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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