CCNet 133/2000 - 15 December 2000

seeing the unimaginable

You lay on your back facing the sky.
The great refractor stretched above, steel sections
bolted and riveted like some old steamship,
the tailpiece near your hands, plateholder and guiding eyepiece.
Grasping the paddle in the winter cold or summer's
insect-busy night, we did it all by hand,
with wheels to work the clamps, ropes to move the tube,
hauling its tons against inertia.
Those young astronomers in their shirt-sleeve rooms
would laugh to see us, as they sit at keyboards watching screens,
yet even that will be outdated - why sit all night
only to watch a screen? The thing works by itself,
folding data by the gigabyte into its memory,
tirelessly obeying the commands you gave it
from half a world away. The future's very near
when every bit of sky is watched each moment
by robot eyes alert for any change, and when they see it,
they'll swing mirrors large as houses, armed with detectors
we would never have imagined, seeing the unimaginable.

Malcolm Miller

    Andrew Yee <>

    Larry Klaes <>

    Andrea Milani <>

    James Oberg <>

    Serge Tabachnik <serge@astro.Princeton.EDU>

    Duncan Steel <>

    Michael Paine <>


From Andrew Yee <>

Northwestern University

Megan Fellman, (847) 491-3115, e-mail:

FOR RELEASE: 12/14/00

Geologist suggests water may reside as ice deep in planets' interior

EVANSTON, Ill. -- In a paper published Dec. 14 in the journal Nature,
Northwestern University geologist Craig R. Bina reports that, in a novel
twist on current thinking, water may be transported into the interior of
planets as a high-pressure form of ice, rather than simply being
transported while trapped within hydrous minerals or escaping as a fluid.

Bina and co-author Alexandra Navrotsky, a chemist and materials scientist
from the University of California, Davis, suggest that this process should
become more important as planets cool, for example on a future Earth or on

Large amounts of a form of water ice, called "ice VII," may be accumulating
deep in the Earth's interior during the process of subduction, where the
oceanic crust is stuffed periodically below the surface crust. (Subduction
is one of the main types of action in plate tectonics.) The most likely
place to look for evidence of such a process, say the researchers, would be
in Tonga, a group of islands in the southwest Pacific Ocean and one of
Earth's coldest subduction zones.

The researchers' calculations indicate that in these subduction zones
conditions do exist that could result in the formation of ice VII, a form of
ice in which the atoms are packed closely together. The high pressures and
low temperatures beneath the surface in an area like Tonga could result in
water being carried deep below the Earth's crust as ice -- which is not very
mobile -- before temperatures are great enough to melt the ice and enable it
to be released as water.

"To my knowledge, we are the first to look at the possibility of the water
being released from the subsumed rock as ice, not as a fluid," said Bina.
"Tonga would be the most obvious place to look for geophysical evidence of
ice VII."

The decreasing availability of fluid water, caused by the accumulation of
ice VII and its subsequent reaction products in a cooling planetary
interior, as in the future Earth or Mars, might eventually lead to a decline
in tectonic activity or its complete cessation.

"Recent discovery of what look like gullies on Mars suggest that the planet
is not completely dry," said Bina. "Water for forming gullies could be
stored at shallow levels beneath the Martian surface, perhaps as normal ice.
Our work suggests that there could also be water stored in the deep interior
as high-pressure ice, which could be released to drive volcanic activity."

Bina and Navrotsky suggest that the state -- fluid versus crystalline -- of
water inside planets can profoundly affect both dynamics and thermal
balance, and that a change in the relative proportions of fluid and solid
water "is one of the important factors influencing the different possible
paths of planetary evolution."

Source contact: Craig Bina, professor of geological sciences, from Dec.
14-19, at . Starting Dec. 20, Bina also can be
reached at 847-491-5097.


From Larry Klaes <>

PLANETARY SCIENCE: Beating Up on a Young Earth, and Possibly Life

Richard A. Kerr

Bits of melted rock in lunar meteorites tell of a brutal battering suffered
by the moon and Earth almost 4 billion years ago, as life was getting

Call it tough love or growing pains--Earth owes its character to the school
of hard knocks. It achieved something like its present size by colliding
with innumerable chunks of rock as big as cities. Then, about 4.5 billion
years ago, a rogue Mars-sized body plowed into the nascent planet and
splashed off enough rock to form the moon. The inner solar system quieted
down considerably within a few hundred million years after that, and
relative peace prevailed. But early analyses of lunar rocks returned by
Apollo astronauts hinted at a sudden violent episode 600 million years after
Earth's birth. Seemingly out of nowhere, a hail of objects pummeled Earth,
the moon, and perhaps the entire inner solar system. Now this "late heavy
bombardment" is getting strong support from analyses of rocks the astronauts
never saw: meteorites that fell to Earth from the moon's back side.

Lunar meteorite analyses reported on page 1754 of this issue reveal a burst
of impacts on the moon 3.9 billion years ago and nothing before that.
Cosmochemists Barbara Cohen, Timothy Swindle, and David Kring of the
University of Arizona, Tucson, conclude that the moon and Earth endured a
storm of impacts 100 times heavier than anything immediately before or
after. Such a lunar cataclysm would have scarred the moon with the great
basins that now shape the man in the moon. On Earth, the same bombardment
would have intervened in the evolution of life, perhaps forcing it to start
all over again. "To me it seems highly likely there was a lunar
catastrophe," says cosmochemist Laurence Nyquist of NASA's Johnson Space
Center in Houston. But skeptics wonder how the solar system could have held
off delivering such a devastating blow for more than half a billion years.

Even a pair of binoculars reveals that the moon has had a rough time of it.
Analyses of impact-battered Apollo rocks suggested that violent collisions
about 3.9 billion years ago--dubbed the terminal lunar cataclysm--disrupted
the isotopic composition of moon rocks. Then, in the early 1990s,
geochronologist Brent Dalrymple of Oregon State University in Corvallis and
planetary scientist Graham Ryder of the Lunar and Planetary Institute in
Houston determined precise ages of 12 bits of Apollo rock apparently melted
in 12 different impacts. They found a flurry of impacts 3.9 billion years
ago but none older. If the impact rate had simply tailed off from the
formation of Earth and the moon about 4.5 billion years ago, as dynamical
astronomers insist it must have, Dalrymple and Graham should have found
impact melts as much as 4.2 billion or 4.3 billion years old. Failing that,
they concluded that a burst of impacts 3.9 billion years ago had overwhelmed
the few impacts that preceded it.

