CCNet, 69/2000 - 14 June 2000

     "According to the Committee’s scientific assessment, there have
     been about 1,800 cases of thyroid cancer in children who were 
     exposed at the time of the [Chernobyl] accident, and if the      
     current trend continues, there may be more cases during the next  
     decades. Apart from this increase, there is no evidence of a major
     public health impact attributable to radiation exposure fourteen
     years after the accident. There is no scientific evidence of
     increases in overall cancer incidence or mortality or in
     non-malignant disorders that could be related to radiation
     exposure. The risk of leukaemia, one of the main concerns owing to
     its short latency time, does not appear to be elevated, not even
     among the recovery operation workers. Although those highly
     exposed individuals are at an increased risk of
     radiation-associated effects, the great majority of the population
     are not likely to experience serious health consequences from
     radiation from the Chernobyl accident.”
           -- United Nations Scientific Committee on the Effects of
              Atomic Radiation, 6 June 2000

    BBC Online News, 13 June 2000


    Ron Baalke <>


    Paul Davies <>

    Leon Jaroff <>


From BBC Online News, 13 June 2000

Chernobyl 'not so deadly'

The Chernobyl nuclear disaster had less impact on public health than
was initially feared, according to UN data cited by the International
Atomic Energy Agency (IAEA).

About 1,800 children did develop thyroid cancer, a treatable disease
which is rarely fatal, and more cases are expected, an IAEA statement
said on Tuesday.

"However, with this exception, there is no scientific evidence of
increases in overall cancer incidence or mortality or in non-malignant
disorders that could be related to radiation exposure," it said.

Thirty-one people died from radiation poisoning in the explosion and
its immediate aftermath.

Radiation exposure

Health experts feared that thousands living nearby would develop
cancers as a result of the high levels of radiation emitted.

But a report by the UN's committee on the effects of atomic radiation
(Unscear) "concludes that there is no evidence of a major public health
impact attributable to radiation exposure 14 years after the accident,"
the Vienna-based IAEA said.

It is thought the thyroid cancers were caused by radioactive iodine -
one of the most serious sources of radiation in the fallout.

Iodine, which is found in certain foods and milk, collects in the
thyroid gland.

The children, who drank more milk and had smaller thyroid glands,
received a radioactive dose about three times higher than adults.

Disputed figures

The precise impact of the Chernobyl disaster has always been disputed.
According to a group representing those who worked in the relief
operations following the explosion about 15,000 people were killed.

Ukraine's own health ministry has estimated that 3.5 million people,
over a third of them children, have suffered some illness as a result
of the contamination.

Levels of radioactivity remain unexpectedly high in some parts of
northern Europe, according to one recent report.

It said restrictions on some foods would have to remain in place for up
to 50 years.

The nuclear power plant, after further minor leaks and safety worries, 
is due to close at the end of the year.

Copyright 2000, BBC

** The U.N. press release can be accessed at:


From, 12 June 2000

Space rock drops in

A METEOR as bright as the Sun was seen over north central Victoria on
Saturday, heading for earth.

Gary Gibson, research director at the Melbourne-based Seismology
Research Centre, said he saw the meteor and was astounded by its speed
and brightness. He has since been contacted by several people who saw
it and felt it, presumably hitting the earth.

They believed there had been an earthquake.

Mr Gibson said the meteor, which he saw at 5.24pm, was visible for only
about three seconds but left a vapor trail which remained in the sky for
almost 10 minutes.

"The sun was still up and it was as bright as the sun, it was just
amazing," he said.

"It started off looking like the vapor train of an aircraft, but instead
of going horizontally it was clearly going downwards.

"I thought, `Oh that doesn't look good' but it came down at such a rate
it could not possibly have been an aircraft."

The meteor may have been part of a shower seen by walkers in northern
Tasmania, who at first thought a light aircraft was in distress.

The walkers said the bright meteor was visible for 20 minutes.

Copyright 2000, WorldNet


From Ron Baalke <>
NEAR image of the day for 2000 Jun 13

Twin Pits

Some impact craters occurring on Earth and on other planetary bodies
come in close pairs. These double craters are sometimes the result of
the chance superimposition of two distinct impact events. However, a
few double craters are also thought to have formed by the impact of 
two similarly sized bodies that are traveling in close orbit or 
touching each other. The near-Earth asteroid 4769 Castalia, which has
been imaged by radar, is one of the most promising candidates for being
such a "contact binary."

