PLEASE NOTE:


*

CCNet 110/2001 - 29 October 2001
================================


Many thanks to CCNet members for their good wishes and
congratulatory messages.
  Pictures of baby Tamara are available at
http://www.staff.livjm.ac.uk/humbpeis/
--Benny Peiser, a happy man and proud father.


(1) LATE PLEISTOCENE MEGAFAUNA EXTINCTION DUE TO NATURAL DISASTER, NOT
HUNGRY AMERICANS
    Eurekalert, 25 October 2001

(2) SCIENTIST URGES GOVERNMENT TO HELP AVERT NATURAL DISASTERS
    Ananova, 22 October 2001

(3) COMET'S DEATH DIVE CAPTURED BY SATELLITE
    CNN, 26 October 2001

(4) METEORITE HUNTERS SCOUR AMERICA'S SOUTHWEST
    Space.com, 28 October 2001

(5) GOLDEN TRADE IN SHOOTING STARS
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(6) INVADERS THAT ROCK THE WORLD
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(7) MIT LINCOLN LABORATORY NAMES ASTEROIDS FOR TOP KIDS, TEACHERS
    Andrew Yee <ayee@nova.astro.utoronto.ca>

(8) THE WORTH OF HUMAN LIFE: SEARCH FOR SMALL NEAR EARTH ASTEROIDS NOT
COST-EFFECTIVE?
    David Morrison <dmorrison@arc.nasa.gov>

(9) SPACE 2002 CONFERENCE: ASTEROID SESSIONS
    Michael Paine <mpaine@tpgi.com.au>

(10) RE: SPACE DRIFTERS (CCNet 19/10/01)
     John Michael Williams <jwill@AstraGate.net>

==================
(1) LATE PLEISTOCENE MEGAFAUNA EXTINCTION DUE TO NATURAL DISASTER, NOT
HUNGRY AMERICANS

>From Eurekalert, 25 October 2001
http://www.eurekalert.org/pub_releases/2001-10/uow-bna102401.php

Contact: Joel Schwarz
joels@u.washington.edu
206-543-2580
University of Washington

Blame North America megafauna extinction on climate change, not human
ancestors

Even such mythical detectives as Sherlock Holmes or Hercule Poirot would
have difficulty trying to find the culprit that killed the mammoths,
mastodons and other megafauna that once roamed North America.

Scientists have been picking over the bones and evidence for more than three
decades but can not agree on what caused the extinction of many of the
continent's large mammals. Now, in two new papers, a University of
Washington archaeologist disputes the so-called overkill hypothesis that
pins the crime on the New World's first humans, calling it a "faith-based
credo" that bows to Green politics.

"While the initial presentation of the overkill hypothesis was good and
productive science, it has now become something more akin to a faith-based
policy statement than to a scientific statement about the past," said Donald
Grayson, a UW anthropology professor

Writing in the current issue of the Journal of World Prehistory and in a
paper to be published in a forthcoming issue of the Bulletin of the Florida
Museum of Natural History, Grayson said there are dangerous environmental
implications of using overkill hypothesis as the basis for introducing
exotic mammals into arid western North America."

He looks askance at the idea of introducing modern elephants, camels and
other large herbivores into the southwest United States. "Overkill
proponents have argued that these animals would still be around if people
hadn't killed them and that ecological niches still exist for them. Those
niches do not exist. Otherwise the herbivores would still be there."

If early humans didn't kill North America's megafauna, then what did?
Grayson points to climate shifts, during the late Pleistocene epoch, which
ended about 10,000 years ago, and subsequent changes in weather and plants
as the likely culprits in the demise of North America's megafauna. The
massive ice sheets that covered much of the Northern Hemisphere began
retreating.

In North America, this icy mantle prevented Arctic weather systems from
extending into the mid-continent. Seasonal weather swings were less dramatic
and didn't reach as far south as they presently do. But with this change,
the climate became more similar to today's, marked by cold
winters and warm summers.

As a result, an unusual patchwork aggregation of plant communities ceased to
exit and there was a massive reorganization of biotic communities. At the
same time, new data developed by Russell Graham, a paleontologist with the
Denver Museum, shows that small mammals such as shrews and voles were moving
about the landscape and becoming locally extinct. And there were the
extinctions of some 35 genera of large North American mammals, including
horses, camels, bears, giant sloths, saber-toothed cats, mastodons and
mammoths.

The overkill hypothesis was proposed by retired University of Arizona
ecologist Paul Martin in 1967 and its basic arguments haven't changed since.
It claims large mammal extinctions occurred 11,000 years ago; Clovis people
were the first to enter North America, about 11,000 years ago; Clovis people
were hunters who preyed on a diverse set of now-extinct large mammals;
records from islands show that human colonists cause extinction; therefore,
Clovis people caused extinctions.

"Martin's theory is glitzy, easy to understand and fits with our image of
ourselves as all-powerful," said Grayson "It also fits well with the modern
Green movement and the Judeo-Christian view of our place in the world. But
there is no reason to believe that the early peoples of North
America did what Martin's argument says they did."

First of all there is no compelling evidence that the majority of the
extinctions occurred during Clovis times, said Grayson. Only 15 genera can
be shown to have survived beyond 12,000 years ago and into Clovis times.

For 30 years, overkill proponents have assumed that since some genera can be
shown to have become extinct around 11,000 years ago, all the big North
American mammals became extinct at that time, he said.

"That's an enormous assumption, even though there is no compelling evidence
of it in North America," Grayson said.

