CCNet 2/2001 - 4 January 2001
"Part of the team that last September presented the government with
a report on "near-earth objects", Sir Crispin said the incident
underlined the importance of one of the taskforce's recommendations:
increased spending on a telescope allowing more accurate monitoring of
space. "We only heard about this asteroid two to three days in advance,
which would not have given us much time to take action if an impact
was imminent," said Sir Crispin, chancellor of the University of
Kent. "The first problem is identification. Finding an object this size in
space is not easy. We need to be watching the skies far more closely."
-- Michela Wrong, The Finanical Times, 3 January 2001
(1) ASTEROID WAS A 'TINY STEP' AWAY
Financial Times, 4 January 2001
(2) SIR CRISPIN TICKELL: "ASTEROID COULD HIT EARTH ANY TIME"
Ananova, 3 January 2001
(3) ASTEROID LANDING DRAWS NEAR
Space.com, 3 January 2001
(4) MIND YOUR HEAD - FALLING ROCKS
The Times Higher Education Supplement, 29 December 2000
(5) SIZZLING SKIES
New Scientist, 4 January 2001
(6) NEW JOURNAL: NATURAL HAZARDS AND EARTH SYSTEM SCIENCES
Duncan Steel <D.I.Steel@salford.ac.uk>
(7) GOOD NEWS FOR PLANETARY DEFENSE: ISRAELI RESEARCHERS FOCUS ON EXOTIC
NUCLEAR FUEL THAT COULD
SPEED UP SPACE TAVEL AND NEO DEFLECTION MISSIONS
Science Daily, 3 January 2001
(1) ASTEROID WAS A 'TINY STEP' AWAY
From Financial Times, 4 January 2001
By Michela Wrong
As television viewers shuddered this week at the sight of a fictional
meteorite destroying civilisation, few will have been aware that we had all
narrowly escaped first-hand experience of a real "deep impact".
An asteroid that streaked across the skies over Christmas missed earth by
only 769,900 kilometres, a "tiny step" in cosmic terms, an expert said on
"The asteroid was 50 metres in diameter, so its impact would have been the
same order of magnitude as the meteorite that hit Siberia in 1908," said Sir
Crispin Tickell, who later addressed a Royal Geographical Society
"If that Siberia meteorite had hit London or Tokyo, there wouldn't have been
very much left."
Part of the team that last September presented the government with a report
on "near-earth objects", Sir Crispin said the incident underlined the
importance of one of the taskforce's recommendations: increased spending on
a telescope allowing more accurate monitoring of space.
"We only heard about this asteroid two to three days in advance, which would
not have given us much time to take action if an impact was imminent," said
Sir Crispin, chancellor of the University of Kent.
"The first problem is identification. Finding an object this size in space
is not easy. We need to be watching the skies far more closely."
While the statistical risk of being killed by an asteroid was one in 25,000,
not much greater than the risk of dying in an aeroplane crash, the
difference was that an eventual impact in a highly populated area would have
a huge death toll.
Warning against complacency, Sir Crispin said most governments were better
prepared for a large nuclear accident than they were for an impact from
The government has yet to respond to the taskforce report, which discussed
methods of avoiding a repeat of the impact believed to have killed off the
These ranged from using spacecraft to nudge the asteroid gently off course
to erecting solar panels that would work like sails and the approach adopted
in the film Deep Impact, in which the asteroid was blown apart in a nuclear
"This is not a fantasy," said Sir Crispin. "We are the only animal species
which would have this amazing capability within its grasp."
Copyright 2001, Financial Times
(2) SIR CRISPIN TICKELL: "ASTEROID COULD HIT EARTH ANY TIME"
From Ananova, 3 January 2001
Huge asteroids could hit Earth at any time, says expert
An academic has warned that a US citizen is more likely to die from an
asteroid impact than from floods.
Sir Crispin Tickell told delegates at a conference in Plymouth that an
asteroid impact with Earth could happen at any time but governments are
better prepared for a nuclear war.
He said the probability of dying in an aircraft accident was one in 20,000,
from an asteroid impact one in 25,000, from a flood one in 30,000 and from
food poisoning one in three million.
The Chancellor of the University of Kent presented a paper called
Catastrophes from Space: Prospects for Planetary Defence to the Royal
Geographical Society's annual conference.
He highlighted the Chicxulub event of 65,000 million years ago when an
object 10km in diameter hit the earth, creating a dust cloud which reduced
temperatures, then led to a rapid greenhouse effect and so led to the demise
of the dinosaurs.
