PLEASE NOTE:


*

CCNet, 58/2000 - 18 May 2000
-----------------------------


     "A comet that passed by unnoticed three years ago has raised new
     fears of a catastrophic collision. Although the comet was bright
     enough to be seen even by amateur astronomers in their gardens, it
     has been detected only because of measurements made accidentally
     by a satellite designed to observe the Sun. 'Because the comet was
     almost constant in brightness over several months, it should have
     been easily observable from the ground.' The failure to do so
     'underlines the need for full-sky surveillance of comets".
        -- Nigel Hawkes, The Times


(1) 'INVISIBLE' COMET TOO CLOSE FOR COMFORT
     THE TIMES, 18 May 2000

(2) NASA TRIES TO REVIVE COMET-CHASING CRAFT
    Space.com, 17 May 2000

(3) ASTEROID PROBE THAT CAN JUMP
    Ron Baalke <baalke@jpl.nasa.gov>

(4) PRESOLAR GRAINS - ENGAGEMENT RINGS FOR BACTERIA
    Larry Klaes <lklaes@bbn.com>

(5) A NUCLEAR SOLUTION TO GLOBAL WARMING?
    Stanford News Service <stanford.report@forsythe.stanford.edu>

(6) AND FINALLY: WAS CARL SAGAN PLANNING TO NUKE THE MOON?
    Rolf Sinclair <rolf@santafe.edu>

==========
(1) 'INVISIBLE' COMET TOO CLOSE FOR COMFORT

From THE TIMES, 18 May 2000
http://www.the-times.co.uk/news/pages/Times/frontpage.html?1986266

By Nigel Hawkes, Science Editor

A COMET that passed by unnoticed three years ago has raised new fears
of a catastrophic collision. Although the comet was bright enough to be
seen even by amateur astronomers in their gardens, it has been detected
only because of measurements made accidentally by a satellite designed
to observe the Sun.

A group of Finnish meteorologists report in Nature that an instrument
on the Solar and Heliospheric Observatory satellite detected radiation
from five comets which crossed the southern skies in 1997. Four of them
had been seen by ground-based observers but one passed by unrecorded.

"Because the comet was almost constant in brightness over several
months, it should have been easily observable from the ground," the
team, led by Teemu Mäkinen, concludes. The failure to do so "underlines
the need for full-sky surveillance of comets".

In some ways comets pose a greater potential hazard than asteroids.
There are fewer of them likely to be on a collision course but
detecting them well in advance is harder because they come from deep
space, from almost any direction and are, on average, larger.

The comet that was missed was a little too dim to be seen with the
naked eye but would have been easily visible with a telescope or even
binoculars.

Copyright 2000, The Times Newspapers Ltd.

==============
(2) NASA TRIES TO REVIVE COMET-CHASING CRAFT

From Space.com, 17 May 2000
http://www.space.com/scienceastronomy/solarsystem/deep_space_fix_000517.html

NASA Tries to Revive Comet-Chasing Craft

By Andrew Bridges
Pasadena Bureau Chief
posted: 07:00 am ET
17 May 2000

PASADENA, Calif. - Reaching across 179 million miles (288 million
kilometers) of space, engineers will shortly begin beaming new software
to a NASA spacecraft in a last-ditch effort to ready the idle probe for
a 2001 rendezvous with a distant comet.

The innovative software, hastily written and tested over the past five
months, will allow NASA's Deep Space 1 to recast the role of its
science camera into that of navigational instrument. The original
instrument, called a star tracker, ceased functioning in November 1999.

That loss, still unexplained, left the spacecraft without a way to use
the stars to orient itself in space. Since then, the spacecraft has
remained in a near slumber.

But that slumber must end soon if Deep Space 1 is to resume its course
so it can pull off a bonus September 2001 flyby of the comet Borrelly.

Full story here:

http://www.space.com/scienceastronomy/solarsystem/deep_space_fix_000517.html

==============
(3) ASTEROID PROBE THAT CAN JUMP

From Ron Baalke <baalke@jpl.nasa.gov>

One giant leap

An asteroid probe that can jump could leave crawlers standing
By Jeff Hecht
New Scientist Magazine
May 13, 2000

HOPPING may be the best way for robotic probes to explore the surface
of comets and asteroids. Japanese engineers have built a cylindrical
prototype that they say could take 9-metre hops in a low-gravity
environment. They propose adding a more advanced version of the probe
to MUSES-C, a Japanese mission to return an asteroid sample to Earth in
June 2006.

