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(meteorobs) Excerpts from "CCNet 72/2001 - 29 May 2001"
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From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 72/2001 - 29 May 2001
Date: Tue, 29 May 2001 11:35:42 +0100
CCNet 72/2001 - 29 May 2001
----------------------------
"In the early darkness of April 23, as Washington was beginning to
relax after the spy plane crisis in China, alarm bells began to go off
on the military system that monitors the globe for nuclear blasts.
Orbiting satellites that keep watch for nuclear attack had detected a
blinding flash of light over the Pacific several hundred miles southwest of
Los Angeles. On the ground, shock waves were strong enough to register
halfway around the world. Tension reignited until the Pentagon could
reassure official Washington that the flash was not a nuclear blast. It
was a speeding meteoroid from outer space that had crashed into the
earth's atmosphere, where it exploded in an intense fireball. [...]
Preliminary estimates, Dr. ReVelle said, are that the cosmic intruder was
the third largest since the Pentagon began making global satellite
observations a quarter century ago. Its explosion in the atmosphere
had nearly the force of the atomic bomb dropped on Hiroshima."
--William J. Broad, The New York Times, 29 May 2001
(1) LISTENING FOR NUKES: A METEOR DETECTION PROJECT
Space.com, 24 May 2001
(2) MILITARY WARNING SYSTEM ALSO TRACKS BOMB-SIZE METEORS
The New York Times, 29 May 2001
[...]
(7) NASA TO BLAST HOLE IN COMET
The Guardian, 26 May 2001
[...]
==============================================================================
(1) LISTENING FOR NUKES: A METEOR DETECTION PROJECT
>From Space.com, 24 May 2001
http://www.space.com/scienceastronomy/solarsystem/nuke_meteor_010524.html
By Robert Roy Britt
Senior Science Writer
If anyone tries to secretly test a nuclear weapon, anywhere in the world,
the U.S. Department of Energy will know about it. Same goes for any large
space rocks that try to sneak past our planet's natural defense system.
The technology that monitors both of these potentially hazardous events is
amazingly simple. A handful of microphones positioned around the United
States listen for a telltale atmospheric pressure wave, a phenomenon that
circles the globe at a frequency too low for the human ear to detect.
A similar system is now under construction worldwide, designed to help
monitor and enforce compliance with the Comprehensive Nuclear Test Ban
Treaty. A recent study, however, questions whether the technology is up to
the task.
The sensitive but simple detection system, which officials say can pinpoint
the source of a nuclear blast by noting when the pressure wave arrives at
each microphone, also routinely detects giant space rocks that slam into
Earth's atmosphere, vaporizing and producing a similar pressure wave.
On April 23, researchers monitoring the set-up from the Los Alamos National
Laboratory detected an explosion out over the Pacific Ocean. After comparing
the data with other monitoring stations, they determined it was not a rogue
nation setting off a bomb, but rather an object the size of a small car
burning up as it raced through the atmosphere toward the planet.
Quite a show
The object plunged into the atmosphere several hundred miles (kilometers)
west of the northern portion of Baja California. It's possible no one saw
it. But that doesn't mean it wasn't there.
The explosion was equivalent to at least 6,000 tons of TNT, according to Los
Alamos scientists Rod Whitaker and Doug ReVelle. Once a space rock enters
our atmosphere, it is called a meteor. And based on the incoming meteor's
energy and speed, the researchers figure it was at least 12 feet (3.6
meters) in diameter.
Whitaker and ReVelle say it would have created a very visible fireball in
the sky, something scientists call a bolide.
"Had anyone seen the April 23 event, they would have seen quite a show,"
ReVelle said. "That meteor was one of the five brightest meteors that have
ever been recorded."
The event, along with a similar one on August 25, 2000, was confirmed by
U.S. Department of Defense (DOD) satellites. Whitaker and ReVelle told
SPACE.com that DOD satellites are able to spot different characteristics in
a meteor or nuclear explosion. "Nuclear explosions would leave radioactive
debris, which could be picked up by radionuclide air samplers," they said.