"Fortunately such major events are extremely rare. But they have occurred at
very roughly 100 million-year intervals throughout the history of the earth
and could, at least in theory, happen at any time."
He suggested no object over 1km in diameter was likely to hit earth within
the next 50 years but warned impacts from smaller objects could still have a
Sir Crispin was part of the Taskforce on Potentially Hazardous Near Earth
Objects which has presented its findings to the Government and is now
awaiting a response. He said they had concluded a greatly improved
telescopic network could predict extra-terrestrial events and a national and
international response was needed.
"This is not a fantasy of such films as Deep Impact or Armageddon," he said.
Copyright 2001, Press Association
(3) ASTEROID LANDING DRAWS NEAR
From Space.com, 3 January 2001
By Leonard David
WASHINGTON -- NASA has okayed a February 12 controlled descent of the Near
Earth Asteroid Rendezvous (NEAR) spacecraft onto the dust-laden, cratered
and boulder-strewn surface of Asteroid 433 Eros.
Ground controllers hope to fire spacecraft engines just prior to hitting the
space rock, perhaps allowing NEAR to briefly bounce off Eros, relay
last-minute science data, then plop itself down at a final resting spot.
The spectacularly successful NEAR Shoemaker probe has been orbiting Eros
since February 14, 2000. Since it began looping the tumbling space rock
almost a year ago -- at a range of high and low altitudes over Eros -- the
craft has amassed an asteroid photo gallery made up of 150,000 snapshots.
Later this month, NEAR is set to make daring flybys of Eros. Pictures
clicked during the maneuvers will show the greatest detail to date of
various features on the celestial hunk.
"Everything continues to go swimmingly," said Robert Farquhar, NEAR mission
manager at the Johns Hopkins University Applied Physics Laboratory (APL) in
Laurel, Maryland. "Right now, NEAR is doing just fine," he told SPACE.com.
APL designed, built and is managing the NEAR mission for NASA.
Now being orchestrated is a progression of low-altitude flybys of Eros by
The spacecraft is set to zoom down between January 24 and 28, skimming over
the ends of the asteroid as it somersaults through space. NEAR may get as
close as about 1.6 miles (2.5 kilometers) above the asteroid's surface,
Last October, NEAR whisked by Eros at approximately 3 miles (5.3 kilometers)
above its surface, shooting over the asteroid at about 14 miles per hour (6
meters per second).
"What we have seen so far in the low orbits has merely whetted our appetite
for more," said Andrew Cheng, NEAR project scientist at APL. "We went up
close to have a better look at the surface than ever before, but we now see
things we do not understand, and we need more information," Cheng said.
Swoop and bounce
NEAR's finale on February 12, swooping down and striking Eros, should give
scientists photos that are 10 times better in resolution than anything
received. Images from only 1,640 feet (500 meters) above the asteroid's
surface are expected.
By firing NEAR's rocket engines just before making asteroid contact, at a
speed of 7 miles per hour (3 meters per second), the craft may hit, then
bounce off Eros. Spacecraft cameras are to be busy during the risky
controlled landing, the world's first touchdown on an asteroid.
"But the uncertainty is pretty large. Who knows what NEAR will do," Farquhar
said. "Even if it's a crash landing...it's a first landing," he said.
NEAR was not built to be a lander. The spacecraft's set of delicate solar
arrays and other hardware will likely succumb to any hard-hitting arrival.
Scott Murchie, NEAR science team member at APL, said that landing on Eros is
gravy, contrasted to the rich bounty of data already gleaned.
"To be honest, with 150,000 images, nobody has had the chance to look at all
of them in detail. We're constantly going back and discovering interesting
details in images that we've taken months ago," Murchie said.
"One thing we've found is that the surface layer is unexpectedly complex,"
Murchie said. That surface covering, called regolith, is not dotted with as
many smaller craters as expected, he said.
Furthermore, the regolith appears relatively mobile, Murchie said, moving
about like a fluid and has "ponded" in certain areas. "So there's a
complicated geological story in the very small-scale surface features," he
For Cheng, having more mysteries than answers simply means more work ahead.
"Perhaps it will not be us, but some future scientists, who will unravel
some of the mysteries we are studying. In any case, we are working hard to
understand the surface of Eros," Cheng said.