Wheeled robots work well on moons and planets, but the very low gravity
of asteroids and comets poses problems. The traction needed for
horizontal motion comes from the vehicle's weight pressing down on the
surface, but on an asteroid only 2 kilometres across the force of
gravity is about 100 000 times weaker than on Earth. That leaves so
little traction that the robot's wheels will slip unless they move very
slowly.

Full story here:

http://www.newscientist.com/news/news_223823.html

=================
(4) PRESOLAR GRAINS - ENGAGEMENT RINGS FOR BACTERIA

From Larry Klaes <lklaes@bbn.com>

http://www.sfgate.com/cgi-bin/article.cgi?file=/examiner/archive/2000/05/15/NEWS2726.dtl

Scientists touch gems older than solar system

Keay Davidson
EXAMINER SCIENCE WRITER
                                                        
May 15, 2000

The oldest substances ever to touch human hands - microscopic gems from
outer space - could change our understanding of the solar system and
the origin of its elements.

So tiny that they're dubbed "engagement rings for bacteria," these
"presolar grains" are found within larger space rocks called meteorites
and in fluffy debris from the tails of comets.

The grains are called "presolar" because of their age. They might be 6
billion years old - more than a billion years older than the sun,
Earth, and other planets - according to Donald D. Clayton, the
scientist who predicted their existence a quarter of a century ago.

"Their very existence shattered the belief that studying objects of
such antiquity on Earth is impossible," yet most of the astronomers
remain almost unaware of the implications of such objects,
says Clayton, a professor at Clemson University in South Carolina. He
is a pioneering figure in study of "nucleosynthesis," the study of the
origin of the chemical elements.

The micro-gems' reality was vigorously debated in the 1970s. Then it
was experimentally confirmed in the late 1980s, when they were found
within meteorites.

Yet more than a decade later, most scientists seem unaware of their
existence - unaware that they now has access to these relics of an
unimaginably distant time, a time long before Earth and the rest of the
solar system formed. "The world of astronomers has been relatively
ignorant of this happening," says Clayton, who campaigns to boost the
visibility of presolar grains.

Examined under a microscope, some grains, which are typically
millionths of a meter wide, resemble macadamia nuts that have been
partly excavated by nibbling mites.

Clayton recently sent a letter to the journal Science, remarking that a
story on trends in planetary science research neglected to stress the
historic relevance of presolar grains. In a response published in the
same issue, the article's author, planetary scientist David J.
Stevenson of Caltech, readily acknowledged the objects constitute an
"important, remarkable, and undisputed development."

Before the solar system formed

Presolar grains tell us "about the stars that contributed to the
material from which the solar system formed. . . . It is a testament to
our origin," Stevenson explained in an e-mail to The Examiner
last week.

Why have astronomers been so slow to pick up on such a fundamental
discovery - of these calling cards, as it were, from the youth of the
Milky Way galaxy?

Clayton offered an explanation: "People are busy pursuing their own
(fields of) expertise - that's how you get to the top - and sometimes
we don't take note of other developments that are happening."

According to present theories, the presolar grains form from chemical
isotopes ejected by exploding stars and red giant stars. Over billions
of years, clouds of gas, molecules and presolar grains accumulate.
Eventually gravity pulls them together. The result is an object massive
enough to undergo nuclear fusion reactions - a star, like our Sun.

The rest of the cloud collapses into a rotating disk, in which matter
gathers into asteroid-like rocks called planetesimals. Many
planetesimals gradually accumulate into planets, like Earth.

Grains ride in meteorites, comets

Presolar grains aren't floating around the solar system by themselves,
waif-like. They travel aboard bigger chunks of matter - meteorites,
asteroids and comets.

For example, over the millions of years during which the cloud
collapsed into the sun-circling disk, the presolar particles chemically
interacted with, and became locked within, asteroids. During collisions
between asteroids, slivers and chunks fly off.

Some of those slivers eventually fall to Earth as meteorites. Flying
many miles per second through space, some meteorites glow brilliantly
as they heat from friction with Earth's atmosphere. A few are
recovered and sent to scientists. They use careful chemical techniques
to recover tiny presolar grains from the celestial visitor.