It's raining rocks
ReVelle said that on the average, 10 or more meteors, each wider than the
average person is tall, enter the atmosphere every year. Typically, they do
not make it to the ground. Some do, however, and every hundred years or so
researchers estimate that one large enough to cause local death and
destruction reaches the planet.
So, of course, scientists who study asteroids appreciate the government's
listening efforts.
"We are bombarded daily by smallish debris, but it is the larger chunks that
can easily penetrate our atmospheric shield and cause physical damage on the
Earth's surface," said Benny Peiser, a researcher at Liverpool John Moores
University who studies how natural catastrophes might affect Earth and its
inhabitants.
Peiser said the DOD and other researchers have routinely published detection
data of atmospheric impacts since the end of the Cold War.
"This data is vital for assessing the impact rate and a better understanding
of the overall impact hazard," he said. But he also noted that the
information contributes to international stability by helping to distinguish
space rocks from nuclear tests.
Leftover technology
During the 1960s, before satellites were common, the U.S. Air Force operated
a network of infrasound stations, as they are called, as a first line of
defense and to listen for nuclear-weapon tests.
The Los Alamos listening devices, four around the country, were installed in
1983. They remain, at least for now, the only infrasonic network left in
full-time operation in the world. Because the system is simple, officials
say it costs very little to maintain.
But it is highly sensitive, able to detect meteors as small as a baseball.
The sonic waves created by such a meteor, or a faraway nuclear explosion,
are well below the range of human hearing, but are detectable as small
changes in atmospheric pressure. The system is like a hypersensitive
barometer used by meteorologists to note incoming storm fronts.
Cheap insurance
The Los Alamos listening devices would not provide advance warning of an
incoming meteor. The pressure wave takes several minutes to hours to reach
the stations. But the stations do have tremendous potential for detecting
clandestine nuclear weapons tests, the researchers say.
Whitaker said other technologies, including satellites, sometimes miss
events that the ground-based microphones pick up.
"Consequently, infrasound is inexpensive insurance for cost-effective
monitoring, and it is something that's available to the entire international
community," he said.
And, interestingly, nature's meteors help the Feds calibrate their
nonproliferation technology efforts.
"Because those two [meteor] events were detected by our four arrays and by
five other arrays operated by the International Monitoring System, we are
able to use the space platform data to calibrate our instruments, and
analyses, to make them better able to pinpoint the exact location where
these events occurred," Whitaker said. "Every time we hear a bolide, we
learn something about this technology and are better able to fine-tune it."
Nuke or meteor?
The International Monitoring System is a developing worldwide network of 321
monitoring stations that use various techniques to make sure no one violates
the Comprehensive Nuclear Test Ban Treaty (CTBT), in which nations agree to
ban all nuclear explosions.
Though the U.S. Senate has not ratified the signed treaty, many other
nations have.
As part of the monitoring system, construction has begun on a global array
of 60 infrasound listening devices. And about 100 stations using other
techniques have been built.
But infrasound technology can also detect explosive volcanoes,
meteorological events and even rocket launches and supersonic aircraft. It
is therefore questionable how accurate it is in monitoring nuclear tests.
A pair of Dutch researchers got some surprising results when they set up a
similar device. On a November night in 1999, a flash of light brightened the
skies above northern Germany. In the Netherlands, Ldslo Evers and Hein Haak
detected the sonic boom associated with the explosion, but could not
distinguish it from the expected signature of a nuclear explosion.
In January of this year, the researchers reported their results in the
journal Geophysical Research Letters, suggesting that the devices might not
be capable of distinguishing between a natural attack from space and a
clandestine nuclear test.
Nonetheless, the worldwide monitoring plan moves forward.
Last month, a CTBT commission announced that the first infrasound station,
in Germany, had been certified for use. The system was constructed deep in
the Bavarian forest, which officials say will help cut down on wind noise
that might fool the microphones. And each sensor is surrounded by a network
of baffles to further block the wind.
More methods
Infrasound will not be the only technology used to enforce the treaty.
Some 170 seismic sensors and 11 underwater listening devices will be used as
well, plus 80 devices that can detect radioactive debris. Information from
all these sensors will funnel via satellite into the International Data
Center in Vienna, where automated results are released two hours after the
data rolls in.
