CCNet 24/2002 - 15 February 2002


"All this shows well that humankind still is not yet ready to face
the threat of dangerous asteroids and comets. Only when humans will
stop planning and conducting big wars among themselves, will the
governments have more time to think about the new danger coming from
space. And ecologists will get mature to the point of not hampering their
governmental agencies to put up missiles and weapons in space if these
are to prevent dangerous asteroids and comets from killing the whole
of humankind, including the ecologists themselves!"
--Claudio Maccone, Center for Astrodynamics, Turin

"The Spaceguard approach is intended to provide decades of advanced
warning of any impact, permitting defensive measures to be carried out far
from the Earth and long in advance of a predicted impact."
--David Morrison

"The planetary defense issues raised by Claudio Maccone's paper and
in subsequent media reports are not as simple or confused as David
Morrison seems to suggest. When David says that "The Spaceguard
approach is intended to provide decades of advanced warning of any
impact", he does not really means *any* impact. What he is trying to say is:
we are currently only concerned with the impact threat posed by *large*
asteroids with *long* warning times. While I agree that it is more likely
to discover a big, km-sized impactor many decades before a collision
with Earth, it seems unwise to ignore the possibility of finding
smaller NEAs (or, for that matter, long-period comets) with much
shorter warning times."
--Benny J Peiser


    Astronautica, Volume 50, Issue 3, February 2002, Pages 185-199

    David Morrison <>

    Benny J Peiser <>

    Christian Gritzner <>

    Michael Paine <>

(7) TO NUKE OR TO NUDGE, 11 February 2002

    Andrew Yee <>

    Morning Journal, 14 February 2002

     Tumbling Stone, 11/2002

     Space Policy, Volume 18, Issue 1, February 2002

     The New York Times, 14 Februar 2002


>From, 14 February 2002

By Robert Roy Britt
Senior Science Writer

Earth is little more than a sitting duck in a cosmic shooting gallery, the
scientists tell us. But that doesn't mean we can't shoot back. If an
asteroid is ever found to have our planet in its sights, a carefully aimed
missile can simply knock the rock off course.

There's one little problem. It's hard to deflect something that's coming
right at you. Any boxer understands this. A slight bit of energy applied to
a punch in the right way can turn a roundhouse into a harmless glancing
blow. But if you try and stop an upper cut by driving your chin directly
into it, you'll go down for the count.

Claudio Maccone at the Center for Astrodynamics in Turin, Italy, has a
boxer's eye for asteroids, and he's developed what he claims is the best
plan for protecting Earth.

Put missiles in space, Maccone says, and hit the asteroids at an angle.

The targets

Some 587 large, potentially threatening asteroids have been found near
Earth. All are bigger than 1 kilometer (0.6 miles), the threshold for what
most researchers agree could cause global catastrophe. None of these rocks
is on course to hit Earth. But there are about 500 more that have yet to be
found, according to leading estimates.

Most of the remaining large asteroids should be detected by the end of the
decade, NASA experts say. If one is ever determined to be a serious threat,
chances are good there will be a decade or more to deal with it.

But thousands upon thousands of smaller rocks, each capable of destroying a
city or even a state, will likely take much longer to find. Warning time
might be just days or weeks. In one case last month, an asteroid that could
have caused significant damage, and which passed Earth just twice the
distance to the Moon, was first spotted barely a month before it flew by.

While a lot of energy and money goes into finding asteroids, almost no
resources have been devoted to developing a plan of action to deal with one
that could wipe out civilization.

Deft deflection

Maccone says the best defense is a set of five missile launchers. Each would
be located at a so-called Lagrangian point, spots where the gravity of Earth
and the Moon roughly balances out, allowing for a spacecraft to maintain a
nearly stable position.

By taking up posts at each of five Lagrangian points, any incoming asteroid
could be hit at a 90-degree angle, Maccone explains. Little energy would be
required, as when a boxer steps aside and deflects a punch with a deft flick
of the wrist.

Maccone's idea is detailed in the journal Acta Astronautica and was reported
yesterday by New Scientist magazine.

The weapons of choice would be nuclear, however, and Maccone worries in his
journal article that there would be significant political hurdles to getting
any plan approved.

Cold War attitude

"Many people's minds are still too much in the Cold War attitude," Maccone
writes. "Since nuclear weapons in space are forbidden by international
treatises, a proposal to locate missiles with possible nuclear warheads at
the Lagrangian points L3 and L1 would immediately be perceived as an attempt
to revive the Cold War."

Maccone thinks a new collective human conscience will need to emerge before
much will be done to face the threat of asteroids.

"Only when humans will stop planning and conducting big wars among
themselves, will the governments have more time to think about the new
danger coming from space," he said.

Terrorism's role

Regardless of any harmonious cooperation between the world's peoples,
serious plans to protect the planet are not likely to hatch soon. Unless we
get hit.

Benny Peiser, a researcher at Liverpool John Moores University in the UK,
monitors the social, political and scientific issues surrounding the
asteroid threat.

"I doubt whether there will be any international initiatives, let alone
consensus on planetary defense, until we have witnessed another
Tunguska-type cosmic disaster," Peiser told

Tunguska is the name given to a 1908 explosion of a comet or asteroid about
five miles above the surface of Siberia. The event flattened hundreds of
thousands of forested acres. No one died, because no one lived there. A
similar event over a populated area could easily kill thousands of people.