"Tiny" is the operative word: A typical carbon-rich meteorite contains
only a minute amount of presolar grains - about one part in 100,000,
Clayton says.

Their presolar origin was determined by examining variations in the
numbers of isotopes within the grains. (Certain elements come in
slightly different forms, dubbed isotopes, that behave the same
chemically but vary in weight because they carry differing numbers of
electrically neutral particles called neutrons.)

Variations in isotopes

As it turns out, presolar grains display wild variations in their
isotopic ratios. This, Clayton says, could have only one credible
cause: They formed in the extremely hot atmosphere of a star or in the
hellish mega-explosion of a supernova or exploding star.

"As the hot gas cools, the gems can solidify before the stellar
isotopes become diluted with the interstellar gas," Clayton says. The
isotopic ratio is "the smoking gun" of the particles' deep-space,
pre-solar system origins, he adds.

Their age cannot be determined because they contain too few atoms for
analysis. But researchers are trying to think of ways to examine such
tiny objects that might eventually yield a precise age, he says. 

"The solar system is 4.6 billion years old - we know that number pretty
well," Clayton says. "All we know for sure is these particles are older
than that."

Why study such substances? Because they hail from a period before the
solar system was born, their composition could shed light on the
chemical composition of the primeval cloud from which it condensed
billions of years ago.

They might also contain clues to old questions of solar system
formation, such as: Did the primeval cloud collapse at least partly in
response to a shock wave from an exploding star?

"The grains, as 'stardust' - pieces of stars - record details of those
stars' production of new elements," Clayton says. "This has shown
several aspects of stars that we were calculating incorrectly. So the
grains are teaching us about stars, about their internal structure,
about the nuclear reactions that happen within them. It's all very
intricate."

In that regard, presolar grains are leftovers from the cosmic process
that made you, me and the world around us possible: nucleosynthesis.

In this process, extreme heat and pressure within stars and supernovae
fuses atomic nuclei to assemble the elements heavier than hydrogen and
helium. Those elements include the elemental building blocks of Earth -
such as iron and silicon - plus those that make life possible: among
them, carbon and oxygen.

"The calcium in your bones and the iron in your hemoglobin in your
blood are atoms that were all created in pre-solar supernova
explosions," Clayton points out.

An introduction to presolar grains is on the World Wide Web at:

http://www.ciw.edu/lrn/psg_main.html

©2000 San Francisco Examiner 

==============
(5) A NUCLEAR SOLUTION TO GLOBAL WARMING?

From Stanford News Service <stanford.report@forsythe.stanford.edu>
05/16/00

CONTACT: Mark Shwartz, News Service (650) 723-9296;
                 e-mail mshwartz@stanford.edu

COMMENT: William C. Sailor (650) 724-5698;
                 e-mail sailor@leland.stanford.edu

                 Bob Van der Zwaan (650) 725-6948;
                 e-mail zwaan@stanford.edu
                 Center for International Security and Cooperation

EDITORS: Sailor and Van der Zwaan`s article, “A Nuclear Solution to
         Climate Change?” appears in the May 19 issue of Science.

EMBARGOED until Thursday, May 18, at 11 a.m. PDT
 
A nuclear solution to global warming?


Nuclear power can play a significant role in preventing catastrophic
global warming, according to a controversial article published this
week in Science magazine.

William C. Sailor and Bob van der Zwaan, visiting Science Fellows at
Stanford`s Center for International Security and Cooperation (CISAC),
co-authored the report, which appears in the May 19 issue of Science.

They are among seven researchers affiliated with "Nuclear Power Issues
and Choices for the 21st Century" - a CISAC project investigating
whether nuclear energy has a legitimate role in preventing global
warming.

"Mankind is facing a tremendous challenge with global climate change,"
says physicist van der Zwaan. "In the coming two decades we have to
consider new energy sources, including nuclear."

But van der Zwaan, on leave from the Free University (Vrij
Universiteit) of the Netherlands, admits that widespread public concern
has led several countries to halt development of nuclear energy.

"Eighty-five percent of all Dutch people are opposed to it," he notes,
and the numbers are similar in other European countries.

Clean-burning fuel

Most of the world`s energy is derived from fossil fuels like coal, oil
and natural gas. Only about 6 percent comes from nuclear power plants.

But burning fossil fuels emits large amounts of carbon dioxide (CO2)
and other gases that trap infrared radiation from the sun.