Lunar sample freebie. Meteorites blasted off the moon hint at an earlier
cataclysm of impacts.


The lunar cataclysm wasn't immediately accepted, however. Critics such as
planetary scientist William Hartmann of the Planetary Science Institute in
Tucson, Arizona, pointed out that the apparent surge might just mean that
cratering was obliterating all traces of earlier impacts until it gradually
slowed to the point where some could survive. And all of the dated moon
rocks had come from the equatorial region of the moon's nearside, Hartmann
noted, where one or two of the huge, basin-forming impacts there could
dominate the record.

With the geographic constraints in mind, Cohen and her colleagues turned to
the other source of moon rocks, the meteorites blasted off the moon by large
impacts. Cohen chose four lunar meteorites containing bits of impact melt
and dated 31 of those bits representing at least seven different impacts.
None was older than 3.9 billion years. More telling, none contained the
distinctive "KREEP" material (rich in potassium, rare earth elements, and
phosphorus) that covers much of the nearside and tags all Apollo samples.
The lunar meteorites seem to have sampled the moon far from Apollo landing
sites, even on the moon's farside.

The latest results from the moon are pushing even the doubters toward a
lunar cataclysm. "When we started this study," says Swindle, "I thought this
would be the way to disprove it. We haven't proved there was a cataclysm at
3.9 billion years, but it passes the test." Hartmann agrees, and he now
concedes that obliteration of an earlier impact record may be harder than he
had thought. "The way out may be a compromise scenario," he says. "Maybe
there was a fairly big spike [superimposed on the tail] 3.9 billion years
ago, and we're just arguing over how big that spike was. But you would still
have the serious problem of where you store this stuff for 600 million
years" before dropping it on the moon.

Astronomers still don't have any good idea of the cataclysm's source.
Simulations show that the gravity of Earth and the other terrestrial planets
would have cleared the inner solar system of threatening debris within a few
hundred million years. Collisions in the asteroid belt can shower Earth with
debris, notes Brett Gladman of the Observatory of Nice, but a cataclysm
would require the breakup of a body larger than 945-kilometer Ceres, the
largest asteroid. The chance of that happening any time in the past 4.5
billion years is nearly nil, he notes.

As a last resort, researchers look to the outer reaches of the solar system.
Dynamical astronomer Harold Levison of the Boulder, Colorado, office of the
Southwest Research Institute and colleagues show in a paper to appear in
Icarus how the newly formed Neptune and Uranus could have tossed icy debris,
along with some asteroids, inward in sufficient quantities to resurface the
moon, give Mars a warm and wet early atmosphere, and sterilize Earth's
surface with the heat of the bombardment (Science, 25 June 1999, p. 2111).
The only catch, says Levison, is that the two large outer planets would have
had to have formed more than half a billion years later than currently
thought. Levison is toying with the idea that Uranus and Neptune started out
between Jupiter and Saturn, where his simulations suggest they could have
orbited for hundreds of millions of years before flying out into the
lingering debris beyond Saturn and triggering a late heavy bombardment.
"That's my fairy tale," he says. Maybe that's just what young planetary
bodies need.


Related articles in Science:

Support for the Lunar Cataclysm Hypothesis from Lunar Meteorite Impact Melt
      B. A. Cohen, T. D. Swindle, and D. A. Kring
      Science 2000 290: 1754-1756. (in Reports) [Abstract] [Full Text]

Copyright 2000, AAAS


From Andrea Milani <>

ANNOUCEMENT: AstDyS (Asteroids Dynamic Site)

14 December 2000

Expanding the information services on asteroids already available from our
site at the University of Pisa (Italy), we have now online the new service
AstDyS. Based on the experience of NEODyS
(, and also on our experience in the
generation and distribution of large proper elements catalogs, AstdyS
contains all kind of dynamical information (orbital elements, observation
residuals, proper elements, ephemerides) on those asteroids for which the
orbits can be considered well determined, because they have been observed
over multiple apparitions.  In the current version, AstDyS contains
information on 54500 asteroids, but this number increases every month.

The main purpose of this site is to document our research in asteroid orbit
determination and long term dynamics. However, we hope it is also useful as
a service to either the observers or the scientists willing to analyse data
on the individual and collective dynamical properties of asteroids. We will
appreciate comments and suggestions on how to improve and expand this site;
development of the algorithms and software, maintenance of the databases and
improvements of the services and user interface will go on. But please
understand that we are supported only for research, and not to provide a

AstDyS is available at the web address

The AstDyS consortium includes Andrea Milani and coworkers (Univ. Pisa),
Zoran Knezevic and coworkers (Astron. Obs. Belgrade) and Hyperborea scrl
(Pisa); we acknowledge contributions from M.E. Sansaturio (Univ.
Valladolid), S. Chesley (JPL) and the OrbFit consortium

In this message we enclose basic explanations on AstDyS, and an announcement
about a new release of OrbFit, which is  the engine under the hood of AstDyS
and NEODyS.


What is AstDyS?

Fundamentally, AstDyS provides information on numbered and multi-opposition
asteroids with a convenient Web-based interface. It is based on a
continually and almost automatically maintained database of asteroid orbits.
This site provides a number of useful services to the asteroid observers and
scientists interested in studying them.

For each asteroid in our database, the results of its orbit determination
are available for inspection and comparison with other sources. Everything
needed by the user to verify the computations is available online, including
our software.