He also said overkill proponents have consistently ignored the possibility
that the Clovis people were not the first humans in the New World. They
reject evidence from a site in Monte Verde, Chile, showing human occupation
that dates some 12,500 to 12,800 years ago. Monte Verde also has yielded
some material that may push human occupation back to 33,000 years before the
present.

Well-accepted Clovis sites dating between 10,800 and 11,300 years ago have
been found in North America, and distinctive, fluted projectile points mark
this culture. Clovis artifacts have been found with mammoth remains in more
than a dozen sites across the Great Plains and the
southwestern United States.

Grayson said there is no reason to doubt that these people scavenged and
hunted large mammals. But he cautioned that while mammoths, mastodons,
horses and camels were the most common large mammals in the late Pleistocene
- 10,000 to 20,000 years ago - only mammoths are found at
kill sites associated with Clovis people.

As for the claim that human colonization of the world's islands resulted in
widespread vertebrate extinction, Grayson said this did not occur simply
because of human hunting.

"No one has ever securely documented the prehistoric extinction of any
vertebrate as a result human predation, though it may certainly have
happened. In virtually all cases, when people colonize an area many other
changes follow - fire, erosion and the introduction of a wide
range of predators and competitors.

"We do know that human colonists caused extinctions in isolated, tightly
bound island settings, but islands are fundamentally different from
continents," he added. "The overkill hypothesis attempts to compare the
incomparable and there is no evidence of human-caused environmental change
in North America. But there is evidence of climate change. Overkill is bad
science because it is immune to the empirical record."

For more information, contact Grayson at 206-543-5587 or
grayson@u.washington.edu

==============
(2) SCIENTIST URGES GOVERNMENT TO HELP AVERT NATURAL DISASTERS

>From Ananova, 22 October 2001
http://www.ananova.com/news/story/sm_430123.html?menu=news.scienceanddiscovery

A leading scientist says action can be taken to protect human beings and
future generations from natural disasters.

Sir Crispin Tickell believes there are practical measures which could avert
disasters.

He has spoken out in advance of a keynote speech he is to deliver at the St
Andrews Prize Inaugural lecture at the Royal Institution in central London.

He will look at the countless disasters that have occurred on the skin of
the planet over the last four billion years, as well as the process of
evolution.

The history of the earth is dotted with impacts from extra-terrestrial
objects, some big - such as that which precipitated the end of the dinosaurs
65 million years ago and some relatively small, like the devastation of
parts of Siberia in 1908.

Sir Crispin told the Radio 4 Today programme: "What I am saying is that
human life and life in general on the planet is a dangerous affair, but
usually our lives are too short to notice. There are discontinuities rather
than continuities throughout history.

"But we can do a great deal about most of these catastrophes."

Asked if much could be done about the threat of catastrophes from outer
space Sir Crispin replied:

"I was a member of a Government Task Force on the subject last year and we
concluded that if you could predict impacts from space, objects coming our
way, you could do a great deal.

"You can prepare for them by getting civil defence measures or you can put
up stuff to deflect the objects that come in.

Copyright 2001, Ananova

============
(3) COMET'S DEATH DIVE CAPTURED BY SATELLITE

>From CNN, 26 October 2001
http://www.cnn.com/2001/TECH/space/10/26/soho.sun.comet/index.html
 
(CNN) -- A comet plunged into the sun on Tuesday and its death dive was
captured by a NASA satellite.

The Solar and Heliospheric Observatory (SOHO) spacecraft orbits about 1
million miles from Earth. Its mission is to monitor the sun.

Scientists theorize that comets that buzz the sun are fragments of a huge
comet, perhaps one spotted by ancient Greek astronomers. It's believed that
the comet broke apart, producing a family of comets that astronomers call
"sungrazers."

Flying toward the sun isn't a healthy move for comets, which are made up of
ice and dust. Scientists say only the biggest comets can survive the blast
of heat from the sun as they fly by.

The image of the comet's death dive snapped by SOHO was created with an
instrument called the Large Angle and Spectrometric Coronograph, or LASCO.
The device creates an artificial eclipse, basically blotting out the
brightest part of the sun so researchers can study the corona, or
atmosphere.

Comet spotting is nothing new for SOHO. In its six years in service, the
satellite has spotted more than 365 comets, according to NASA. Scientists
say that makes it the most prolific comet finder in the history of
astronomy.

SOHO is a project of international cooperation between NASA and the European
Space Agency.

Copyright 2001, CNN

============
(4) METEORITE HUNTERS SCOUR AMERICA'S SOUTHWEST

>From Space.com, 28 October 2001
http://www.space.com/scienceastronomy/astronomy/meteorite_hunters_011028.html

By Foster Klug
Associated Press

PHOENIX (AP) _ The sunshine sparkling on his meteorite-encrusted wedding
ring and Van Halen blaring from his car stereo, Bob Haag rolled into
Portales, N.M., looking for space rocks.

He had heard the news less than 24 hours earlier: Rare iron-rich stone
meteorites had landed near the eastern New Mexico town. Armed with a pocket
full of $100 bills and banking on another big score, the self-styled
``long-haired hippy kid from Tucson'' hit the road.

He was in town before the stones had time to cool.

This is the world of the meteorite hunter, where a handful of pros like Haag
and legions of metal detector-toting amateurs comb the Southwest in search
of celestial tidbits more valuable than gold.

``Without a doubt, I have the best job in the galaxy,'' Haag said. ``But you
don't have to be a rocket scientist. You do a little research, find where
meteorites have fallen, and just go there and look. That's it. There's no
magic.''

In 25 years of hunting meteorites, Haag has followed ``million-dollar
falls,'' multiple meteorite drops that happen about every 1,000 days, to
Egypt, Russia, Japan and more than 50 other countries.