This image, taken on June 10, 2000, from an orbital altitude of 51
kilometers (32 miles), caught an obliquely illuminated view of a double
crater on Eros. The two craters are so close to each other that they
merge into  the single dumbell-shaped depression in the center of  the
image. Each of the two craters is about 550 meters (1800 feet) across.
The whole  scene is 1.9 kilometers (1.2 miles) across.
Built and managed by The Johns Hopkins University Applied Physics
Laboratory, Laurel, Maryland, NEAR-Shoemaker was the first spacecraft
launched in NASA's Discovery Program of low-cost, small-scale planetary
missions.  See the NEAR web site for more  details 


From SCIENCE-WEEK (Shareware Edition)
June 16, 2000 -- Vol. 4 Number 24


The Sun, a *main-sequence star 1.4 million kilometers in diameter,
is composed predominantly of hydrogen and helium (approximately 70
percent hydrogen by mass, 28 percent helium by mass, and 2 percent
heavier elements by mass) and it generates its energy via nuclear
fusion processes, particularly via the *proton-proton chain
reaction. As a result, the Sun is losing mass at a rate of
approximately 4 million metric tons per second.

The generation of energy occurs in the "central core", which has a
temperature of approximately 15 million degrees kelvin, is
approximately 400,000 kilometers in diameter, and contains
approximately 60 percent of the mass of the Sun in 2 percent of
its volume.

Outside the core is the "radiative zone", an envelope of unevolved
material through which energy from the core is diffusively
transported by successive absorption and emission of radiation in
collisions between atomic particles. It has been estimated that it
may take from 1 million years to as long as 10 to 20 million years
for the energy generated in the core to reach the surface.

The radiative zone extends to within 200,000 kilometers of the
surface. In the surface layer (the "convective zone"), where the
temperature is only 1 million degrees kelvin, convection is the
most important mode of energy transport.

* Eugene N. Parker (University of Chicago, US) presents a review
of the physics of the Sun, the author making the following points:

1) The Sun is essentially a thermonuclear core enclosed in an
opaque shroud that insulates the high temperature of the core from
the cold Universe outside. The core is brighter than 10 supernovas
at maximum light, but the enclosing shroud turns back all but one
part in 2 x 10^(11) of the thermal radiation. The outward journey
of the energy from the core takes approximately 1 million years,
which illustrates the immense opacity and thermal capacity of the

2) Approximately 10^(-5) of the outflowing energy from the core of
the Sun is diverted into magnetic fields that produce a variety of
exotic effects, including *coronal mass ejection, *solar flares,
the million degree corona, the *solar wind, and x-ray emission.
These phenomena are of interest to the physicist because they
represent unanticipated manifestations of classical physics,
extrapolations to astronomical scales of basic principles
traditionally studied in terrestrial laboratories.

3) The total luminosity of the Sun varies with time, and
systematic monitoring of several Sun-type stars during the past 4
decades reveals magnetic activity cycles comparable to that of the
Sun. The luminosities of some of those stars have been monitored
for approximately 15 years, and the data show approximately the
same variation as the magnetic activity.

4) The Earth contains a great deal of information about past solar
activity. The rate of production of carbon-14 depends directly on
the intensity of *cosmic rays, and such rays are partially
excluded from the Solar System by the outward sweep of magnetic
fields in the solar wind. Thus the cosmic ray intensity and
carbon-14 production vary oppositely to the general level of
solar activity.

