CCNet 123/2000 - 28 November 2000

"The discovery of new strains of bacteria is practically a daily
event and does not constitute evidence for an extraterrestrial origin."
   -- Matthew Genge, The Natural History Museum, London, 27 November

"To claim an extraterrestrial origin, a microbe needs to be captured
hundreds (preferably thousands) of kilometers away from Earth by a
sterilized spacecraft."
      -- Andrew Glikson, Australian National University, 27 November

"With the rapid accumulation of data that goes generally in the
direction of supporting panspermia, the adoption of an intransigent
Earth-bound view of life would surely be a risky business!"
    -- Chandra Wickramasinghe & Sir Fred Hoyle, 27 November 2000



    NearEarth Net, 26 November 2000

    Ilan Manulis <>

    NASA Astrobiology Institute

    MSNBC News, 27 November 2000


    Matthew Genge <>

    Chandra Wickramasinghe & Sir Fred Hoyle <]

     Andrew Glikson <>

     Physics News <>


From, 27 November 2000

By Robert Roy Britt
Senior Science Writer

A group of scientists says it has collected an alien bacterium 10 miles
above Earth, plus signatures of other extraterrestrial microbes even higher
in the atmosphere. The claims were met with immediate skepticism by other

The bacterium was collected 10 miles (16 kilometers) high by balloon
operated by the Indian Space Research Organization. Chandra Wickramasinghe,
who leads a study into the results, called the microbe a previously unknown
strain of bacteria and said it likely came from a comet.

Wickramasinghe and a colleague, Fred Hoyle, say the findings support an idea
they pioneered, called panspermia, which holds that the seeds of life are
everywhere in space and are the source for life on Earth.

Matthew Genge, an expert on meteorites and cometary debris at London's
Natural History Museum, said he was flabbergasted by the claim.

"I don't believe the authors have provided the kind of evidence that would
be needed to support their claim," Genge said. "Their announcement appears

Genge, who does not rule out panspermia as a possibility, said nonetheless
that the supposed alien bacteria could have been previously unknown strains
of terrestrial bacteria.

"Hitherto unknown strains of bacteria are found virtually every day," Genge
told "If no one had ever seen or heard of an elephant and
suddenly one was discovered this wouldn't be evidence that it comes from

Wickramasinghe countered that procedures precluded the instruments aboard
the balloon from being contaminated on the ground or on the way up, but he
acknowledged the possibility of contamination at the point where the
collection was made.

"Earthly bacteria could get up to 15 kilometers from several sources,"
Wickramasinghe told "Also there is a chance that unknown strains
of bacteria were lofted from the heights of the Himalayas."

Wickramasinghe said his group wouldn't reveal details until the microbe is
studied further.

High-flying bacteria

Genge echoed the cautions of other scientists in saying that dust carrying
terrestrial bacteria had been found in found the collection filters of NASA
U2 aircraft doing similar research for 15 years.

"There is in fact enormous amounts of dust from the Earth's surface at high
altitude, both artificial and natural in origin, and some of it undoubtedly
carries bacteria," Genge said.

"Another possible form of contamination could also be human waste," Genge
said. "Passenger aircraft fly at 10 miles altitude and eject human waste
into the atmosphere. A fine spray of such liquid released into the
atmosphere at high altitude will form tiny ice grains containing bacteria
these will become widely dispersed."

NASA also commented on the claim, pointing out that living spores have been
found previously as high as 10 miles.

"While NASA's astrobiology effort has certainly not come down on the side of
panspermia, it has identified panspermia as worthy of serious investigation,
along with more conventional ideas about the origin of life on Earth," said
a press release out of NASA's Ames Research Center.

Other scientists also urged caution in interpreting the results. Meanwhile,
recent studies by other groups have boosted panspermia into the spotlight,
and many leading researchers are warming to the idea that microbes may be
hardy enough to endure the rigors of space travel.

More evidence of alien microbes

Wickramasinghe and his colleagues, based at the recently formed Cardiff
Centre for Astrobiology in Wales, also studied data from a 1999 Leonid
fireball, collected at 52 miles (83 kilometers) altitude. The original study
on this data, produced by a team led by Ray Russell of the Aerospace
Corporation, found organic compounds indicating that the building blocks of
life could have survived a trip from space to Earth.

Working with the Leonid fireball data in a separate study, the Cardiff team
concluded that the fireball actually did contained a signature of microbes
that rained down from space. The study analyzed the infrared light emitted
by the fireball, which the researchers say showed signs of burning bacteria.
Further, they say this signature resembled the infrared spectra of comet

"There is little chance if any of Earthly bacteria resident at such great
heights," Wickramasinghe said.