He has built an extensive collection, which he said has been appraised at
$25 million.

``These are pieces of stars that have never been seen on Earth before,''
Haag said. ``It's so 2001 Space Odyssey, so Buck Rogers spaceman, so Marvin
the Martian. These are today's new treasures, and we don't even have to
leave the planet to get them.''

During his search in Portales in 1998, Haag started working the residents
immediately, handing out pictures of the meteorite and posting ``Wanted!''
posters at the town's barber shop and Wal-Mart promising a reward.

Soon, a crew of housewives, teen-agers and retired men were scouring the
desert scrub behind their homes.

Haag shelled out about $15,000 for three of the 60 meteorites that were
eventually recovered _ including $5,000 to a child on a bike. He guesses
that the three rocks are worth at least twice what he paid, though he hasn't
sold them.

Most hunters agree there's more to the quest than money.

``The excitement with meteorites is that these samples are parts of planets
that once existed somewhere in outer space,'' said David Kring, professor of
planetary studies at the University of Arizona in Tucson. ``Meteorites are a
piece of a very old puzzle _ 4 1/2 billion years of the solar system's
history that can be partially unraveled by studying the meteorite you hold
in your hand.''

The dry, wide-open spaces of the Sonora, Chihuahua and Mohave deserts of the
southwestern United States make for ideal meteorite hunting terrain.
Would-be collectors just have to be able to recognize them.

About 800 baseball-sized or larger meteorites have fallen in Arizona alone
in the past 300 years, but only about 40 have been recovered, Kring said.

He said he finds about one or two meteorites among the 600 rock samples
brought to his office by amateur rock hunters each year.

Jim Kriegh, a retired University of Arizona civil engineering professor,
wasn't even looking for meteorites when he made his big find.

While hunting for gold in remote northwestern Arizona in 1995, Kriegh
stumbled across a strewn field, the scattered fragments of a huge rock that
dropped out of its orbit between Jupiter and Mars about 15,000 years ago and
exploded over the desert.

Over two years Kriegh and his partners pulled more than 2,400 meteorite
pieces from what would become the Gold Basin Strewn Field. One of only two
strewn fields in Arizona, it is believed to be the oldest in the world
outside of Antarctica, Kring said.

To date, more than 5,000 meteorite pieces have been recovered in the area.

``It evokes all sorts of mysterious thoughts,'' said Kriegh's hunting
partner, Twink Monrad. ``There were wooly mammoths and prehistoric lions and
tigers and small horses in the area, and it just makes you wonder what they
saw when this space rock exploded. It's amazing.''

Monrad was a homemaker before Kriegh invited her to explore the strewn
field. Now, she makes the seven-hour trip from her home near Tucson to Gold
Basin a couple of times a month.

In 1999, she discovered a separate meteorite lying in the strewn field,
called the Golden Rule Meteorite after a nearby mountain peak. She
attributes her success to persistence.

``I firmly believe that if a person were to go over any square mile, time
after time, anywhere in the world, they'd also eventually find meteorites,''
she said.

This strategy, employed by Monrad, Kriegh and others who trek to Gold Basin,
is the same method favored by professionals like Haag.

Haag said he makes his money by simply being able to recognize the rocks
better than his competitors. He plucked his most valuable find, a rare moon
rock, from a pile of low-priced meteorites a collector was displaying at a
gem show.

But while he often sells the gemlike meteorites he finds for hundreds of
dollars per gram, some are off-limits.

A few years ago, Haag spent two months in a desert on the Libyan-Egyptian
border hunting for a rare Howardite stone meteorite. One night, he said, he
dreamed he saw the meteorite streaking through the sky and then bursting
into five fiery pieces. Two days later he found five Howardite pieces lying
neatly in the sand.

``This wasn't something to be bought or sold,'' he said. ``This was
something sent from heaven just for me.''
 
Copyright 2001, Space.com

===============
(5) GOLDEN TRADE IN SHOOTING STARS

>From Andrew Yee <ayee@nova.astro.utoronto.ca>

[ http://www.news.com.au/common/story_page/0,4057,3133525%255E421,00.html ]

Sunday, 28 Oct 2001

Golden trade in shooting stars

SHOOTING stars landing in Australia are being plundered and sold to
collectors.

The meteorites, seen as fiery trails through the night sky, can be worth up
to 3000 times their weight in gold.

The Nullarbor Plain is one of the best places to find them, making it a
popular hunting ground for dealers undaunted by five-year jail terms or
fines of up to $100,000.

All meteorites found in Australia are protected by the Federal Protection of
Movable Cultural Heritage Act.

Despite the penalties, many space stones are sold overseas.

"They sell for big money these days and it is just too tempting for some
people," associate professor Vic Gostin, of Adelaide University, said. "It's
basically stealing."

Dealers often break meteorites into fragments, selling the pieces for
between $30 a gram and, in rare cases, $60,000 a gram. Gold is worth about
$20 a gram.

2001 News Limited

============
(6) INVADERS THAT ROCK THE WORLD

>From Andrew Yee <ayee@nova.astro.utoronto.ca>

[ http://www.guardian.co.uk/Print/0,3858,4284568,00.html ]

Thursday, October 25, 2001

Invaders that rock the world

Are we really descendants of bacteria that rode on cosmic cannon balls,
asks Matthew Genge

By Matthew Genge

In 1969 Michael Crichton wrote the Andromeda Strain in which a deadly
extraterrestrial virus was returned to Earth to infect the unsuspecting
populace. Films followed suit and in 1978 we watched as the spores of alien
body snatchers once again drifted down through the atmosphere and replaced
even the insomnia-ridden Donald Sutherland. Strangely, this notion that
extraterrestrial organisms can reach the Earth is a real scientific
possibility. It is known as panspermia.