Asteroid mean and proper elements (analytic and synthetic) are also
available together with the software used to compute them.
Our observation prediction service provides ephemeris predictions and finder
charts with information on the linear or semi-linear confidence region as
Files with the data for downloading are available in different suitable
A powerful search engine provides direct acces to every required information
in the basic and auxiliary data files.
On-line Info and Help facilities, README files provided with
straightforwardly accessible FTP pages, links to the papers explaining the
theoretical background of our procedures and to the related sites, as well
as numerous comments embedded into the software are all there to make AstDys
as useful and easy-to-use as possible.


This message announces the new improved distribution 2.2 of  the free
software OrbFit.

The purpose of the software system we are distributing, maintaining and
continously upgrading, is to make available to observers of asteroids an
easy to use, but accurate and reliable, software to compute preliminary
orbits, ephemerides, improved orbits (by differential corrections),
identifications, and other auxiliary functions, to allow the processing of
astrometric observations and the planning of observational campaigns (for
example to recover lost objects).

The are many improvements with respect to the previous versions, but the
main focus of our effort has been to increase reliability. This because we
are now using the Orbfit libraries to compute more than 700,000 asteroid
orbits every month.

The software can be downloaded from

while the online documentation can be directly accessed from

This software system has been developed by a consortium including A. Milani
(Pisa University), S. Chesley (JPL), M. Carpino (Astronomical Observatory
Milano/Brera), Z. Knezevic (Astronomical Observatory Belgrade), G. B.
Valsecchi (CNR Rome), M.E. Sansaturio (Polytechnic of Vallaldolid).

Copyright (C) 1997-2000 OrbFit Consortium

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

To contact us:,,,



From Jim Oberg <>

In CCNet 14 December, Philip Ball is quoted:

"But in the Monthly Notices of the Royal Astronomical Society 1,2,
Evans and Tabachnik ask: how many asteroids are associated with the
inner planets, and how easy would it be to spot them, given that
they'd be proportionately smaller than those of Jupiter?"

Why should they be proportionately smaller? Gravity is gravity and the mass
of a trojan object seems irrelevant to me in computing its orbit.

Jim Oberg


From Serge Tabachnik <serge@astro.Princeton.EDU>

Dear Benny,

About James Oberg's comment, I think there is slight misunderstanding.

We do not infer any real constraint on the size/mass distribution of Trojan
populations in the inner Solar System, rather on the extent of the stability
zones associated with the L_4 and L_5 Lagrange points. Of course Jupiter,
having a mass 318 larger than the Earth, is more propitious to
retain/capture Trojan-like asteroids than the inner planets. Another factor
of importance is the different formation processes associated with the
terrestrial and the gas-giant planets. The difference in timescales,
temperatures, relative velocities of planetesimals, etc, prevent us from
correlating directly the Jovian Trojan population with similar putative
stability zones in the inner Solar System. Still, it is reassuring to notice
that the confirmed 2 Martian Trojans have orbital elements compatible with
our results. If a comparatively puny body like Mars possesses Trojans, it is
indeed quiet likely that more massive planets like the Earth and Venus also
harbour such satellites.

Best Regards,

Serge Tabachnik

Princeton University 
Department of Astrophysical Sciences    
Peyton Hall, Ivy Lane 
Princeton, New Jersey 08544-1001
Phone : +1 (609) 258 0026
Fax   : +1 (609) 258 1020

Abstracts :

1. Tabachnik, S. A. & Evans, N. W. Asteroids in the inner solar system - I.
Existence. Monthly Notices of the Royal Astronomical Society 319, 63-79

Ensembles of in-plane and inclined orbits in the vicinity of the Lagrange
points of the terrestrial planets are integrated for up to 100 Myr. The
integrations incorporate the gravitational effects of the Sun and the eight
planets (Pluto is neglected). Mercury is the least promising planet, as it
is unable to retain tadpole orbits over 100-Myr time-scales. Mercurian
Trojans probably do not exist, although there is evidence for long-lived,
corotating horseshoe orbits with small inclinations. Both Venus and the
Earth are much more promising, as they possess rich families of stable
tadpole and horseshoe orbits. Our survey of Trojans in the orbital plane of
Venus is undertaken for 25 Myr. Some 40 per cent of the survivors are on
tadpole orbits. For the Earth, the integrations are pursued for 50 Myr. The
stable zones in the orbital plane are larger for the Earth than for Venus,
but fewer of the survivors (~20 per cent) are tadpoles. Both Venus and the
Earth also have regions in which inclined test particles can endure near the
Lagrange points. For Venus, only test particles close to the orbital plane
are stable. For the Earth, there are two bands of stability, one at low
inclinations and one at moderate inclinations The inclined test particles
that evade close encounters are primarily moving on tadpole orbits. Two
Martian Trojans (5261 Eureka and 1998 VF31) have been discovered over the
last decade and both have orbits moderately inclined to the ecliptic (203
and 313 respectively). Our survey of in-plane test particles near the
Martian Lagrange points shows no survivors after 60 Myr. Low-inclination
test particles do not persist, as their inclinations are quickly increased
until the effects of a secular resonance with Jupiter cause destabilization.
Numerical integrations of inclined test particles for time-spans of 25 Myr
show stable zones for inclinations between 14° and 40°. However, there is a
strong linear resonance with Jupiter that destabilizes a narrow band of
inclinations at ~29°. Both 5261 Eureka and 1998 VF31 lie deep within the
stable zones, which suggests that they may be of primordial origin.
2. Evans, N. W. & Tabachnik, S. A. Asteroids in the inner solar system - II.
Observable properties. Monthly Notices of the Royal Astronomical Society
319, 80-94 (2000).

This paper presents synthetic observations of long-lived coorbiting
asteroids of Mercury, Venus, the Earth and Mars. Our sample is constructed
by taking the limiting semimajor axes, differential longitudes and
inclinations for long-lived stability provided by simulations. The intervals
are randomly populated with values to create initial conditions. These
orbits are re-simulated to check that they are stable and then re-sampled
every 2.5 yr for 1 Myr. The Mercurian sample only contains horseshoe orbits,
whereas the Martian sample only contains tadpoles.

