PLEASE NOTE:
*
CCNet 71/2003 - 10 September 2003
--------------------------------
"Today, we know an asteroid killed 90% of all living things
- dinosaurs
and all kinds of other things. And that it was that asteroid that
actually stimulated our own evolution. I have never been in favor
of
people dying out and a new world taking over. I would rather have
evolution based on dreamed possibilities. So I advocate the
building
of telescopes, the prediction of collisions, and the deflection
of
objects, such as asteroids."
--Edward Teller
(1) EDWARD TELLER (1908-2003) - FATHER OF PLANETARY DEFENCE
(2) EDWARD TELLER: THE NEED FOR EXPERIMENTS ON COMETS AND
ASTEROIDS
(3) EDWARD TELLER (1908 - 2003)
(4) AN INTERVIEW WITH EDWARD TELLER:
(5) RE: "MUM'S THE WORD AS THE WORLD'S MEDIA FAIL TO RETRACT
HYPED ASTEROID ALARM"
(6) THE FRUIT SALAD SCALE
(7) AND FINALLY: BRITISH HUMOUR AT ITS BEST....
===========
(1) EDWARD TELLER (1908-2003). FATHER OF PLANETARY NEO DEFENCE
Benny Peiser <b.j.peiser@livjm.ac.uk>
Edward Teller, one the 20th century's most important and most
controversial
scientist died yesterday, aged 95. He was the unsung hero of the
free world
who was instrumental in the West's defeat of both Nazi Germany
and Sowjet
dictatorship.
Most people outside our small community do not know, however,
that he was also
the spiritus rector of our planetary defence initiatives aimed at
preventing
asteroid impacts to occur in the future. He was the main driving
force behind
these activities in the US and a strong supporter of the
Spaceguard project. He
was particularly successful in convincing the British Government
to set up
a Task Force on Near Earth Objects.
With Teller, the NEO community has lost our most influencial
voice and
scientific advisor to the White House.
In memory of his invaluable and unique contribution to the ideals
of
universal freedom, international security and scientific
progress,
I have attached a couple of papers and interviews. I would
wellcome
any additional notes of remembrance by colleagues who have met
and
worked with him over the years.
Benny Peiser
=============
(2) EDWARD TELLER: THE NEED FOR EXPERIMENTS ON COMETS AND
ASTEROIDS
Dr. Edward Teller
Lawrence Livermore National Laboratory
paper given at the Planetary Defense Workshop
http://www.llnl.gov/planetary/
Lawrence Livermore National Laboratory
Livermore, California
May 22-26, 1995
http://www.llnl.gov/planetary/pdfs/Summary/01-Teller.pdf
First of all, I would like to thank Academician Khariton for his
kind
words to all of us and tome especially. We are really sorry that
he is
not with us. I am glad to see all the people who are here from
China,
Japan, Italy, and very particularly from Russia.
Now, I would like to say a few things in a straightforward and
very
serious manner. I believe we are here - in fact, we all know we
are
here - to look into a situation that is unique in the size of the
trouble we are looking at and in the improbability of these big
troubles.
For mathematicians, it is easy to multiply the two and to say
that this
trouble is like other troubles because the product is the same.
For
politicians who are trained to look carefully at what happens
during
their terms of office and less carefully at everything beyond,
the same
does not hold as for the mathematicians. And we, in turn, depend
on the
politicians to make it possible for us-in the form of dollars, or
rubles, or anything else-to do what is needed to be done.
I think it is extremely important that we present a credible case
so
we can go ahead. I would like to suggest a few points of view on
how
to present the case that we are talking about-presenting it very
truthfully but emphasizing the things that ought to be
emphasized.
Here is the situation that, in my mind, is a scandal, and I think
people
can understand that it is a scandal: There is a probability of a
few
percent in the next century of the arrival of a stony
asteroid-not the
biggest possible but a fairly big one, approximately a hundred
meters
in diameter. It delivers on impact maybe 100 megatons. It is a
practical
certainty that, when and if such an object should bump into us,
it will
come completely unannounced [remember, that paper was given in
1995, BP].
We won't have any indication of it. Yet such an object is apt,
with a
fairly high probability, to do a lot of damage-for instance,
cause a
tsunami if it falls into the ocean. Damage would be concentrated
on the
shores region, where people like to aggregate. So the effect of
the
asteroid and the pmple are attracted to the same meeting
point-hence,
a lot of damage. Just in dollars it could be billions, and in
lives it
might reach millions. Yet, no warning whatsoever.