Copyright 2001, Space.com
(4) MIND YOUR HEAD - FALLING ROCKS
As 2001 nears, Arthur C Clarke warns Earthlings against space invaders
during the coming century
From The Times Higher Education Supplement, 29 December 2000
Shoemaker by Levy: The Man Who Made an Impact
By David H Levy
Princeton University Press, 303 pp, £17.50
Thanks to one of the most remarkable events in the entire history of
astronomy, the names Shoemaker and Levy are now inextricably linked. When
comet Shoemaker-Levy 9, named after its co-discoverers Eugene Shoemaker
and David Levy, crashed into Jupiter in the summer of 1994, it immortalised
them -and reminded humankind that their planet could just as easily be bombarded
Unlikely as it now seems, until this century few scientists believed there
could be any direct contact between Earth and the celestial sphere.
President Jefferson famously remarked after hearing reports of a meteorite
fall: . "I would rather believe that two Yankee professors lied, than that
stones fell from the sky." Well, now we know that mountains can fall from
the sky, and Shoemaker was the first to prove this awesome fact beyond
David Levy's book has three main themes - biography, geology and astronomy -
neatly intertwined in a triple helix. One strand is devoted to his progress
from amateur stargazer to professional comet hunter: no trade union would
tolerate the exorbitant hours and the miserable pay, but if you are lucky,
the outcome can be immortality in the heavens. Levy now has more than 30
comets bearing his name.
Shoemaker became interested in comets by a more roundabout route, through
studying the numerous craters scattered over the face of the Earth -and later the Moon.
At one time he had hoped to become an astronaut, but when medical problems
ruled that out, he was able to playa key role in creating the new science of
lunar geology. (Oh, very well - selenology.) He left the Apollo programme to
become chairman of the California Institute of Technology's division of
geological and planetary sciences -while the lunar missions were still under
way, and at the start of the planning for major planetary missions. Levy
describes how Shoemaker tried to balance teaching and research work with
administrative responsibilities; the latter sometimes suffering from his
abundant enthusiasm for the former. With a combination of fascinating
insights into the Earth's past and a fondness for field investigations, he
inspired a whole generation of geologists who have been at the forefront of
planetary exploration for three decades.
Shoemaker's favourite field visits were to the Grand Canyon and the Meteor
and Sunset craters, where he showed students the Earth's geology at its
best. It had, of course, been known for millennia that volcanoes would
produce splendid craters of all shapes and sizes. When the telescope was
invented it was immediately observed that the Moon was covered with craters,
and although many of them were far larger than any on Earth, it seemed
reasonable to assume that they too were volcanic. Moreover, the so-called
lunar seas could best be explained as vast outpourings of lava. There
appeared no need to look for any other explanation - once he Moon, or on the
Earth. Nasmyth and Carpenter's classic The Moon (1874), with its beautiful
photo-replicas of lunar landscapes modelled in plaster, said the last word
on the matter for almost a century: 'There is a feature in the majority of
the ring-mountains... that seems to stamp the volcanic character upon the
crater-forms. This special feature is the central cone, so well known as
characteristic of terrestrial volcanoes."
Nevertheless, there were always a few heretics who pointed out some problems
with this theory and advanced explanations of their own - some perfectly
Perhaps the most popular alternative was the one that we now know to be
correct: that they were caused by impacts from space. Yet to many, this
theory appeared to have one obvious and fatal defect. As one astronomer put
it, echoing Nasmyth and Carpenter: "The presence of central peaks completely
rules out the meteoric hypothesis."
The debate was still raging when Percy Wilkins and Patrick Moore published
their own authoritative volume The Moon in 1960. They concluded that "there
is a remote possibility that the Maria may have been formed by the impact of
large meteors, but it is certain that the origin of the vast majority of the
lunar cavities cannot be so explained, and the volcanic theory seems to
correctly apply:" However, they wisely (and, for that time, rather daringly)
went on to say: "Only when the first spaceships take off to the Moon, and we
are able to view the surface at close quarters... will this question be
Yet even before then, conclusive evidence had been obtained that Arizona's
famous Meteor Crater was correctly named. A variety of quartz - coesite -
that could be produced only by enormous pressures had been found at its rim.
Although some geologists put up a spirited rearguard action in defence of
volcanoes, it was finally agreed that only an impactor from space could
produce the extreme conditions necessary to create this material. Indeed,
coesite is now regarded as definite proof of such an event - though not
necessarily on the same hemisphere, because the compressed quartz may have
been hurled halfway round the Earth.
After the dawn of the space age in 1957, the very first probes to Mars
showed that it was covered with impact craters; though to complicate
matters, it also boasted volcanoes that dwarfed any on Earth. Later images
from Mercury showed a terrain almost indistinguishable from the Moon, and we
now know that all the solid bodies in the solar system received such a
battering 3 to 4 billion years ago, and that some of them were literally
shattered into pieces.
