS, WILL ANYBODY HEAR IT?

From Phil Burns <pib@nwu.edu>

John Bowman of the San Jose Business Journal takes a dim view of
NASA's suggestions for a waiting period about possible impactors at:

     http://www.amcity.com:80/sanjose/stories/060198/editorial1.html

Tim Madigan of the Star Telegram in "The sky is falling!" discusses
the impact thread and includes comments from Eleanor Helin, Jack Hills,
Clark Chapman, and Brian Marsden:

     http://www.star-telegram.com:80/news/doc/1047/1:ENTNEWS21/1:ENTNEWS21060198.html

A Los Angeles Times story talks about the growing trend of publicly
auctioning "natural history" items such as dinosaur fossils and meteorites:

     http://www.latimes.com:80/CNS_DAYS/980601/t000051057.html

-- Phil "Pib" Burns
   Northwestern University, Evanston, IL.  USA
   pib@nwu.edu
   http://pibweb.it.nwu.edu/~pib/

================
(3) NASA WANTS TO PLAY THE ROLE OF BIG BROTHER

From San Jose Business Journal
     http://www.amcity.com:80/sanjose/stories/060198/editorial1.html

June 1, 1998
 
EDITORIAL
 
IF THE SKY DOES FALL, WILL ANYBODY HEAR IT?
NASA wants to shield us from asteroids, comets ... ourselves
 
John Bowman Business Journal Editor
 
The National Aeronautics and Space Administration has decided it wants
to play the role of Big Brother in the event an asteroid or comet threatens
to slam into Earth, ending life as we know it.
 
Not that NASA wants to protect us from such a doomsday rock; its
scientists don't have the right stuff to do that just yet.
 
No, it's the news that the end might be near that the space agency wants
to save us from--at least until the government has had time to decide
whether we should ever hear about it at all. The idea, NASA claims, is
not to hide the truth--just to avoid an unnecessary panic.
 
At NASA's request, professional astronomers whose work is funded by
the space agency have agreed to keep discoveries of potentially
cataclysmic comets and asteroids under wraps for 48 hours while they
double-check the numbers to see if the end really is near.
 
NASA then plans to hold the information for an additional 24 hours
before going public. The space agency would like to extend these rules to
all professional astronomers.
 
This is a lousy idea. Fortunately, it won't work.
 
Like other NASA PR schemes over the years, this one likely would
backfire if ever put to the test: Three days of comet rumors not only
would create a panic, but also destroy any credibility the government
might need to "manage the situation."
 
Haven't NASA bureaucrats ever heard of the Internet? Maybe they also
haven't noticed the army of several hundred thousand amateur
astronomers, many armed with huge telescopes, who've been discovering
most of the new comets for the past decade or so?
 
These stargazing hobbyists can get information out over the World Wide
Web faster than Hollywood can say "Armageddon."
 
And, speaking of Hollywood, let's not allow this summer's two doomsday
movies to convince us that the idea of a major asteroid collision is science
fiction.
 
It's more like a scientific certainty that there's a giant rock out there with
Earth's name on it. The only variable is time.
 
Want proof? Check out the surface of the moon with a good pair of
binoculars. See all those craters inside craters inside craters?
 
Were it not for the cosmetic effects of wind, water and continental drift,
the surface of our own planet would be just as pockmarked from
bombardment by space rocks.
 
Every day, about 100 tons of space debris slams into our atmosphere;
when it happens at night, we call these impacts "shooting stars." Next time
you see one, make a wish: Don't ever let a big one hit us.
 
On average, one big enough to destroy most of life on Earth hits us every
100 million years or so. The last of these "global extinctors" wiped out the
dinosaurs about 65 million years ago.
 
Smaller impacts are a lot more common. In 1908, an asteroid about the
size of Adobe's downtown San Jose headquarters flattened hundreds of
square miles in remote Siberia. The same explosion anywhere near the
Bay Area today would kill hundreds of thousands of people.
 
And we're going to trust NASA to decide when to let us in on these little
secrets? If the agency had its way, we still wouldn't know the Eagle
almost crash-landed on the moon.
 
NASA was terribly annoyed in March when it found out through the
media that astronomers had discovered an asteroid that might threaten
Earth in 2028. It turned out to be a false alarm, and now the agency
points to that affair to justify its new plan. Balderdash.
 
Today's media-wary Americans are more likely to ignore a real threat
from space than they are to panic over a bogus one.
 
Apparently, the same is true for the government itself.
Because of a lack of funding, there are fewer professional astronomers
searching the heavens for possible doomsday rocks right now than there
are teenagers working at your neighborhood McDonald's.
 