What we need to rectify this situation is half a dozen arrays of
charge
- coupled devices and appropriate (not very big) telescopes,
amounting to
probably not much more than ten million dollars altogether. If
such a
catastrophe should occur, afterwards we'll be able to point out
on
existing pictures where the asteroid has approached, but we
wouldn't know
it ahead of time because nobody would have looked at those
pictures.
I shouldn't have said nobody; I should have said hardly anybody.
And
actually, to find them would be extremely difficult. The CCDS can
be
systematically trained to scream when there is something
suspicious,
and in this way we could have information a week ahead of time.
To my
mind, such action would correct a very large incompleteness in
our
safety system. And I think that should be a very salable item.
So, we know ahead of time that something is coming. What do we do
about
it? We would know ahead of time with sufficient accuracy, for
instance,
what shorelines have to be evacuated. A week is not plenty of
time, but
it is very considerably more than nothing.
I was interviewed today and the question was asked: Is the
international
situation ripe for such action? I'm answering with every
confidence:
It is. I have no doubt that if there is such a danger from
outside, if
we know that people in certain spots will have to move to save
their
lives and can't move to save their property, then it will be
psychologically not only a necessary thing but an easy thing to
get
help from all over the world to whoever has to evacuate. I hope
that
the same thing holds for all the other measures that we might be
willing and able to take in order to improve the situation,
bwause
I certainly don't want to stop at the point of just saying
"evacuate."
The next point that I feel is a real necessity is to know what
more to
do. We have the power to reach out into space and to deliver what
is
needed. But we don't know how the objwts behave that will arrive.
Very particulwly, we will know rather little about the actual
object
that has been a mere spot on the best photographic plate and that
has
grown for the last couple of days a little more to not very much
more
than a bigger spot.
What do we do about it? I claim that the next thing we ought to
do is
to gather knowledge about what can be done. What is the variety
of things
that can be done? Such knowledge can be obtained in a number of
different
ways. The one I prefer (and that all of us will not necessarily
prefer)
is to make expenments - one or two or three per year - on objects
that#
are getting close to the Earth, to the approximate distance of
the Moon,
more or less one light-second away from the Earth. Whatever we do
can
be observed from the Earth very easily. And to get out there is
not
very difficult.
And what do we do there? Well, we can do a number of things. I
would
recommend that, to begin with, we do the very simplest thing on
which
we can agree: Put up sharp tungsten knives for the purpose of
cutting up
the incoming object if it's of an appropriate size-something like
300 feet or 100 meters in diameter. Of such objects,
approximately a
few approach in a year. We make experiments on them. Can every
one of
them be sliced up sufficiently so that if the fragments fall on
the
Earth, they will be burned up in the high atmosphere in a
completely
harmless manner? This certainly can be found out by experiments
on
objects that have already passed the Earth. I think such
experiments
will contribute, to a considerable extent, to safety in the
one-percent-per-century case that such a danger might actually
occur.
Now, if we find that the biggest or toughest of these objects
will not
be completely sliced up, then, after we have become familiar with
the
slicing up, we should take the big step-using a nuclear
explosive.
If, for instance (which I think is a plausible situation), on a
300-meter-diameter object, we have succeeded in slicing up 20
meters
of the surface, we can then put a nuclear explosive close to the
surface,
which will irradiate the rubble that we have atready created.
This tends
to homogenize this rubble and push it one way, while, by
reaction, the
remaining ninety percent of the material is pushed the other way.
The reaction on the main body will be very powerful, and there
can
be no doubt that appropriate deflections can be arranged.
Objects a kilometer or more in diameter are apt to create
worldwide
disaster. On the average, they are expected once in a million
years.
We hope to discover them several months in advance. The use of
nuclear
explosives as outlined might or might not suffice to deflect
them. A more
radical method of using several nuclear explosives may be needed.
We
might use them to create the rubble, and this maybe followed by
one
big blast as mentioned above.
Or we might attempt to bore a hundred-meter-deep hole by
successive
nuclear explosives and then blow up the object by one big, deeply
located explosion. Such methods cannot be relied upon without
experimentation on objects that have safely passed the Earth.