A spokesperson at Los Alamos said the lab "has always maintained that
infrasound is only one tool in the entire nonproliferation toolbox and
probably should not be regarded as a standalone nonproliferation
technology," but that it can help make other systems more effective.
The CTBT, adopted in 1996, has been signed by 160 nations, but ratified by
only 76. An additional 33 have not signed on at all.
Arms control advocates had campaigned for the adoption of a test ban treaty
since the early 1950s. The first one was adopted in 1963 -- a Partial Test
Ban Treaty that banned nuclear tests in the atmosphere, underwater and in
space.
Neither China nor France signed that first international test-ban treaty,
and negotiations for stricter treaties have continued ever since.
Copyright 2001, Space.com
==============================================================================
(2) MILITARY WARNING SYSTEM ALSO TRACKS BOMB-SIZE METEORS
>From The New York Times, 29 May 2001
http://www.nytimes.com/2001/05/29/science/29ROCK.html
By WILLIAM J. BROAD
In the early darkness of April 23, as Washington was beginning to relax
after the spy plane crisis in China, alarm bells began to go off on the
military system that monitors the globe for nuclear blasts.
Orbiting satellites that keep watch for nuclear attack had detected a
blinding flash of light over the Pacific several hundred miles southwest of
Los Angeles. On the ground, shock waves were strong enough to register
halfway around the world.
Tension reignited until the Pentagon could reassure official Washington that
the flash was not a nuclear blast. It was a speeding meteoroid from outer
space that had crashed into the earth's atmosphere, where it exploded in an
intense fireball.
"There was a big flurry of activity," recalled Dr. Douglas O. ReVelle, a
federal scientist who helps run the military detectors. "Events like this
don't happen all the time."
Preliminary estimates, Dr. ReVelle said, are that the cosmic intruder was
the third largest since the Pentagon began making global satellite
observations a quarter century ago. Its explosion in the atmosphere had
nearly the force of the atomic bomb dropped on Hiroshima.
The episode shows how the system that warns of missile attack and
clandestine nuclear blasts is fast evolving to detect bomb-size meteors as
well. Now, it finds them about once a month, on average. But Dr. ReVelle, a
scientist at the Los Alamos National Laboratory in New Mexico, said in an
interview that the developing system was likely to find many more of the
natural blasts in the years ahead.
"The real number is probably bigger," he said. "There's no doubt about that.
But we don't know how much bigger."
Already, the system has shown that the planet is being continually struck by
large speeding rocks, and that the rate of bombardment is higher than
previously thought. The blasts light the sky with brilliant fireballs but
people seldom see the blasts because they usually occur over the sea or
uninhabited lands.
The rocky objects are anywhere from a few feet to about 80 feet wide. They
vanish in titanic explosions high in the atmosphere, their enormous energy
of motion converted almost instantly into vast amounts of heat and light.
The Air Force did not publicly disclose its imaging of the recent blast
until late May, more than a month afterward. In a terse release on May 25,
its Technical Applications Center, at Patrick Air Force Base in Florida,
said the flash was "non- nuclear" and consistent with past observed meteor
explosions.
A Defense Department satellite, the Air Force said, detected bright flashes
over a period of more than two seconds.
After that disclosure, Los Alamos got the military's permission to reveal
its own detection of the April event. Its ground-based sensors are even more
sensitive than orbiting satellites to the repercussions of meteor blasts.
The ground-based sensors work like sensitive ears to detect very
low-frequency sound waves, which radiate outward from an exploding rock over
hundreds and thousands of miles.
The sensors record sounds well below the range of human hearing, including
those from underground nuclear tests as well as atmospheric blasts.
Dr. ReVelle said four arrays of the lab's sound sensors had picked up the
April blast. In addition, he said, sound detectors in Los Angeles, Hawaii,
Alaska, Canada and Germany had picked up its shock waves. Two sensors in
South America made tentative detections, he added.
"It was a big event," he said. "There are people worrying about impacts on
the earth, and these things are giving us a better understanding of the
impact rate. That's the real byproduct scientifically."