But Genge flatly refuted the group's analysis of the Leonid fireball data.

"The infrared spectra of the Leonid meteors are not evidence for bacteria,
nor are the infrared spectra of comets," Genge said. He added that the data
show a feature that is common in all organic material.

"If you took me, put me in an oven, dried me at 300 degrees and then took my
infrared spectra, I'd have (this feature) too. This would certainly not be
evidence that you'll find Matt Genges on comets.

The whole debate is reminiscent of claims of microscopic fossils in a
meteorite from Mars, reported by NASA scientists in 1996. Scientists are
still debating that finding.

Copyright 2000,


Circular No. 7526
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138,
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)


On Nov. 19, S. Nakano, Sumoto, Japan, reported the visual discovery on Nov.
18 by Syogo Utsunomiya (Aso, Kumamoto; 25x150 binoculars) of a possible
comet with coma diameter 5' moving
rapidly southeastward in Vela. Attempts by several observers (including A.
Hale, D. Seargent, J. Biggs, T. Urata, and J. Kobayashi) to confirm the
object, at the request of Nakano and the
Central Bureau, were unsuccessful.  On Nov. 25, A. C. Gilmore (Mount John
University Observatory) reported the visual discovery of an apparent comet
by Albert F. Jones (Nelson, New Zealand,
0.078-m f/8 refractor, 30x) while observing the variable star T Aps at dawn;
Jones reported the comet as being diffuse with coma diameter about 4' in
morning twilight. The possibility that Jones' object might be the same as
that reported by Utsunomiya was explored by the Central Bureau, and a search
ephemeris from plausible parabolic orbital elements fitted to the Nov. 18
and 25 approximate positions was circulated to numerous southern-hemisphere
observers.  Confirming CCD astrometry was made by Gilmore with the 1.0-m
f/7.7 reflector at Mt. John.

     2000 UT             R.A. (2000) Decl.        m1    Observer
     Nov. 18.817      9 04.0       -41 22        8.5    Utsunomiya
          18.833      9 04.2       -41 27        8.5       "
          18.847      9 04.4       -41 31        8.5       "
          25.64      13 49.8       -77 05        8      Jones
          26.42295   15 36 22.31   -76 23 51.5          Gilmore
          26.42506   15 36 37.51   -76 23 31.7            "
          26.42772   15 36 57.31   -76 23 05.1            "
          26.42998   15 37 13.94   -76 22 43.8            "
          26.55906   15 52 38.76   -76 00 58.0            "
          26.56010   15 52 46.20   -76 00 47.4            "
          26.56126   15 52 54.24   -76 00 34.8            "
          26.56207   15 52 59.84   -76 00 25.6            "

The following preliminary parabolic orbital elements by B.G. Marsden are
heavily weighted toward the Mt. John accurate positions:

     T = 2000 Dec. 26.56 TT           Peri. =  51.52
                                      Node  =  10.81    2000.0
     q = 0.3214 AU                    Incl. = 160.16

                      (C) Copyright 2000 CBAT
2000 November 26               (7526)            Daniel W. E. Green


From NearEarth Net, 26 November 2000

By Mark Kidger

On November 18th a Japanese amateur astronomer found a moderately bright
comet with 25x150 binoculars. Syogo Utsunomiya said that the comet was
magnitude 8.5 and moving rapidly, indicating that it was close to the Earth.
Utsunomiya is not a beginner in this as he had already discovered the
moderately bright Comet C/1997 T1. A whole series of very experienced
observers tried to confirm the discovery and failed. This is not actually an
unknown situation as some comets move so fast that they can be extremely
difficult to relocate, particularly when close to Earth so that parallax may
even shift the comet significantly for one observer with respect to another.

Then, at dawn on November 25th, a New Zealand amateur astronomer, Albert
Jones, saw what appeared to be a comet in the field of the variable star T
Aps when observing with his 3-inch reflector. Jones is a reputable comet
observer and was well-prepared for this moment even though he had never
discovered a comet himself. Even though Jones's comet was some 90 degrees
away from the one seen by Utsunomiya, it was immediately suspected that they
might be one and the same.

The following morning, Mount St. John observatory in New Zealand recovered
the comet using an ephemeris prepared assuming that the two comets were one
and the same. In just 18 hours, it had moved another 6 degrees.