Although a detailed theory of panspermia was proposed as early as 1900, it
was not until 1996, when structures resembling fossilised bacteria were
discovered by NASA in a martian meteorite, that panspermia suddenly seemed
to be a real possibility. Virtually overnight a new and exciting
field of science, astrobiology, appeared.

The controversy over fossilised bacteria in martian rocks sparked research
into the transfer of organisms between planets on meteorites. Rocks could,
it appeared, be hurled into space from the surface of a planet on the impact
of asteroids and comets. Some of these rocks could even escape the enormous
heat and pressure generated when an asteroid, five kilometres in diameter
slams into a planet's surface at 20km/s. Could these rocks contain microbes
capable of colonising another world? In the case of terrestrial rocks, the
answer is probably yes. Take away the rocks, the oceans, and the atmosphere
and our planet's surface would be traced out in every detail in a
translucent layer of micro-organisms. Earth bacteria quite probably beat
humans into space by hundreds of millions of years.

Could microbes survive being cast from a planet at enormous speeds and
exposed to the harsh environment of space? Experiments suggest bacteria
certainly suffer little damage from acceleration and some multicellular
bacteria can even benefit from the white-knuckle launch into space since
they split into smaller units which increases their reproduction. Exposure
to radiation in space and typical journey times between planets of millions
of years are a more daunting challenge to wannabe microbial colonists. The
discovery in 250M-year-old salt crystals of viable bacteria spores, however,
suggests that in hibernation microbes can do
a geologically significant Rip Van Winkle impression. Microbial cells will
nevertheless still be subject to damage by radiation, with energetic
particles ripping through their DNA like cosmic cannon balls. Although some
live bacteria, such as Deinococcus radiodurans, can survive such irradiation
by constantly repairing their genetic material, spores will not have this
ability. Only within rocks large enough to shield their passengers from
radiation are viable microbes likely to survive.

So what are the chances that living organisms could arrive on Earth? We
already know of 15 martian meteorites which have landed on Earth in the last
2M years and the real number must be thousands of times higher than this
since finding meteorites is such a haphazard business.

What about microbes from outside our solar system? Jay Melosh from the
University of Arizona suggests that one rock from a planet in another
planetary system will, by chance, land on Earth once every 10Bn years even
given the most favourable conditions. By contrast, the Earth itself
is only 4.6bn years old. Panspermia between solar systems has long odds
indeed.

The conclusive evidence for panspermia would be to find alien microbes on
Earth. Here there is one important lesson that has been learned in
astrobiology. Where microbes are concerned, contamination is difficult to
avoid. Every meteorite examined has been crawling with terrestrial
bacteria and fungi. These are after all the ultimate opportunists and have
conquered virtually every habitat on Earth, including those that
occasionally fall from space.

It is for this reason that the discovery of bacteria at 41km altitude in the
atmosphere announced by Chandra Wickramasinghe of Cardiff University is not
evidence for alien microbes. Prof Wickramasinghe and the late Sir Fred Hoyle
envisaged that microbial life may have evolved on comets and are delivered
on the 40,000 tonnes of comet dust that falls through the Earth's atmosphere
each year. They have even suggested that cometary microbes may have caused
influenza pandemics and BSE. Yet again provocative theories have made
panspermia controversial.

Comets do contain an intriguing mixture of organic chemicals synthesised
entirely in the absence of biology in space, which includes amino and
nucleic base acids -- the basic building blocks DNA and proteins, and it is
possible that comet dust raining down on the early Earth may have
provided a ready-made "cake mix" for life. Why then are microbes not
expected to be present on comets? The answer lies in their icy nature.
Comets consist of ice and dust and liquid water cannot exist on these
objects due to the low pressures. The metabolic reactions which form
the basic machinery of simple living organisms all have one thing in common,
they all occur in water. No water, no life.

The discovery of bacteria in the high atmosphere is thus quite probably a
testament to the pioneering abilities of our own terrestrial microbes rather
than evidence for life from outer space. Even if alien microbes are falling
through our atmosphere, however, there is no cause for concern since they
will have been doing it for millions of years. Stockpiling antibiotics is
thus not necessary and if you should wake up and find your partner somehow
changed, then it's more likely to be a hangover than the invasion of the
body snatchers.

[Dr Matthew Genge is a meteorite scientist at the Natural History Museum.]

Guardian Newspapers Limited 2001

===========
(7) MIT LINCOLN LABORATORY NAMES ASTEROIDS FOR TOP KIDS, TEACHERS

>From Andrew Yee <ayee@nova.astro.utoronto.ca>

News Office
Massachusetts Institute of Technology

CONTACT:
Patti Richards, MIT News Office
Ph: 617-253-8923
prichards@mit.edu

Georgia Juvelis, Discovery
Ph: 202-589-0620
Georgia_Juvelis@discovery.com

OCTOBER 23, 2001

MIT Lincoln Laboratory names asteroids for top kids, teachers

CAMBRIDGE, Mass. -- The asteroids zinging around our solar system have
largely been named for their discoverers, or for famous people like Ella
Fitzgerald, Vincent Van Gogh and the Beatles. Tonight, 40 middle-school
science students and their teachers can claim the honor as well, thanks
to MIT Lincoln Laboratory.

This week, 40 finalists are competing in Washington, D.C., for the title of
"America's Top Young Scientist of the Year" in the third annual Discovery
Young Scientist Challenge (DYSC), a national middle school science contest.
Each of the 40 students tonight will receive a certificate officially
acknowledging their link to an extraterrestrial piece of real estate. Each
student's science teacher will be similarly honored.