One final possibility should be considered. Of the hundred-meter
diameter objects, there are approximately a million. They could
be
discovered, cataloged, and their orbits computed. If a huge,
hundred-kilometer object approaches and is apt to hit the Earth
within
a year, then one of the hundred-meter objects is almost certain
to approach it to within approximately one Light-second before
this
can happen. Careful deflection of this smaller object could steer
it
into the path of the bigger one. The expected result would be to
prevent
a collision with the Earth, which would be the ultimate
catastrophe.
One must add that collision of a hundred-kilometer object with
Earth
is not apt to be predicted even in a billion years.
I would like to conclude with emphasizing one obvious principle:
We
scientists are not responsible and should not be responsible for
making decisions. But we scientists are uniquely and absolutely
responsible for giving information. We must provide the
decision-makers
with the data. On the basis of this, they will have the best
chance
to make the right decisions. That is the main reason why I say
that
we must pursue and must be given the means to pursue the
knowledge as
to when and how objects will arrive and the knowledge as to
possible
ways to deal with them. The choice of how to deal with them can
be
and should be delayed. If need be, it can be done and probably
will
be done in the last moment. But knowledge - the firm knowledge,
not
merely guesses on how asteroids will react but knowledge based on
experiments - should become available. That is our
responsibility.
And I believe we should argue, in a carefully considered manner,
so that we can acquire, in the most efficient manner, as much of
the relevant knowledge as is possible.
I can add only two words: Good luck!
=================
(3) EDWARD TELLER (1908 - 2003)
http://www-hoover.stanford.edu/bios/teller.html
Edward Teller, a senior research fellow at the Hoover Institution
since 1975, where he specialized in international and national
policies concerning defense and energy, died Tuesday, September
9, 2003. He was 95.
Teller was most widely known for his significant contributions to
the first demonstration of thermonuclear energy; in addition he
added to the knowledge of quantum theory, molecular physics, and
astrophysics. He served as a member of the General Advisory
Committee of the U.S. Atomic Energy Commission from 1956 to 1958
and was chairman of the first Nuclear Reaction Safeguard
Committee.
He had been concerned with civil defense since the early 1950s.
He was a member of the Scientific Advisory Board of the U.S. Air
Force, a member of the Advisory Board of the Federal Emergency
Management Agency, and on the White House Science Council.
Teller received numerous honors, among them the Presidential
Medal of Freedom, the Albert Einstein Award, the Enrico Fermi
Award, the Harvey Prize from the Technion-Israel Institute, and
the National Medal of Science.
He was a fellow of the American Physical Society and the American
Nuclear Society and was a member of the National Academy of
Sciences and the American Academy of Science.
His books include Memoirs: A Twentieth-Century Journey in Science
and Politics (written with Judith Shoolery, 2001), Conversations
on the Dark Secrets of Physics (Plenum Press, 1991), Better a
Shield Than a Sword (Free Press, 1987), Pursuit of Simplicity
(Pepperdine Press, 1980), and Energy from Heaven and Earth (W. H.
Freeman, 1979).
He was director of the Lawrence Livermore Laboratory from 1958 to
1960, at which time he accepted a joint appointment as a
professor of physics at the University of California and as
associate director of the laboratory. He held these posts until
his retirement in 1975. He continued as a consultant at the
Lawrence Livermore National Laboratory.
From 1954 to 1958, he served as Associate Director at the new
Lawrence Livermore Laboratory. He became a consultant to the
laboratory in 1952.
In 1946, he became a professor of physics at the University of
Chicago but returned to Los Alamos Scientific Laboratory in 1949.
In 1942, having served as a consultant to the Briggs committee,
Teller joined the Manhattan Project. His efforts during the war
years included work on the first nuclear reactor, theoretical
calculations of the far-reaching effects of a fission explosion,
and research on a potential fusion reaction.
In 1935, Teller and his wife came to the United States, where he
held, until 1941, a professorship at George Washington
University. The Tellers became U.S. citizens in 1941.
In 1934, under the auspices of the Jewish Rescue Committee,
Teller served as a lecturer at the University of London. He spent
two years as a research associate at the University of
Goettingen, followed by a year as a Rockefeller fellow with Niels
Bohr in Copenhagen.
Born in Budapest, Hungary, in 1908, he received his university
training in Germany and completed his Ph.D. in physics under
Werner Heisenberg in 1930 at the University of Leipzig.