At present there are just three positions for the comet and only one of
those - the Mount St. John confirmatory CCD observation - is an accurate
position. The very rough orbit suggests though that this comet is unusually
close to the Earth and will reach perihelion at the orbit of Mercury.
According to this orbit, closest approach was 0.280AU (41 million
kilometres) on November 25th. The comet is expected to reach perihelion
around midday on Boxing Day - December 26th - at 0.32AU (48 million
kilometres) from the Sun.

By mid December the comet should be slightly brighter than magnitude 7,
having brightened only slightly from its current magnitude 7.5. Although
currently near the South Pole, it will rise rapidly in declination a s it
approaches perihelion and will be north of the Sun in mid-December and
observable from the northern hemisphere. However, additional observations
may change this orbit substantially and, almost certainly will change it.

However, this is a very small and diffuse object. Its absolute magnitude is
estimated to be 10.5 - this would be its theoretical brightness when
simultaneously at 1AU from the Sun and the Earth. This is nearly 50 times
fainter than an "average" new comet and 400 times fainter than Comet Halley.
Such comets often fail to even reach perihelion, let alone survive it. My
best guess is that the comet will probably disappear before perihelion
unless we are unusually lucky. This doesn't mean a LINEAR-type fragmentation
- such disappearances usually involve a comet getting larger and diffuser
until it finally fades out of sight. Comet C/1997 N1 (Tabur) had an
identical absolute magnitude and just vanished four weeks after discovery
and well before reaching perihelion at almost the same distance from the

MODERATOR'S NOTE: I wish to make one correction to Mark's report: I
understand that Albert Jones actually has been credited with the discovery
of a comet before. He discovered a comet in August 1946, and in being
credited with comet discoveries more than 54 years apart, he has broken a
new record. Furthermore, at the age now of 80, be seems to be the oldest
person credited with the discovery of a comet, the previous age record being
held by Lewis Swift, who was 79 when he found his last comet in 1899.
Congratulations, Albert!


From Ilan Manulis <>

Dear Benny,

I think the information provided in the following Web page might interest
the readers of CCNet. It portraits a possibility that life, in its most
primitive form, might have existed even during the Late Heavy Bombardment
period (between 4.1 and 3.8 billion years ago).

Best regards,

Ilan Manulis

Chairman, Solar System Small Objects Section
The Israeli Astronomical Association


From NASA Astrobiology Institute

No-one knows when life first established a firm foothold on Earth. Ask
around in the scientific community, though, and you'll probably hear that
the surface of early Earth, before about 3.8 billion years ago, was too
hostile an environment for even a lowly microbe to set up shop.

The main problem, as the conventional argument goes, was that between around
4.1 and 3.8 billion years ago, Earth was constantly being bombarded by
comets and asteroids. The disastrous effects of these impacts would have
rendered the Earth's surface uninhabitable.

Not necessarily so, say a team of astrobiologists who are studying the
oldest known sedimentary rocks on Earth. They have come to the conclusion
that conventional wisdom on the subject may need some revision. Their
conclusions will be published in a forthcoming issue of the Journal of
Geophysical Research.

The rocks in question appear to be a banded iron formation, or BIF, from
Akilia Island in West Greenland. BIFs were deposited on Earth's ocean floors
during the first 2 billion years of the planet's history. Iron and oxygen
present in the oceans combined to form rust, which settled to the sea floor
in layered sediments. Movements of the Earth's crust later pushed some of
these sediments to the surface, where they can now be studied.

It's not possible to date the Akilia BIF sediments directly because they
have undergone metamorphism - pressure cooking - so that traditional
radioactive dating techniques cannot be used to determine their age. But
jutting into these sediments are younger igneous rocks that can be
accurately dated with these techniques.

An earlier analysis of this igneous rock, performed by a group headed by Dr.
Allen Nutman of the Australian National University, put its age at 3.85
billion years. And because the igneous rock intrudes into the banded iron
formation, it must have formed later than the sediments did. So the Akilia
sediments must have been formed at least 3.85 billion years ago. Exactly how
old they are, there is no way to know. But they are more ancient than any
other sedimentary rocks found so far on Earth.

Rocks this old are rare on Earth because tectonic recycling action has
crushed, buried and melted all of the material that formed the Earth's crust
during its first half-billion years of existence. Finding sedimentary rocks
this old is important to geologists because they provide invaluable clues
about what Earth was like in its early years.