All these discoveries attracted relatively little interest outside the
astro-geological fraternity, but in the late 1978 the situation changed
abruptly when the father and son team, Luis and Walter Alvarez, came across
a curious anomaly. There was a wholly disproportionate concentration of the
heavy metal iridium in a thin layer deposited 65 million years ago, and the
fossils of micro-organisms, which were extremely common below this layer,
were rare or even non-existent, above it. Some worldwide catastrophe had
evidently caused a mass extinction - and it seemed more than a coincidence
that the dinosaurs disappeared at around this time.
In a classic paper published in Science in 1980 "Extraterrestrial cause for
the Cretaceous- Tertiary extinction", Alvarez and his colleagues claimed to
have solved a mystery that had long baffled palaeontologists. They pointed
out that iridium, though very rare in the Earth's outer crust (because most
of it has sunk down to the core) is relatively common in meteorites - and
presumably in asteroids, which are believed to be their parent bodies. Here,
perhaps, was the "smoking gun" that had committed the crime of the aeons.
It took a decade for this theory to be generally accepted, partly because
there have been many other extinctions that can be more easily attributed to local
causes: Mother Earth is quite capable of large-scale infanticide without any
assistance from the Cosmos. But what appeared to be the final proof came in
1991 with the location of an enormous buried crater near Mexico of just the
right age and size.
Sadly, Luis Alvarez did not live to see this spectacular vindication of his
theory, but he never doubted its correctness. In the last letter I received
from him, he wrote: "It's no longer a theory but a fact." (Perhaps I should
mention that I was privileged to join his radar team in 1943: my only non-SF
novel, Glide Path, is dedicated to him. Its partly fictitious hero wins the
Nobel prize -and in 1968, "Luie" obligingly fulfilled my prediction.)
These discoveries were widely and understandably publicised, because they
raised an awesome question. Could what had happened in the past happen
again: the patient toil of amateur astronomers - often regarded with mild
amusement by the man in the street - had suddenly become relevant to the
survival of the human race. Few could doubt this after comet Shoemaker-Levy
9 smashed into Jupiter on July 18 1994, giving that giant world a series of
black eyes as large as the Earth, and lasting for several weeks.
S-L9's cataclysmic demise was probably watched by more telescopes than any
event in history, and for a while the Levy and Shoemaker families had
virtually no private lives. However, the resulting fame gave them greater
opportunities to continue their work on a more lavish scale - without having
to waste so much time pleading for funds. Shoemaker had always been running
at least a dozen projects at once (not all of them very efficiently) but now
began to focus attention on the continent that he and his - wife Carolyn had grown to love
-Australia. Its vast deserts were the best places on Earth to look for
craters that had not been erased by the ravages of time.
On July 18 1997 - exactly three years after S-L9's impact on Jupiter -
Shoemaker was driving through the outback, where any approaching car could
be seen a mile away by its dust cloud. Then, "out of nowhere, a Land Rover
materialised in front of them". Shoemaker was killed instantly but his wife
Carolyn fortunately survived, to continue working with the Levys. In January
1998, they watched Lunar Prospector lift off from Cape Canaveral, carrying
an ounce of Shoemaker's ashes to the Moon.
While I was writing this review, the following email message arrived from
the International Astronomical Union: "Object 2000 SG344 was discovered on
September 2 by David J. Tholen and Robert J. Whiteley using the
Canada-France-Hawaii 3.6-meter aperture telescope... Nasa's Jet Propulsion
Laboratory estimates a one-in-500 chance of the object hitting the Earth on
September 21 2030."
Before anyone gets too alarmed, later observations ruled out a 2030
encounter - but improved (?) the odds for one after 2071. Even in the very
unlikely event that SG344 eventually does hit the Earth, it is a rather
small object and may not do much damage. But there are uncounted bigger
comets and asteroids out there: sooner or later, there will be a major
impact, though hopefully not on the Cretaceous- Tertiary scale.
Almost three decades ago, I described such a disaster in my novel Rendezvous
with Rama (1973), and the resulting establishment of Project Spaceguard to
ensure that "no meteorite large enough to cause catastrophe would ever again
be allowed to breach the defences of Earth". I am indeed happy to say that
the name has been widely adopted: at the request of Congress, Nasa issued
The Spaceguard Survey in 1992, and Spaceguard organisations have since been
established in many countries to rally government and public support for the
cause. Following enlightened discussions in the House of lords, the UK
government has recently agreed to spend money on this most important defence
project of all time. (Amazingly, it was Byron who first proposed, in 1822,
that the human race might need to destroy comets to save itself!)