===========
(4) AN INTERVIEW WITH EDWARD TELLER:
http://www.achievement.org/autodoc/page/tel0int-1
When did you first realize that you were interested in your
subject?
When I was maybe five years old, maybe not yet five years old, it
is one of my earliest memories. I was supposed to go to sleep and
didn't, and I invented a game. I was trying to find out how many
seconds in an hour, or in a day, or in a year. And that, of
course, obviously, I did it in my head. Quite naturally, I got
different answers in my head every time I did it. And that made
the game more interesting. I don't know how unique it is; I don't
know how many other children did that, but I played with numbers.
I was taught German and Hungarian at the same time. The earliest
words I remember are a mixture of the two. My mother spoke German
much better than Hungarian. My father's German was quite poor.
His legal books, of course, were Hungarian. The literary books in
our house were German.
I am sure I must have been awfully confused about what all these
people talked about, using different sounds for the same objects.
I did not catch on! The one thing with which I felt familiar,
were numbers. There, at least, was something that hung together.
My father had an older friend who was a retired mathematics
professor. His name was Leopold Klug, and he is probably the man
who had the greatest influence on my life. He was a retired
mathematics professor, and he got me a book. Algebra by Leonhard
Euler. I was ten years old. The problems that came up were too
difficult for me to solve, but not too difficult to understand.
Klug gave me that book and I read it. It was my favorite book.
Klug was the first grown-up whom I met who loved what he
was doing.
Who did not get tired. He even enjoyed explaining things to me.
That, I think, is when I made up my mind very firmly that I
wanted to do something that I really did want to do.
Not for anyone else's sake, not for what it might lead to, but
because of my inherent interest in the subject. I knew one other
exception in the whole world to the rule that grown-ups were
unhappy.
My mother played the piano beautifully. She really wanted to be a
concert pianist and she really wanted me to become a concert
pianist, as a kid. Practicing (piano) was much too hard.
Multiplying numbers was not.
My interest in mathematics was soon discouraged. It so happened
that we had a very good math teacher, who was a Communist. I
remember having learned from him something that I never forget:
the rule of nines. A simple point: you add up the numerals in a
number, and if the original number was divisible by nine, then
the sum of the figures also is. For instance, you take a number
like 243. Two and four and three is nine. Therefore, 243 must be
divisible by nine. Actually it is nine times 27. The rule is
interesting because its so simple. What was really interesting is
to us ten year-olds is that our math teacher proved it. The proof
is not terribly difficult, but it was one of the first simple and
not quite obvious mathematical proofs that I encountered. That
actually was a little before I read Euler's Algebra.
Then the Communists took over for a few months in Hungary, and
our math teacher talked about some very strange things which I
can't say I liked. After communism ended he was replaced as a
teacher by a Fascist. The new teacher was less interested in
mathematics, but interested in how to write equations so that the
writing should be easily legible. I think my writing improved
slightly, but my school mathematics vanished. I blame him only in
part, because a real interest should not have been stopped that
easily. I got interested in reading fantastic stories like Jules
Verne, and I got interested even more in reading about
technology.
After a few years, I also got interested in the lectures on
physics. I had started to read Einstein's relativity, and did not
quite understand what it was all about. I went to the teacher and
he asked me to bring him the book. I brought it to him and I
didn't see the book again for a year. When I passed the final
examination, the teacher gave the book back, and said, "All
right, now you can read it." This time I read it and I did
understand it.
In our teaching system, we consider mathematics and science as
exact. It is so, it is proven, it is indisputable. All of it is
true. But this misses the point. The interesting thing in the
"exact" sciences is what is not yet known, what is in
doubt. That element of doubt, of contradiction, which actually
occurs as science changes from century to century, should be
reproduced in every student's mind. I think, as a matter of fact,
it is being reproduced in every good student's mind.
FULL INTERVIEW at http://www.achievement.org/autodoc/page/tel0int-1
=========== LETTERS ==========
(5) RE: "MUM'S THE WORD AS THE WORLD'S MEDIA FAIL TO RETRACT
HYPED ASTEROID ALARM"
Paul Sutherland <paul.sutherland@the-sun.co.uk>
You wrote:
> Not a single of Britain's national papers or media outlets
> (with the sole exception of 7 lines in today's Daily
Telegraph) has...
Actually this is not correct, Benny. The Sun also reported the
same day (Sept 4)
that the asteroid would miss as soon as the Press Association
report was received.