Few people dispute the notion that between 4.1 and 3.8 billion years ago,
our planet was heavily bombarded by debris from space, a period known as the
Late Heavy Bombardment. If you look up at a full moon on a clear night, you
see that its surface is riddled with impact craters. Scientists who study
the size and distribution of those craters see clear evidence that the Moon
underwent an intense period of impacts between 4.1 and 3.8 billion years
ago. Although no craters from this time remain on Earth, because the Earth
and Moon are so near each other, the assumption is that Earth suffered a
similar fate.

Ariel D. Anbar, an Assistant Professor in the Department of Earth and
Environmental Sciences at the University of Rochester, working with Gail L.
Arnold, a graduate student, decided to look for traces of this bombardment
in the Akilia sediments. Comets and asteroids contain greater quantities of
the chemical element iridium than does the Earth's crust. So Anbar and
Arnold, members of the NASA Astrobiology Institute (NAI), probed the Akilia
sediments for abnormally high traces of iridium.

They didn't find them. "Our naive expectation going in," explained Anbar,
was that "these sediments date from this bombardment period, so we should
see evidence of the bombardment in them, right? So we looked for iridium in
these rocks and didn't find any. They were clean as a whistle."

But earlier study of the Akilia sediments by one of Anbar's collaborators,
Steve Mojzsis, had turned up a very different type of signature in the
Akilia formation - a signature of biological activity. Mojzsis, also a
member of the NAI, performed his analysis of the Akilia sediments while at
the University of California San Diego.

Carbon atoms come in two distinct forms, or isotopes. Carbon-12 atoms, the
lighter of the two, contain 6 neutrons; carbon-13 atoms contain 7 neutrons.
Microorganisms that take in carbon dioxide prefer to use the lighter
carbon-12 atoms to construct the organic building blocks of which they are

When ancient ocean-dwelling organisms died, the carbon that was formerly
part of their living tissue settled to the ocean floor, becoming part of the
sedimentary material deposited there. When Mojzsis found that the Akilia
sedimentary rock samples contained higher-than-normal quantities of
carbon-12, he concluded that biological activity must have been taking place
at the time the sediments were formed - at least 3.85 billion years ago.

So Anbar, Arnold and Mojzsis were faced with seemingly contradictory
evidence. Life appeared to have been flourishing during the period of the
Late Heavy Bombardment, at a time when Earth's surface was thought to be
uninhabitable. And traces of the bombardment were nowhere to be found in the
Akilia rocks.

The solution lay in quantifying more carefully the effects of bombardment,
using models developed by NAI member Kevin Zahnle at the NASA Ames Research
Center. The essence of these models is that they treat the bombardment as a
series of impact episodes, rather than assuming continuous pummeling of the
Earth. They also take into account that smaller impact events are far more
common than larger ones.

The Akilia sediments would not be expected to contain telltale traces of
extraterrestrial iridium unless a massive asteroid had slammed into the
Earth, spewing iridium into the global environment, precisely during the
period when the Akilia formation was being deposited. Zahnle's models
indicate, however, that even during the Late Heavy Bombardment, such massive
impacts were rare - too rare for there to be much chance of seeing their
signs in sediments like those found on Akilia Island. So it made perfect
sense that the sediments didn't contain elevated levels of iridium.

Anbar and his colleagues reason that if the bombardment had a
smaller-than-expected effect on the composition of sediments, it may also
have had a smaller-than-expected effect on early life. Although small
impacts were more common during the Late Heavy Bombardment than at any time
since then, each such impact would destroy life at the surface only in one
small area, not globally. Only the rarest, most massive impacts had the
potential to wipe out all life on the planet's surface.

Zahnle's models indicate such impacts occurred only once every ten to one
hundred million years. Moreover, the worst of their effects lasted for only
about ten thousand years, after which time conditions on the Earth's surface
returned to normal. "So during most of this violent period of Earth's
history," says Anbar, "the Earth's surface - if you're a microbe, anyway -
was a perfectly balmy place to be. Which runs contrary to this picture that
is out there that this was a very inhospitable period of time for life."