Peiser figures that a plan like Maccone's would have to be led by the U.S.
Military, which already sees space as a necessary strategic outpost.

The current response to terrorism, Peiser said, "has led the U.S. to
significantly increase the budget for space-based defense paraphernalia
which inadvertently enhances the prospects for advanced planetary defense

Copyright 2002,

Acta Astronautica, Volume 50, Issue 3, February 2002, Pages 185-199

Claudio Maccone,
Via Martorelli 43, I-10155 Torino (TO), Italy

The Cold War ended about ten years ago, but many people's minds are still
too much in the Cold War attitude. Since nuclear weapons in space are
forbidden by international treatises, a Proposal to locate missiles with
possible nuclear warheads at the Lagrangian points L3 and L1 would
immediately be perceived as an attempt to revive the Cold War. So, it is
realistic to take for granted that any such a Proposal, if put forward
officially to any country's political institutions, would immediately be
rejected by politicians as well as by the public at large. Just think of all
the problems that NASA and ESA are having with ecologists just in order to
put radioactive thermal generators (RTGs) aboard their spacecrafts.
Ecologists against RTGs actually support a narrow-minded view of ecology,
based on the oversimplified belief that whatever is "nuclear" is
"dangerous". This is the heritage of the Cold War and of all wars that went
before it.

Still the problem of doing Planetary Defense from space does exist.

The threat of asteroids and comets creating havoc on the Earth's surface is
a real threat, as it was quite well proven by the Tunguska event of 1908.
However, (fortunately!) the Tunguska disaster took place in a lonely forest
of Siberia, and so there were no casualties, and, on the other hand, back in
1908 not even the scientific community was ready to accept that such an
disaster could possibly occur, not to mention that governments and lay
people were not ready at all to learn the Tunguska lesson. So, everything
went on just as if nothing had happened at Tunguska, until the first
scientists took some notice in 1927.

All this shows well that humankind still is not yet ready to face the threat
of dangerous asteroids and comets. Only when humans will stop planning and
conducting big wars among themselves, will the governments have more time to
think about the new danger coming from space. And ecologists will get mature
to the point of not hampering their governmental agencies to put up missiles
and weapons in space if these are to prevent dangerous asteroids and comets
from killing the whole of humankind, including the ecologists themselves!

In conclusion, this new conscience of a single fate for the whole of
humankind will finally take over in the vast majority of humans, and prepare
them to the deep changes of new millennium.


>From David Morrison <>

NEO News (02/14/02) Confusion on NEA defense?

Dear friends and students of NEOs:

Both the New Scientist and Space.Com have posted stories about a
newly-published paper by Claudio Maccone of Turin on defense of the Earth
against NEOs. These press reports deal with how best to intercept an
asteroid on its final approach to impacting the Earth. It is worth noting
that to my knowledge no one seriously planning for defenses against NEOs
anticipates any such last-minute
defense. The Spaceguard approach is intended to provide decades of advanced
warning of any impact, permitting defensive measures to be carried out far
from the Earth and long in advance of a predicted impact. In fact, unless a
deflection force is applied years in advance, it is probably not possible to
change the momentum of a NEO sufficiently to miss the Earth without also
disrupting the NEO. From this perspective, the paper by Maccone seems to be
a solution in search of a problem. The generally accepted strategy for
dealing with the hazard of asteroid impacts is (1) to carry out a
comprehensive survey (starting with the larger asteroids, which pose the
greatest risk) in order to identify any threatening object, and (2) in case
we do find something that is likely to hit the Earth, to use the decades of
warning provided to initiate a program to deflect it so that it will not hit
our planet, thus avoiding the catastrophe entirely.

David Morrison


>From Benny J Peiser <>

The planetary defense issues raised by Claudio Maccone's paper and in
subsequent media reports are not as simple or confuded as David Morrison
seems to suggest. When David says that "The Spaceguard approach is intended
to provide decades of advanced warning of any impact", he does not really
means *any* impact. What he is trying to say is: we are currently only
concerned with the impact threat posed by *large* asteroids with *long*
warning times. While I agree that it is more likely to discover a big,
km-sized impactor many decades before a collision with Earth, it seems
unwise to ignore the possibility of finding smaller NEAs (or, for that
matter, long-period comets) with much shorter warning times. That NASA's
current Spaceguard approach only focuses on large NEAs does not negate the
fact that smaller impactors will in all likelihood have much smaller warning

Large NEAs such as 1999 AN and others make a close approach of Earth every
few decades. Since we have become aware of the potential impact risk due to
the gravitational effects of resonant returns, we understand that virtual
impactors have to pass through certain "keyholes" before the impact
probability will rise significantly. Once an impact solution is finally
confirmed, this would theoretically allow us decades of planning for
planetary defense.

Thus, it is very unlikely to find a big impactor with only a few weeks or
months warning: We may indeed have 20 or more years of "warning time".
That's the good news. The bad news is that, at some crucial date during that
period of time, we would have to make a decision about initiating a
planetary defense initiative. It is by no means clear how long it would take
to kick off any substantial action.