As a result, say many climatologists, our atmosphere is heating up like
the inside of a greenhouse, and unless we reduce the rate of CO2 gas
emissions, the temperature of the Earth will increase by as much as 6 F
in the next century.

Such global warming, according to worst-case scenarios, will cause
disastrous floods, droughts and erratic changes in ocean currents, and
even will spread tropical diseases and parasites throughout the planet.

Advocates say that nuclear power will help prevent global warming
because nuclear reactors produce virtually no greenhouse gases. They
point to France, where about 60 pollution-free power plants provide
three-fourths of the country`s electricity.

But critics argue that nuclear power is inherently dangerous and
prohibitively expensive. They point out that accidents like the 1986
Chernobyl power plant disaster in the former Soviet Union can result in
radiation poisoning that lasts many generations.

Opponents also maintain that safely storing radioactive waste is
difficult, and that newly designed breeder reactors could make it
easier for plutonium fuel to get into the hands of terrorists and
others eager to build small-scale nuclear weapons.

Nuclear solution?

Van der Zwaan and Sailor address these arguments in the Science
article.

"Nuclear power can play a significant role in mitigating climate
change," they write.

The authors point to recent studies showing that, to prevent dangerous
climate change from occurring in the next 50 years, CO2-gas emissions
must remain at their current levels - despite a projected 50 percent
population increase by the year 2050 that could double or triple world
demand for energy.

"Lacking a crystal ball that tells us the future," write Van der Zwaan
and Sailor, "we simply select one possible scenario that achieves the
emissions target."

Their scenario envisions a world in which one-third of all energy comes
from fossil fuels; one-third from renewable resources, like solar and
wind power; and one-third from nuclear power.

To achieve that ambitious goal, all the nations of the world would have
to consume less oil, coal and natural gas than they do today, while
increasing renewable and nuclear energy sources at least tenfold.

To accomplish that will require increasing the number of nuclear
reactors on Earth from about 430 to roughly 4,000, which means that
more than one nuclear reactor would have to be built every week for the
next 50 years.

"That would require a massive industrial effort," van der Zwaan
concedes, costing trillions of dollars, but he believes that developed
nations like the United States can achieve this objective if there is
strong popular support.

According to the Department of Energy, the United States has 104
nuclear reactors in operation today. Twenty-eight have been shut down
permanently since 1953, and there are no plans to build new ones.

"The first thing that has to happen is a general acceptance by the
public that fossil fuels create a threat to our future," notes Sailor,
who holds a doctorate in nuclear engineering. "Once that`s generally
recognized, then all alternatives to nuclear power must be thoroughly
investigated."

But he argues that renewable forms of energy such as hydro, wind and
solar power are fraught with technical or environmental problems that
make them unlikely substitutes.

"Once it`s realized that we cannot make ends meet without nuclear
energy, there is a chance that public opinion will turn greatly so that
nuclear power will once again be acceptable," he notes.

Before that can happen, he says, the issues of safety, cost, waste and
proliferation must be addressed.

Exaggerated risks?

"The risks of radioactivity from nuclear reactors are sometimes
overstated, so the feeling of many people is just biased," according
to van der Zwaan.

He and Sailor write that, with the exception of Chernobyl-type
reactors, the present generation of nuclear power plants has a good
safety record, experiencing only one accidental meltdown at the Three
Mile Island (TMI) plant in Pennsylvania in 1979.

"However, changes in equipment and operating procedures since TMI
suggest considerably improved safety," they note. "There are also
well-developed designs for a next generation of reactors, which promise
still greater safety."

The authors maintain that the risk of contamination from stored nuclear
wastes is also exaggerated, noting that the U.S. government has
outlined a rigorous standard of protection for people living near the
proposed nuclear waste repository at Yucca Mountain, Nev.

"If the U.S. repository is found to meet the standard and is opened,"
they write, "it will be able to handle all the U.S. wastes expected
through the next few decades. However, a large expansion of nuclear
power may require using alternative disposal approaches.

"Any nuclear waste project will have to fight legal challenges, which
will be political in nature. For instance, the State of Nevada has
already spent considerable effort fighting the Yucca Mountain Project,
which the state claims has been forced upon it.

"Public support for these claims could decrease if nuclear energy were
seen as a necessary part of a solution for climatic problems and,
overall, as environmentally beneficial. Nevadans might then be more
willing to accept the minuscule risks resulting from having a
repository in their state."

