CCNet DIGEST, 22 June 1998
(1) ED GRONDINE'S WASHINGTON REPORT: THE CONGRESSIONAL LUNCHEON
BRIEFING ON THE IMPACT HAZARD AND NASA'S PLANS
E.P. Grondine" <firstname.lastname@example.org>
(2) SPACEGUARD TRADEMARK?
Sir Arthur C Clarke
(3) JAPANESE OBJECTIONS TO THE USE OF NUCLEAR DEVICES IN PLANETARY
Syuzo Isobe <email@example.com>
(4) COSMIC DUST AND ATMOSPHERIC METALS
W.J. McNeil et al., USAF, RES LAB,
(1) ED GRONDINE'S WASHINGTON REPORT
From E.P. Grondine" <firstname.lastname@example.org>
THE CONGRESSIONAL LUNCHEON BRIEFING ON THE IMPACT HAZARD
AND NASA'S PLANS
Monday I made a leisurely mid-morning drive up to Washington for
the Congressional Luncheon Briefing on the impact hazard and NASA's
response to it. All in all it went much better than the House Space
Subcommittee briefing, so here goes -
HOW TO DO IT RIGHT
The luncheon, which was sponsored by the American Astronautical
Society, was held in a banquet room in the Rayburn House Office
Building. The speakers were Dr. Carl Pilcher, Don Yeomans, and Dr. Lucy
McFadden from the University of Maryland speaking on NEAR, and the lunch
menu featured turkey, ham, and cheese club sandwiches, roast beef on
rolls, accompanied by an assortment of hors d'oeuvres, condiments,
drinks, and desserts.
The AAS did things exactly right, as the free food attracted about
130 attendees, including about 80 voluntarily impoverished summer
interns from the Congressional offices. These young people usually go on
to become the leaders of U.S. industry and government, and they seemed
to enjoy both the presentation as well as the free sandwiches. Most
importantly, these young people will be working this summer in the
Congressional offices as the NASA appropriations bill wends its way
through the legislature.
Also in attendance, alongside the senior staff members of the House
and Senate Space Committees, were about 20 journalists, who with
practiced skill acquired through long experience arrived early and
managed to discretely get to the buffet and return to their seats
before most of the other attendees arrived.
NASA'S LOW ESTIMATE OF THE IMPACT HAZARD
Dr. Carl Pilcher spoke first, and started with an introduction to
asteroids and comets. He gave an estimate of 2,000 near Earth asteroids
(only for those 1 kilometer and greater in size, which is all that NASA
is worried about right now), with about 1/3rd as many comets. (Since
this comes to 666, I suggest that in the future he may wish to say
nearly 700, lest he attract the more superstitious members of the
public.) Dr. Pilcher claimed that NASA had catalogued about 1/10th of
the 1 kilometer NEAs and told the audience that he would leave it to Don
Yeomans to describe NASA's effort to find at least 80% of the rest of
Next, Dr. Pilcher claimed that asteroids were identical to
meteorites. (This may also raise some eyebrows on the list, but for a
brief introduction it seems sufficiently accurate). He went through the
types of meteorites, and showed the audience both a small meteorite as
well as a 10 kilogram Namibian iron with fine aerodynamic pocks on the
table in front of the podium.
Dr. Pilcher then set out the three reasons why it was important to
study asteroids. His first reason was that they provide a window into
the formation of the solar system. Sensing boredom, Dr. Pilcher quickly
moved on to the second part of his presentation, the impact hazard,
starting with a chart showing NASA's estimate of the hazard.
While Dr. Pilcher bracketed his estimate for Tunguska class events
at 1 per 100 to 1,000 years, he set out 1 per 300 years as NASA's best
estimate for their rate of impact. With 1 out of 10 of these being over
a densely inhabited area, he placed the rate for catastrophic Tunguska
class impacts at 1 per 3,000 years. (This stands in marked contrast to
the current consensus among many NEO researchers, who place the estimate
for Tunguska class events at 1 per 100 years, with maybe 1 per 200 years
as an upper limit.)