This dilemma results from the fact that we would not know for a very long
time, perhaps for most of this "warning period", whether or not the object
will in actual fact hit us. The chaotic nature of asteroid orbits is such
that we would be unable to calculate a 100 percent impact probability for
the impactor until perhaps 1 or 2 years before it actually hits the Earth. A
large fraction of the hypothetical warning time might thus be wasted by
scientific disagreement and to political hullabaloo.

The uncertainty dilemma raises a crucial question: how high has the impact
probability to rise before a political decision is finally taken to initiate
critical planetary defense action? In short, at what point during these long
years of "warning time" would scientists and military planners advise
Governments to dispatch nukes into space (if that is what's required)?

Even more difficult than that problem are the medium-sized NEAs such as 2001
YB5 which have revolution periods of 4 years or less. It is these objects
that one would expect to have significantly lower warning times as their
rate of resonant returns is much higher. Can you imagine the public reaction
to an announcement that YB5 would impact the next time it returned to Earth
in 2005? While this scenario is not likely to occur in the near future, it
unwise to deny it altogether.

Benny J Peiser


>From Christian Gritzner <>

Hi Benny,

please note that Mr. Lutz Voelker, one of our students, has completed a
study on solar concentrators for NEO deflection (first proposed by Melosh
and Nemchinov). The study is written in German and may be obtained from me
as a pdf-file on request!

Titel: "Konzeption von Solar-Spiegelsystemen zur Bahnänderung von NEOs"

Abstract: "The present study deals with the development of solar mirror
systems for deflection of near-Earth objects (NEOs). With a solar collector
sunlight will be focussed on the surface of the NEO. Due to the evaporation
of the surface material a continuous thrust impulse develops which deflects
the NEO from its original orbit. The aim is to analyse different system
solutions as well as to compare the presented concepts with each other. In
the system comparison several aspects as complexity, life cycle, success,
and operating time of different models were considered. For each of the
concepts a specific equation for the estimation of mass was established, and
the construction of the unique systems is presented. Furthermore, system
specific problems and possible solutions were discussed."

Best wishes from Dresden,

Dresden University of Technology
Institute for Aerospace Technology
Dr.-Ing. Christian Gritzner, Senior Engineer
D-01062 Dresden, Germany

Phone: +49-(0)351-463-38234 (Fax: -38126)


>From Michael Paine <>

Dear Benny

I would like to remind subscribers of the article about asteroid deflection
that I wrote for in Feb 2000
To Nuke or To Nudge

As recently stated by David Morrison, the main idea is to find them decades
before a collision. In particular, "Earth buzzers" that need to pass through
a critical "keyhole" several orbits (ie a decade or so) before a collision
only need to be nudged a few hundred kilometres over
several years in order to be made safe (that is, not pass through the

In any case, Nuclear weapons stored in Earth orbit (or Lagrangian points) do
not seem to me to be a particularly well placed to go chasing an asteroid in
orbit around the sun. Getting nuclear weapons into space in not the problem
- having a booster rocket large enough to deliver the payload to the
asteroid is. Maybe there is a (tenuous) case for storing some large fuelled
booster rockets in Earth orbit for such a purpose - with the Shuttle
delivering the nuclear weapons when necessary (shudder shudder)

Michael Paine


>From, 11 February 2002

By Michael Paine

An asteroid is heading for Earth. With just days to go before the collision
a beefed-up space shuttle is sent to intercept it. A brave team of
astronauts and oil-rig workers drills deep into the space rock, plants a
nuclear bomb and blows it in two. The two halves fly apart and miss the

Dream on!

The idea of blowing up an asteroid makes for good movie scripts, but is not
the way to do it in the real universe. Many of the fragments would remain on
a collision course and like the blast from a shotgun; the fragments can do
up to ten times as much damage as the original, intact object.

In any case, Erik Asphaug from the University of Southern California has
modeled "rubble-pile" asteroids and finds that blowing them up with bombs
may be much more difficult than with asteroids made of solid rock. It is a
bit like the difference between hitting a sandbag and a solid sandstone
block with a sledgehammer -- the sandbag absorbs the impact with little
disruption but the sandstone block shatters.

Applying a nuclear "nudge"

"Stand-off" nuclear explosions are favored by some scientists (see below)
and might work with both solid and rubble-pile objects.

A nuclear bomb is detonated several hundred yards away from the object.
Surprisingly, it is the intense radiation generated by the explosion that
does the job. In one scenario, the radiation grills one half of the asteroid
and causes a very thin surface layer to vaporize and fly off into space.

Tens of tons of material blasting off the asteroid at high speed would be
sufficient to jolt the asteroid in the opposite direction. The effect is
like the recoil of a rifle -- a small bullet moving at high speed causes the
heavier rifle to recoil at low speed.

One thing most scientists agree on is there is no need to maintain an
arsenal of nuclear weapons in space ready to intercept rogue asteroids. They
also point out that there are ways to deflect asteroids that don't require
nuclear explosions and we should be looking at these methods more closely.

In theory, an asteroid that is found to be on a collision course with our
planet can be deflected to avoid an impact.

The deflection involves changing the asteroid's course with a sideways push
or, preferably, changing its orbital speed so that it arrives before or
after, rather than when Earth crosses its path. In either case the
deflection is far more effective if it can be carried out years or decades
ahead of the predicted collision.