That still leaves open one important question: Where could life hang out in
safety during those rare, massive impact events that caused the surface
literally to boil away? One suggestion is that hydrothermal vents might have
filled that role. If life migrated down to these vents - or perhaps even
began there - it could have continued on during major impact events,
oblivious to what was going on the surface. And when the environment topside
returned to habitability, life could have moved back up and recolonized the

"So as long as microorganisms had places on the Earth where they'd be
sheltered from really massive impact events," concluded Anbar, "there's no
reason that they couldn't have repopulated the surface multiple times. And
therefore there's no reason not to expect to find evidence of life if you
find sediments from the earth's surface during the period of heavy


* Radioactive dating techniques are explained about halfway down the
Web page, "Solar System Fluff."  
* For an introduction to crater-counting techniques
* Information about life in deep-sea  hydrothermal vents
* Stephen J. Mojzsis's research, which detected signs of ancient life
in the Akilia sediments
* For a look at the instruments and laboratories used by Ariel D.
Anbar and Gail L. Arnold to measure iridium in the Akilia sediments

From MSNBC News, 27 November 2000
Nov. 27 -  New images from the orbital camera aboard NASA's Mars Global
Surveyor have documented the change of seasons on Mars, with eerie patches
of frost within craters in the north and south.   

IT IS SPRING in Mars' northern hemisphere, and the frost that accumulated
during the most recent six-month-long winter has been retreating since May.
The examples of frost-rimmed craters include Lomonosov and an unnamed crater
farther north.

The unnamed crater has a patch of frost on its floor that is expected to
persist through the Martian summer, based on how it looked during the 1970s
Viking missions. Meanwhile, it's autumn in the southern hemisphere, and
frost was seen as early as August in some craters. Later in the season, the
southern frost line crept farther north, and a dusting of frost began to
appear in Lowell Crater in mid-October.



Call for abstracts for the Mineralogical Society Spring Meeting "Mineral
particules and the Environment", Kingston, Surrey, April 19-20th, 2001.

This meeting will include a session on the effects cosmic and volcanic dust
on the terrestrial environment. Papers on climatic change caused by cosmic
and impact-related dust are particularly encouraged. Selected papers from
the meeting will form the basis of a mineralogical society special

Abstract deadline: 31 Jan, 2001.

For more information see the meeting website at To
discuss your abstract before submission contact Matthew Genge, The Natural
History Museum 



From Matthew Genge <>

Dear Benny,

There are three reasons why the recent unpublished data of Wickramasinghe
and Hoyle (CCNET, 27 Nov 2000) do not represent evidence for the presence of
bacteria on cometary dust in the atmosphere.

(1) Contamination during balloon collection.

Even though contamination can be avoided during preparation and launch it
cannot during collection of dust particles at altitude. In the collections
of dust on inertial impactors mounted on U2 aircraft (flown at 20 km) the
majority of particles are terrestrial in origin (both natural and
artificial). Some of these particles will carry terrestrial bacteria and
will definitely be collected along with cosmic dust at altitude.
Contamination by terrestrial materials is thus unavoidable. NASA abandoned
the collection of cosmic dust particles in preference to U2 aircraft in the
mid 1970s because of the higher yields and lower contamination from the
collection vehicle that the U2's offer.

Commercial passenger aircraft also fly at altitudes ~11 km and eject human
waste. This is an excellent means of introducing aerosols containing
bacteria at high altitude.

(2) Nothing new in new bacteria.

The discovery of new strains of bacteria is practically a daily event and
does not constitute evidence for an extraterrestrial origin.

(3) The 3.4 micron band in infra red spectra.

Bacteria do show a 3.4 micron feature in the infra red, so do many other
things including the abiotic macromolecular carbonaceous materials found in
cometary dust particles collected by NASA in the atmosphere. The presence of
this band in the infra red spectra of comets and the leonid meteors is thus
merely evidence for the presence of organic compounds with appropriate C-H
bonds not bacteria.

Matthew Genge
The Natural History Museum, London, UK.


From Chandra Wickramasinghe & Sir Fred Hoyle <]

Dear Benny:

We cannot respond in detail to (1) and (2) of Matthew Genge's comment
because the details are still under embargo. On point (3) the relevant
question is how one could have organic dust that mimics the 3.4 micron
profile of a bacterium in the material around the persistent meteor trail.
A similar question relates of course to the detection of 3.4 micron
bacterial features in cometary and interstellar dust. In these latter cases
we have argued in extenso that the simplest way to account for the fact that
nearly one third of the carbon in interstellar space is tied up in the form
of particles that are spectroscopically indistinguishable from bacteria, is
to invoke well-attested processes in biology (eg replication) rather than
some ill-defined chemical processes. It is in such a much broader cosmic
context that we attempted to model the Leonids data, which of course would
not be easily understood by a person ideologically antagonistic to

With the rapid accumulation of data that goes generally in the direction of
supporting panspermia the adoption of an intransigent Earth-bound view of
life would surely be a risky business!