Lincoln Laboratory has discovered thousands of near-Earth asteroids, or
minor planets, since 1998 via the Lincoln Near Earth Asteroid Research
(LINEAR) program. LINEAR currently detects about 70 percent of the asteroids
discovered every year.

Dr. David L. Briggs of the Massachusetts Institute of Technology, director
of Lincoln Laboratory, has wanted to encourage science education in the
middle and secondary schools. Together with Dr. Grant Stokes, LINEAR's
principal investigator, they came up with the idea of naming minor planets
for top science students and their teachers in grades five through 12.

To find potential honorees, Stokes approached Science Service, which
organizes three major science competitions for students, including the
Discovery Young Scientist Challenge, which is the first science challenge to
include the asteroid honor. Stokes himself is a former high school science
fair winner in New Mexico.

Lincoln Laboratory and Science Service plan to expand the honor to students
and mentors for other competitions, including the Intel Science Talent
Search and the Intel International Science and Engineering Fair.

In addition to the official certificates, students and teachers will receive
information on how to find their asteroids in the sky. Stokes noted,
however, that honorees will have to go to an observatory to see their
namesakes, as the asteroids are too tiny to detect with the naked eye or a
standard telescope. But size is relative. According to Dr. Stokes, "Each
asteroid is several kilometers in diameter, which is a pretty big piece of
real estate."

Operated by MIT for more than 50 years, Lincoln Laboratory carries out
research and development in support of national security for the Department
of Defense and other government agencies. The LINEAR program is supported by
the United States Air Force and NASA.

                               --END--

ABOUT THE DISCOVERY YOUNG SCIENTIST CHALLENGE (DYSC)

Created by Discovery Communications, Inc., in 1999, the DYSC is a national
middle school science contest that encourages the communication, exploration
and understanding of science among America's youth. Each year, the
Smithsonian Institution hosts the DYSC finalists, granting them
unprecedented access to renowned scientists and historians as well as to
museum laboratories and other research facilities. More information:
www.discovery.com/dysc

ABOUT SCIENCE SERVICE

One of the most respected nonprofit organizations advancing the cause of
science, Science Service conducts high-quality competitions on the national
and international level, including the Intel Science Talent Search and the
Intel International Science and Engineering Fair. More information:
www.sciserv.org/

===============
(8) THE WORTH OF HUMAN LIFE: SEARCH FOR SMALL NEAR EARTH ASTEROIDS NOT
COST-EFFECTIVE?

>From David Morrison <dmorrison@arc.nasa.gov>

NEO News (10/26/01) Finding Small NEAs

Dear Friends & Students of NEOs:

A persistent issue among those planning asteroid (NEA) surveys such as
Spaceguard is how far to go. The NASA Spaceguard Goal is to discover 90% of
the NEAs larger than 1 km diameter by 2008. The 1 km size was selected
because it is near the lower limit for an impact that would likely cause a
global ecological catastrophe. Such "civilization threatening" impacts
dominate the risk statistics. We are each at much greater risk from a
potential impact by an asteroid 1 km or greater in diameter than by the
cumulative risk of all smaller and more frequent impacts. Put simply, a
global ecological catastrophe places us all at risk, while even the largest
impact below the threshold for global catastrophe leaves most of the world
unscathed.

More recently there has been growing interest in "raising the bar" by
lowering the NEA size for which completeness is sought. Last year's UK NEO
Task Group was among those advocating a shift toward smaller (hundreds of
meter diameter) NEAs. Of course, we are finding more sub-km NEAs today than
those above 1 km in diameter. We don't throw these small NEAs back, as we
might when we catch small fish. But the present surveys will take a very
long time to achieve completeness as 500 m or 300 m diameter.

In the NEO News of 10/19 I distributed a story by reporter Rob Britt that
included a discussion of shifting emphasis toward finding smaller NEAs.
Today we have two additional comments on this issue, the first from Al
Harris of JPL, the second taken from a review paper in preparation my
Morrison, Harris, Sommer, Chapman, and Carusi.

Harris argues that below the global catastrophe thershold (of 1-2 km), down
to the atmospheric cut-off at about 50 m, there is no strong gradient in
risk. That is, we are roughly at the same risk from 500 m NEAs as from 50 m
NEAs. So there is no natural stopping point once we move our focus to
smaller objects, except for one imporatant thing. The cost of discovering
NEAs goes up sharply as we move our goal toward smaller sizes. Thus the risk
stays roughly constant, but the cost-effectiveness of the survey becomes
much worse as we try to achieve completeness at ever smaller sizes.

David Morrison

=====================================

COMMENT FROM AL HARRIS

The NEO News (10/19/01) Space.com story stated: So NASA funding for asteroid
search programs today is driven primarily by the goal of finding objects 1
kilometer or larger. Many smaller objects are found in the course of these
searches. But some researchers think it is time to begin focusing on the
smaller rocks."We need bigger telescopes to come down to the 100-meter
limit," Tate said. "There is a substantial risk from undetected 100-meter
sized objects." .......

The Space.com story by Robert Roy Britt reiterates the frequently heard
claim that NASA is "ignoring small impactors."  The quote from Jonathan Tate
is quite correct, as far as it goes, that "[t]here is a substantial risk
from undetected 100-meter sized objects," but fails to address the other
side of the equation: the cost of detecting them. Deciding how small NEAs
one should attempt to discover is simply a matter of cost-benefit analysis.
One must weigh the cost of detection against the "benefit" in the form of
ability to protect against a future impact.

