CCNet, 93/2000 - 22 September 2000

     "There is no evidence that meteorites have ever left a
     dent on human civilization."
        -- Philip Ball
           Nature, 21 September 2000

     "The size of crater A indicates that the impact body
     was about 150m in diameter, resulting in an estimated
     energy release of ~350 megatons (TNT equivalent), 30
     times larger than the 1908 Tunguska event. [...] The
     age of the emplaced loess, the excellent preservation
     state of the smaller craters, the preserved glassy
     sheen on the impactite and the state of the recovered
     chondrite all suggest an age considerably less than
     10,000 years. Consequently, it is conceivable that
     this event was witnessed by early inhabitants of South
        -- P.H. Schultz & R.E. Lianza,
           Nature, 16 January 1992

    Alan Harris /DLR <>

    Ivan V. Nemtchinov <>

    Ron Baalke <>
    Ron Baalke <>

    Michael Paine <>

    Yahoo! News, 21 September 2000

    Jens Kieffer-Olsen <>
    James Oberg <>
     Joel D. Gunn <>

     DISCOVER Vol. 21 No. 10 (October 2000)


From Alan Harris & Gerhard Hahn/DLR <>

Dear Benny,

We offer the following statement in the name of Spaceguard
Germany in response to the release of the UK Task Force


Gerhard Hahn
Alan Harris

Statement from Spaceguard Germany:

We are very impressed with the UK Task Force report and
would like to add our congratulations to all concerned..
Indeed, we are rather envious of what the NEO community in
Britain has managed to achieve and note that there has
been, as yet, no comparable government-level response to the
NEO issue in Germany, despite the considerable lobbying
efforts of Spaceguard Foundation Germany.

We note that the question of European collaboration is a
major aspect of the Report's recommendations and we will
continue to do everything we can to awaken interest at
Government level in Germany. Despite its current rather
silent and indifferent official stance, there is no
question that Germany has the expertise and resources, not
to mention moral obligation, to become a major player in
this field. We hope that Germany's official attitude will
now change, at the latest when the UK government responds
positively to the Report's recommendations.

Indeed, we would like to point out that a great deal of NEO
research is currently in progress here, mainly under the
auspices of the German Aerospace Center (DLR), including
projects in areas such as impact cratering, orbit dynamics,
NEA searches, physical characterisation (including infrared
and optical observations at the Keck and other leading
telescopes), etc. For more details see the web sites listed
below. Furthermore, the DLR is currently considering a
proposal for a German-led NEA flyby and rendezvous space
mission. However, much of this work continues to be
performed outside of the main funding channels and does not
enjoy the protection and status of formally recognised and
encouraged projects. We are working hard to change this

There is vast scope here for European collaboration in NEO
work - we "simply" have to get the right heads to talk to
each other!

Spaceguard Foundation e.V. (Germany)

Some aspects of German NEO work can be found at:


From Ivan V. Nemtchinov <>

Institute for Dynamics of Geospheres
Russian Academy of Sciences 

21 September 2000

Dear Dr. Peiser,

The UK Task Force has issued a clear and consise report on
potentially hazardous Near Earth Objects. We agree with the
essential point that the research has to be international.
Our Institute has, for a rather long time (i.e. since the
Conference on Hazards due to Asteroids and Comets held in
Tucson) participated in international efforts in assessing
the risks and the consequences of impacts and has
elaborated measures to mitigate such impacts. Since the
Tuscon conference, we have become more amd more convinced
that in the modern epoch, as nuclear and chemical
facilities are being built in increasing numbers and
throughout the world, and as civilization has become
increasingly dependent on electronic communication,
that humanity has become more vulnerable to cosmic
punctuations than dinosaurs in the past. Consequently,
smaller impactors - which hit the Earth more frequently -
are to be considered as hazardous, and new efforts are
necessary to estimate this hazards and the means of
mitigation more precisely.

The Institute for Dynamics of Geospheres RAS has already
proposed some new research programs, which, as we now see,
are in accordance with some recomendations of the UK Task
Force Report. One of such research programs has recenty
been submitted to the International Science and Technology
Center (ISTC) in Moscow (Project 1814) but has not been
discussed at yet the ISTC panel. We are open for critical
remarks and support..

We hope that the new British initiative will be accepted by
the UK Government (and hopefully followed by other European
Governments). We also hope that the support of the
scientific NEO community will help to realize this and
other research programs and finally solve the problem of
risk assesments and hazard mitigation.