(It arrived too late for the first edition which may be the one
you monitored).
[it was indeed the morning editions of the British papers I
checked, BP].
My own comment piece, printed the previous day alongside the
original news
story, had said that this was likely to be the case.
ATB
Paul
------------
DON'T PANIC SAYS SUN SPACEMAN
The Sun, 3 September 2003
By Paul Sutherland
WE have been here before. Other space rocks have been discovered
on a collision
course with Earth - only for the all-clear to sound when closer
monitoring
showed they would whizz by. The chances are that asteroid 2003 QQ
47 will
do the same. So are astronomers guilty of scaremongering?
Absolutely not.
Countless asteroids travel the spaceways. Enough cross our orbit
for there
to be a significant threat. We need a network of telescopes to
discover them
earlier. Big impacts are rare. But somewhere out there is an
asteroid with
the Earth's name on it. It is not a matter of if - but when.
MODERATOR'S NOTE: For readers not aquainted with the British
media, The Sun newspaper
in Britain's biggest selling paper with 12 million people reading
it everyday.
It most certainly doesn't need any asteroid scares to increase
its circulation!
Famous for it's page three topless models (who at times can be
seen to assess
the risk of heavenly bodies), it's by far Britain's most popular
newspaper.
It says something about its quality that its science
correspondent and long-time
CCNet subscriber got the QQ47 (non-)story spot on, right from the
start! BP
=============
(6) THE FRUIT SALAD SCALE
Konrad Ebisch <kebisch@lgc.com>
Dear Benny Peiser,
It has always seemed to me that the Torino scale is based on two
estimates. (1) How
likely is that rock to hit us? (2) How much damage will it do if
it hits us? Mixing
two very different things into just one number can be a confusing
over-simplification.
Apples times Oranges = [fruit salad ?]
Konrad Ebisch
========
(7) AND FINALLY: BRITISH HUMOUR AT ITS BEST....
The Sun, 6 September 2003
"Whenever they tell us that an asteroid is on a collision
course with Earth,
you can be absolutely certain it will miss. Because when they do
eventually
find one that's coming to kill everyone, you can be assured you
won't be told."
--Jeremy ('Top Grear') Clarkson, The Sun, 6
September 2003
-----------
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*
Sent: 10 September 2003 16:51
NASA RELEASES NEAR-EARTH OBJECT SEARCH REPORT
"The Team recommends that the search system be constructed
to produce a catalog that is 90% complete for potentially
hazardous objects (PHOs) larger than 140 meters."
--NASA NEO SEARCH REPORT, September 2003
NASA NEO Program, 10 September 2003
http://neo.jpl.nasa.gov/neo/report.html
NASA has released a technical report on potential future search
efforts for near-Earth objects after a year of analysis by
scientists working on this issue. This Science Definition Team
was chartered to study what should be done to find near-Earth
objects less than 1 kilometer in size. While impacts by these
smaller objects would not be expected to cause global
devastation, impacts on land and the tsunamis resulting from
ocean impacts could still cause massive regional damage and still
pose a significant long-term hazard.
In 1998 NASA commenced its part of the "Spaceguard"
effort, with the goal of discovering and tracking over 90% of the
near-Earth objects larger than one kilometer by the end of 2008.
An Earth impact by one of these relatively large objects would be
expected to have global consequences and, over time scales of a
few million years, they present the greatest impact hazard to
Earth. Approximately 60% of the estimated 1,000 to 1,200 large
near-Earth objects have already been discovered, about 45% since
NASA efforts started, and each of the five NASA-supported search
facilities continue to improve their performance, so there has
been good progress toward eliminating the risk of any large,
undetected impactor.
To understand the next steps to discovering the population of
potentially hazardous asteroids and comets whose orbits can bring
them into the Earth's neighborhood, NASA turned to this Science
Definition Team of 12 scientists. The Team, chaired by Dr. Grant
Stokes of the MIT Lincoln Laboratory, was asked to study the
feasibility of extending the search effort to the far more
numerous, perhaps hundreds of thousands, of near-Earth objects
whose diameters are less than one kilometer.
NASA considers the Science Definition Team's findings to be
preliminary, and a much more in-depth program definition,
refining objectives and estimating costs, would need to be
conducted prior to any decision to continue Spaceguard projects
beyond the current effort to 2008.
The link below will allow a download of the complete Science
Definition Team report (pdf format) and the Executive Summary of
this report follows.