The critics of NASA's chosen threshold of ~1 km are quite correct that the
"benefit" side of the equation is nearly constant over a substantial size
range extending down from 1 km diameter to less than 100-m diameter, or
Tunguska-sized events. For example, Chapman and Morrison (Nature 367, 33,
1994, quoted in the British Task Force report) estimate an annual fatality
rate of about 20/year from Tunguska-sized impacts (~5,000 fatalities every
250 years), and an identical rate from large subglobal events (~500,000
fatalities every 25,000 years). Indeed the uncertainties in both frequency
and consequence of events over this size range make it hard to know even if
the slope is up or down. That is, are the many smaller events more lethal on
average than the fewer larger ones? To fair approximation, the "spectrum" is
flat, so based only on this side of the equation it is hard to justify any
particular cut-off of concern in the sub-km size range.

The other side of the equation, the cost of detection, is much steeper. The
cost of detection for extinction level NEAs (10-km diameter range) is zero:
we already know them all. We believe our current census is complete down to
around 4 or 5 km, except perhaps for an odd "Damocloid" or two, plus
long-period comets (that's a separate subject). Going down to 1-km diameter,
the present surveys are progressing very well, and while they may fail to
reach the "Spaceguard Goal" by 2008, they should get there in not much
longer than that. The total cost including preparatory and ancillary work
for this level of survey is between $25 M and $100 M, depending on how you
do the arithmetic. The basic requirement of doing this survey is simply to
scan the entire sky to about magnitude 20.5 continuously for ten years. If
you want to estimate what it takes to go for smaller and smaller objects,
you can just increase the threshold magnitude correspondingly. If you wish
to choose 300-m as your completeness goal, you will need to go 2.5
magnitudes fainter, to around 23.0. This can be done, and in fact a plan to
do this is a recommendation of the U.S. National Research Council "Decadal
Survey of Astronomy and Astrophysics" report, in the form of an 8.4-m "Large
Aperture  Synoptic Survey (LSST) telescope". My guess is that the total
lifetime cost of a project of this sort, for the 15 or so years to build and
run it, will be of the order of $1 B. Going the next step to reach 100-m
size objects requires another 2.5 magnitudes, or down to about 25.5.  This
is getting close to the magnitude threshold for HST, and beyond the range
that is efficiently reachable from the ground due to background sky and
limitations on resolution.  Going into space with a small aperture doesn't
do it either, because the targets are moving too fast (or actually, the
telescope is moving too fast) for more than few-second exposures. So you
have to go into space with really big telescopes of multi-meter aperture.
Very, very expensive, I would guess many tens of billions of dollars, if not
hundreds. Paving the tops of every suitable mountaintop in the world with
multiple Keck telescopes might accomplish it from the ground, but the cost
would be comparable.

With these numbers in hand, we can evaluate what is being done, and what is
sensible to advocate with present technology. In the >1-km size range it's
overwhelmingly favorable: the estimate is 1.5 billion fatalities every
half-million years, or 3,000 deaths per year. That's weighed against a cost
of several to perhaps as much as ten million dollars per year. Going down to
the 300-m size range, the marginal gain (additional protection in
lives-per-year) is about 100 per year (where here I have integrated the
fatality/frequency function from 1 km down to 0.3 km). It might be as high
as 300. On the cost side, it is probably a project of order $1B to do this,
or $100M per year. In the usual crass currency of cost per life saved, it is
usually considered a good buy to spend up to $1M per life. So extending the
limit down to half a kilometer diameter as recommended by the British Task
Force is a sensible recommendation. Continuing down to 100-m diameter, we
are looking at an incremental value of about 100 lives per year, as in the
previous half-decade of size, but here the cost jumps up to tens of billions
of dollars, at least several billion of dollars per year. Thus the cost per
life saved is in the range of tens of millions of dollars, generally
considered to be unaffordable, even in the first world. If one does the
equation in terms of only first-world lives (the ones paying the bills), the
number of fatalities per year is an order of magnitude less but the cost is
the same.

In summary, even though the "spectrum" of benefit is quite flat in the range
from 1 km down to 0.1 km, the cost function is as steep as a stone wall, and
the point of diminishing return is  rather firmly defined at somewhere
around 0.5 km diameter, maybe as small as 0.3 km. The threshold of global
catastrophe" at around 1.5 to 2 km makes a catagorical difference in value,
so NASA's stated goal of discovering most NEAs down to ~1 km is a sensible
first goal. Continuing down to 0.5 km as recommended by the British task
force is a sensible follow-on goal, using present technology. Extending
significantly further down to smaller objects should await the development
of more cost-effective technology. No doubt that will come naturally in
time. And time is on our side. Even the present level of surveying stands a
better than even chance of discovering the next "Tunguska" before it finds
us. But it is likely to be more than ten years.

Alan Harris
Jet Propulsion Laboratory
email:  Alan.W.Harris@jpl.nasa.gov

==================================================

 From Chapter for Asteroids III (draft of 9/18/01)

DEALING WITH THE ASTEROID IMPACT HAZARD

David Morrison (NASA ARC), Alan Harris (JPL), Geoff Sommer (RAND), Clark
Chapman (SWRI, Boulder), Andrea Carusi (IAS, Roma)

NEA Population and the Spaceguard Survey

The first formal proposal for a survey of potentially threatening NEOs was
made by the U.S. Congress in 1991. At the request of the House of
Representatives, NASA appointed a study group to evaluate the impact hazard
and propose ways to dramatically increase the detection rate of
Earth-crossing objects. That group proposed an international "Spaceguard
Survey" to be carried out by ground-based optical telescopes equipped with
state-of-the-art wide-field detectors and automated search capability
(Morrison 1992)  The term "Spaceguard" was borrowed (with permission) from
Arthur C. Clarke who had used it to describe a radar warning system designed
to protect the Earth from impacts in his novel Rendezvous with Rama.