For example, after twenty years, a nudge of just 1 m.p.h. (1.6 kilometers
per hour) would change an asteroid's location in space by about 170,000
miles (273,500 kilometers). That is more than halfway to the moon.

Recent discoveries suggest that deflection of some Earth-threatening
asteroids may be easier than first thought. Most schemes for nudging
asteroids into a safer orbit assumed a single catastrophic encounter with
Earth. This meant changing the course of the object by at least 4,000 miles
(6,300 kilometers) -- the radius of Earth.

Nuclear Deflection: A safer, more effective procedure

Alan Harris, from NASA's Jet Propulsion Laboratory, explains that scientists
now realize an asteroid will usually make several close passes by the Earth
before a collision occurs.

The recently discovered 1000-yard (1-kilometer) wide asteroid designated
1999 AN 10 provides an instructive example. It will make a close pass of
Earth every few decades. During each pass the asteroid is deflected slightly
by the Earth's gravity.

Astronomers in Italy have calculated that a critical deflection could occur
in 2027. This would involve the asteroid passing through an imaginary hoop
in space they call a "keyhole". If the asteroid were to pass through this
keyhole, which is only about 60 miles (100 kilometers) across, then it would
collide with the Earth on its return in 2039.

When the initial calculations were made, astronomers didn't know the orbit
well enough to determine if it might pass through the keyhole. After
important follow-up observations were made they have now pinned down the
orbit enough to be sure that it will not pass through any keyhole in 2027
and there is no chance that it will collide with Earth in the next century
or so.

If, however, they had determined instead that there was a chance it would
pass through a keyhole in 2027, then a mission to place a transponder, like
a radio homing device, on the asteroid would have been wise so that its
orbit could be determined precisely.

Harris explains that such a high level of precision would likely be required
to determine for sure if the asteroid were on a course through a keyhole
and, if it came to be, to measure the success of any deflection efforts. In
this case a deflection of just a few hundred miles prior to the 2027 keyhole
event would be all that was needed to avoid the 2039 collision.

Deflection of dangerous asteroids that are not in a "keyhole" orbit is more
difficult because a larger change in course is required. The task is still
feasible provided that sufficient warning time is given.

If a serious global effort is made to discover most large near-Earth
asteroids within the next decade, then we should have decades, or even
centuries of warning before a devastating impact. With such lead times only
a relatively small nudge is required to change an asteroid's course so that,
decades later, it will miss Earth.
Copyright 2000,


>From Andrew Yee <>

Office of University Communications
University of Maryland

Lee Tune, 301.405.4679,
Lucy McFadden
Deep Impact, Science Team EPO Manager

For immediate release: February 8, 2002

No. 02010r

Maryland Led Project Takes Big Step Toward 2005 Comet Collision

COLLEGE PARK, Md. -- NASA's Deep Impact project, led by University of
Maryland Professor Michael A'Hearn, has passed another milestone on
its road toward a January 2004 launch and a July 2005 encounter with
a speeding comet.

The Deep Impact project, which will be the first mission to punch a
spectacular football field-sized crater seven stories deep into a comet,
successfully completed a three-day critical design review last week. After
examining details of the mission, three independent review boards concluded
that there are no significant flaws in the design and that the project can
proceed with building and testing the project's two spacecraft.

"This was a major step for us in ensuring both ourselves and NASA that our
designs are solid and reliable," said A'Hearn, who directs the mission as
principal investigator. "It is truly exciting to see the first pieces of
hardware beginning to arrive at Ball Aerospace and to realize that we are
well on our way."

Comet Science

The Deep Impact mission is the eighth mission in NASA's Discovery Program
and the third targeted at a comet. The Stardust mission, which is currently
en route to comet Wild 2, will bring back a sample of dust from the comet's
atmosphere to study in Earth-based laboratories. The CONTOUR mission, which
is scheduled to launch in July of this year, will fly past at least two
comets of very different histories to understand the evolutionary
differences on their surfaces. Deep Impact will intercept comet Tempel 1 in
July of 2005. Its flyby spacecraft will release a 770-pound impactor that
will excavate a large crater in the comet's nucleus, thus allowing both the
flyby spacecraft and Earth-based observers to study the differences between
the surface material and the interior of the cometary nucleus and to
determine key physical properties of the outer tens of meters of the

Comets are essentially giant dirty snowballs orbiting the sun. They are
thought to preserve, particularly in their ices, a unique record of
conditions in the early solar system when the planets were being formed.
Previous passages near the sun by Tempel 1, the target comet for the Deep
Impact mission, have led to significant evolutionary changes in the outer
layers of the comet's nucleus. However, the nature of this evolution is not
understood. Even basic properties, such as mass and density, have never been
measured for any cometary nucleus. Deep Impact should allow determination of
the density of the surface layers, although no currently planned mission is
intended to determine the mass and overall density of any comet until the
European Rosetta mission arrives at comet Wirtanen in 2011. Deep Impact will
provide the first data probing below the very surface of a cometary nucleus.

Countdown to Deep Impact

The mission launches in January 2004 and orbits the sun for one year,
passing again very close to Earth in January 2005. At the Earth flyby, the
instruments are tested and calibrated and the spacecraft pair is diverted to
comet Tempel 1, arriving in July 2005. On July 3, 2005, the impactor is
released from the flyby spacecraft and takes over its own operation, aiming
for an impact at 10 kilometers/second on July 4, 2005. Meanwhile, the flyby
spacecraft slows down by 100 meters/second and diverts to watch the impact
happen and fly past the nucleus at a distance of 500 kilometers (310 miles),
14 minutes after the impact.