Maybe you shouldn't make any big plans for the weekend.
 
© 1998, The Business Journal

================
(4) TUNGUSKA YIELD

From Duncan Steel <dis@a011.aone.net.au>

Thanks for the note, Mark. That is useful and interesting to me.

A follow-on point: if your (say) 3.5 Mton value is correct, does this imply
that Tunguska-type events are more frequent than we have assumed until now?
e.g., IF Tunguskas occurred once per 300 yr, based on a calculated
energy-to-size conversion for the bolide and then the estimated population
of objects larger than that on Earth-crossing orbits, then would your lower
energy yield lead to a calculated frequency of (say) one such event per 50
or 75 years?

If so, then perhaps you could send Benny Peiser a further message pointing
out this implication.  Knowing that 'Tunguskas' occur on average once or
more per lifetime, rather than once per five lifetimes, would be a very
important conclusion with substantial ramifications for policy.

Best,

Duncan

======================  
(5) COSMIC DUST TO GET CLOSE EXAMINANTION

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

Tiniest of space bodies to get close examination

June 2, 1998

A NASA/Marshall Space Flight Center news release

As astrophysicists turn their telescopes to probe the origins of stars
and planets, they will start giving more attention to the smallest of
astronomical bodies - dust particles - which both make them and also
obscure the view.

"We're developing an experimental method to measure scattering and
extinction cross sections for dust particles in the solar system," said
Dr. James Spann of NASA's Marshall Space Flight Center. Spann is
leading development of the Dusty Plasmas Laboratory. In it, a single
grain of dust is suspended by static electricity while it is bombarded
with electrons and light and its reactions measured.

Dust might seem like a lowly object to receive such attention, but it's
an important factor in the vacuum between planets and stars. Dust
particles drift through space where they absorb and scatter light.

How rapidly they extinguish light over the millions or billions of
miles of "empty" space determines how visible the source will be.

"We think we can devise an experiment that replicates the environment
of these particles in planetary or preplanetary atmospheres," Spann
said.

The observations planned by Spann and another Marshall scientist, Dr.
Mian Abbas, will balance between two well known areas of optics,
Rayleigh scattering and geometrical optics. Rayleigh scattering, where
an object is much smaller than a wavelength of light, is why the sky is
blue. Geometrical optics, where an object is much larger than a
wavelength of light, is why lenses bend light.

Between these two is the Mie theory covering light scattered by objects
that are about the same size as a wavelength of light.

"It's a very beautiful theory," Spann said. "It's incredibly
fascinating for a lot of reasons."

One of those reasons is how infrared light is scattered by dust grains
which are much larger than visible light, but about the size of
longer-wavelength infrared.

Little work has been done in this area - it's mostly extrapolated from
visible light observations or from the bulk properties of dust. The
work won't be easy.

"Part of the challenge in this experiment is that these grains are
irregularly shaped," Spann explained. "Unless you're dealing with
liquid droplets, which are spherical, the  orientation of the grain is
important." Thus, a grain may be larger than a wavelength of light
across its length, but much smaller across its width.

Interplanetary dust particles range from 5 to 100 microns in length; 30
microns is typical. They can be spherically or irregularly shaped, and
made of silicate or carbonaceous materials. In total, it's a complex
range of particles that Spann and Abbas will try to measure in detail.

With the Dusty Plasmas Laboratory, Spann and Abbas will be able to make
unique measurements of how dust particles polarize light - convert its
vibrations so they are all in one plane - and the angles at which the
light is reflected.

"We can make significant contributions to planetary missions," Spann
said.

"All planetary atmospheres have dust, aerosols and grains hanging in
the atmosphere." Even Mars with its tenuous atmosphere has months-long
dust storms that obscure the surface.

Results from the Dusty Plasmas Laboratory will also help in
understanding what is seen in the thick dust clouds in deep space where
planets are slowly condensing. Infrared telescopes can see little of
what is happening because the view is obscured by the very dust that
eventually will become planets, comets, asteroids, or just the dust
that, as in our solar system, reflects sunlight back to give the sky a
slight glow along the plane of the planets.

Knowledge of the distribution of interplanetary and circumsolar dust
particles and their physical and optical characteristics provides
valuable information about many issues dealing with the origin and
formation of the solar system. Interplanetary dust particles (IDPĚs)
are considered to have their origin in cometary, asteroidal, and
meteoritic sources, along with possible contributions from planets and
the pre-solar molecular cloud.