This was not the only type of impact event for which Dr. Pilcher
gave low estimates. He estimated the rate of occurrence for 1-2
kilometer diameter impactor hits as as being between 1 per 100,000 to
1,000,000 years, with 1 per 1,000,000 years as being most likely,
telling the audience that there was a 1 in 1,000 chance of a hit by an
impactor of this size in the next century (100 years). He identified
this as the type of impactor of greatest concern, as its effects would
be global, and it would raise enough dust to cause global cooling.
The rate for Extinction Level Events he estimated at about 1 per
100 million years, while these are well known to be semi-periodic at a
rate of about 1 per 26 million years.
With such a low estimate for the impact hazard, it should come as
no surprise that Dr. Pilcher's third point was that asteroids might
play a useful role in man's development of the solar system, as they
provide an easily reachable source for metals, organic compounds, and
most importantly water for life support and the production of
NO ABORT MODES
(While emphasizing the benefits of manned travel to an asteroid, Dr.
Pilcher ignored the hazards, and I'm pretty sure that if he has any
ideas about abort modes for such a mission, i.e. how astronauts would be
able to get back to safety if anything went wrong, the Office of Space
Flight would sure like to know about them.)
SOURCE OF NEAs
Dr. Pilcher told the audience that asteroids get placed in near
Earth orbits due to collision with each other in the asteroid belt and
then being captured by the gravity of Jupiter. (Once again this seems
sufficient for an introduction.)
He closed his presentation with slides of Mathilde, Gaspra, Ida and
ESTIMATES FOR NEOs
Throughout his lecture Dr. Pilcher had given estimates for NEOs and
the NEO threat by type, with 70% coming from asteroids, 20% from Short
Period Comets, and 10% from Long Period Comets. Each time he said that
Don Yeomans would go into this in more detail in his presentation, but
Yeomans never did.
THE ART OF THE LECTURE: JPL'S DON YEOMANS
While Dr. Pilcher's presentation had been interesting, Don Yeomans
demonstrated his mastery of lecture by enthralling the audience with a
superb presentation embellished with an excellent set of color slides
Yeomans opened his presentation with a slide of the Peekskill car,
and giving brief mention to the science and resource justifications,
immediately moved on to the crux of the matter, the impact hazard. He
contrasted the Peekskill car (slide change) with Meteorite Crater and
told the audience that it was caused by a 60 meter slab of stainless
steel. To emphasize the point he showed the Canyon Diablo iron (which
Dr. Pilcher had returned to him), which he then passed out to the
audience, calling their attention to the cut, etched, and lacquered
Widmanstatten pattern in it. (This looked to me like Ron Baalke's work.)
To emphasis the size of meteorites he also had the large 10 kilogram
Namibian iron which had been placed on the table in the front of the
Yeomans quickly passed once again through the types of NEOs, and
then started to describe NASA's NEO discovery programs and its efforts
to determine composition of asteroids and comets. He showed a chart
with Spacewatch, NEATS, LINEAR, the Lowell NEO search, University of
Arizona's Catalina, University of Texas McDonell Observatory's orbital
confirmation effort, and briefly outlined each, mentioning but
minimizing the Air Force's role in the discovery effort, as well as the
non-NASA origin of these efforts.
Yeomans then went on to describe NASA's probes, emphasizing the
benefits of spectral studies in determining the composition of asteroids
and comets. Yeomans continued this part of his presentation by noting
that in 1970 he had started trying to get a comet or asteroid mission
set up, and that after 25 years of 0 missions, NASA now had 7 missions
planned for the next 10 years. He briefly described some missions, but
went into some detail on Muses B mission, the joint mission with Japan
to land a small rover on an asteroid, describing its rover and
operations in some detail. (It is clear that JPL expects to get the same
data from Muses B as from Clementine II, and for some reason is ignoring
that Clementine II would provide the Air Force with experience in
Yeomans moved on to Stardust and passed out 2 samples of aerogel in
plastic cases to the audience for their examination, and then described
other cometary missions briefly with colored slides illustrating each.