The Institute for Dynamics of Geospheres is open for
international co-operation in the efforts directed to
reach this goal.

Prof. Julius I. Zetzer, Deputy Director IDG
Prof. Ivan V. Nemtchinov, Head of Laboratory



Donald Savage
Headquarters, Washington, DC              September 21, 2000
(Phone:  202/358-1547)

Michael Buckley
Johns Hopkins University Applied Physics Laboratory, Laurel, MD
(Phone:  240/228-7536)

Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-5017)

Martha Heil
Jet Propulsion Laboratory, Pasadena, CA
(Phone:  818/354-0850)



The asteroid Eros is so ancient it could have witnessed the
formation of the Earth, according to findings from NASA's
Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft
published today. 

Four scientific papers published in the September 22 issue
of the journal Science represent the largest one-time
release of scientific data about Eros since the mission
began. The NEAR Shoemaker spacecraft has been in orbit
around the primitive Manhattan-sized asteroid since last

The four scientific teams publishing this week include the
NEAR X- ray Gamma-Ray Spectrometer (XGRS) team, the
Multispectral Imager and now-silent Near-Infrared
Spectrometer team, the Laser Rangefinder team and the Radio
Science team.

The NEAR mission is managed by the Johns Hopkins University
Applied Physics Laboratory (APL) in Laurel, MD, for NASA's
Office  of Space Science.

The NEAR Shoemaker web site contains the latest results and
high-resolution images and information:


From Ron Baalke <>

News Service
Cornell University

Contact: David Brand
Office: 607-255-3651


Mystery of tiny asteroid Eros -- so much rock but so little
gravity -- detailed in Science report

ITHACA, N.Y. -- How could something so small have so much
debris lying around? That is the puzzle presented by
asteroid 433 Eros in the first major reports on the
composition and history of the 21-mile-long body, the solar
system's first asteroid to be subjected to close study.

Writing in the latest edition of the journalScience (Sept.
22), Joseph Veverka of Cornell University describes tiny
Eros as having a surface "saturated" with tiny craters
smaller than 1 kilometer (0.6 miles) in diameter and
"abundant" with rocks 30 to 100 meters (33 to 109 yards)
across. The craters and the boulders, says Veverka,
indicate many violent collisions with the asteroid over
time. But the gravity on Eros is so weak "that intuition
and calculation tell you that most of the debris produced
in a collision would have escaped -- but the surface is
full of it."

Veverka explains: "We have several possibilities. One is
that we simply don't understand cratering events on small
objects, and somehow the debris gets thrown out at very low
speeds. Or the ejected material ends up in the same orbit
as Eros, and over time the asteroid runs back into its own
debris and gathers it up, which is equally bizarre. We
simply don't understand this."

Veverka, professor of astronomy at Cornell, is the
principal investigator on the multi-spectral imager (MSI),
or camera, and the NEAR infrared spectrometer (NIS), two of
the five instruments on board NASA's Near Earth Asteroid
Rendezvous spacecraft (known as NEAR Shoemaker), which has
been in orbit around Eros since Feb. 14. Between that date
and April 1, the four teams managing the instrument
packages probed the elongated asteroid for its mass
distribution, elemental composition and topography and
elevation. Their four reports in Science form the most
detailed view yet of an asteroid. The Veverka team's
report, "NEAR at Eros: Imaging and Spectral Results," notes
rock debris, "presumably blocks of ejecta," scattered
across the asteroid, but not uniformly. A strong
concentration of blocks, the report says, occurs in the
complex depression west of the saddle, a 10-kilometer
(6-mile) depression. The distribution of blocks shows a low
density at high northern latitudes, but the rocks do not
seem to have collected in low-lying areas of the asteroid.

"What is striking about Eros," says Veverka, "is that if I
look at the moon in great detail, I see lots of tiny 
craters and fewer blocks of rock. But on this object, when
I get down to sizes the size of a car, there are very few
craters and lots of boulders." And yet, he says, the
surface of Eros shows clear evidence of violent impacts.

The astronomer concedes that little is known about
collisions on small bodies with low gravity -- "we have to
extrapolate a lot," he says. But calculations indicate that
the gravity on Eros is so low that a ball thrown from the
surface would escape into space. "Most of the ejecta from a
violent collision would be traveling at a reasonable speed,
and you would expect it to escape. So we simply don't
understand why the surface is littered with so many
blocks," says Veverka.