Dust particles in the interplanetary medium are produced by a variety
of sources and have a diverse size range. Particles ranging from 5 to
100 microns contribute to most to the zodiacal light, with a typical
particle size of 30 microns. The major constituents of the spherical or
irregularly shaped circumsolar and IDPĚs are believed to be silicates
and carbonaceous materials, as indicated by analyses of stratospheric
dust particles of interplanetary origin.

An experimental technique being developed in the laboratory at Marshall
Spaced Flight Center for measurements of scattering and extinction
cross sections of some commonly known interplanetary and circumsolar
dust particles will be presented. This technique is based on
irradiating a single charged dust particle suspended by electrodynamic
balance in a cavity and measuring the scattered radiation as a function
of angle. Comparison with Mie theory calculations leads to simultaneous
determination of the particle radius, the complex refractive index, and
the scattering and extinction cross sections.

An application of this technique will also be discussed for
investigation of rotational bursting phenomena whereby large size
cosmic and interplanetary particles are believed to fragment into
smaller dust particles.

===========================
(6) WORLD PREMIERE OF 'ARMAGEDDON' AT KENNEDY SPACE CENTER

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

Countdown begins for star-filled June 29 'Armageddon' world premiere at
Kennedy Space Center

Touchstone Pictures, Burbank News Release June 2, 1998

BURBANK, Calif. - Marking the imminent arrival of its spectacular new
motion picture "Armageddon," Touchstone Pictures has invited 500 VIP
guests to the Kennedy Space Center in Florida on Monday, June 29, for a
world-premiere screening, a private party and a power-packed
performance by legendary rock band Aerosmith (who have four songs on
the film's soundtrack), it was announced Monday by Richard Cook,
chairman of The Walt Disney Motion Pictures Group.

Joining the select group of celebrities and media will be "Armageddon"
stars Bruce Willis, Billy Bob Thornton, Ben Affleck, Liv Tyler and
Steve Buscemi, as well as producer Jerry Bruckheimer and director
Michael Bay.

Commenting on the announcement, Cook said: "Jerry Bruckheimer and
Michael Bay have created an extraordinarily entertaining film with
'Armageddon,' and we wanted to give it a 'send-off' that would capture
the excitement and spectacle. The Kennedy Space Center is the perfect
site.

"With its unique blend of adventure, humor and emotion, we believe that
'Armageddon' holds a special place among the summer releases and is
sure to be a major crowd pleaser with a wide range of moviegoers."

The screening will take place in a special state-of-the-art theater,
which is being constructed just for the evening outside the
Apollo/Saturn V Center. Before and after the film, guests will have a
chance to see many of the sites actually used in the film and explore a
wide range of exciting NASA artifacts and displays.

The evening will conclude with an exclusive appearance by Aerosmith,
during which the band will perform "I Don't Want to Miss a Thing,"
their new smash-hit single from the soundtrack of "Armageddon," for the
very first time. The film is scheduled to hit theaters everywhere on
July 1.

In preparation for the event, Disney's technical wizards are building a
state-of-the-art theater in a tent just outside the Apollo/ Saturn V
area at the Kennedy Space Center. As part of this, a 20-by-44-foot
screen, 35mm projection equipment and a fully operational Dolby Digital
sound system are also being installed just for the occasion.

After the screening, guests will be seated under an enormous 363-foot
Saturn V rocket for dinner, following which they will go outside to
enjoy Aerosmith's special guest performance.

"Armageddon" follows the fiery trail of an asteroid the size of Texas
that is heading directly toward Earth at 22,000 miles per hour. NASA's
executive director, Dan Truman (Thornton), has only one option -- to
send up a crew to destroy the asteroid. He enlists the help of Harry S.
Stamper (Willis) -- the world's foremost deep-core oil driller -- to
drill into its surface and drop a nuclear device into the core.

On this heroic journey, they face the most physically and emotionally
challenging conditions ever encountered ... to save the world and
prevent ARMAGEDDON.

==========================
(7) METEOR ECHOS & ELECTRON DENSITIES FROM GROUNDSCATTER

D. Andre*), G.J. Sofko, K. Baker, J. MacDougall: SuperDARN
interferometry: Meteor echoes and electron densities from
groundscatter. JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, 1998,
Vol.103, No.A4, pp.7003-7015

*) UNIVERSITY OF SASKATCHEWAN, INSTITUE OF SPACE & ATMOSPHERIC STUDIES,
116 SCI PL, SASKATOON, SK S7N 0W0, CANADA

The SuperDARN radars are now able to measure the angles of arrival of
the backscattered radiation. We describe the analysis procedure and
present results for meteor scatter from slant ranges below 500 km and
ground scatter from either the E region or the F region at greater
slant ranges which can be used to determine peak electron densities and
their heights. The angle of arrival measurements can also be used to
identify 'unwanted' backscatter from the backward lobes of the antenna
radiation pattern. Electron densities can also be measured in the back
lobes. Copyright 1998, Institute for Scientific Information Inc.