Yeomans then turned the podium over to Dr. Lucy McFadden.
DR. LUCY MCFADDEN
After such a masterful and exciting presentation, Dr. Lucy
McFadden faced the unenviable task of trying to get the audience excited
about NEAR. The highlights of McFadden's talk were a television clip
showing the Mathilde flyby, and the third group shot of the Earth and
the Moon together. (The two other group shots of the Earth and Moon came
from Apollo and Clementine.)
Dr. McFadden expressed surprise at cohesion to impact asteroid
Mathilde shows in light of its low estimated over-all density, and
ascribed this to Mathilde having a different internal structure, as
well as its loose rubble carrying away part of the force of impact.
While this would be of great interest at any scientific conference, it
was probably lost on the summer interns, as were her following
descriptions of NEAR's instrument suite, its cooperative management
structure, maneuvers (which featured the Earth-Moon group shot), and
Dr. McFadden did manage to regain the audience's attention with the
Mathilde fly-by video, and once again with a clip showing NEAR's Earth
flyby and the Earth rotating.
HOW DO YOU GET PEOPLE ON THEM TO STOP THEM?
Following Dr. McFadden's presentation questions were taken from
the audience. The first question was about using the method shown in
Deep Impact to stop a potential Earth impactor, which was met with a
groan from the audience. Instead of embarrassing the questioner by
pointing out that the technique shown in Deep Impact is nonsense,
Don Yeomans diplomatically went into some detail about how easy it would
be to land men on a NEA. (See the comment above about the lack of abort
modes for such a mission.)
ARE YOU PROPOSING AN R&D PROGRAM TO DEVELOP THE TECHNOLOGY FOR ALTERING
THE ORBIT OF AN EARTH APPROACHING ASTEROID?
Clearly stating that he was speaking for himself, Yeomans replied
that no, he certainly was not. He thought that what we needed to do was
to find the entire population of Earth approaching objects and monitor
them. Once an Earth impactor was found, that would be the right time to
begin a mitigation campaign.
(Yeomans thus limits the time available for those who would be
responsible for this mitigation effort.)
Returning to this topic in his response to the next question, Dr.
Pilcher stated that conventional wisdom was that it would not be too
hard to divert an Earth approaching asteroid, but that if they were
loose piles of rock they might just shatter into smaller pieces and it
might be worse than before.
Yeomans concurred and went on that for an iron you would probably
use a stand off nuclear charge to divert it, but for a ruble pile you
might might want to blow it up into pieces that would be small enough so
they would burn up in the Earth's atmosphere, though the problem had not
been studied to any great extent. (I'm sure that the researchers at Los
Alamos will be absolutely astounded to hear this.)
Continuing, Yeomans stated that in either case you would want to do
it very early, and locate any such object decades in advance. Yeomans
stated that you would not want to do this at the last minute and could
not do this at the last minute.
THE RUSSIAN PLANETARY DEFENSE PLAN -
Given Yeomans lack of knowledge about the work being done at Los
Alamos on planetary defense, this seems an appropriate place to remind
CC readers of the theoretical work done by Russian scientists at the
Snezhinsk nuclear research center, and of the international meeting
which was held there in 1992. Among the many western scientists
attending was Dr. Teller, who noted that while the Russian scientists
understood the difference between a nuclear weapon and a nuclear device,
in America not everyone understood the distinction. Tom Gehrels, also
in attendance, viewed the dangers from nuclear charges and Dr. Teller's
proposal to explode a charge next to asteroid as being a greater danger
than that posed by impactors.