The Science Definition Team members include:
Dr. Grant H. Stokes (Chair) MIT Lincoln Laboratory
Dr. Donald K. Yeomans (Vice-Chair) Jet Propulsion
Laboratory/Caltech
Dr. William F. Bottke, Jr. Southwest Research
Institute
Dr. Steven R. Chesley Jet Propulsion
Laboratory/Caltech
Jenifer B. Evans MIT Lincoln Laboratory
Dr. Robert E. Gold Johns Hopkins University, Applied
Physics Laboratory
Dr. Alan W. Harris Space Science Institute
Dr. David Jewitt University of Hawaii
Col. T.S. Kelso USAF/AFSPC
Dr. Robert S. McMillan Spacewatch, University of Arizona
Dr. Timothy B. Spahr Smithsonian Astrophysical Observatory
Dr./Brig. Gen. S. Peter Worden USAF/SMC
Ex Officio Members
Dr. Thomas H. Morgan NASA Headquarters
Lt. Col. Lindley N. Johnson
(USAF, ret.) NASA Headquarters
Team Support
Don E. Avery NASA Langley Research Center
Sherry L. Pervan SAIC
Michael S. Copeland SAIC
Dr. Monica M. Doyle SAIC
------
Study to Determine the Feasibility of Extending the Search for
Near-Earth Objects to Smaller Limiting Diameters
Report of the Near-Earth Object Science Definition Team
August 22, 2003
Prepared at the Request of
National Aeronautics and Space Administration
Office of Space Science
Solar System Exploration Division
Full 166-page report available here as a PDF document:
http://neo.jpl.nasa.gov/neo/neoreport030825.pdf
------
EXECUTIVE SUMMARY
A Study to Determine the Feasibility of Extending the Search for
Near-Earth Objects to Smaller Limiting Diameters
In recent years, there has been an increasing appreciation for
the hazards posed by near-Earth objects (NEOs), those asteroids
and periodic comets (both active and inactive) whose motions can
bring them into the Earth's neighborhood. In August of 2002, NASA
chartered a Science Definition Team to study the feasibility of
extending the search for near-Earth objects to smaller limiting
diameters. The formation of the team was motivated by the good
progress being made toward achieving the so-called Spaceguard
goal of discovering 90% of all near-Earth objects (NEOs) with
diameters greater than 1 km by the end of 2008. This raised the
question of what, if anything, should be done with respect to the
much more numerous smaller, but still potentially dangerous,
objects. The team was tasked with providing recommendations to
NASA as well as the answers to the following 7 specific
questions:
What are the smallest objects for which the search should be
optimized?
Should comets be included in any way in the survey?
What is technically possible?
How would the expanded search be done?
What would it cost?
How long would the search take?
Is there a transition size above which one catalogs all the
objects, and below which the design is simply to provide warning?
Team Membership
The Science Definition Team membership was composed of experts in
the fields of asteroid and comet search, including the Principal
Investigators of two major asteroid search efforts, experts in
orbital dynamics, NEO population estimation, ground-based and
space-based astronomical optical systems and the manager of the
NASA NEO Program Office. In addition, the Department of Defense
(DoD) community provided members to explore potential synergy
with military technology or applications.
Analysis Process
The Team approached the task using a cost/benefit methodology
whereby the following analysis processes were completed:
Population estimation - An estimate of the population of
near-Earth objects (NEOs), including their sizes, albedos and
orbit distributions, was generated using the best methods in the
current literature. We estimate a population of about 1100
near-Earth objects larger than 1 km, leading to an impact
frequency of about one in half a million years. To the lower
limit of an object's atmospheric penetration (between 50 and 100
m diameter), we estimate about half a million NEOs, with an
impact frequency of about one in a thousand years.
Collision hazard - The damage and casualties resulting from a
collision with members of the hazardous population were
estimated, including direct damage from land impact, as well as
the amplification of damage caused by tsunami and global effects.
The capture cross-section of the Earth was then used to estimate
a collision rate and thus a yearly average hazard from NEO
collisions as a function of their diameter. We find that damage
from smaller land impacts below the threshold for global climatic
effects is peaked at sizes on the scale of the Tunguska air blast
event of 1908 (50-100 m diameter). For the local damage due to
ocean impacts (and the associated tsunami), the damage reaches a
maximum for impacts from objects at about 200 m in diameter;
smaller ones do not reach the surface at cosmic speed and energy.