5) The carbon-14 record indicates that over the last 70 centuries
the Sun has been without normal activity for 10 centuries and
hyperactive for 8 centuries. The other 52 centuries were variable
but more or less normal. The most recent quiescent period was from
1645 to 1715, the period called the "Maunder Minimum". The 12th
century "Medieval Maximum" is the most recent epoch of
hyperactivity. The empirical relation between the total luminosity
and magnetic activity, based on many Sun-type stars, suggests that
the Sun was fainter during the *Maunder Minimum by 0.4 +- 0.2
percent, and perhaps brighter by a comparable amount during the
Medieval Maximum. The mean annual temperature in the northern
temperate zone was lower than normal by 1 to 2 degrees centigrade
during the Maunder Minimum and higher by 1 to 2 degrees centigrade
during the Medieval Maximum. The fractional change in temperature
is comparable to the fractional change in solar brightness, with
the implication that the Sun is the driver of the climate. The
consequences for agriculture were severe during both periods, the
Maunder Minimum being disastrous in northern Europe and China, and
the Medieval Maximum disastrous in the semi-arid regions. These
periods of abnormal activity of the Sun are without explanation,
as are the variations within the so-called "normal centuries".
6) The general level of solar activity doubled or tripled from
1900 to 1950, an estimate based on sunspot numbers and on the
intensity of geomagnetic activity. This increase suggests an
increase in solar luminosity by perhaps one part in 2000, and the
author suggests it is interesting to note that the mean
temperature in the northern temperate zone, as well as the surface
sea water temperatures, rose during the same period. "Warmer seas,
of course, reduce the rate at which atmospheric carbon dioxide is
absorbed into the oceans. It appears that the global warming since
1950 is in part a consequence of the continuing increase in solar
brightness, seriously aggravated by the extravagant burning of
fossil fuel. So the mystery of the variations in the total
luminosity of the Sun is part of the complicated picture of global
[Editor's note: See report #3 in this issue for another approach
to millennial-scale climate changes.]
Eugene N. Parker: The physics of the Sun and the gateway to the
stars. (Physics Today June 2000)
QY: Eugene N. Parker, University of Chicago 312-702-9808.
Text Notes:
* main-sequence star: The Main Sequence is a region on the
* Hertzsprung-Russell diagram where most stars lie, including our
own Sun. The evolution of a star can be diagrammed as a movement
along the Main Sequence and an eventual branching off the Main
Sequence to regions associated with various types of old stars.
* Hertzsprung-Russell diagram: The Hertzsprung-Russell diagram is
a plot of stellar absolute magnitude against spectral type, and is
perhaps the most useful diagrammatic aid in astrophysics. It
allows the portrayal of the evolution of a star as occurring along
various paths in the diagram.
*proton-proton chain reaction: A chain of nuclear reactions inside
a star that converts hydrogen to helium, with the associated
release of energy. In the reaction, 4 hydrogen nuclei (protons)
fuse to form one nucleus of helium, with the production of a
number of intermediate nuclei such as deuterium and isotopes of
lithium, beryllium, and boron. The proton-proton reaction is the
most important stellar reaction at temperatures below 18 million
degrees kelvin, and thus operates chiefly in stars of less than 2
solar masses.
* coronal mass ejection: The corona is the Sun's faint outer
atmosphere, where the temperature is 2 million degrees kelvin or
more, the corona consisting of a low-density hot gas that glows
with a pale white color.
* solar flares: A solar flare is a sudden release of energy in the
corona of the Sun, the phenomenon usually lasting up to several
hours (in rare cases, up to more than a day).
* solar wind: The solar wind is the steady flow of charged
particles, consisting primarily of protons and electrons, from the
solar corona into interplanetary space. The solar-wind particles
have energies high enough to enable the particles to escape the
Sun's gravitational field, but the wind is influenced by the Sun's
magnetic field, and the particles can be trapped by planetary
magnetic fields.
* cosmic rays: Highly energetic particles moving at close to the
speed of light and continuously bombarding the Earth's atmosphere
from all directions. The energies of the particles are enormous
and range from 10^(8) to over 10^(19) electronvolts.
* Maunder Minimum: Named after the astronomer Edward W. Maunder
(1851-1928), who first noted the absence of reports of sunspots in
the period 1645 to 1715.
Summary & Notes by SCIENCE-WEEK 16Jun00
For more information:
Related Background:

The science of helioseismology is the study of the solar interior
using observations of solar surface manifestations of resonant
sound waves (pressure modes; p-modes) traveling in the solar
interior. In other words, helioseismology is the study of the
solar interior structure by using the oscillations of its surface.
Since p-mode frequencies are *Doppler-shifted by motions in the
line of sight, they can also be used to study the internal
dynamics of the Sun, such as internal rotation and convection.

* P. Demarque and D.B. Guenther (2 installations, US CA) present a
review of current research in helioseismology, the authors making
the following points:

1) In 1962, Leighton et al discovered patches of the surface of
the Sun moving up and down with a velocity of the order of 15
centimeters per second, with periods of approximately 5 minutes.
Called the "5-minute oscillation", the motions were originally
believed to be local in character and somehow related to turbulent
convection in the solar atmosphere. In 1970, Ulrich suggested that
the phenomenon is global and that the observed oscillations are
the manifestation at the solar surface of resonant sound waves
(pressure modes or "p-modes") traveling in the solar interior.