Though there is little that we could do, at the present stage of our
technology, to protect the home planet against a major impact, that should
not be the case by the end of the 21st century. We must acquire the ability
to go into space, and move threatening objects out of the way. Shortly
before his own untimely death, Carl Sagan summed up the lesson of S-L9: "In
the long term, all civilisations must be space-faring. The ones that aren't,
Sir Arthur C. Clarke is chancellor, International Space University, and
chancellor, University of Moratuwa, Sri Lanka.
Copyright 2000, The Times Higher Education Supplement
(5) SIZZLING SKIES
From New Scientist, 4 January 2001
Meteors and auroras shine high up in the atmosphere. So how come you can
hear them whispering in your ear, asks Harriet Williams
NINETY MINUTES before sunrise on 7 April 1978, an extraterrestrial guest
arrived over Eastern Australia. For about 20 seconds it streaked across the
sky leaving a bright trail that turned night into day, before finally
exploding into glowing fragments that vanished into the sea. This meteor was
just one of thousands that enter our atmosphere every year, yet dozens of
witnesses in Newcastle and Sydney reported something particularly strange
about this visitor. Just before it blew apart, it produced an unearthly
soundtrack of hisses, crackles and pops.
Reports of noisy meteors appear in the Bible, yet the cause of their bizarre
sounds has always been a mystery. One person might hear the popping and
whooshing clearly while another, standing just a few metres away, hears
nothing. Explaining this oddity is especially tricky since there is almost
no hard scientific data to go on: even if you spent two hours every night
looking for them, you might have to wait fifty years to hear one.
Yet researchers believe they are finally closing in on the origins of these
strange sounds. All they need now are some meteors on which to test their
theories. But rather than waiting around for one to show up, they're hoping
that artificial meteors--redundant satellites brought down from orbit to
burn up in the atmosphere--will give them the vital data they need to settle
it once and for all. At the same time, there's a good chance that they will
solve another age-old mystery--the ghostly, rustling songs sometimes heard
by observers of the northern and southern lights.
One of the pioneers of these studies is Colin Keay, a physicist at the
University of Newcastle in Australia. The day after the New South Wales
fireball fell to Earth, Keay was phoned by a colleague at the Australia
Museum in Sydney who asked him if he would search for any fragments of the
meteorite that might have landed on dry ground. During this hunt, he
discovered something about the fireball that would change the course of his
The meteorite, Keay calculated, had streaked across the sky at almost 20
kilometres per second, 30 kilometres up, yet he met dozens of reliable
witnesses who claimed to have heard it produce strange noises as it flew
overhead--anything from "a low moaning" to "an express train travelling at
high speed". If these sounds had come directly from the meteorite, people on
the ground below shouldn't have heard them until almost a minute after it
exploded. It would be like seeing a distant flash of lightning and hearing
the thunderclap at the same instant.
What finally clinched it for Keay was meeting two witnesses who claimed the
sounds first alerted them to the meteorite trail. "When two people reported
hearing the sounds before seeing the light of the fireball, I knew it
couldn't be psychological," says Keay. "There had to be something to it."
Intrigued, he set to work to uncover the mechanism behind these noises. He
spent months creating and discarding one physical model after another.
Finally, he settled on one that he suspected was the only way to explain how
an observer could hear a meteor's fiery entry at the same time as seeing it.
It all comes down to electromagnetic radiation.
Keay suspected that the light given off by a meteor's trail must be
accompanied by invisible electromagnetic radiation in the form of very low
frequency (VLF) radio waves at frequencies from 10 hertz to 30 kilohertz.
Travelling at exactly the same speed as visible light, these waves would
reach the observer as soon as the meteorite itself came into view. The
problem is that you can't hear radio waves. The only way you might hear them
is with the help of a suitable "transducer"--an object that acts rather like
a loudspeaker, converting electromagnetic signals into audible vibrations.
After some experiments in a soundproof chamber, Keay found that all kinds of
things can act as transducers. Aluminium foil, thin wires, pine needles or
dry, frizzy hair all respond to a VLF field. The radio waves induce small
charges in such objects, and these charges force the object to vibrate in
time with the oscillating waves, effectively making them act like the
diaphragm in a loudspeaker. Even a pair of glasses, he discovered, will
vibrate slightly. And since they rest against the bones of the skull,
glasses could increase an observer's chances of hearing VLF waves.