In 1994 the U.S. Congress asked the NASA Administrator to submit a Program
Plan to locate all NEOs greater than 1 km diameter (roughly the lower limit
to the threshold for global catastrophe). The resulting NASA study
(Shoemaker 1995) articulated the "Spaceguard Goal" to discover and catalog
at least 90% of all NEAs larger than 1 km in diameter in the next ten years.
A strong rationale was presented that the NEAs with D > 1 km are the most
dangerous and deserve the highest priority for detection, as discussed in
the previous section. However, the 1-km objects specified in the goal can
also be thought of as a convenient metric, since an optical survey does not
distinguish between small nearby objects and large distant objects in the
telescope field of view. While the largest (brightest) objects are the
easiest to discover, at no point has anyone suggested "throwing the little
ones back" as in fishing. The Spaceguard Goal is a convenient metric for
assessing progress, not an end point after which we should cease surveying.
As we approach the present goal (which is likely to be reached near 2010,
assuming continuing improvements in search systems), it might be well to
switch to a new metric (smaller reference diameter for completeness), as has
been suggested (for example) in the recommendations of the UK NEO Task Force
(Atkinson et al. 2000).

In order to design an optimum search system it is sensible to simulate
discovery efficiency as a function of sky area covered, limiting magnitude,
and various other parameters. This was done by
Muinonen and Bowell as a part of the Spaceguard Survey Report (Morrison
1992) and has been extended by others both for evaluating survey efficiency
and for bias-correcting survey discoveries to estimate asteroid populations
(see Jedicke et al., this book). Harris
(1998, 2001) has provided perhaps the most thorough discussion in the open
literature of such a survey simulation, showing that it is generally better
to sacrifice depth of coverage (limiting magnitude) in favor of sky coverage
to maximize discovery rate. One gains breadth of coverage inversely
proportional to integration time, but one gains depth of coverage only
proportional to the square root of integration time. For example, by cutting
integration time by one fourth, four times the area can be searched to half
the depth (in units of intensity). This strategy is of course limited by
cycle time (to move the telescope and process the image), and ultimately by
the finite area of sky available. Currently operating surveys cover most of
the visible sky each month, with the exception of the southern sky below
about -30 degree declination, so to a good approximation our evaluation can
be limited to "all sky" coverage........

The current telescopes in the Spaceguard Survey are not necessarily an
optimum design, but they are doing the job. If we wish to augment the
capability of the system, the primary requirement is to reach fainter
magnitudes without giving up sky coverage. This could be achieved with
larger apertures; today's survey telescopes are almost all in the 1-meter
class, which is very small by current astronomical standards. It is also
desirable to have at least one telescope in the
Southern Hemisphere, since currently about 20% of the sky is not being
covered. However, we note that while a southern telescope is desirable, it
is not an absolute requirement. A NEA that is missed one year because it is
too far south will likely be picked up on a subsequent pass. This gap in the
south is not qualitatively different from, for example, the gap in coverage
caused by the monsoon weather that typically closes down observatories in
Arizona and New Mexico during the summer months. The primary effect of these
gaps is simply to slow completion of the survey. Fortunately, a Southern
Hemisphere survey telescope at a good site could go a long way toward
filling both gaps.

Telescopes in space could also be used to augment the survey, but most of
the systems that have been proposed are not likely to be cost-effective
compared to ground-based observatories. The
cost-effectiveness would be greatly improved, of course, if the NEA survey
activity were incorporated as a secondary goal into a spacecraft being
launched for other purposes. There is no intrinsic advantage of
Earth-orbiting observatories, other than continuously clear sky (in fact,
some orbiting telescopes actually have lower duty cycles than ground-based
telescopes at good sites). Telescopes looking from interior to the Earth's
orbit have an advantage in discovering asteroids that spend most of their
time inside the Earth's orbit, but we already know that there are relatively
few of these. Any given survey system should be judged on its merits, of
course, and there is no reason that a mix of space-based and ground-based
instruments could not contribute to NEA surveys.......

Recent experience with the output of the NEA survey programs has led to more
sophisticated treatments of impact probability (e.g., Milani & Valsecchi
1999, Chodas et al. 1999, Milani et al. 2000). Those NEAs that might pose a
future threat usually pass close to the Earth on
previous orbits. On these close passes the Earth's gravitational field
substantially alters the orbit, so that typically only a very few specific
possibilities will lead to a subsequent impact or even another close pass.
If we look at the target plane (passing through the Earth and normal to the
asteroid orbit) and consider the error ellipse of the NEA, these few very
specific locations will generally occupy only a tiny fraction - perhaps one
part in 10^4 - of the target error ellipse. Only if the trajectory passes
through one of these so-called "keyholes" is there a risk of future impact
(say within the next century). There may be several keyholes corresponding
to possible impacts on different future dates. The estimate of risk then
depends on the probability that the actual trajectory will take the NEA
through one of the keyholes. The rest of the target plane is safe, and
corresponds to the NEA being scattered back into the general population with
an impact probability that is not substantially greater than that of typical
newly discovered objects.

>From a hazard perspective, the goal is to assure that the NEA does not pass
through the keyhole. If it does, and thus finds itself on a future collision
course with the Earth, then it will follow a very specific and highly
constrained orbit. Such an NEA is termed a virtual impactor. To eliminate
the possibility of impact, one is required only to make a negative
observation along this virtual trajectory. If the virtual NEA is not seen,
then we know it missed the keyhole and it poses no further near-term threat.