2) Stellar oscillation theory, the main theoretical framework for
helioseismology, also predicts the existence of buoyancy driven
modes (gravity modes, or "g-modes") that have been observed in
other astrophysical contexts, but it is not clear at present
whether g-modes are excited in the Sun. G-modes are expected to be
exponentially damped in convective regions, so their amplitudes at
the top of the solar convective envelope are expected to be much
smaller than in the radiative core. In contrast to p-modes, which
have maximum amplitudes in the outer parts of the Sun, g-modes
exhibit their largest amplitudes in the solar core. If observable,
g-modes would be sensitive probes of the solar core, where p-modes
are least sensitive.

3) There are many facets of helioseismology, and the field has
contributed to the study of stellar evolution and to astrophysics
and physics in general. The interpretation of a wealth of
ground-based data, most recently provided by the Global
Oscillation Network Group (GONG) project, a network of observing
stations distributed around the globe to observe the Sun
continuously, and the Solar and Heliospheric Observatory (SOHO)
space mission, have led to many advances. The most important
accomplishments of helioseismology include the following:

a) The testing of the physical assumptions of stellar evolution
b) The determination of the depth of the solar convection zone.
c) The reconstruction of the internal rotation profile in the
outer half of the solar radius.
d) The detailed probing of the *superadiabatic transition layer
near the solar surface.
e) The realization of the important role played by the diffusion
of helium in the interior of the Sun and the seismic determination
of the helium abundance in the convection zone.
f) The determination of the age of the Sun by seismic means.
g) The setting of a strong constraint on *varying-
gravitational-constant cosmologies.
h) The demonstration that the *solar neutrino discrepancy is
likely to reveal fundamental new knowledge about neutrinos and
their interaction with matter.
P. Demarque and D.B. Guenther: Helioseismology: Probing the
interior of a star. (Proc. Natl. Acad. Sci. US 11 May 99 96:5356)
QY: P. Demarque, Yale University, 203-432-4771.
Text Notes:
* main-sequence star: See main report.
* proton-proton chain reaction: See main report.
* Doppler-shifted: In general, the term "Doppler shift" refers to
the change in wavelength of electromagnetic radiation as a result
of relative movement between the source and the observer.
* superadiabatic transition layer: An adiabatic process is any
thermodynamic process, reversible or irreversible, that takes
place in a system without exchange of heat with the surroundings
of the system. All real processes are nonadiabatic in the sense
that some heat exchange always occurs. But close approximation to
an adiabatic ideal can be realized in practice. In the context of
this report, the "superadiabatic transition layer" is the
transition between deep convection, where the temperature gradient
is nearly adiabatic, and the shallow outer layers of the Sun,
where radiative losses dominate.
* varying-gravitational-constant cosmologies: In general, this
term refers to cosmological theories dependent on a time-varying
universal gravitational constant. Recent helioseismological data
have provided a strong limit on the variation of the universal
gravitational constant during the lifetime of the Sun, and this
limit is stronger by almost one order of magnitude than previous
* solar neutrino discrepancy: Neutrinos are fundamental particles
with zero charge, possibly zero mass, and an angular momentum
factor (spin) of 1/2. Various processes produce neutrinos: stellar
nuclear reactions, reactions occurring during supernova
explosions, cosmic ray collisions with matter, etc. Measurements
of solar neutrinos have produced a mystery: the neutrino density
measured by detectors is approximately one-third that expected
from theoretical calculations of solar neutrino emission. Two
kinds of solutions have been proposed to resolve this mystery, one
solution involving revisions to the theory of stellar structure,
and the other solution involving revisions to nuclear particle
Summary & Notes by SCIENCE-WEEK 30Jul99
For more information:



Over the course of geologic history, the environment on Earth has
been far from static. Geologic evidence suggests that 600 million
years ago the atmosphere lacked sufficient oxygen to support
animal life. More recently, as indicated by sediments recording
conditions over the past 500,000 years, the climate of the planet
varied between at least two different states. The record from the
past 150,000 years is particularly well-preserved, offering
details concerning repeated climate changes.

Between approximately 131,000 and 114,000 years ago, a warm period
similar to the climate of today occurred. This was followed by
what is called the "Wisconsin ice age", which ended approximately
12,000 years ago when the current relatively warm *Holocene period

Records of changes in Earth's climate are particularly clear in
high-resolution ice cores, which can preserve histories of local
climate (as reflected in snowfall and temperature), regional
climate (as reflected in wind-blown dust, sea salt, etc.), and
broader climate (as reflected in trace gases deposited from the
atmosphere) -- all on a common time scale that can demonstrate
synchrony of climate changes over wide regions.