The impactor, which is a fully functional spacecraft, will take pictures of
the nucleus with ever-increasing resolution as it closes with the comet.
These pictures are for scientific purposes and for automatic navigation to
ensure an impact. The camera is intended to provide the highest resolution
pictures of the cometary surface ever taken, providing unique information
about the surface that will give clues to its formation and evolution. The
flyby spacecraft has two cameras and an infrared spectrometer to observe the
formation process of the crater and the final crater. The measurements are
intended to tell scientists about the composition of the interior and the
surface and, by observing the crater's formation process, determine the
physical properties of the nucleus. The size of the final crater and the
length of time it takes to form are key measurements, since these are
controlled by the physical properties of the cometary nucleus, properties
that are now totally unknown.

The Deep Impact Team

A partnership among the University of Maryland, the Jet Propulsion
Laboratory (JPL), and Ball Aerospace & Technologies Corp., is carrying out
the Deep Impact mission. The university, through Principal Investigator
Michael A'Hearn, is responsible for the entire mission and directly manages
the scientific effort, the education and outreach effort, and the
development of the instruments on the spacecraft. The science team includes
a dozen scientists from the United States and Germany working with several
additional supporting scientists. The Jet Propulsion Laboratory, through
Project Manager Brian Muirhead, provides the overall project management,
provides selected items of hardware and portions of the software, and
carries out the in-flight operations. Ball Aerospace & Technologies Corp.,
under the direction of Deputy Project Manager John Marriott, is building
both the two spacecraft and all the instruments.

The Discovery Program

NASA's Discovery Program consists of a series of cost-capped, competitively
selected missions proposed by individual scientists and their chosen teams.
Using the results of peer reviews by both scientists and engineers, NASA has
typically selected one or two new missions every two years. Deep Impact was
selected from a proposal submitted in 1998. The total budget for Deep Impact
is capped at $279 million in real-year dollars ($240 million in FY99 dollars
before adjustment for inflation). This includes all launch costs,
communications and operations during flight, delivery of the calibrated data
to the scientific community, and education and public outreach activities.

NASA Reviews

The Critical Design Review is, for all NASA's missions, the point at which
NASA gives approval to the detailed design and authorizes the project to
complete the building of all the hardware and preparing it for launch. For
this mission, the CDR had three separate review boards. The Deep Impact
project has its own standing review board of personnel from outside the
project, who follow the project closely. JPL's System Management Office
appointed a review board to ensure that JPL management is aware of all
aspects of the mission. NASA appointed an Independent Assessment Team to
provide an independent assessment of mission readiness at this stage of
development. All three review boards found that the Deep Impact system
design is mature and the project is fully ready to start the spacecraft and
science instrument fabrication, assembly, integration and test phases.

The next major review of the system will be in February 2003. Known as the
integration and test readiness review, it is conducted prior to shipping the
Deep Impact spacecraft to Cape Canaveral for integration into the launch

Note to editors: digital images of initial components of the Deep Impact
spacecraft are available on the web at or


>From Morning Journal, 14 February 2002

By KRISTY FOSTER, Journal Staff Writer February 14, 2002
WINONA - Look in the sky ... It's a plane. It's a bird. No it's a meteor
shower. Hanover Township, Guilford Lake, and Winona firefighters were called
to a home on Schneider Road after a giant fireball looked like it landed in
an area near Tower Road and state Route 9.

Jessi Woodall, the resident who made the initial call - one of three from
the Hanover Township area - after witnessing the sight in the sky, said that
the sight scared her because she thought it was a plane coming down.

The Salem Police Department reported being inundated with calls from people
reporting that they saw a ball of fire in the sky.

Woodall was in her family room watching television, the one night of the
week when she gets to sit back and relax because of work and school
commitments, when something caught her eye out of the sliding glass door.

When she got up to look, she saw a ball of fire heading for a tree line at
the edge of her parents' property.

She said she called for her dad, but he couldn't see it. The young lady then
called other relatives to see if they had seen it. All of them reported no.
But she was sure she had witnessed something.

She said that after landing, it sent out shooting blue lights and then
quickly extinguished after lasting a few minutes.

"It looked close, but it was moving so fast," Woodall said.

She described it as being a bright yellow ball with red and orange on the
outside similar to the sun.

After a 45-minute search of the wooded area, area firefighters reported
being unable to find anything and had began to call off the search.

Just when the members of the fire department were frustrated by searching
for the mystery ball ...

The Columbiana County Sheriff's Department told the firefighters via scanner
that the Federal Aviation Administration had reported a meteor shower was
occurring in much of the area between the states of Ohio and Wisconsin.
©Morning Journal News 2002 


>From Tumbling Stone, 11/2002

by Livia Giacomini - copyright Tumbling Stone 2002 version

Quantifying a risk is not an easy problem, in any field. An example over
all: how dangerous can a car, running on a certain road, be? Obviously, the
answer depends on many factors (its speed, the road, the pilot
skillness...). Even if we were able to formalise the connections between
these parameters, it would still be necessary to define a statistical tool
to quantify the specific danger (since a risk is always a statistical
probability!) .