Yours sincerely

Chandra Wickramasinghe
Fred Hoyle


From Andrew Glikson <>

Dear Benny,
I refer to recent "news" (CCNet 27.11.2000) purporting to claim the capture
by a scientific balloon of an "extraterrestrial bacteria" some 16 km high in
the stratosphere. The following comments may be relevant, with full respect
to proponents of the panspermia theory:
1. Unsterilised rockets and satellites, as well as scientific and weather
balloons, routinely pass through stratospheric and higher altitudes,
inevitably contaminating the stratosphere and outer space. A small fraction
of the finest grained terrestrial carbon soot can also rise to significant
altitudes, conceivably carrying microbes. To claim an extraterrestrial
origin, a microbe needs to be captured hundreds (preferably thousands) of
kilometers away from Earth by a sterilized spacecraft.
2. It is claimed that the bacteria is "unlike any known strain on Earth",
but I am unaware of any molecular biological evidence regarding this
absolutely critical point. To date only a small part of terrestrial microbe
species have been identified and classified. To substantiate an
"extraterrestrial" claim, the microbe will need to be shown to be distinct
from known terrestrial microbes in some fundamental sense, for example if
its nucleic acids and proteins show different structural symmetry
(chirality) such as distinguishes meteoritic from terrestrial amino acids
(Zhao and Bada, 1989).
3. Since microbe spores are known for their remarkable resilience under a
range of pressure, temperature, pH and radiation conditions - which is the
very basis for the panspermia hypothesis of their space transport - why
can't such microbe spores be released from the Earth surface for as short
distances as 16 km upward? After all - the microbes have to be originally
released from SOMEWHERE (i.e. another planet? or a comet?) - why not from
4. According to Okham's Razor principle - central to scientific research -
while working hypotheses can always be entertained, where a simpler
explanation (one invoking fewer unknown variables) exists for an observation
it is to be preferred to a novel explanation - at least until clear evidence
emerges. To claim an extraterrestrial origin of a 16 km-high bacterium is,
in principle, no different than claiming that nanobacteria which have
actually been documented in drill cores several kilometers beneath the Earth
surface (e.g.. Uwins et al., 2000) are derived from the Earth's mantle ...!
"Extraordinary claims require extraordinary evidence" (Carl Sagan). 
Andrew Glikson
Canberra, ACT 0200


From Physics News <>

PHYSICS NEWS UPDATE                        
The American Institute of Physics Bulletin of Physics News
Number 513 November 22, 2000  by Phillip F. Schewe and Ben Stein         

THE INTERNET IS SURPRISINGLY ROBUST, and it remains connected on a global
scale even if a randomly chosen 99% of its connection points break down.
However, it is relatively fragile if
its most highly connected points are selectively  knocked out. These are the
conclusions of researchers applying physics principles and precise
mathematical models to the study of the
worldwide computer network. The Internet consists of computer networks (most
commonly, "local area networks") connected by various devices, known as
routers and hubs. For simplicity's sake,
researchers consider each connection point as a generic "node." Previous
work suggests the fraction of Internet nodes having k connections is
proportional to k^-a, for some number a.  This is a "scale-free power law
distribution," which occurs commonly in nature and appears in the frequency
of earthquakes and the size distributions of clouds and mountains. Unlike an
exponential distribution, a scale-free power law distribution decays very
slowly, meaning in this case that there is a large proportion of computers
that still have a significant amount of connections. Recent computer
simulations of scale-free networks have shown that the Internet is resilient
for this reason (Albert et al., Nature, 27 July; Albert-Laszlo Barabasi,
Notre Dame, 219-631-5767,; see also The Industrial Physicist,
December 2000). The latest work now puts this conclusion on a firm
mathematical footing. Two independent groups (Reuven Cohen, Bar Ilan
University, Israel, 011-972-8-9370131,; Duncan
Callaway, Cornell, 607-255-9174; apply percolation theory,
developed by geophysicists interested in estimating how much oil they could
extract from reservoirs in a porous medium. Percolation theory deals with
systems containing points ("sites") and connections between them, and it
analyzes the behavior of the system when one removes some of the sites or
connections. Combined with the insights from the scale-free distribution,
the powerful percolation-based approach may help Internet architects to
maximize resistance against Internet attacks, by controlling the
distribution of nodes having certain numbers of connections. (Cohen et al,
Phys. Rev. Lett, 20 Nov (Select Articles); Callaway et al., Phys. Rev.
Lett., upcoming.)

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