High resolution ice-core and deep-sea sediment-core records over
the past million years show evidence of abrupt changes in climate
superimposed on slow alternations of ice-ages and interglacial
warm periods.

The term "solar irradiance" refers to the amount of solar
irradiation received from the Sun, and this can vary considerably
and with a complex of periodicities. In 1920, the meteorologist
Milutin Milankovic (1879-1958) proposed that small changes in
Earth's orbit, *precession, and *inclination affect the heat
balance and modify climate (the alterations called "solar
forcing"). The Milankovic hypothesis was not taken seriously
until 1976, when teams studying sediment cores from the ocean
floor constructed a history of ocean temperature that matched the
predictions of the Milankovic hypothesis, with two different
ocean cores providing similar results.

* C.D. Keeling and T.P. Whorf (University of California San Diego,
US) present a proposal to explain sudden climate changes on the
scale of thousands of years, the authors making the following

1) Variations in solar irradiance are generally believed to
explain climatic change on 20,000- to 100,000-year time-scales in
accordance with the Milankovic theory of the ice ages, but there
is no conclusive evidence that variable solar irradiance can be
the cause of abrupt fluctuations of climate on time-scales as
short as 1000 years.

2) The authors propose that such abrupt millennial changes, seen
in ice and sedimentary core records, were produced in part by well
characterized almost periodic variations in the strength of the
global oceanic tide-raising forces caused by resonances in the
periodic motions of the Earth and Moon. A well-defined 1800-year
tidal cycle is associated with gradually shifting lunar
declination from one episode of maximum tidal forcing on the
centennial time-scale to the next. An amplitude modulation of this
cycle occurs with an average period  of approximately 5000 years,
associated with gradually shifting separation intervals between
*perihelion and *syzygy at maxima of the 1800 year cycle.

3) The authors propose that strong tidal forcing causes cooling at
the sea surface by increasing vertical mixing in the oceans. The
authors suggest that on the millennial time-scale, this tidal
hypothesis is supported by findings, from sedimentary records of
*ice-rafting debris, that ocean waters cooled close to the times
predicted for strong tidal forcing.
C.D. Keeling and T.P. Whorf: The 1800-year oceanic tidal cycle: A
possible cause of rapid climate change. (Proc. Natl. Acad. Sci. US
11 Apr 00 97:3814)
QY: Charles D. Keeling []
Text Notes:
* Holocene period: The most recent epoch of the geologic time
scale, from approximately 10,000 years ago to the present.
* precession: In general, the wobbling motion of a spinning top or
gyroscope in which the axis of rotation gradually sweeps out a
conical volume. The spinning Earth undergoes a slow precession due
to the combined gravitational attraction of the Sun, Moon, and
* inclination: In general, the angle between the orbital plane of
a body and the reference plane centered on the object around which
the body is revolving.
* perihelion: The point in an elliptical orbit around the Sun
which is nearest the center of the Sun.
* syzygy: In this context, those points in the orbit of the Moon
where the Moon, Earth, and Sun are in a straight line.
* ice-rafting debris: In general, in this context, "ice-rafting"
is the transport of rock particles and other materials by floating
Summary & Notes by SCIENCE-WEEK 16Jun00
For more information:
Related Background:
* Richard B. Alley (Pennsylvania State University, US) reviews
current ice-core research, the author making the following points:

1) Dating and accumulation: On some glaciers and ice sheets,
sufficient snow falls each year to form recognizable annual layers
that are marked by seasonal variations in physical, chemical,
electrical, and isotopic properties. These variations can be
counted to determine ages of the layers, and accuracy of the
determination can be assessed by a number of ways, including
comparison to the chemically identified fallout of historically
dated volcanoes.

2) Paleothermometry: Ice cores are essentially local
paleothermometers. The classic paleothermometer is the stable
isotopic composition of water in the ice core. Natural waters
typically contain a fraction of 1 percent of isotopically heavy
water molecules, and the vapor pressure of this heavy water is
less than ordinary or "light" water. The result is that as an air
mass is cooled and precipitates, it preferentially loses heavy
water and must increasingly precipitate light water. Both
empirically and theoretically, isotopic composition of
precipitation and site temperature are strongly correlated in
time and space.

3) Aerosols: Anything in the atmosphere can eventually end up in
an ice core. Some materials are reversibly deposited, but most
materials remain in the ice unchanged. Although details of the
air-snow transfer process are complex and not yet completely
elucidated, large changes in concentrations of most materials in
ice can with confidence be said to reflect changes in the
atmospheric loading of these materials.