The Veverka team also confirms previous reports that Eros
-- an S-type asteroid, the most common classification -- is
a primitive relic of the emergence of the solar system from
a cloud of gas and dust.

"We basically know that Eros is an example of a very
primitive body in which nothing much has happened other
than formation and cratering. If you want the most pristine
material in the solar system that has had the least happen
to it, then Eros is a good example," Veverka says.

The imaging team says there is no evidence that Eros has
gone through an Earth-like process of heating and
segregation of metal from silicates to form an iron core
and rocky mantle. From an analysis of surface elements --
by measuring radiation emissions -- and measurements of the
gravity field, it was determined that the asteroid is

Other institutions on the MSI and NIS team are Northwestern
University, the Southwest Research Institute; Rensselaer
Polytechnic Institute, the U.S. Geological Survey, the
University of Hawaii, Malin Space Science Systems, the
University of Maryland, the Jet Propulsion Laboratory, and
the Applied Physics Laboratory, at Johns Hopkins
University, which designed and built the NEAR spacecraft
and manages the mission for NASA.

Other Cornell researchers on the team include Peter Thomas,
James Bell, Ann Harch, Maureen Bell, Brian Carcich, Beth
Clark, Jonathan Joseph and Colin Peterson. Steven Squyres,
professor of astronomy at Cornell, is an author of another
of the Science papers, "The Elemental Composition of
Asteroid 433 Eros: Results of the NEAR-Shoemaker X-ray

Related World Wide Web sites:

The following sites provide additional information on this
news release. Some might not be part of the Cornell
University community, and Cornell has no control over their
content or availability.

* Near Earth Asteroid Rendezvous


From Ron Baalke <>

PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011

Contact: Martha J. Heil (818) 354-0850

FOR IMMEDIATE RELEASE            September 21, 2000


Eros, the chunky asteroid named after the god of love, is
slowly revealing to scientists the mysteries of its size,
rotation and other properties.

Eros has been studied by the Near Earth Asteroid Rendezvous
(NEAR)-Shoemaker spacecraft since last Valentine's day when
a careful maneuver put the spacecraft in orbit around the
asteroid to determine its properties. Some of those
findings, such as Eros' mass and bulk density, appear in
the Sept. 22, 2000 edition of the journal Science in a
paper by principal author Dr. Don Yeomans of NASA's Jet
Propulsion Laboratory. Yeomans is the radio science team
chief for NEAR-Shoemaker. The journal also features three
other research reports on Eros.

Scientists have learned that Eros is most likely made of
rocky material with a uniform density throughout. The
asteroid's bulk density is similar to that of Earth's
crust. Like Earth, the surface of Eros is covered with a
layer of looser rock and soil.

Though it is about 6,700 trillion kilograms (14,700
trillion pounds) in mass, Eros is a fragment from the
breakup of a once larger asteroid. "It's a chip off a
larger block from millions of years ago," said Yeomans.

Eros is rotating around its shortest axis, making one
revolution every 5 hours and 16 minutes. As though thrown
in a tight spiral pass by some cosmic quarterback, Eros'
rotation axis appears to remain steady on its journey
through space. Because the asteroid is so much smaller with
much less gravity than Earth, it wouldn't take an Olympic
athlete to jump entirely off the surface into space.

Scientists were able to study Eros' rotation, mass
distribution and structure based on a series of
observations taken onboard the spacecraft. By photographing
the asteroid and measuring infrared light reflected from
it, scientists could determine its mass, detect minerals
and record its motion. As the craft edged into closer and
closer orbits around the asteroid, it took fresh data that
helped determine the asteroid's size, shape and mass
distribution. These activities were critical for navigating
the spacecraft in to tighter orbits about Eros so that
close-up images could be taken.

"If we didn't know the precise size, shape and mass
distribution of the asteroid ahead of time, it would not
have been safe to send the spacecraft to within a few
kilometers of the asteroid's surface," said Yeomans.

By the mission's end in February 2001, the total surface of
the asteroid will have been imaged and measured.

Johns Hopkins University manages the NEAR mission for NASA,
and JPL is performing navigation support. Bobby G.
Williams, also an author on the paper, is the navigation
team leader. For the latest images and announcements of
mission progress and discoveries visit the NEAR web site at .