The authors conclude, "There are no insurmountable technical barriers
to nuclear expansion, but the expansion must be performed under very
high safety standards."

Unresolved issues

A greater challenge for advocates of nuclear power, say van der Zwaan
and Sailor, are the unresolved concerns over the spread of nuclear
weapons and the high cost of nuclear energy.

"There must be international confidence that nuclear power can be used
throughout the world without increasing weapons proliferation," they
write.

"To date, commercial nuclear power has played little, if any, role as a
bridge to national entry into the nuclear arms race, nor are there any
known cases in which individuals or sub-national groups have stolen
materials from nuclear power facilities for use in weapons.

"However, development of nuclear weapons has been aided in at least
three countries (India, Iraq and Israel) by use of research reactors
obtained under the cover of peaceful research programs. Absent
effective safeguards, nuclear power could provide a similar cover to
future weapons efforts.

"Additional fears are raised by the possibility that with a major
nuclear expansion, plutonium-fueled breeder reactors will be widely
used to stretch uranium resources, creating risks of plutonium
diversion for weapons purposes.``

The authors conclude that "all fuel cycles pose some proliferation
risk, and even the elimination of nuclear power would not eliminate the
possibility of a country embarking on a nuclear weapons program.

"Thus, improved international safeguards institutions are needed, with
strength and responsibility at an entirely new level of capability,
even in the absence of a major expansion of nuclear power."

Economics is another major obstacle to the development of nuclear
power. The average nuclear power plant costs about $1.5 billion and
takes four years to build, according to the authors. But natural gas
power plants are cheaper and faster to build, so the authors recommend
gradually phasing in a "carbon tax" of about 30 cents per gallon on
petroleum to make nuclear power more competitive.

"In the meantime," they suggest, "the Department of Energy and other
agencies worldwide should increase reactor research efforts aimed at
simplified designs and economies of scale in construction."

Open dialogue

Sailor, who is currently on a one-year sabbatical from the Los Alamos
National Laboratory in New Mexico, says that the mission of CISAC`s
"Nuclear Power Issues and Choices" project is to publish a neutral,
unbiased study next year analyzing the future prospects for nuclear
energy.

Study participants include three other co-authors of the May 19 Science
article: David Bodansky, University of Washington professor emeritus of
physics; Chiam Braun, senior vice president of Altos Management
Partners, Inc., in Los Altos, Calif.; and Steve Fetter, associate
professor at the University of Maryland`s School of Public Affairs.

The project also will conduct a one-day workshop at CISAC on June 23
that will include panelists representing a broad spectrum of opinion on
nuclear energy issues.

"No technology, including nuclear, can be a panacea," notes van der
Zwaan, but he maintains that it is important for the public to set
aside fears and prejudices and reconsider nuclear energy as part of the
solution to global warming.

"I have a feeling we are at a crossroads as far as public opinion," he
adds.

-By Mark Shwartz-

=============
(6) AND FINALLY: WAS CARL SAGAN PLANNING TO NUKE THE MOON?

From Rolf Sinclair <rolf@santafe.edu>

Hi Benny --

In case you didn't see this article in the NY Times. (It refers to
an earlier letter in Nature.) Such a study may well have been
made, as a way of studying all options, but it's hard to know now
just how seriously it was pursued.

Cheers,
Rolf

***********
U.S. PLANNED NUCLEAR BLAST ON THE MOON, PHYSICIST SAYS

From The New York Times, 16 May 2000

The United States weighed a plan to detonate a nuclear bomb on the
moon as a show of military and technical strength during the
feverish post-Sputnik days of the cold war, a physicist involved
in the plan said. The physicist, Leonard Reiffel, 72, said
yesterday that he was in charge of a highly classified study of
the blast's visibility, its possible science benefits and its
effects on the moon's face. His research got under way in 1958,
sponsored by the Air Force special weapons center in Albuquerque,
and involved up to 10 people on his staff, including Carl Sagan,
then a young astronomer and later a famous popularizer of science.

"The foremost intent was to impress the world with the prowess of the
United States," Dr. Reiffel said in an interview. "It was a P.R.
device, without question, in the minds of the people from the Air
Force."

FULL STORYT at
http://www.nytimes.com/library/national/science/051600sci-us-nuke.html>

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