The transducer effect would explain why some people heard noises from the
Australian meteor while others close by heard nothing. Those who heard
sounds were simply nearer to the "speakers"--transducers such as pine trees,
for example. It would even explain why attempts to record these sounds have
always failed. Scientists go out of their way to place their microphones
well away from any possible sources of interference such as trees or
electric cables. But without any transducers nearby, the meteors would
So the transducer effect seems a plausible source of the strange noises, but
how do meteors generate VLF waves? "I was getting nowhere until I got the
idea to look at turbulence," Keay says. He remembered a theory put forward
by physicist Fred Hoyle which used turbulent plasmas to explain sunspots.
Perhaps, thought Keay, interactions between the Earth's magnetic field and
the plasma in a meteor's trail could somehow create VLF waves.
When a meteor crashes into the Earth's dense atmosphere, it ionises the air
around it, leaving a blazing trail of plasma. For a few metres behind the
meteor, this trail flows smoothly, but a little further back it becomes
turbulent. Since a plasma is a mixture of ions and electrons, it can trap
and hold the Earth's magnetic field. "The plasma is swirling so fast that
the magnetic field is trapped and scrambled up like magnetic spaghetti,"
explains Keay. But as the meteor races across the sky, the plasma left
behind cools, and the electrons and ions in it recombine almost immediately.
Without the electrical charges to keep the magnetic field lines tangled,
they suddenly pop free and vibrate like a plucked violin string. It is these
vibrations, Keay believes, that broadcast VLF electromagnetic waves over a
range of several hundred kilometres (see Diagram, below).
Sound and fury: a large meteor hitting the atmosphere creates a plasma which
tangles up the Earth's magnetic field (large image). The release of the
field lines generates a burst of VLF radiation, which is heard on the ground
via transducers. Smaller meteors may also generate VLF when charges
separate, creating an electric field (inset)
Keay has named the sounds generated by these radio waves "electrophonic"
noise. He even believes that VLF waves are responsible for another eerie
effect: the rustling and sighing sounds of the northern and southern lights.
For centuries strange noises have been said to accompany the exquisite
curtains of colour seen in the sky near the Earth's magnetic poles. These
sounds are heard often enough to be known as the "whisper of souls of the
dead" in Eskimo folklore. Yet just as with the burps and whistles of
meteors, some people hear the swish of the aurora while others nearby are
left in silence--one reason the sounds were often written off as a
Auroras are created as the Earth's magnetic field captures charged particles
from the solar wind. These particles stream along the field lines and down
towards the magnetic poles. Here they strike the upper atmosphere and ionise
nitrogen and oxygen molecules to produce the characteristic red and green
glow of the auroras. During these electrical "storms", scientists have
recorded abnormally high electric fields and many believe these fields are
responsible for the noises auroras emit. They suggest that they cause "brush
discharge", which occurs when electric fields induce an electric potential
gradient in objects on the ground. If these objects have points or
spikes--such as those on leaves or pine needles, for instance--there can be
an electric discharge at their tips that creates an audible crackling.
But Keay believes that the electric fields are rarely strong enough to
create brush discharge. The whispering of the auroras must have another
cause, he says. He believes that just as with meteor noises, auroral sounds
are generated by VLF waves acting on transducers such as hair. These waves
seem to be produced by ions and electrons from the solar wind that are
reflected back and forth in the Earth's magnetic field.
Keay's model might explain sounds from large meteors and auroras, but it
doesn't seem to explain the noises that very small meteors make. In November
1998, astronomers from all over the world flocked to Mongolia for the
biggest Leonid meteor display in decades. Over two nights, they witnessed
more meteors than they could hope to see in four years of normal
observations. There were even seven reports of electrophonic
sounds--including the first brief meteor "pop" ever captured on tape,
recorded by the Croatian-based group, International Leonid Watch.
Previous recordings of meteors had produced a time delay between the visual
observation and the sound, allowing the possibility of interference or even
the odd sonic boom to slip in. But the Croatian researchers showed that the
VLF signal picked up by radio receivers coincided with the sounds picked up
by microphones and an image recorded on video to within one-hundredth of a
second: enough to convince all but the most sceptical that this wasn't a
Yet according to Keay's theory, there shouldn't have been any noise at all.
Leonids are small objects made of porous, fragile material. Weighing no more
than a dried pea, the average Leonid burns up long before it reaches the
lower atmosphere, where turbulence in its plasma tail can generate VLF
waves. According to Keay's model, only a giant Leonid, upwards of one metre
across would stand any chance of producing electrophonics. "When you
calculate how bright a meteor of that size would be, the number becomes
enormous and would violate the observations," says Dejan Vinkovic, an
astrophysicist from the University of Kentucky who attended the Mongolian
display. Also, the sounds from Leonids are short pops or clicks, quite
different from the prolonged hisses accounted for by Keay's theory.