From Michael Paine <>

Dear Benny,

There was another item of interest at the Nature website. A
copy is below. The first sentence is irritating for a
science journal. In the second paragraph "no evidence" can
(and probably does) mean nobody has looked! The 540AD issue
raised on CCNet the other day seems to indicate that
climate disruptions do occur without volcanic eruptions.

From the rough calcs I did on the AAAS simulation results,
"year without summer" type climate disruption is more
likely to be due to a volcanic explosion (average say once
per 2000 years compared with about once per 10 to 20,000
years for a significant impact). This is far from
dismissing impacts as a cause of climate disruption. Also
Duncan Steel reminded me that the impact frequency (as used
by John Lewis in his computer simulation) is based on a
random distribution in time but there is plenty of evidence
to suggest that some types of impact come in clusters -
such as due to the breakup of a comet.
Michael Paine

Earth : What a blast


While fashion tells us that Armageddon may descend from the
skies in the form of a giant meteorite impact, there may be
more to fear from the ground beneath our feet.

There is no evidence that meteorites have ever left a dent
on human civilization. But volcanic eruptions have provided
ample indication of their destructive potential. New
research in Geophysical Review Letters1 shows just how far
this disruption can reach: a massive eruption in Greece
three and a half millennia ago seems to have caused
environmental devastation even in Sweden.

Håkan Grudd from the Climate Impacts Research Centre in
Kiruna, Sweden and colleagues have studied the growth rings
in pine trees preserved in a peat bog in south-central
Sweden. They have used radiocarbon dating to determine the
age of the trees, finding that their samples grew during a
200-year period between 1695 and 1496 BC -- during the
Bronze Age.

The tree rings became abruptly very narrow around 1637 BC
(with an uncertainty of about 65 years in either
direction). The researchers conclude that this blip was
probably caused by harsher climate conditions at that time,
suppressing growth of fresh wood.

What could have instigated this disturbance? Several
earlier studies have uncovered evidence of a similar
phenomenon further south. An analysis of pine tree rings in
the USA showed that the growth had been severely affected
by cold in 1627 BC. The same thing was found in Irish,
English and German oaks, starting at just the same time.
And the same signature has been found in Turkey.

All the signs imply that there was some catastrophic event
in 1627/28 whose effects, the new work shows, were felt at
least throughout the entire western Northern Hemisphere.

Historians and climate scientists are fairly sure they know
the culprit. Some time around the middle of the 17th
century BC, the Santorini volcano on the island of Thera in
the Aegean Sea in Greece blew its top in one of the largest
eruptions of the past 10,000 years. This explosion was
considerably greater than that at Krakatoa in 1883, which
was equivalent to the detonation of 200 million tons of

The Santorini eruption released about seven cubic miles of
magma, and scattered ash over much of the eastern
Mediterranean and Turkey. It blasted a crater perhaps 80
square kilometres in area, and buried the Minoan city of
Akroteri, on the southern part of Thera, under about two
metres of ash. The damage wrought by the eruption is widely
thought to have caused the end of the Minoan civilization,
which centred on the island of Crete.

The volcanic dust holds the key to its longer-ranged
environmental impact -- for, injected into the upper
atmosphere in a plume perhaps 23 miles high, it would have
been carried right around the globe. Scattered in the air,
it would have blocked out some of the sun's light and heat,
triggering probably worldwide climate cooling.

A small drop in global mean temperature -- a few tenths of
a degree -- was detected after the eruption of Mount
Pinatubo in 1991. Larger eruptions have more severe
effects: the eruption of Tambora volcano in Indonesia in
1815 caused summer frost in New England and produced the
latest wine harvest since 1482. But it seems that the
Santorini eruption was even more terrible, prompting a kind
of mini-ice age lasting several years.

© Macmillan Magazines Ltd 2000 - NATURE NEWS SERVICE

From Yahoo! News, 21 September 2000

By LAURIE COPANS, Associated Press Writer

BEIT SHEMESH, Israel (AP) - Mohammed Sobhi looked out
across 800 square meters of solar panels absorbing sun
power to air-condition an Israeli office building. He
envisioned a similar system producing electricity in the
desert south of Cairo.

Sobhi, a senior official in the Egyptian Ministry of
Electricity and Energy, joined energy officials from the
United States and Japan on Wednesday as Israel-based Solel
Solar Systems switched on the power source it says will in
the coming days replace 70 percent of its own conventional
electricity needs.