The speeding boulder was perhaps 12 feet wide, he added.
An even more sensitive global ear is emerging as the world's nations try to
monitor the Comprehensive Test Ban Treaty, a tentative accord that seeks to
end the exploding of nuclear arms and to police compliance. When finished in
the next year or so, the global acoustic system is to consist of 60 arrays
that give complete global coverage, increasing the odds that even more large
meteor impacts will be detected.
The disclosure of such intruders is seen as bolstering the idea that the
earth is periodically subjected to strikes by even larger objects, including
doomsday rocks a few miles wide. Objects this size are predicted to hit once
every 10 million years or so, causing mayhem and death on a planetary scale.
Copyright 2001, The New York Times
==============================================================================
(7) NASA TO BLAST HOLE IN COMET
>From The Guardian, 26 May 2001
Scientists to study results of Deep Impact mission
James Meek, science correspondent
The Guardian (Manchester & London)
Saturday May 26, 2001
It may go down in history as the earliest act of deliberate cosmic
vandalism, mankind's first halting steps at preventing its own extinction,
or - as the scientists involved modestly hope -
an explosive, useful experiment in the wilds of space.
Whatever it is, the Deep Impact mission, just given the go-ahead by Nasa,
will be unlike any previous space venture in the scale of the planned damage
to a celestial object, a comet called Tempel 1.
Scientists will fire a 350kg bullet into the heart of the comet as it passes
between Earth and Mars, gouging out a crater seven storeys deep and 100
metres wide.
The blast, to be broadcast on television and the internet from cameras
mounted on the mother ship, is scheduled for July 4 2005. With a mission
price tag of about #200m, it will be the
most expensive Independence Day fireworks.
The "bullet" itself, known as an impactor, will have a camera to record its
last moments as it slams into the comet at 10km a second (22,300mph).
The scientific goal is to gain the first glimpse of a comet's interior by
studying the walls of the crater and the debris thrown out by the impact.
That is if there is a crater. Astronomers' best guess is that the nuclei of
comets are a cocktail of ice, frozen alcohol and methane, with a sprinkling
of rock and dust.
But they cannot be sure. Tempel 1, discovered in 1867, orbits the sun every
five-and-a-half years and is only about 1km wide. The impactor could shoot
straight through or break the comet into large pieces.
"I wouldn't be at all surprised if it broke into several chunks - comets are
pretty fragile," said Duncan Steel, a comet specialist at the University of
Salford, Greater Manchester. "We see several of them of them breaking apart
every year."
This would pose no danger to Earth, he added. "The chunks would still follow
the comet's orbit, which is outside Earth's orbit," said Dr Steel.
Around 40,000 tonnes of space debris rain down on Earth each year, and the
destruction of a small comet close to the planet would risk doubling that.
Dr Steel said Nasa had sensibly gone for a comet far enough away to avoid
that problem. "The chances of being hit by a big lump are essentially zero.
We've got much worse things to worry about, like all the asteroids we
haven't found yet."
He dismissed any aesthetic or moral objections that space environmentalists,
a largely unformed body as yet, might have to gouging holes in pristine
parts of the solar system.
"As soon as we landed on the moon and made footprints you could say we were
polluting the moon," he said. "A lot of these airy fairy ideas are pretty
absurd, aren't they."
Deep Impact is due to be launched in January 2004 and orbit the sun for a
year before swinging out to intercept Tempel 1 in July 2005. It will release
the cylindrical impactor into the comet's
path before moving to watch the crash from a safe distance.
The US scientists involved claimed they came up with the title Deep Impact
long before the writers of the 1998 film of the same name. In the movie,
astronomers discover a comet on a collision course with Earth. A manned
spacecraft is sent to intercept it, plant nuclear charges and destroy or
deflect it before it can wipe out human life. Nasa's Deep Impact is not a
trial run for such an emergency, but the knowledge gained will inevitably be
useful if a planetary defence programme is set up.
Nasa recently landed a space probe on a small, peanut-shaped asteroid, Eros,
and in 2011 the European space agency will try to land its unmanned Rosetta
craft on a comet. Deep Impact will go further than either of these missions
in altering the course of a comet, or breaking it up.