For both Venus and the Earth, the greatest concentration of objects on the
sky occurs close to the classical Lagrange points at heliocentric ecliptic
longitudes of 60° and 300°. The distributions are broad especially if
horseshoes are present in the sample. The FWHM in heliocentric longitude for
Venus is 325° and for the Earth is 328°. The mean and most common velocity
of these coorbiting satellites coincides with the mean motion of the parent
planet, but again the spread is wide with an FWHM of 27.8 and 21.0 arcsec
h-1 for Venus and the Earth, respectively. For Mars, the greatest
concentration on the sky occurs at heliocentric ecliptic latitudes of ±12°.
The peak of the velocity distribution occurs at 65 arcsec h-1, significantly
less than the Martian mean motion, while its FWHM is 32.3 arcsec h-1. The
case of Mercury is the hardest of all, as the greatest concentrations occur
at heliocentric longitudes of 160 and 3485 and so are different from the
classical values. The fluctuating eccentricity of Mercury means that these
objects can have velocities exceeding 1000 arcsec h-1 although the most
common velocity is 459 arcsec h-1, which is much less than the Mercurian
mean motion.

A variety of search strategies are discussed, including wide-field CCD
imaging, space satellites such as the Global Astrometry Interferometer for
Astrophysics (GAIA), ground-based surveys like the Sloan Digital Sky Survey
(SDSS), as well as infrared cameras and space-borne coronagraphs.


From Duncan Steel <>

Dear Benny,

I note the listing of the following paper in CCNet 14 December 2000:

D. Vokrouhlicky, A. Milani: Direct solar radiation pressure on the orbits of
small near-Earth asteroids: observable effects? ASTRONOMY AND ASTROPHYSICS
362: (2) 746-755 OCT 2000

The abstract for that paper ends with the following sentence:

"...As an example we demonstrate that for the asteroid 1566 Icarus, during
its next close approach to the Earth, the orbit displacement due to the
direct solar radiation forces might be, under reasonable assumptions,
comparable to the orbit determination uncertainty, thus potentially

This is a very significant statement. If it is correct then it may be read
to indicate that asteroids (i.e., inert objects that do not undergo
outgassing, and so are not subject to the type of endogenous
non-gravitational force that causes large perturbations of the paths of
comets) do in fact suffer a type of non-gravitational perturbation which
would be of importance vis-a-vis the prediction of impacts upon the Earth.
This would be of exogenous origin (due to the solar radiation field) and so
should be recognised as being quite distinct from the usual meaning of
"non-gravitational force" in connection with comets.

Previous research on perturbations of asteroid orbits of radiative origin
has been mentioned in CCNet in recent months, in particular the effect of
the Yarkovsky (Yarkovsky-Radzievskii) force, which is due to the
non-isotropic re-radiation as infra-red photons of the energy absorbed from
the (visible) solar flux by a spinning object. Quite simply, the post-noon
sector is hotter than the pre-dawn sector of the surface, and this provides
for more momentum being emitted in one direction than the other. This has
the effect of causing an acceleration of the object (or a deceleration,
depending upon the spin sense compared to the orbital motion direction).

This, then, is due to the object's spin. The Poynting-Robertson effect,
mentioned by Vokrouhlicky & Milani, is due to the object having an orbital
speed which is an appreciable fraction of the speed of light. In consequence
the leading hemisphere of the object emits infra-red photons which are
blue-shifted through the doppler effect, whereas the trailing hemisphere
emits red-shifted photons, and so more momentum is radiated in the foward
direction, and the outcome is always a deceleration of the object. The
result is that orbital size is decreased, and the object slowly spirals in
towards the Sun.

The radiation pressure, which is the main concern of Vokrouhlicky & Milani,
is independent of the object's motion, as such. I had previously thought
that, as the radiative flux drops off as an inverse-square, just like the
solar gravitational attraction, the consequence of radiation pressure would
simply be an effective reduction in the gravitational constant, G. The
conventional way of writing this is to use a factor in the Newtonian gravity
equation of G(1 - beta) where beta is a parameter depending upon the
object's size and scattering properties, and which is extremely small for
objects larger than a metre or so in size. Indeed, it has usually been
thought that all of the above radiative effects (radiation pressure,
Poynting-Robertson effect, Yarkovsky-Radzievskii effect) must be
insignificant for objects larger than metre-sizes, and only really something
to consider for small meteoroids and dust. Generally the accelerations
produced by radiative effects drop off as the reciprocal of the particle
size (because the mass increases as the size cubed, whereas the area
increases only as the size squared).

In case readers wish to know more about these radiative effects, I would
mention my own paper on their application to meteoroids:
D. Olsson-Steel: 'The dispersal of the Geminid meteoroid stream by radiative
effects,'  Monthly Notices of the Royal Astronomical Society, 226, 1-17 (1987).

There was also an excellent review of these radiative effects published in
Icarus in 1979 by Burns, Lamy and Soter.

It may seem surprising that the solar radiation field might affect the
motion of small bodies in so many ways. I seem to recall once receiving a
letter from Max Wallis in which he claimed  another effect. As he is, I
believe, on the CCNet list, he might wish to comment. Perhaps he, or
someone else, may know of some other perturbative influence that should be
considered in this context.

Immediately a matter which would be of interest is whether an implication of
the work by Vokrouhlicky & Milani is that the prediction of impacts upon the
Earth, or even the estimation of impact probabilities, is thrown into
question by the possibility that asteroids, too, are subject to
non-gravitational forces (radiative forces). The specific asteroid studied
by Vokrouhlicky & Milani is 1566 Icarus, which was discovered in 1947. With
a half-century of data collection I imagine that the orbit determination
uncertainty for that object is small, making (as they state) possibly
observable the effect of radiation pressure. For recent asteroid
discoveries, even those with small perihelion distances, the  orbit
determinations would be poorer (except, perhaps, if radar data are
available), and the radiative perturbations would be too small in a relative
sense to be discernable.

On the other hand, if the radiative perturbations can amount to a level
comparable to the measurement uncertainties over a half-century time-span,
does this imply that calculations of impact probabilities for some decades
into the future - based on an assumption of purely gravitational motion -
are unreliable? For example, are statements of "zero" probability actually
invalidated because one of the underlying assumptions is invalid?

