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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