Imagine applying this easy example to the field of NEOs (dict.), to the
attempt of setting the impact probability of a certain asteroid with Earth.
This case is much more complicated than the example of our car, first
because the orbit of a NEO is highly chaotic over long periods of time (see
what chaos is in this issue of T.S.), second because this orbit can only be
known under a statistical point of view (this is the concept of region of
uncertainty, see dict). Sounds like trying to measure the risk that our car
will have an accident, without knowing exactly who is driving it, at what
speed, on which road etc.!

All these problems make scientists' task of evaluating the risk associated
to each new NEO very complicated. Of course, evaluating this risk is
fundamental to alert the scientific world - and the media - of a possible
danger! Today, just to make this difficult evaluation more precise, a little
revolution is taking place in the astronomical community. In fact the IAU
committee has just introduced a new tool for the quantification of impact
danger, called Palermo scale, and presented for the first time at the
international meeting held in Palermo last year (see Tumbling Stone number
5: special issue) .

One thing at a time. You don't need to be a specialist to know that a method
of evaluation of impact danger already exists since the year 1999: the very
famous Torino Scale. How does this scale work and why a new tool has become

The Torino Scale uses two parameters to classify the danger of an impact,
its kinetic energy and its impact probability (see box about the Torino
Scale). Being initially established for public communication, this tool
avoids complexity presenting a very clear and simple measure of the hazard
by a ten point integer scale.

Avoiding complexity is at the same time the reason why the Torino scale
presents several aspects that are considered problematic for scientific
purposes, and that can be resumed in three main points:

- the length of time before the impact itself, is not taken in account. In
other words, similar scenarios get the same score whether they should occur
90 days or 90 years from now! On the other hand, to defend Earth, the period
of time before the impact is very, very important! (see Tumbling Stone
number 9: "Methods of mitigation" by Germano D'Abramo)

- using an integer parameter, the Torino scale makes it impossible to
recognize when events that have the same scale value are actually far apart.

- the Torino scale assigns a zero value to all impacts with energy below 1
MT (dict.), no matter their probability. For this reason, the scale is not
useful for events of great scientific interest but low public outreach (such
as fireballs!)

It's to solve these problems, that the new Palermo Scale has been
introduced. But how does this new tool work exactly?

First of all, the new scale provides a different measure of the hazard posed
by the event itself, without any refernece to the background risk of the
collision. To achieve this goal, a new parameter of classification of an
impact, called expected energy E^, can be introduced. E^ is in a real sense
a probabilistic energy, being the average energy that would be expected
given a large statistically consistent sample of the entire range of
potential orbits consistent with the impact.

This energy can be defined using two very intuitive parameters, the impact
energy E and the impact probability P:

              E^ = E x P

E is simply the energy released by the collision, which can be defined as
the kinetic energy of the body (E = 1/2 x mv^2). Although this parameter is
conceptually simple, its value cannot be perfectly known for a NEO, due to
the uncertainty in the object's mass. With the absence of more precise
physical observations, the mass is usually evaluated from the volume, the
shape and the mean density deduced from the spectral type of the asteroid.

P is the impact probability and is calculated with numerical simulations,
taking into account how the orbits that belong to the region of uncertainty
meet the target plane.

A comparison of the two scales: lines of constant E for the Palermo scale
and the areas corresponding to different values of the Torino scale (click
on the image to see it bigger)

The expected energy is the appropriated parameter to evaluate an individual
encounter with a NEO in term of its human, economical and environmental
threat, in a much similar way to the Torino Scale.

In fact, the first scale was based on a similar method, classifying objects
on different areas of the same parameter space (which was defined in much
the same way by the impact energy and impact probability, as the picture on
the left shows).

But, differently from the Torino scale, the new tool introduced by the IAU
also deals with the time at which the impact should take place, measuring
the danger of a certain event relative to the statistical threat coming from
the entire asteroid and comet population averaged over long periods of time.

This background hazard is quantified by the parameter R, called normalized
risk, related to the impact probability P previously defined with the

              R = ________
                   f x DeltaT

the f x DeltaT product is normally what is called background hazard and it
corresponds to the probability that a body of equal or bigger dimension than
the considered asteroid should impact Earth over a period of time f is the
impact frequency and can be deduced from the observation of craters.

Without going into further details, it is obvious how the Palermo scale is a
more technical and precise tool than the first Torino scale, which will
continue absolving the task of giving an immediate and simple description of
the threat of a certain impact. On the other hand, thanks to the Palermo
Scale, monitoring NEOs programs will be able to run automatically and in a
very precise way, taking into account the mere observation data to create an
observational priority for the various objects discovered.


Space Policy, Volume 18, Issue 1, February 2002

Book review
Target Earth: How Rogue Asteroids and Doomsday Comets Threaten our Planet
Duncan Steel; Time-Life Books, New York, 2000

Duncan Lunan
Flat 65, Dalriada House, 56 Blythswood Court, Glasgow G2 7PE, UK

Target Earth is the follow-up to Duncan Steel's previous book, Rogue
Asteroids and Doomsday Comets. That had a Foreword and this has an Afterword
by Sir Arthur C. Clarke; the Foreword this time is by Drs. Andrea Carusi and
Brian Marsden, both prominent in the field. They emphasise that, although
impacts occur seldom, such large deathtolls may result that the statistical
chances of an individual's dying in an impact are stronger than those for
any other natural event.