One way to look at the Spaceguard survey is as an effort to find each NEA
and declare it "safe". Once the NEA is safe, it is not necessary to
calculate its orbit with very high precision, although there may be good
scientific reasons to do so (such as identifying it as a future target for
radar imaging). So far, all the NEAs discovered by Spaceguard have been
declared safe.

+++++++++++++++++++++++++++++++++++++++++++

NEO News is an informal compilation of news and opinion dealing with Near
Earth Objects (NEOs) and their impacts. These opinions are the
responsibility of the individual authors and do not represent the positions
of NASA, the International Astronomical Union, or any other
organization. To subscribe (or unsubscribe) contact dmorrison@arc.nasa.gov.
For additional information, please see the website:
http://impact.arc.nasa.gov.  If anyone wishes to copy or redistribute
original material from these notes, fully or in part, please include this
disclaimer.

============================
* LETTERS TO THE MODERATOR *
============================

(9) SPACE 2002 CONFERENCE: ASTEROID SESSIONS

>From Michael Paine <mpaine@tpgi.com.au>

Dear Benny

Mark Sonter has just circulated some information about the Space 2002
Conference in in Albuquerque in March 2002. Below is an extract. Note that
Mark and Andy Smith are on the organising committee.

regards
Michael Paine

EXTRACT FROM MINUTES OF PLANNING MEETING FOR SPACE 2002
8. ASTEROID SESSIONS

Andy Smith is working on planetary protection from asteroids. This topic is
to be presented through asteroid sessions at Space 2002 and Robotics 2002.
We will have an excellent program on asteroid/comet emergency prevention and
preparedness and resource development. Key people in this effort are Jim
Benson, Mark Boslough, Jeff Kargel, David Kuck, Bryan Laubscher, and. Mark
Sonter.

Andy has contacted Russian colleagues. The Russians have  referred to the
Phobos spacecraft as a possible interceptor/deflector ID) vehicle and Andy
will get inputs from them and from other programs, like NEAR, with an ID
capability. Also, Andy  hopes we can get companies interested
in developing mining spacecraft to talk about a possible emergency response
role for this hardware. Andy  wishes to weigh the possibilities for getting
companies interested in developing mining spacecraft to talk about a
possible emergency response role for this hardware. The Mars natural
satellite Phobos provides an interesting objective for a possible resource
recovery demonstration mission. Some useful hardware may be available which
has already been developed.

If we have an asteroid/comet emergency, in the next decade or two, it may be
the asteroid mining programs that will have the best chance of saving us. It
looks like the R&D community would take at least 2 years to put together and
launch a system...and they are likely to have to work the interface hardware
and software problems on the spot.

Perhaps the mining community can include a defensive back-up plan in their
thinking and cut this time, at least in half. The mining community would
need to be able to deliver at least a 1,000-pound payload to the asteroid or
comet. Maybe we can get a paper or two on this.

There are many important problems related to emergency readiness for
asteroid impact on Earth. Sessions can be developed. Andy expects good new
data to be available (and a few papers) from Japanese, Italian, Russian, UN,
UK and German colleagues. Andy will contact them.

We want a session on tsunami-resistant tall structures....maybe even have a
panel or a workshop on it. Apparently not much has been written or
discussed, on this in terms of mitigation of damage from asteroid impact
induced effects.  We will get input from the civil engineering community on
tsunami resistant high-rise construction (per discussion). It would be good
to advertise that session in some Civil Engineering publication. Look for
ways to do this.  Maybe there could be a paper in Civil Engineering
Magazine.

==============
(10) RE: SPACE DRIFTERS (CCNet 19/10/01)

>From John Michael Williams <jwill@AstraGate.net>

Hi Benny.

The article by Duncan Steel was very interesting: In the Poynting-Robertson
effect, opposite frequency shifts in the two tangential directions would add and would
cumulate, the different tick counts of the two radiative clocks cumulating over centuries.

There may be yet another force related to these: If we assume an
irregularly-shaped small object orbitting the Sun and not rotating except secularly, the center of
mass will tend to be located closer to the Sun than the geometric center, in the radial
direction.  Somewhat like the equilibrium rotation rate of Earth's Moon.

This implies that the total surface area receiving sunlight will be less
than that shaded, or directed away, from the Sun:  The average such object
will have less surface area lighted than unlighted.

If we assume the object approximately in thermal equilibrium, there then
will be a net flow of heat away from the Sun side and into the larger-area,
cooler side. Imagine a teardrop-shaped object of fairly uniform density: Its
tail will tend always to be oriented away from the Sun, and the greater
surface area of the tail will lose heat faster than the Sunward area
(equilibrated with sunlight). 

Heat flow is energy flow, and radiated photons carry momentum as well as
energy.

Therefore, one would expect a net transfer of linear momentum tending to
accelerate the object radially toward the Sun. This alone merely would in effect increase G
slightly, making the average orbit slightly smaller than one without sunlight.

However, the angular momentum required to orbit such an object rigidly would
make the more distant side slightly lag the center of mass, on the average,
giving the linear momentum just mentioned a small tangential component,
accelerating the object slightly in its orbital direction.

The direction of the net force would be the same as that of the Yarkovsky
force, but it would not require rapid rotation.  It only would require an
irregular shape and an equilibrium state making the rotation rate, on the
average, equal to the time for a recently completed orbit.
--
                         John
                     jwill@AstraGate.net
                     John Michael Williams


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