Search technology - Broad ranges of technology and search systems
were evaluated to determine their effectiveness when used to
search large areas of the sky for hazardous objects. These
systems include ground-based and space-based optical and infrared
systems across the currently credible range of optics and
detector sizes. Telescope apertures of 1, 2, 4, and 8 meters were
considered for ground-based search systems along with space-based
telescopes of 0.5, 1, and 2 meter apertures. Various geographic
placements of ground-based systems were studied as were
space-based telescopes in low-Earth orbit (LEO) and in solar
obits at the Lagrange point beyond Earth and at a point that
trailed the planet Venus.
Search simulation - A detailed simulation was conducted for each
candidate search system, and for combinations of search systems
working together, to determine the effectiveness of the various
approaches in cataloging members of the hazardous object
population. The simulations were accomplished by using a NEO
survey simulator derived from a heritage within the DoD, which
takes into account a broad range of "real-world"
effects that affect the productivity of search systems, such as
weather, sky brightness, zodiacal background, etc. Search system
cost - The cost of building and operating the search systems
described herein was estimated by a cost team from SAIC. The cost
team employed existing and accepted NASA models to develop the
costs for space-based systems. They developed the ground-based
system cost estimates by analogy with existing systems.
Cost/benefit analysis - The cost of constructing and operating
potential survey systems was compared with the benefit of
reducing the risk of an unanticipated object collision by
generating a catalog of potentially hazardous objects (PHOs).
PHOs, a subset of the near-Earth objects, closely approach
Earth's orbit to within 0.05 AU (7.5 million kilometers). PHO
collisions capable of causing damage occur infrequently, but the
threat is large enough that, when averaged over time, the
anticipated yearly average of impact-produced damage is
significant. Thus, while developing a catalog of all the
potentially hazardous objects does not actually eliminate the
hazard of impact, it does provide a clear risk reduction benefit
by providing awareness of potential short- and long-term threats.
The nominal yearly average remaining, or residual, risk in 2008
associated with PHO impact is estimated by the Team to be
approximately 300 casualties worldwide, plus the attendant
property damage and destruction. About 17% of the risk is
attributed to regional damage from smaller land impacts, 53% to
water impacts and the ensuing tsunamis, and 30% to the risk of
global climatic disruption caused by large impacts, i.e. the risk
that is expected to remain after the completion of the current
Spaceguard effort in 2008. For land impacts and all impacts
causing global effects, the consequences are in terms of
casualties, whereas for sub-kilometer PHOs causing tsunamis, the
"casualties" are a proxy for property damage. According
to the cost/benefit assessment done for this report, the benefits
associated with eliminating these risks justify substantial
investment in PHO search systems.
PHO Search Goals and Feasibility
The Team evaluated the capability and performance of a large
number of ground-based and space-based sensor systems in the
context of the cost/benefit analysis. Based on this analysis, the
Team recommends that the next generation search system be
constructed to eliminate 90% of the risk posed by collisions with
sub-kilometer diameter PHOs. Such a system would also eliminate
essentially all of the global risk remaining after the Spaceguard
efforts are complete in 2008. The implementation of this
recommendation will result in a substantial reduction in risk to
a total of less than 30 casualties per year plus attendant
property damage and destruction. A number of search system
approaches identified by the Team could be employed to reach this
recommended goal, all of which have highly favorable cost/benefit
characteristics. The final choice of sensors will depend on
factors such as the time allotted to accomplish the search and
the available investment (see Figures 9.3 and 9.4).
Answers to Questions Stated in Team Charter
What are the smallest objects for which the search should be
optimized?
The Team recommends that the search system be constructed to
produce a catalog that is 90% complete for potentially hazardous
objects (PHOs) larger than 140 meters.
Should comets be included in any way in the survey? The Team's
analysis indicates that the frequency with which long-period
comets (of any size) closely approach the Earth is roughly
one-hundredth the frequency with which asteroids closely approach
the Earth and that the fraction of the total risk represented by
comets is approximately 1%. The relatively small risk fraction,
combined with the difficulty of generating a catalog of comets,
leads the Team to the conclusion that, at least for the next
generation of NEO surveys, the limited resources available for
near-Earth object searches would be better spent on finding and
cataloging Earth- threatening near-Earth asteroids and
short-period comets. A NEO search system would naturally provide
an advance warning of at least months for most threatening
long-period comets.