Martin Beech, an astronomer at the University of Regina, Canada, believes he
can resolve the problem. He has studied noisy Leonids on and off for the
past decade and has just written a paper that expands his theory to explain
these strange pops. "We produced the name 'burster' to distinguish them from
the longer-duration sounds that Keay researched," says Beech.
In a model developed with colleague Luigi Foschini, the electromagnetic
signal is formed suddenly when a fast, light meteor breaks up. When this
happens, says Beech, a shock wave explodes out into the plasma trail just
behind it. Since the electrons and ions in the plasma have different masses,
the lighter electrons tend to ride the front of the shock and are separated
out from the slower-moving ions. "That sets up something called the space
charge," says Beech, "where you've got a separation of the negative charge
of the electrons from the positively charged ions." This separation is
unstable and the charges recombine almost immediately, but not before the
short-lived electric field generates a sudden pulse of VLF waves. When this
burst reaches the ground it creates audible sound in the same way as the
radio waves from larger meteors (see Diagram, opposite).
Keay likens these electrophonic pops to the audible "click" that occurs at
the moment a nuclear bomb detonates. "A nuclear bomb is a violently
exploding plasma that causes such a shock to the Earth's magnetic field that
it generates a pulse of electromagnetic radiation," says Keay. Beech agrees
that the physics may be similar. "But to do that you need something that is
literally like a nuclear explosion, and in the case of bursters they just
don't have that kind of energy," he says. Despite the progress, it seems
that there is still no single theory that can explain all the effects
("Small, medium and large", p 15).
The real problem is that Beech and Keay simply don't have enough data to go
on. "With bursters, it is not entirely clear yet what sort of signal you'd
expect to see, and it's hard to look for something when you don't know what
it looks like," says Beech. To collect more information, he has set up an
all-sky video camera and microphone at the University of Regina. "Progress
in the future is going to depend upon getting reliable data," he says.
Vinkovic is also busy hunting for noisy meteors. Last year he set up the
Global Electrophonic Fireball Survey to gather reports of meteor noises. So
far it has 20 separate incidents on its database, and Vinkovic plans to
collect further electrophonic information by persuading other international
meteor surveys to start listening for sounds.
He is also looking to artificial meteors for help. "Even when you observe
electrophonic sounds from a meteor, you don't know what properties that body
had when it entered the atmosphere. You don't know the physical parameters,"
he says. The answer, he has realised, is to listen to satellites as they
burn up in the atmosphere. They will behave just like natural meteors, but
you know their size and exactly what material they're made from. If you can
find out when and where they're coming down, he says, you should be able to
get a good idea of what's going on.
Recently, when Motorola drew up plans to dispose of its 66 Iridium
satellites, Vinkovic thought that he had hit the electrophonic jackpot. Now
a rescue package means the Iridium network looks set to stay up there for
the time being, but Vinkovic is not too despondent. Other artificial
meteors, such as failed communications satellites, are regularly brought
burning down to Earth. The Russian space station Mir is coming down in
February. And there are even unconfirmed reports that the space shuttle
returns to Earth with an electrophonic crackle. Vinkovic has a busy time
ahead, but he knows that only hard evidence will silence the sceptics.
Colin Keay, on the other hand, feels that electrophonics and the theory he
has pioneered are on a firm enough footing to put the ball back into the
cynics' court. "I believe that I've solved the problem and started a new
science," he says. "It is healthy for people to doubt, but the onus is on
them to prove their doubts." The challenge to physicists is clear--you may
not subscribe to these theories, but do you have any better ideas?
Small, medium and large
THE researchers admit that their efforts to account for electrophonic sound
do not provide anything like the whole picture. Colin Keay's
plasma-turbulence theory works well for long-duration sounds from large
fireballs, and Martin Beech's burster model may work for lightweight
meteors, but there are still a number of reports that neither can explain on
its own. The real answer may lie in a mixture of both. If a Leonid
disintegrates gradually on entry rather than its more typical catastrophic
break up, for instance, a repeated burster effect could resemble the
longer-duration sound modelled by Keay. There may well be other mechanisms
at work that scientists just haven't considered yet. "Personally, I don't
think there is one single theory that can explain everything going on out
there," says Dejan Vinkovic of the Global Electrophonic Fireball Survey. He
thinks that meteors must be able to distort the Earth's magnetic field, even
at heights where the air is too thin to create turbulence. In preliminary
calculations, Vinkovic has found that this distortion could start at the
edge of the ionosphere, some 100 kilometres above the ground. But the
question remains, how?