There is thought to be a one in a thousand chance of an undiscovered
asteroid or comet 1km or more across hitting earth in the next century.
In the 1990s Nasa planned a mission called Clementine-2, a mother ship
carrying three 1.5-metre harpoons to be fired into three asteroids at 10km a
second, to test the technology.
But President Bill Clinton vetoed the project in 1997, on the grounds that
it was an overly aggressive hangover from the Star Wars era which would
needlessly alarm the Russians and Chinese.
) Guardian Newspapers Limited 2001
==============================================================================
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
FOR IMMEDIATE RELEASE May 24, 2001
NASA GIVES GO-AHEAD TO BUILD 'DEEP IMPACT' SPACECRAFT
The Deep Impact mission, the first mission to ever
attempt to impact a comet nucleus in order to answer basic
questions about the nature of comets, has successfully
completed its preliminary design phase and has been approved
by NASA to begin full-scale development for a launch in
January 2004.
The Deep Impact team of scientists, engineers and mission
designers, from the University of Maryland, NASA's Jet
Propulsion Laboratory and Ball Aerospace and Technologies
Corporation, Boulder, Colo., have been working for more than
18 months designing the mission, the dual spacecraft and three
science instruments. The encounter with Comet Tempel 1 on
July 4, 2005 will reveal clues to the origin of comets and the
composition and structure of perhaps the most mysterious
objects in our solar system.
Now the Deep Impact team is completing the final design
details and will begin building the mission's two spacecraft:
a flyby spacecraft and a 350-kilogram (771-pound) impactor
spacecraft. They will be launched together in early 2004 and
travel to Comet Tempel 1's orbit where they will separate and
operate independently. The flyby spacecraft will release the
impactor into the comet's path, then watch from a safe
distance as the impactor guides itself to collide with the
comet, making a football field-sized crater in the comet's
nucleus.
"This is a major milestone for us," said Dr. Michael
A'Hearn, the prinicipal investigator and director of the Deep
Impact mission, from the University of Maryland, College Park,
Md. "We have now shown NASA that we have a viable design for
the spacecraft and the mission to carry out a truly rare,
large-scale experiment on another body of the solar system."
"The Deep Impact mission follows in the tradition of
other Discovery missions like Mars Pathfinder and the Near-
Earth Asteroid Rendezvous by doing first of a kind science on
a low-cost, highly focused project," said Brian Muirhead, the
manager of the Deep Impact mission, of NASA's Jet Propulsion
Laboratory, Pasadena, California. "The project team is fully
prepared to implement this technically challenging and
scientifically unique mission."
As the gases and ice inside the comet are exposed and
expelled outward by the impact, the flyby spacecraft will take
pictures and measure the composition of the outflowing gas.
The images and data will be transmitted to Earth as quickly as
possible. Many observatories on Earth should be able to see
the comet dramatically brighten just after the impact on July
4, 2005.
Scientists refer to comets as time capsules that hold
clues about the formation and evolution of the solar system.
Comets are composed of ice and dust, the primitive debris from
the solar system's earliest and coldest formation period, 4.5
billion years ago. They would also like to learn much more
about a comet's composition, structure and how its interior is
different from its surface. The controlled cratering
experiment of the Deep Impact mission will provide answers to
these questions.
Comet Tempel 1 was discovered in 1867. Orbiting the Sun
every 5.5 years, it has made many passages through the inner
solar system. This makes it a good target to study
evolutionary change in the mantle, or outer crust, of a comet.
"Ball Aerospace is pleased and proud to be involved with
JPL and the University of Maryland in working on this first of
a kind deep space mission," said Ball's John Marriott, deputy
project manager.
Principal investigator A'Hearn oversees Deep Impact's
scientific investigations. Project manager Brian Muirhead, of
NASA's Jet Propulsion Laboratory manages and will operate the
Deep Impact mission for NASA's Office of Space Science,
Washington D.C. JPL is managed by the California Institute of
Technology, Pasadena, Calif., for NASA. John Marriott of Ball
Aerospace and Technology Corporation manages the spacecraft
development in Boulder, Colo.
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