Detailed studies on planetary defense had been made by that date
by the Makayev Production and Design Bureau as well as by the NII 4 (now
the Russian Artillery Rocket Academy, which has charge of flight
dynamics and explosive mechanics. Several schemes had been studied in
detail, the shortest one assuming a 30 to 90 day warning. Makayev
proposed adapting their Briz or Bar rocket for the interception stage,
and Snezhinsk proposed converting a 100 megaton nuclear warhead into the
My guess is that at present if they had a couple of days warning
the Russians would simply load Snezhinsk's 100 megaton nuclear charge
onto whatever launcher happened to be on the pad for commercial work and
then let it rip.
It is also interesting to note that Dr. Teller had access to data
from US reconnaissance satellites, while Dr. Gehrels did not. This may
have affected their estimates of the rate of impact and thus led in some
part to the argument between too much and too little, with no one
advocating just enough.)
HOW FAST WILL YOU FIND 100% OF THEM?
Yeomans stated that the goal is to find 90% of them in a decade.
The next question was along the same lines, and Yeomans described the
currently planned and funded searches, and concluded that there was no
way that that goal would not be met.
WHAT ABOUT THE FUNDING LEVEL?
According to Dr. Pilcher, NASA does not know if the correct
funding level is $3.4 or $3.5 million dollars, but they feel they
are in the right ball park.
ARE WE DOING THIS ALONE? WASN'T THE AUSTRALIAN EFFORT TERMINATED?
Yeomans confirmed the end of Duncan Steel's program, but then
went on to mention the Japanese effort, Maury's French effort, and said
there were others, but admitted that the US was doing the lion's share
of the work.
IS THERE AN OBJECT OUT THERE THAT COULD CAUSE AN EXTINCTION LEVEL EVENT
WHICH WOULD NOT BE SEEN UNTIL IT WAS A YEAR AWAY?
Yeomans claimed that the vast majority of objects which could
intercept the Earth were asteroids, which we would almost certainly
detect a few decades before predicted impact. The same was true for
short period comets, which have orbital periods of 5 to 6 years. The
only wild card was long period comets, which would not be detected until
they began gassing inside the orbit of Jupiter. These comprised 10% of
the threat, and were the only objects for which we would not have
several years warning. (Once again: NASA limits itself to 1 kilometer
diameter objects and excludes anything 100 meters or so across.)
WHAT ABOUT THE WARNING GUIDELINES?
Dr. Pilcher said that NASA is trying to work internationally to
figure out the right thing to do. Right after 1997 XF11, NASA had a
meeting to develop interim guidelines on warning. Since then the
National Academy of Sciences has sponsored another meeting, and this is
just the beginning of the dialogue that will be conducted both
nationally and internationally to try and figure out warning guidelines.
WHAT WILL HAPPEN TO NEAR?
Right now there is a debate between 2 options: go to another
asteroid or land on (crash into) Eros. Dr. McFadden said that the
leading option right now was to land on Eros to try and gather
WHAT ABOUT THE SMALLER NEOs?
Yeomans stated that objects which are about 50 meters in size or
less do not get through the Earth's atmosphere. Objects that are less
than 1 kilometer in size will only cause local disasters, but 2/3 of the
Earth is ocean, and the other 1/3 is sparsely populated.
Yeomans thought that the major worry is the 1 kilometer and larger
size objects were the main threat, and that the strategy within the
scientific community was to worry about the big ones first, and then go
on to the smaller ones.
Dr. Pilcher added that in the course of the currently planned
survey NASA expected to detect a lot of the objects between 1 kilometer
and 100 meters.
(As I am not an astronomer, I can't evaluate in detail whether Dr.
Pilcher's estimate is correct or maybe just a little too optimistic.
What is clear is that NASA as a whole simply downplays the hazard from
Tunguska class stony impactors smaller than 100 meters, which they
estimate hit only once every 300 years or so. Whether NASA's inability
to detect objects this size has influenced their estimate, or whether
their low impact estimate has led to their not planning to locate them,
probably ranks with the chicken and egg as a which came first question.)