From Jens Kieffer-Olsen <>

Dear Benny Peiser,

A brief follow-up to Michael Paine's letter on the British
Task Force Report: 

>From Michael Paine <>

>   The main conclusions of the report are:
> * Impacts by asteroids and comets present a real and significant risk to
>   humans and other life on Earth
> * Means now exist to avoid or reduce the fatalities caused by such
>   impacts but only if the threatening objects are detected
>   well in advance of the collision.
> * Search programs should give priority to "Near Earth
>   Asteroids" (NEAs) down to 300 m diameter rather than the
>   1 kilometer goal adopted by NASA.

While >300m asteroids present a global danger indeed, I
find it hard to believe that not all asteroids capable of 
producing blasts equivalent to hydrogen bombs 500 times
more powerful than Fat Boy are worthy of search programs. 
So, what is the actuarial cost associated with randomly
scattered 10 MT Tunguska-like detonations? Surely many of
them will cause only limited damage to human settlements,
but even if no lives are lost the economical and
environmental consequences of a hit tomorrow is bound to be
non-trivial regardless of impact coordinates.
Were the search program to include asteroids >50m its cost
would rise dramatically, since the effort of spotting and
tracking these 500,000 (?) smaller NEOs totally dwarfs the
task of mapping their 1,000 >1km cousins. Yet the cost of
actually deflecting a 50m object is many magnitudes lower
than that of nudging out of harm's way a 1km behemoth.

Unless the UK effort is proposed as mere windows dressing
its scope must include thoughts on how a follow-up in outer
space will take place. Even if that means relying on the
United States to launch an interplanetary missile, there is
no reason why the UK and other capable countries should not
accept the cost of mapping ALL small asteroids, leaving to
the US the decision whether or not in the end to deflect a
harmless impactor, i.e. harmless from a global perspective.

Jens Kieffer-Olsen, M.Sc.(Elec.Eng.)
Slagelse, Denmark


From James Oberg <>

The Bad Astronomer writes, CCNet 21/09/00:

<< Friction does initially heat them, but the outer parts
ablate away, leaving the relatively cool interior exposed
on impact. Once they reach terminal velocity, they cool as
they fall. >>

Actually, friction has nothing to do with it -- although
this is a common, careless, misconception. The source of
heat on an entering object is the shock compression of the
air piled up in front of it, which conducts its heat to the
object both by pure conduction as hot air moves across the
object (at subsonic speeds), and at higher entry
velocities, by radiation from the hot plasma. If it were
really air-on-material friction, how could space shuttle
glass-fiber tiles, that even a fingernail can crease and a
pencil-tap can break, survive during atmospheric entry?

James Oberg


From Joel D. Gunn <>

Dear Benny,

I was pleased, maybe relieved, to see 21 September 2000
note on a conference in Spain about solar influences on
climate. My first encounter with solar emissions and
climate was reading a 1937 report by a Travelers Insurance
Company research scientist on droughts in Texas. One of the
conclusions he reached was that the solar cycle appeared to
have an influence on the periodic drought in Texas. I lived
in Texas during the 70s and 80s and saw droughts come and
go, generally with the solar cycle. I also noticed that my
archaeology student's seemed to sunburn more severely
during the years of high solar emissions. I sponsored a
symposium on climate change that was published in a 1994
issue of Human Ecology. One of the contributors was John
Eddy who has a lifetime of encouraging people to think
about solar emissions; his research included information on
increases of melanoma during high solar cycles. Now we are
back around to severe drought in Texas and high solar
output. I think that J. Lean's study of sun-like stars is
extremely insightful in terms of detecting and estimating
long-period changes in solar emissions. It is healthy that
researchers are turning toward looking at the amplification
mechanisms of the sun's energy. I and a colleague (Gunn and
Folan 2000) have an article in a recent book analyzing the
discharge of three rivers in the Yucatan Peninsula viz
global parameters.  When analyzed with earth system
parameters, one of these rivers is influenced by changes in
solar emissions while the other two are not. The one that
is influenced has large pools of water, swamps, along its
course that act as solar collectors. I hope we hear more
about his conference.