Before anyone gets too excited about that, let us be clear that it is
already tacitly understood that certain assumptions may not be true. For
example, we assume that our near-miss asteroids for 30 or 40 years hence are
not going to happen to run into a metre-sized rock in space and so be slowed
just that little bit needed to make a collision possible.

What I am wondering about here has wider implications than just whether the
teams (like Andrea Milani's own) running software to look for possible
impacts, and thus deriving impact probabilities based upon spreads of
initial orbital elements governed by the observational uncertainties,
actually need to add some flexibility or uncertainty spread due to feasible
radiative effects. The implication of a demonstration that asteroids may be
subject to significant (radiative) non-gravitational forces would be very
significant for the observational part of any Spaceguard-type program. If
only gravity is considered, then the dynamics of an object are independent
of its size and physical nature: a dust grain obeys the same rules as a
ten-kilometre asteroid. If any form of non-gravitational force is shown to
be significant ('significant' here implies any change in path affecting the
impact probability), then we would be needing to make a suite of physical
observations for each NEA found to have a future passage within some
orbit-dependent distance from the Earth, or indeed any other trajectory that
might make an impact on our planet feasible. (For example, could it suffer a
slight tweak in its Venus-miss distance due to a non-gravitational force
resulting in a subsequent Earth impact despite the fact that the purely
gravitational solution indicates this to be 'impossible'.) By 'physical
observations' I mean such things as deductions of its size, albedo, mass
(yes: virtually impossible, I know), scattering properties, composition.
Obviously much more would required than the simple orbit determination
needed if only gravitational forces are involved in its detailed orbital

In view of the above the paper by Vokrouhlicky & Milani may turn out to be
of fundamental significance for the future of the Spaceguard idea.

Duncan Steel


From Andrea Milani <>

Dear Duncan,

I do not want to add a long comment to your letter; after all, what I have
to say is written in the two papers, in Astronomy and Astrophysics and in
Icarus, just published. I only would like to point your attention on the
orders of magnitude of the effects we are talking about. The
non-gravitational perturbations on km-sized asteroids can be of the order of
kilometers in the asteroid position, over time spans of decades. This is
much more than the observational accuracy if these asteroids are ranged by
radar: the range errors can be as small as 50 meters (RMS). Thus, these
effects can be observable, under especially favourable conditions. On the
other hand, these effects are negligible with respect to the diameter of the
Earth. Thus the non-gravitational perturbations are not a serious concern
for the asteroid impact risk (unless you want to know if your house is going
to be hit :-). They can be significant either for much
smaller bodies, a few tens of metres across (but then they are not a
significant risk) or for comets with much larger non gravitational forces
due to outgassing (but we are not monitoring possible impacts by comets) or
for possible impacts hundreds of years from now, with the uncertainty
amplified by the action of chaos (but we have our hands full with monitoring
for impacts in the next 50-100 years).

Yours Andrea Milani


From Duncan Steel <>

Dear Andrea,

I agree with you, of course: clearly this is a tiny effect. As you point
out, maybe a few km retardation, much less than the size of the Earth, for
km-sized asteroids. What I was wondering, though, was whether your results
could be significant in some particular cases. For example, a 100 metre
asteroid would suffer a retardation about a  hundred times that for a 1 km
asteroid in the same orbit (factor of ten, squared, as it will vary as the
area of the objects). This could lead to variations in the miss distances of
hundreds of km, on a par with optical (as opposed to radar) astrometry in
some cases, and thus another source of uncertainty for some of the 'keyhole'
evolutionary tracks you and others have investigated. I just thought that
this is something to highlight for future consideration.




From Max Wallis <>

Of radiative forces on above metre-sized bodies, Andrea Milani's radial
force is surely largest, and has significance for orbit determination. The
non-radial components are relevant (only) for the orbit's evolution, and
were given an excellent review in the quoted Burns-Lamy-Soter paper of 1979.
Subsequent work tended to find that the classical Poynting-Robertson drag
force (PR) was not the largest. The solar wind deviates a few degrees from
radial and sputtering of surfaces by solar wind ions gives a non-radial
force that exceeds PR for siliceous material (Mukai & Yamamoto 1982).
Non-spherical objects scatter radiation asymmetrically and the average for
spinning objects gives forces 10s or 100s times PR (Voschinnikov and Il'in 1983).
Perturbations via solar wind E and B-fields acting on charged objects can
exceed transverse radiative forces but only for micro-grains (a micrometre
or smaller), where radiation pressure is comparable to solar gravity. 
For Duncan's metre-sized bodies, the PR and other non-radial forces come
into play only for slow evolution over thousands of orbits. Collisions also
come into play, with a bias due to the average being prograde.

Max Wallis

School of Maths, Cardiff University,
Senghenydd Road, Cardiff CF2 4YH           tel. 029 20874201

From Andrea Milani <>

Dear Duncan,

Please take into account that the relevant parameter for the ratio
nongrav/gravitational forces is Area/mass, thus it is inversely proportional
to the first power of the radius. Thus what you say is correct, but only for
objects of sizes of a few tens of meters, and as in my comment, this is not
really relevant for impact risk assessment. E.g., 2000 SG344 is a case in
which our computations based on gravitational perturbations only are of a
limited accuracy; but this is also because SG344 is 1) painted white, thus
smaller than expected on the basis of an average albedo 2) an empty shell,
thus has A/m much higher. This assuming it is an Apollo third stage, as I
think is very likely.

In my comments I was stressing again the fact, that you also have pointed
out, that not enough is done about comets. Although I am sorry but I have to
disagree with you every time you repeat your unfounded statements on comets
being more dangerous than asteroids, the comets are a smaller but
not negligible fraction of the risk. I am not monitoring them, while JPL is
monitoring only by means of linear theory, which means only above a
probability level of about 1 in 1000. They take into account the increase of
the position uncertainty due to the uncertainty in nongravitational
forces, to my understanding they do it in a correct way.

yours Andrea Milani


From Michael Paine <>

Dear Benny,

It was interesting to read the CNN report "NASA: Satellite odds of hitting
someone 250-1"

It seems to discuss a similar risk to that of small NEO airbursts (recall my
rough estimate is a 1 in 1000 chance of a populated region somewhere on
Earth being struck in any one year). However, the time period for re-entry
of the Iridium satellites is not clear from the article.