4) Gases: Trapped gases in ice-core bubbles are highly reliable
records of atmospheric composition, as indicated by comparisons
among cores from different ice sheets, and comparison with
instrumental records and the air in the *firn above the
bubble-trapping depth. The slight differences between bubble and
air composition caused by gravitational and thermal effects are
well understood and recognizable.

5) Geographic coverage: The ice-core record of abrupt climate
changes is clearest in Greenland. Although no other record is
available that spans the same time interval with equally high time
resolution, it appears that ice cores from the Canadian arctic
islands, high mountains in South America, and Antarctica also
contain indications of the same abrupt changes. Dating is
considered secure for some of the Antarctic ice cores.

6) The author suggests that as the world slid in and out of the
last ice age, the general cooling and warming trends were
punctuated by abrupt changes, and climate shifts up to half as
large as the entire difference between ice age and modern
conditions occurred over hemispheric or broader regions in mere
years to decades. Such abrupt changes have been absent during the
few key millennia when agriculture and industry have arisen.

7) In summary, ice-core records indicate that climate changes in
the past have been large, rapid, and synchronous over broad areas
extending into low latitudes, with less variability over
historical times. These ice-core records come from high mountain
glaciers and the polar regions, including small ice caps and the
large ice sheets of Greenland and Antarctica.
Richard B. Alley: Ice-core evidence of abrupt climate change.
(Proc. Natl. Acad. Sci. US 15 Feb 00 97:1331)
QY: Richard B. Alley []
Text Notes:
* firn: The term "firn" refers to the transitional layer between
snow and glacier ice. The layer consists of snow that has melted
during one summer melt season, the layer in the process of
transforming to glacier ice as the temperature decreases.
Summary & Notes by SCIENCE-WEEK 14Apr00
For more information:

Copyright (c) 1997-2000 SCIENCE-WEEK/Spectrum Press Inc.
All Rights Reserved



From Paul Davies <>

Dear Dr. Peiser,

Nicholas Wade's mystery about life originating on an asteroid-battered
Earth (CCNet 13 June 2000) is easily resolved. First, the earliest life
on Earth probably dwelled some kilometres below the surface, where it
would be largely protected from even the biggest impacts. So subsurface
life was possible once the crust had cooled sufficiently. Secondly,
Mars was a suitable abode for life long before Earth. Being a smaller
planet, it cooled quicker, so the comfort zone for deep-living
organisms was deeper sooner. Since the sporadic transfer of microbes
from Mars to Earth inside impact ejecta was virtually guaranteed
(assuming there were any Martian organisms), an obvious resolution of
Wade's 'mystery' is that life started on Mars and came to Earth in
martian meteorites, eventually establishing itself here when the
bombardment abated somewhat. I give a full explanation of this scenario
in my book 'The Fifth Miracle: the search for the origin of life,'
published by Penguin.

Yours sincerely,

Paul Davies


From Leon Jaroff < >

Dear Benny,

Russell Hoffman writes that <<it can be fairly argued that a nearly
instant asteroid death would be a blessing in comparison to what is
being done here spill by spill, dilution by dilution, leakage by
leakage, drop by drop. There is No Minimum Dose, and humanity suffers
daily from the effects of choosing the nuclear "solution" to each
problem we face.>>

Well, Mr. Hoffman can opt for instant asteroid death, but most of us
would choose the nuclear option, which might be the only methodology
feasible in the likely event that a large, threatening asteroid is
discovered too late in the game. No other source would be able deliver
the energy needed to divert or destroy it. Indeed, scientists at Los
Alamos and at the Lawrence Livermore National Labs here in the U.S.
have worked out a number of ingenious schemes for diversion without
fragmentation, including stand-off nuclear explosions that would
vaporize one side of the asteroid, in effect producing an expulsion of
hot gases that would push the asteroid off in the opposite direction.

Also, like many anti-nuclear activists, Mr. Hoffman apparently knows
little about the medical effects of low-level radiation. There indeed
must be a minimum dose, because we are all exposed to hundreds of times
more natural background radiation than any emitted by an operating
nuclear plant. Yet humanity has somehow survived the radiation that we
get from cosmic rays, radon gas, granite cliffs, beach sand, etc.

I suspect that Mr. Hoffman is from the school of anti-nuclear activists
(like those here on Long Island, New York) who believe that low-level
radiation is responsible for Lyme Disease, the AIDS epidemic, lower SAT
scores, lower birth weights and greater infant mortality. Sometimes
they seem totally out of control.


Leon Jaroff

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