At first glance I feared that Target Earth would be lightweight compared
with its predecessor, because it is in the familiar Time-Life format of
treating each double page as a separate chapter, and heavily illustrated.
However, to quote Angus McAllister, who writes legal textbooks as well as
thrillers, "The circle can be squared. Books don't have to be badly written
and obscure because they're academic, nor do they have to be derivative and
trivial because they're popular." Target Earth is both popular and thorough,
packed with information. However, the technique of printing larger
illustrations as background with text over them is not successful because
some of them are too faint, hardly visible except in strong light.

The book begins by emphasising the amount of matter in the Solar System
additional to the classically known planets, covering the discoveries of the
outer planets and the asteroids. Even here there is new information to pick
up, e.g. that the Voyager 2 flybys have redetermined the masses of Uranus
and Neptune and accounted for the perturbations previously attributed to a
10th planet, so that it is now known that there can be no such planet even
as massive as the Earth within 10 billion miles of the Sun. The class of
objects now known as `the Kuiper Belt' was first suggested by an Irish
astronomer, Kenneth Edgeworth, and if Pluto had been reclassified as one, it
would have been designated asteroid No. 10,000. Duncan Steel endorses the
suggestion of Drs. Victor Clube and Bill Napier that Kuiper Belt objects, as
well as the Centaur-class objects in the outer Solar System, are
`super-comets'; if they enter the inner System, they can break up with
disastrous consequences for the inner planets, including Earth. The Kreuz
group of Sun-grazing comets, one of which was seen to split into two by
Ephorus in 372 BC, are all products of one such ancient break-up.

Comets, of course, have been known for a long time, and the history of their
observation is covered¯¯including the one in the summer of 44 BC, over the
games commemorating the death of Julius Caesar¯¯as is the tradition that the
wines produced in `comet years' are particularly good vintages. `Great
comets' are tabulated in 1557, 1664, 1680, 1843, 1860, 1880, 1882 and 1887;
apparently the parent of the Perseid meteors, Comet Swift-Tuttle, doesn't
qualify, although it was known at the time as `The Great Comet of 1862', on
which I've written elsewhere.

Chapter 2 is entitled `Craters, Craters Everywhere' and is a concise tour of
the Solar System, noting impact features everywhere, including one 300 miles
across and eight miles deep on the asteroid Vesta, many fragments of which
are found in the Asteroid Belt and have reached Earth as meteorites. Chapter
3 repeats the `Target Earth' title, though at the end of the book comes the
chilling line, "Most of Target Earth is Target Ocean". As we all know, the
consequences of land impacts are quite bad enough but Worse Things Happen at
Sea. Two million years ago, for example, a 4 km (2.5 mile) diameter asteroid
struck off the tip of South America, generating tsunamis 60¯80 m high all
round the Pacific Rim and on the southwestern coast of Africa, as well as
diffracting round New Zealand to sweep the south coast of Australia. Two
underwater craters are now known in the Baltic, in addition to coastal
features such as Chesapeake Bay, 35 million years ago, Deep Bay in
Saskatchewan, and Chixulub, the dinosaur killer.

Barringer Crater in Arizona, still perhaps the best known impact feature,
was originally classified as volcanic, but the first one to be recognised as
impact-generated was the Odessa crater in Texas. Many more are now known,
and Duncan Steel undertakes a comprehensive, illustrated global tour. It is
estimated that 800-m objects strike the Earth every 100,000 years on
average, while major cometary impacts may be as rare as one in 10 million
years. But smaller objects can do a great deal of damage, and there were at
least three in the 20th century alone¯¯all three, by pure chance, in
unpopulated areas.

The big question is, will it take a full-scale disaster to prompt
international action on the hazard (assuming that civilisation survives the
disaster)? The first watch for Near-Earth Objects was initiated by Gehrels
at Kitt Peak in the 1980s to make use of a telescope whose drive was worn
out, so that it was forced to scan the sky in strips as the Earth turned.
Most searches since have been similarly haphazard and piecemeal, e.g. the
USAF searches for asteroids with its GEODSS system around midnight, when the
artificial satellites it normally tracks are invisible in the Earth's
shadow. Steel's Chapter 7 is devoted to Project Spaceguard, which has had a
remarkable degree of success in the UK, not just by raising public awareness
of the issue but by getting the government to set up a task force and
propose joint initiatives with other nations, especially with our partners
in ESA.

There is still the question as to what could or should be done if an impact
threat is discovered. The MIT Project Icarus in 1967 calculated that six
Saturn V launchers carrying 100 nuclear warheads would be needed to divert
that asteroid if it became a hazard, as in its present orbit it conceivably
could. Saturn V is no longer available but a similar effort could no doubt
be mounted, given sufficient warning. The problem is the `Deflection
Dilemma': if you can deflect asteroids or comets away from the Earth, that
raises the possibility of deflecting them towards it. Duncan Steel's answer
to that is not to build such a system until an actual threat is detected,
but there's still the possibility of things sneaking up on us: one reason
why we're still arguing about the nature of the Tunguska object in 1908 is
that it approached from the direction of the Sun and wasn't seen until it
entered the atmosphere. Watching for that would require eternal vigilance in
space as well as on Earth, and we know how quickly governments tire of such
things: the US administration turned off the science stations left by
astronauts on the Moon only 5 years after Apollo, and cancelled the Search
for Extraterrestrial Intelligence long before there was a realistic chance
of success.