Michael Paine

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"Given 200 boats, 8.1 million tons of iron, and, say, 11 percent of
the world's ocean, Markels says, he could zero out global warming. Next
question? Sure, he says, global warming might be real, and it might
even change things - but not necessarily for the worse. Markels
believes the real danger isn't a greenhouse-warmed Earth - it's a
greenhouse- panicked public. He ticks off various irritants that occur
when too many people are running scared: high fuel prices, rioting
environmentalists, 3.4 billion taxpayer dollars budgeted in 2000 to
keep tabs on the global bogeyman. But, since folks are so fired up, there's
only one way to hose them down: Solve the damned thing."
     --Charles Graeber, Wired Magazine, November 2000

    SpaceDaily, 13 December 2000

    SpaceDaily, 14 December 2000

    Anatta <anatta@UCAR.EDU>

    BBC News Online, 14 December 2000

    CO2 Science, 13 December 2000

    CO2 Science, 13 December 2000

    Larry Klaes <>

    Herald Sun, 14 December 2000


From SpaceDaily, 13 December 2000

Mooted new climate talks now definitively off: report
HAMBURG, Germany (AFP) Dec 13, 2000

Hopes of new climate talks that would bring the European Union, the United
States, Canada, Australia and Japan to a negotiating table in Oslo are now
definitively broken, the German newspaper Der Spiegel said on its website

Efforts to take another stab at fleshing out measures to battle global
warming foundered after a video conference involving representatives from
those countries fell apart apart Tuesday, it said.

The video conference itself was called after the failure of climatic change
talks in The Hague last month attended by 181 countries which were to have
given content to the 1997 Kyoto accord that calls for cutbacks in greenhouse
gas emissions.

Various efforts have been made since the unsuccessful end of those talks to
get some sort of agreement back on the rails.

The talks failed largely due to differences between the United States -- the
world's top producer of greenhouse gases -- and Europe.



From SpaceDaily, 14 December 2000

UN's climate treaty looks shaky after Bush win
PARIS (AFP) Dec 14, 2000

Hopes for implementing a key UN treaty to fight the threat of global warming
look at best uncertain after George W. Bush's election win, analysts say.
Under a Bush presidency, the US is likely to delay or even reject the Kyoto
Protocol, leaving the European Union (EU) and other parties to try to make
the treaty work without the country which is the biggest source of the
problem. [...]

Tony Carritt, head of the environment practice at the Brussels consultancy
Adamson BSMG Worldwide, said Bush could well try to renegotiate Kyoto. [...]

"Pro-Kyoto Americans will want to play for time... and wait till the mood
changes of its own accord, with more natural disasters or whatever it is
that gets people thinking that maybe it should be ratified after all."

Mike Hulme, executive director of the Tyndall Centre for Climate Change
Research at the University of East Anglia, in Norwich, eastern England, said
Kyoto without the US was probably unworkable, given that America by itself
accounts for a quarter of greenhouse gas pollution.

But mounting evidence, plus the likelihood of more storms or extreme
weather, would enable Kyoto to be revived or reshaped, possibly in a
slimmed-down form.

"Over the next five to 10 years, much clearer and starker messages will come
out of the global climate system... there's going to be less and less room
for politicians and international negotiators" to deny the danger, Hulme

© 2000 Agence France-Presse


From Anatta <anatta@UCAR.EDU>

FOR IMMEDIATE RELEASE: December 13, 2000

New Study Shows Global Warming Trend Greater without El Nino and Volcanic

S.F. Marriott Hotel (Dec. 14-19)
Hotel tel. 405-896-1600
Office tel. 303-497-8604

Tom Wigley
S.F. Marriott (Dec. 15-18)
Hotel tel. 415-896-1600
Office: tel. 303-497-2690

BOULDER--Removing the masking effects of volcanic eruptions and El Nino
events from the global mean temperature record has reveals a more gradual
and yet stronger global warming trend over the last century, according to a
new analysis by Tom Wigley, a climate expert at the National Center for
Atmospheric Research (NCAR). The analysis supports scientists' claim that
human activity is influencing the earth's climate. The findings are
published in the December 15 issue of Geophysical Research Letters. NCAR's
primary sponsor is the National Science Foundation.

"Once the volcanic and El Nino influences have been removed," says Wigley,
"the overall record is more consistent with our current knowledge, which
suggests that both natural and anthropogenic
influences on climate are important and that anthropogenic influences have
become more substantial in recent decades."

Volcanic emissions cool the planet by blocking sunlight, while El Nino
events raise global temperatures through warmer ocean waters. Sometimes the
two occur simultaneously, muddying evidence of any underlying warming trend.
During the past two decades, two massive volcanic eruptions--El Chichón in
April 1982 and Mt. Pinatubo in June 1991--coincided with significant El
Ninos, making trend detection more difficult.

Wigley quantified the effects of major volcanic eruptions and El Nino
episodes on global mean temperatures. Overall, he found the cooling effect
from sun-blocking volcanic emissions was slightly stronger than the warming
effect of the coincident El Ninos. He then removed both from the temperature
record to reveal an intensified, step-like warming trend over the past

In the raw temperature record--not adjusted for the influence of volcanic
eruptions and El Nino events--the warming trend during the past two decades
is similar in intensity to an earlier warming (1910 to 1940). Several
decades of slight cooling separate the two warm periods. However, "When ENSO
and volcanic effects are removed," writes Wigley, "the recent warming trend
increases to 0.25 degree Celsius [from 0.18 degree  C] per decade and
becomes highly significant compared to the earlier period." (ENSO stands for
El Nino-Southern Oscillation, a term that describes interannual changes in
both sea surface temperatures and atmospheric pressure across the Pacific

The overall result is a long-term warming trend that intensifies by
century's end, in sync with increasing emissions of greenhouse gases. Using
the raw data, greenhouse skeptics have claimed that the earlier warming's
similarity to the later one suggests that both were due to natural
variations rather than human activity.