AFTER THE BRIEFING
After the briefing Dr. Pilcher was approached by the House Space
Subcommittee's Majority Staff Council, who asked him if he was sure NASA
had enough money to do the job. Dr. Pilcher told him that he thought
that they did, and the Staffer told him that more money was available if
they needed it, as the constituents were demanding a defense. He
offered to bet Dr. Pilcher a steak dinner that NASA would need more
money, and Dr. Pilcher accepted the wager.
THE CONSTITUENTS ARE DEMANDING IT
The Majority Staffer was correct, the voters are demanding it.
Several weeks ago I suggested to Alan Boyle at the MSNBC internet news
that they conduct a poll on the matter, and they did. Of 8480
responses, 27% wanted action now and 29% added it to their list of
worries, for 56% favoring some action. 27% thought that the threat was
being exaggerated, while 17% held other or no opinion.
These numbers were taken after Deep Impact opened, and it will be
interesting to see what effect Armageddon has on them.
MY INTERVIEW WITH DR. PILCHER
After the Majority Staffer left, I asked Dr. Pilcher what role the
MPC would play in the new NASA effort. He told me that that decision
would be up to the new Program Manager. Asked when the decision about
the new Program Office would be made, he responded that it should be
about 2 to 3 weeks. (He told me this on 15 June, and note that
Armageddon will premier at Kennedy Space Flight Center on 29 June.)
When I asked if the Lunar and Planetary Institute was in the running,
Dr. Pilcher got a pained look on his face which told me better than
words could that the lobbying by the different NASA field centers and
research groups for this role had been intense. He offered that he
could tell me that the new program office would be at an existing NASA
MY INTERVIEW WITH DON YEOMANS
I asked Don Yeomans if he saw the MPC functioning as the
international clearing house for orbital observations, and he said yes.
He also went on to mention that the MPC is short of funds.
By now the NASA party was leaving, and Dr. Yeomans excused himself
and left with them.
THE PERFECT CANDIDATE FOR HEAD OF THE NEW NASA PROGRAM OFFICE
In conclusion, I certainly sympathize with Dr. Pilcher and the
difficult task he has facing him. If one could combine Don Yeomans'
presentation and political skills with Clark Chapman's understanding of
the hazard, he would have half of the candidate he needs to do the job.
One problem that both of these researchers have is that both have
little understanding or appreciation of the Air Force's efforts to deal
with this problem, and little sympathy for the Los Alamos researchers
either, for that matter.
In the past week I have learned that the late Gene Shoemaker was
completely familiar with these programs. My curiosity was piqued
several months ago when Harrison Schmitt told me that Dr. Shoemaker had
been trying to recover air detonation data from weather barometers. I
immediately remembered that an acoustic array which was constructed many
years ago to detect nuclear testing had been picking up air detonations,
and suspected that Dr. Shoemaker had been trying to duplicate this data
from public sources.
My suspicions have now been confirmed by an acquaintance of Dr.
Shoemaker, who discussed this with him over a couple of six packs of
Mexican beer. Dr. Shoemaker had complete access to all data that the
Air Force had gained, not only from the acoustic array but from its
reconnaissance satellites as well, and he had worked with them on the
Unfortunately for Dr. Pilcher and for NASA, Dr. Shoemaker is no
longer available for the job. While it is known that "he was fed up
with the NASA bullshit", I think it likely that Dr. Goldin and Dr.
Huntress would have enjoyed giving him the shovel with which to clear it
In conclusion, my guess is that Dr. Pilcher will have to assemble a
team of at least four to five people in order to fill the place of the
Well, Benny, that's it for now.
Until the next time ...
(3) SPACEGUARD TRADEMARK?