===============================
(8) DETECTION OF METEORIC CONTRAIL AND METEORIC DUST

M.C. Kelley*), C. Alcala, J.Y.N. Cho: Detection of a meteor contrail
and meteoric dust in the Earth's upper mesosphere. JOURNAL OF
ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS, 1998, Vol.60, No.3,
pp.359-369

*) CORNELL UNIVERSITY, SCHOOL OF ELECTRICAL ENGENEERING, PHILLIPS HALL,
   ITHACA, NY, 14853

In 1983 a series of small rockets were launched from the Poker Flat
Rocket Range near Fairbanks, Alaska to study what has come to be called
Polar Mesospheric Summer Echoes (PMSE). We report here on a fortuitous
simultaneous 50-MHz radar and rocker detection of what seems to be a
meteor contrail produced over the Poker Flat Rocket Range. The two data
sets are mutually consistent and taken together suggest some very
interesting properties for the trails of large meteors. Most notable is
the first evidence that the ablated material can coagulate into
particles the order of 50 nm in radius. This estimate is based
primarily on the fall speed deduced from both the Doppler shift of the
VHG radar signal and the time rate of change of the target as it fell
through the beam. In addition the very existence of the radar target,
the extremely sharp edges of the trail, and the existence of electron
density structures inside the trail more than an order of magnitude
smaller than the Kolmogorov microscale, all require large charged
aerosols and a very high Schmidt number. Curiously the environment
leading to PMSE (the study of which was our primary mission), is very
similar to the properties of a large meteor trail some minutes after it
is formed. In the Ph ISE case ice particles grow and become charged by
the plasma and, a hen more than half the charge is tied up on the ice,
the plasma diffusion coefficient becomes so small that structure can be
supported at VHF scattering scales. In the late-time meteor case large
aerosols coagulate and tie up both natural charge in the plasma and the
original meteor trail electrons. Following the work of Rosinski and
Snow (1961) and Hunten et al. (1980) we conclude that the incident
meteor was the order of 100 g and would have had a visual magnitude of
about -5. This dust production process may resolve some open questions
concerning long-lived meteor radar echoes. For example, in the event
studied the electron density was well into the underdense condition and
yet was detected for over 6 min. Classical meteor scatter theory has no
explanation for such a long duration underdense event. (C) 1998
Elsevier Science Ltd. All rights reserved.

==========================
(9) OBSERVING THE GEMINIDS AND QUADRANTIDS

P. Brown*), W.K. Hocking, J. Jones, J. Rendtel: Observations of the
Geminids and Quadrantids using a stratosphere-troposphere radar.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 1998, Vol.295, No.4,
pp.847-859

*) UNIVERSITY OF WESTERN ONTARIO, DEPARTMENT OF PHYSICS & ASTRONOMY,
   LONDON, ON N6A 3K7,CANADA

Radar observations of the 1996 Geminid and 1997 Quadrantid showers are
reported using the CLOVAR stratosphere-troposphere (ST) radar. A method
for determining the limiting sensitivity of a radar system using
observed number-amplitude data from a single shower is presented, and
the result compared with more conventional measurements. This technique
is capable of providing very precise measurement of the mass index for
a shower in cases where large numbers of echoes are available. The mass
index profiles for both showers are presented and found to be U-shaped
with a minimum near the time of peak flux. Peak flux values are found
to be 0.19 +/- 0..02 meteoroid km(-2) h(-1) at 261.degrees 82 +/-
0.degrees 2 for the Geminids and 0.14 +/- 0.01 meteoroid km(-2) h(-1)
at 283.degrees 08 +/- 0.degrees 08 for the Quadrantids to a limiting
radio magnitude of 7.7. The locations of maximum are found to coincide
with the visually determined position. No significant difference in the
location of maximum is detected for either stream over a range of 2
radio magnitudes or in comparison with the visual results. The Geminid
radar flux curve is found to be very broad near maximum with a plateau
in activity lasting nearly 2 d, while the-visual curve shows a FWHM of
24 +/- 4 h and modest asymmetry with a slow build-up to maximum. The
Quadrantids are found to have a sharp maximum following a Gaussian
profile to first order with a full width to the 1/e flux positions of
12 h. Copyright 1998, Institute for Scientific Information Inc.

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