Wigley also quantified and removed the warming influence of the 1997-98 El
Nino from the temperature record of the past decade. He found that of the 16
months in 1997-98 announced by the National Climatic Data Center as record
breakers, at least six can be attributed to El Nino rather than to a
longer-term global warming. "The sequence is still unusual, but no more
unusual than 1990-91, when an equal number of records occurred in the
ENSO-adjusted data," writes Wigley. Nevertheless, the past decade's warmth
is striking in the overall record.

NCAR is managed by the University Corporation for Atmospheric Research, a
consortium of more than 60 universities offering Ph.D.s in atmospheric and
related sciences.


From the BBC News Online, 14 December 2000


Earlier models had ignored volcanoes and other natural influences

By environment correspondent Alex Kirby

UK scientists say only a combination of natural and human causes can explain
the Earth's warming during the twentieth century.

They combined data on greenhouse gas emissions, ozone and sulphate aerosol
levels, solar variations, and volcanic aerosols in different versions of a
state-of-the-art climate model.

Natural causes, they found, mattered more early in the century, and
human-induced factors during the present warming.

They say their work increases their confidence in predictions of human
contributions to future warming.

The scientists, from the Hadley Centre for Climate Prediction and Research,
part of the UK Met. Office, and the Rutherford Appleton Laboratory, report
their findings in the magazine Science.



From CO2 Science, 13 December 2000

Perry, C.A. and Hsu, K.J. 2000. Geophysical, archaeological, and historical
evidence support a solar-output model for climate change. Proceedings of the
National Academy of Sciences USA 97: 12433-12438.

What was done
Noting that "the most direct mechanism for climate change would be a
decrease or increase in the total amount of radiant energy reaching the
earth," the authors developed a simple solar-luminosity model and used it to
estimate total solar-output variations over the past 40,000 years, as well
as 10,000 years into the future.  The model was derived by summing the
amplitude of solar radiation variance for fundamental harmonics of the
eleven-year sunspot cycle throughout an entire 90,000-year glacial cycle.
The results of this exercise were compared with geophysical, archaeological
and historical evidence of climate variation during the Holocene.

What was learned
The model output was well correlated with the amount of carbon 14 (which is
produced in the atmosphere by cosmic rays that are less abundant when the
sun is active and more abundant when it is less active) in well-dated tree
rings gong back to the time of the Medieval Warm Period (about A.D. 1100),
which finding, in the words of the authors, "supports the hypothesis that
the sun is varying its energy production in a manner that is consistent with
the superposition of harmonic cycles of solar activity."  The model output
was also well correlated with the sea-level curve developed by Ters (1987).
Present in both of these records over the entire expanse of the Holocene was
a "little ice age"/"little warm period" cycle with a period of approximately
1,300 years. In addition, the climate changes implied by these records
correlated well with major historical events.  Specifically, the authors
note that "great civilizations appear to have prospered when the
solar-output model shows an increase in the sun's output," while they state
that such civilizations "appear to have declined when the modeled solar
output declined."

What it means
"Current global warming commonly is attributed to increased CO2
concentrations in the atmosphere," the authors note. "However," they
continue, "geophysical, archaeological, and historical evidence is
consistent with warming and cooling periods during the Holocene as indicated
by the solar-output model." They therefore conclude that the idea of "the
modern temperature increase being caused solely by an increase in CO2
concentrations appears questionable." Their findings also clearly suggest
that as far as humankind is concerned, warmer is better.

Ters, M. 1987. Variations in Holocene sea level on the French Atlantic coast
and their climatic significance. In: Rampino, M.R., Sanders, J.E., Newman,
W.S. and Konigsson, L.K. (Eds.) Climate: History, Periodicity, and
Predictability. Van Nostrand Reinhold, New York, NY, pp. 204-236.
Copyright © 2000.  Center for the Study of Carbon Dioxide and Global Change


From CO2 Science, 13 December 2000

Will Global Warming Devastate Crops?  Read All About It!

Every once in a while - much more often, in fact, than one would hope would
be the case - a great hue and cry is raised over an experimental finding
reported in a peer-reviewed scientific journal. Worse than that, much is
often made of an isolated report in a non-referred science magazine. There
are even cases where word-of-mouth accounts of research that has not yet
been submitted for publication, much less even written in a suitable format
for journal review, make their way into the news services. And all of a
sudden, the dramatic new finding - based on only the claims of its authors -
becomes the mantra of some pre-existing movement (such as the Climate
Alarmist Craze) that realizes how the new information can be used to promote
its own agenda.
A case in point concerns a University of Florida study that enjoyed a bit of
prominence just a couple weeks ago. Some news services (Environment News
Service's AmeriScan of 1 Dec and Daily University Science News of 4 Dec) ran
headlines stating that global warming could reduce rice harvests, describing
the phenomenon as extremely bad news for Third World countries and the two
billion people who obtain 40% of their daily calories from rice.  In
addition, the story implied much the same about peanuts, soybeans and kidney
beans, hinting at the possibility that most all seed-producing plants were
similarly threatened.

What is one to make of such reports?  For starters, one should realize that
even the best of scientists can be wrong, as almost all of us are now and
then, and that nearly all researchers - whether they've published 10, 100 or
1000 papers - periodically have a paper rejected.  When this happens the
authors sometimes revise the manuscript and submit it to a different
journal, sometimes succeeding and sometimes failing once again to have it
published.  If the paper never sees the light of day, chances are it
suffered from true deficiencies; and if it is ultimately published
somewhere, chances are it will be significantly different than it was in its
first incarnation.  In either event, the bottom line is basically the same:
the original story was not all it was cracked up to be.