From Sir Arthur C Clarke
"By the way, is Spaceguard any kind of a NASA trademark?" (Alain Maury)
No! It's mine, if anyone's - I invented it in RENDEZVOUS WITH RAMA
(1973) and was delighted when NASA adopted it. Morgan Freeman (US Prez
in DI) has just optioned it.
(3) JAPANESE OBJECTIONS TO THE USE OF NUCLEAR DEVICES IN PLANETARY
From Syuzo Isobe <email@example.com>
National Astronomical Obersavtory Japan
I read the Statement on the Threat of Impact by Near-Earth Asteroids by
Dr. Clark R. Chapman and found three important items which I want to
1. He wants to create a new US organization replacing the MPC.
2. He intends to solve the NEO problem mainly by efforts of the US
although the word 'international' is seen at some places.
3. He says 'There will be no debate about using nuclear weapons'.
Since items 1. and 2. have been discussed on the CCNet, I don't wish to
repeat them here but just underline that I am against his ideas.
Instead I would like to voice my opinion, (and that of the Japan
Spaceguard Association and, I believe, that of a large fraction of the
Japanese people) about item 3.
First of all, I would like to stress that all the nations on the earth
should abandon nuclear weapons. I believe it is much more dangerous to
reserve nuclear weapons than the NEO collision hazard. Since 5
countries, including the US, have nuclear weapons, India and Pakistan
may have an argument when testing explosions of nuclear weapons.
With regard to the NEO problem, the first thing which we should do
under international collaboration is to detect all the hazardous
objects within a certain time (20 years or maybe more). If we find a
possible NEO collision say more than 50 years in future, we can solve
the problem without nuclear devices. Of course there is a certain
probability that we may face a hazardous collision with a NEO within a
decade; yet that probability is still lower than the risk of
experiencing nuclear war should nuclear bombs not be abandoned. If a
collision would happen several hundred years from now, we would loose
large amounts of money (maybe the total annual budget of Japan) every
year only to keep nuclear weapons ready to attack NEOs.
We strongly request the US to abandon keeping nuclear weapons. At
least, Dr. Chapman should realize that there is a very serious debate
about using nuclear weapons in any given situation.
(4) COSMIC DUST AND ATMOSPHERIC METALS
W.J. McNeil*), S.T. Lai, E. Murad: Differential ablation of cosmic dust
and implications for the relative abundances of atmospheric metals.
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 1998, Vol.103, No.D9,
*) USAF,RES LAB,VSBS,29 RANDOLPH RD,HANSCOM AFB,MA,01731
Although it is generally accepted that extraterrestrial material is the
source of metals in the upper atmosphere, the relative abundances of
mesospheric metal atoms and ions present us with a conundrum. Lidar
observations have consistently shown that the abundances of neutral
metals in the atmosphere and the abundances of these metals in the
meteoric material that falls to Earth are significantly
disproportionate. The column density of neutral sodium is perhaps 2
orders of magnitude larger than that of calcium, while the abundances
in meteorites are approximately equal. By contrast, ion mass
spectroscopy has shown that the abundances of the meteoric ions match
reasonably well those in the meteorites. We present here a model that
attempts to address these discrepancies. At the heart of the model is
the concept of differential ablation, which suggests that more volatile
metals sublimate earlier in the descent of a cosmic dust particle than
do the less volatile components. We model three different meteoric
metals: sodium, magnesium, and calcium. Results suggest that sodium
ablates to a greater extent than does calcium and that it ablates at a
substantially higher altitude. Deposition at lower altitudes leads to
more rapid conversion of the atomic calcium into complexes through
three-body reactions. Thus the depletion of calcium arises from both a
decrease in deposition and an increase in the rate of removal of that
which is deposited. We examine the behavior of the model in several
respects, comparing predicted results with measurements and finding
reasonable agreement. We argue that the success of this model indicates
that differential ablation is a key factor in the determination of the
relative abundances of meteoric metals in the mesosphere. Copyright
1998, Institute for Scientific Information Inc.
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