Harriet Williams is a science writer based in London
From New Scientist magazine, 06 January 2001.
© Copyright New Scientist, RBI Limited 2001
(6) NEW JOURNAL: NATURAL HAZARDS AND EARTH SYSTEM SCIENCES
From Duncan Steel <D.I.Steel@salford.ac.uk>
- GENERAL INFORMATION - GENERAL INFORMATION -
For the world of natural hazards a new journal owned and produced by the
European Geophysical Society:
NATURAL HAZARDS AND EARTH SYSTEM SCIENCES (NHESS)
Volume 1, number 1-4, 2001
- No page or handling charges for authors
- No extra charges for colour illustrations
- Free PDF offprint files for authors
- Moderate institutional subscription rates and further discounts for
For subscription to this international, interdisciplinary, peer-reviewed
- EGS Membership Subscription Form
- EGS Institutional Subscription Form
We also welcome your next article for publication in NATURAL HAZARDS AND
EARTH SYSTEM SCIENCES.
EGS OFFICE Tel.: +49-5556-1440
Max-Planck-Str. 13 Fax.: +49-5556-4709
37191 Katlenburg-Lindau email@example.com
(7) GOOD NEWS FOR PLANETARY DEFENSE: ISRAELI RESEARCHERS FOCUS ON EXOTIC
NUCLEAR FUEL THAT COULD SPEED UP SPACE TAVEL AND NEO DEFLECTION MISSIONS
From Science Daily, 3 January 2001
Source: Ben-Gurion University Of The Negev (http://www.bgu.ac.il)
Date: Posted 1/3/2001
Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks
Beer-Sheva, December 28, 2000 - Scientists at Ben-Gurion University of the
Negev have shown that an unusual nuclear fuel could speed space vehicles
from Earth to Mars in as little as two weeks. Standard chemical propulsion
used in existing spacecraft currently takes from between eight to ten months
to make the same trip. Calculations supporting this conclusion were reported
in this month's issue of Nuclear Instruments and Methods in Physics Research
A (455: 442-451, 2000) by Prof. Yigal Ronen, of BGU's Department of Nuclear
Engineering and graduate student Eugene Shwagerous.
In the article, the researchers demonstrate that the fairly rare nuclear
material americium-242m (Am-242m) can maintain sustained nuclear fission as
an extremely thin metallic film, less than a thousandth of a millimeter
thick. In this form, the extremely high-energy, high-temperature fission
products can escape the fuel elements and be used for propulsion in space.
Obtaining fission-fragments is not possible with the better-known
uranium-235 and plutonium-239 nuclear fuels: they require large fuel rods,
which absorb fission products.
Ronen became interested in nuclear reactors for space vehicles some 15 years
ago at a conference dedicated to this subject. Speaker-after-speaker
stressed that whatever the approach, the mass (weight) of the reactor had to
be as light as possible for efficient space travel. At a more recent
meeting, Prof. Carlo Rubbia of CERN (Nobel Laureate in Physics, 1984)
brought up the novel concept of utilizing the highly energetic fragments
produced by nuclear fission to heat a gas; the extremely high temperatures
produced would enable faster interplanetary travel.
To meet the challenge of a light nuclear reactor, Ronen examined one element
of reactor design, the nuclear fuel itself. He found at the time that of the
known fission fuels, Am-242m is the front-runner, requiring only 1 percent
of the mass (or weight) of uranium or plutonium to reach its critical state.
The recent study examined various theoretical structures for positioning
Am-242m metal and control materials for space reactors. He determined that
this fuel could indeed sustain fission in the form of thin films that
release high-energy fission products. Moreover, he showed how these fission
products could be used themselves as a propellant, or to heat a gas for
propulsion, or to fuel a special generator that produces electricity.
"There are still many hurtles to overcome before americium-242m can be used
in space," Ronen says. "There is the problem of producing the fuel in large
enough quantities from plutonium-241 and americium-241, which requires
several steps and is expensive. But the material is already available in
fairly small amounts. In addition, actual reactor design, refueling, heat
removal, and safety provisions for manned vehicles have not yet been
"However, I am sure that americium-242m will eventually be implemented for
space travel, as it is the only proven material whose fission products can
be made available for high speed propulsion. Indeed, Carlo Rubbia has also
recognized that this is the most probable fuel that will be getting us to
Mars and back. I think that we are now far enough advanced to interest
international space programs in taking a closer look at americium-based
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