Joel D. Gunn

Eddy, John A. (1994) Solar History and Human Affairs. 
  Human Ecology 22:23-36.
Gunn, Joel D. and William J. Folan (2000) Three Rivers: 
  Subregional Variations in Earth System Impacts in the
  Southwestern Maya Lowlands (Candelaria, Usumacinta, and
  Champoton Watersheds). In The Way the Wind Blows:
  Climate, History, and Human Action, edited by R.
  Mcintosh, J. Tainter, and S. Mcintosh,  pp. 263-270,
  Columbia University Press, New York.
  Lean, Judith, Andrew Skumanich, and Oran White (1992)
  Estimating the Sun's Radiative Output during the Maunder
  Minimum.  Geophysical Research Letters


From DISCOVER Vol. 21 No. 10 (October 2000)

20 Ways the World Could End

Swept away.

By Corey S. Powell

We've had a good run of it. In the 500,000 years Homo
sapiens has roamed the land we've built cities, created
complex languages, and sent robotic scouts to other
planets. It's difficult to imagine it all coming to an end.
Yet 99 percent of all species that ever lived have gone
extinct, including every one of our hominid ancestors. In
1983, British cosmologist Brandon Carter framed the
"Doomsday argument," a statistical way to judge when we
might join them. If humans were to survive a long time and
spread through the galaxy, then the total number of people
who will ever live might number in the trillions. By pure
odds, it's unlikely that we would be among the very first
hundredth of a percent of all those people. Or turn the
argument around: How likely is it that this generation will
be the one unlucky one? Something like one fifth of all the
people who have ever lived are alive today. The odds of
being one of the people to witness doomsday are highest
when there is the largest number of witnesses around- so
now is not such an improbable time.

Human activity is severely disrupting almost all life on
the planet, which surely doesn't help matters. The current
rate of extinctions is, by some estimates, 10,000 times the
average in the fossil record. At present, we may worry
about snail darters and red squirrels in abstract
terms. But the next statistic on the list could be us.

Natural Disasters

1) Asteroid impact. Once a disaster scenario gets the
cheesy Hollywood treatment, it's hard to take it seriously.
But there is no question that a cosmic interloper will hit
Earth, and we won't have to wait millions of years for it
to happen. In 1908 a 200-foot-wide comet fragment slammed
into the atmosphere and exploded over the Tunguska region
in Siberia, Russia, with nearly 1,000 times the energy of
the atomic bomb dropped on Hiroshima. Astronomers estimate
similar-sized events occur every one to three centuries.
Benny Peiser, an anthropologist-cum-pessimist (sic!) at
Liverpool John Moores University in England, claims that
impacts have repeatedly disrupted human civilization. As an
example, he says one killed 10,000 people in the Chinese
city of Chi'ing-yang in 1490. Many scientists question his
interpretations: Impacts are most likely to occur over the
ocean, and small ones that happen over land are most likely
to affect unpopulated areas. But with big asteroids, it
doesn't matter much where they land. Objects more than a
half-mile wide- which strike Earth every 250,000 years or
so- would touch off firestorms followed by global cooling
from dust kicked up by the impact. Humans would likely
survive, but civilization might not. An asteroid five miles
wide would cause major extinctions, like the one that may
have marked the end of the age of dinosaurs. For a real
chill, look to the Kuiper belt, a zone just beyond Neptune
that contains roughly 100,000 ice-balls more than 50 miles
in diameter. The Kuiper belt sends a steady rain of small
comets earthward. If one of the big ones headed right for
us, that would be it for pretty much all higher forms of
life, even cockroaches.

For 19 other ways to terminate your love-affair/s check:

MODERATOR'S NOTE: Now this is what I would call Chutzpah,
with a capital C: Corey Powell calls me a "pessimist" for
pointing out, at the last AAAS meeting in Washington, that
human societies have repeatedly been punctuated by cosmic
impacts. Given the physical evidence for minor and moderate
impacts during the Holocene, together with statistical
calculations based on the current asteroidal flux, this is
generally accepted - even by most of the most skeptical of
impact researcher. It is the rather speculative
consideration of what ecological and cultural effects the
known (as well as all the undiscovered) Holocene impact
events may have had, that remains controversial, and
rightly so.

At a time when environmental doom-and-gloom prophecies
are severely damaging the reputation of science in
general and science journalism in particular, I believe
that we need to look at our place in space from a more
blanced and less hysterical point of view. A skeptical
perpective might not be as popular as selling bad news, 
but it still may help us to develop 20 ways to make our
Earth a safer place.

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