But those of us who would like to see deflection systems developed now can
take heart from a contribution to the 2001 Charterhouse conference on
British rocketry by David Asher and Nigel Holloway. They made headlines with
an outline of what it would take to bring down a 500-m asteroid on Telford
and devastate England from the Scottish Borders to Devon. It was worth
attending just to witness the stunned silence in which veterans of Britain's
nuclear weapons programme heard details of how a single asteroid, under
malevolent control, could reduce the UK to rubble. As one 80-year-old
remarked, "If it takes 12 years and 15 nuclear warheads to bring down an
asteroid on us, why not just use the weapons in the first place?" On the
more serious level of preventing the impacts, another old-timer remarked
that the UK share of the events wouldn't pay for a new housing estate, let
alone what it would cost to rebuild the country after such an occurrence.
But the study demonstrates that using asteroids as weapons takes much more
effort than simply turning them aside from Earth, so the Deflection Dilemma
has lost much of its force.
Copyright © 2002 Elsevier Science Ltd. All rights reserved.


>From The New York Times, 14 Februar 2002

When the American Museum of Natural History opened its gleaming new
planetarium two years ago, it gave its highest place of honor to the
Willamette meteorite, the pitted, 15 1/2-ton boulder that fell to Earth more
than 10 millennia ago.

But unknown to most of its admirers - or until recently to the Oregon tribe
that considers it sacred - the meteorite has a flat spot at the top, created
by museum curators in 1998 when they cut off a 28-pound chunk and traded it
to a private collector for half an ounce of Mars.

On Sunday, the collector, Darryl Pitt of New York City, sold a six-inch,
3.4-ounce slice off that chunk for $11,000 at an auction.

A second, smaller piece of a meteorite Mr. Pitt obtained in a trade with the
Natural History Museum in London a couple of months ago sold for $3,300.

"This is not anything that is unusual," said Mr. Pitt, whose Macovich
Collection is the largest private collection of meteorites in the world.

But the auction dismayed descendants of the Clackamas Indians of Oregon who
regard the meteorite as a spiritual union of earth, sky and water.

"Would someone want to auction off a crucifix, one of the holy statues out
of the Catholic Church or something like that?" asked Kathryn Harrison,
former chairwoman of the Confederated Tribes of Grand Ronde, which includes
the Clackamas.

The Oregonian, the state's largest newspaper, took up the cause, accusing
the American museum in an editorial on Saturday of showing "disgraceful
stewardship" of the meteorite. "If we had our way, it would be heading back
on the next westbound freight train," the newspaper said.

Dr. David Wheeler, a chiropractic physician in West Linn, Ore., who bought
the smaller thumbnail-size piece that weighs a third of an ounce, said he
wanted to discuss with the tribal members how he might share his new
purchase with them.

"I did it, because I wanted to bring a small part of the meteor back to
Oregon," Dr. Wheeler said. "I may end up donating it to them."

Matt Morgan, a meteorite trader in Colorado who runs the Internet site Mile
High Meteorites, bought the larger piece "because it's a historic American
meteorite and one which I don't have," he said. "It's one of the things you
always read about in the books."

Mr. Morgan said he and two other investors would cut that piece into six or
seven smaller pieces, keeping some for themselves and selling the others.
"We'd like to recoup some of the investment we made," he said.

The Willamette meteorite, the largest meteorite ever found in the United
States, is believed to have originally landed in Canada, and then was pushed
by glaciers to Oregon's Willamette Valley thousands of years ago. The
American Museum of Natural History bought it in 1906.

Two years ago, after the opening of the museum's Rose Center, the tribes
demanded that the meteorite be returned.

The tribes and the museum settled their dispute with an agreement in which
the meteorite remains in New York and tribal members can conduct a private
ceremony once a year at the center.

But dozens of pieces of the Willamette meteorite were removed over the years
and scattered to institutions around the world.

Meteorite collectors trade pieces of space rock the way boys once traded
baseball cards: a slice of Mars for a chip of carbonaceous chondrite, a Moon
rock for a new meteorite find from the Sahara.

Unlike curators of art or fossils, where great value is placed on the
integrity of objects, meteorite curators at major museums participate in the
trading game, giving samples of their collection to private collectors in
exchange for newly discovered rocks.

"In meteoritics, it's long been a tradition to trade pieces of specimens,"
said Dr. Michael J. Novacek, provost of science at the American Museum of
Natural History. Scientists routinely cut meteorites apart for scientific
study exchange and send pieces back and forth for different laboratories to

Trading pieces of the museum's meteorites with private collectors allows the
museum to acquire new, rare meteorites, Dr. Novacek said. "It ultimately had
a scientific purpose," he said.

In exchange for the 28-pound piece of the Willamette meteorite, Mr. Pitt
gave a part of the Governador Valadares meteorite, which landed in Brazil in
1958, one of a few known to have come from Mars.
Copyright 2002 The New York Times Company | Privacy Information 

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