What is technically possible? Current technology offers asteroid
detection and cataloging capabilities several orders of magnitude
better than the presently operating systems. NEO search
performance is generally not driven by technology, but rather
resources. This report outlines a variety of search system
examples, spanning a factor of about 100 in search discovery
rate, all of which are possible using current technology. Some of
these systems, when operated over a period of 7-20 years, would
generate a catalog that is 90% complete for NEOs larger than 140
meters (see Figure 9-4).
How would the expanded search be done? From a cost/benefit
point-of-view, there are a number of attractive options for
executing an expanded search that would vastly reduce the risk
posed by potentially hazardous object impacts. The Team
identified a series of specific groundbased, space-based and
mixed ground- and space-based systems that could accomplish the
next generation search. The choice of specific systems will
depend on the time allowed for the search and the resources
available.
What would it cost? For a search period no longer than 20 years,
the Team identified several systems that would eliminate, at
varying rates, 90% of the risk for sub-kilometer NEOs, with costs
ranging between $236 million and $397 million. All of these
systems have risk reduction benefits which greatly exceed the
costs of system acquisition and operation.
How long would the search take? A period of 7-20 years is
sufficient to generate a catalog 90% complete to 140-meter
diameter, which will eliminate 90% of the risk for sub-kilometer
NEOs. The specific interval depends on the choice of search
technology and the investment allocated.
Is there a transition size above which one catalogs all the
objects, and below which the design is simply to provide warning?
The Team concluded that, given sufficient time and resources, a
search system could be constructed to completely catalog
hazardous objects with sizes down to the limit where air blasts
would be expected (about 50 meters in diameter). Below this
limit, there is relatively little direct damage caused by the
object. Over the 7-20 year interval (starting in 2008) during
which the next generation search would be undertaken, the Team
suggests that cataloging is the preferred approach down to
approximately the 140-meter diameter level and that the search
systems would naturally provide an impact warning of 60-90% for
objects as small as those capable of producing significant air
blasts.
Science Definition Team Recommendations
The Team makes three specific recommendations to NASA as a result
of the analysis effort:
Recommendation 1 - Future goals related to searching for
potential Earth-impacting objects should be stated explicitly in
terms of the statistical risk eliminated (or characterized) and
should be firmly based on cost/benefit analyses.
This recommendation recognizes that searching for potential Earth
impacting objects is of interest primarily to eliminate the
statistical risk associated with the hazard of impacts. The
"average" rate of destruction due to impacts is large
enough to be of great concern; however, the event rate is low.
Thus, a search to determine if there are potentially hazardous
objects (PHOs) likely to impact the Earth within the next few
hundred years is prudent. Such a search should be executed in a
way that eliminates the maximum amount of statistical risk per
dollar of investment.
Recommendation 2 - Develop and operate a NEO search program with
the goal of discovering and cataloging the potentially hazardous
population sufficiently well to eliminate 90% of the risk due to
sub-kilometer objects.
The above goal is sufficient to reduce the average casualty rate
from about 300 per year to less than 30 per year. Any such search
would find essentially all of the larger objects remaining
undiscovered after 2008, thus eliminating the global risk from
these larger objects. Over a period of 7-20 years, there are a
number of system approaches that are capable of meeting this
search metric with quite good cost/benefit ratios.
Recommendation 3 - Release a NASA Announcement of Opportunity
(AO) to allow system implementers to recommend a specific
approach to satisfy the goal stated in Recommendation 2.
Based upon our analysis, the Team is convinced that there are a
number of credible, current technology/system approaches that can
satisfy the goal stated in Recommendation 2. The various
approaches will have different characteristics with respect to
the expense and time required to meet the goal. The Team relied
on engineering judgment and system simulations to assess the
expected capabilities of the various systems and approaches
considered. While the Team considers the analysis results to be
well-grounded by current operational experience, and thus, a
reasonable estimate of expected performance, the Team did not
conduct analysis at the detailed system design level for any of
the systems considered. The next natural step in the process of
considering a follow-on to the current Spaceguard program would
be to issue a NASA Announcement of Opportunity (AO) as a vehicle
for collecting search system estimates of cost, schedule and the
most effective approaches for satisfying the recommended goal.
The AO should be specific with respect to NASA's position on the
trade between cost and time to completion of the goal.