Discretion thus suggests that overly dramatic scientific claims should not
be given too much credence until they have in fact been published in the
scientific literature.  Even then, skepticism is still in order, especially
in the biological realm, where all sorts of confounding factors have the
potential to affect an experiment. A case in point is the growth response of
plants to atmospheric CO2 enrichment. In one of the largest reviews of this
subject ever undertaken, Idso (1992) surveyed a total of 1,087 individual
experimental results, finding that fully 93% of them were positive. One
implication of this finding is that the other studies may not have been
conducted properly. Another possibility is that they were done correctly but
that 7% of the plants studied just don't respond positively to atmospheric
CO2 enrichment. In either case, the few neutral or negative responses are
not characteristic of the responses of the great bulk of earth's vegetation.
And this observation highlights the importance of not relying too heavily on
just one experiment, or even a small group of studies, especially in
important matters about which there is much controversy.

Another thing to remember is that even if a study is correct in its
findings, the spin that is put on the results by the authors and/or other
interested parties may not be correct. In the case of the claim that future
warming will reduce the yields of rice, peanuts, soybeans and seed-producing
crops in general, for example, one must consider additional changes in the
global environment that may occur concurrently. And in this regard, the
ongoing rise in the air's CO2 content - which is even more certain than
future warming - must figure prominently.

Several studies published in peer-reviewed scientific journals have
conducted just such analyses.  Alexandrov and Hoogenboom (2000a), for
example, recently used the output from various general circulation models of
the atmosphere to assess the likely performance of soybeans and peanuts (two
of the supposedly temperature-threatened crops) over the next few decades in
the southeastern United States.  As was implied in the news service reports
of the University of Florida study, the predicted increase in air
temperature, along with predicted decreases in precipitation, implied future
decreases in the yields of both soybeans and peanuts.  However, when the
growth-promoting effects of the likely concomitant increase in the air's CO2
content were included in the analysis, yield increases were predicted for
both crops. And in a similar analysis of winter wheat in Bulgaria,
Alexandrov and Hoogenboom (2000b) obtained the same result: yield decreases
due to warming alone, but yield increases due to elevated air temperature
and CO2 concentration together.

Many other peer-reviewed scientific journal studies could be cited in
support of the conclusions of the analyses of Alexandrov and Hoogenboom, as
well as in support of the general principle that increases in the air's CO2
content typically tend to overpower the deleterious effects of all sorts of
environmental stresses, as indicated in the massive review of this subject
produced by Idso and Idso (1994).  There are also many similar studies that
have been produced subsequently.(1)

So, take heart, Third World countries, and do not be misled by the Climate
Alarmists who wring their hands and weep great Elephant Tears for you; the
future yet looms bright. Only by overtly meddling with the world's economy
in a fruitless and likely counter-productive effort to curtail anthropogenic
CO2 emissions will we likely screw things up for the biosphere, including
our agricultural enterprises. The great bulk of pertinent scientific
knowledge, i.e., all the evidence, clearly suggests that Kyoto spells
disaster for man and nature alike, and that the rising CO2 content of
earth's atmosphere is actually a godsend, a truly remarkable blessing in

Dr. Craig D. Idso
Dr. Keith E. Idso

1. Reviews of a number of these studies can be found on our website, most
notably under the general Subject Index heading Growth Response to CO2 with
Other Variables.

2. See, for example, our Editorial The Fortunate Coupling of Atmospheric CO2
and Temperature Trends and our Journal Review Rising CO2 Concentrations Help
Plants Adapt to Rising Temperatures.

Alexandrov, V.A. and Hoogenboom, G. 2000a. Vulnerability and adaptation
assessments of agricultural crops under climate change in the Southeastern
USA. Theoretical and Applied Climatology 67: 45-63.

Alexandrov, V.A. and Hoogenboom, G. 2000b. The impact of climate variability
and change on crop yield in Bulgaria. Agricultural and Forest Meteorology
104: 315-327.

Idso, K.E.  1992. Plant responses to rising levels of atmospheric carbon
dioxide: A compilation and analysis of the results of a decade of
international research into the direct biological effects of atmospheric CO2
enrichment. Climatological Publications Scientific Paper #23. Office of
Climatology, Arizona State University, Tempe, AZ.

Copyright © 2000.  Center for the Study of Carbon Dioxide and Global Change


From Larry Klaes <>

From, November 2000

Ecohacker Michael Markels claims he has a megafix for global warming:
Supercharge the growth of ocean plankton with vitamin Fe and let a zillion
CO2 scrubbers bloom.

By Charles Graeber

In October 1993, the Columbus Iselin, a ship loaded with 23 scientists from
15 international research institutes, left Panama on a mission to study one
of the great riddles of oceanography. The mystery involved a dark,
relatively lifeless stretch of the equatorial Pacific, a huge patch of water
250 miles southwest of the Galapagos Islands that 19th-century mapmakers
called the Desolate Zone. The zone is desolate because it's short on
phytoplankton, the tiny, floating surface algae that perform 50 percent of
Earth's photosynthesis. Although it is rich in most of the nutrients
required for plant life (phosphorous, nitrogen, silicon), the area has very
little phytoplankton, a condition that scientists call "high nutrient/low
chlorophyll," or HNLC. Twenty percent of the world's ocean water is HNLC,
and for 70 years nobody could figure out why.

The Columbus Iselin set out to test a hypothesis that emerged in 1989, when
an oceanographer named John Martin published a startling new theory in
Nature. Martin believed HNLC ocean water was missing a vital ingredient:
iron. Plants require minute quantities of iron to produce chlorophyll, and
Martin was convinced that HNLC zones were, essentially, anemic. Sprinkle
iron in the waters, he said, and they would bloom like Eden. Martin also
theorized that if you grew enough phytoplankton in HNLC zones worldwide, you
could lock up billions of pounds of carbon dioxide - phytoplankton converts
CO2 gas to solid carbon mass, which is effectively removed from the system
when the dead plants sink to the deep ocean floor into a kind of permanent
cold storage. In other words, you could potentially redirect the earth's

Strange though this sounds, it's possible. Scientists have long recognized
that Earth's average temperature is altered by the atmospheric concentration
of CO2, a V-shaped molecule that traps heat in the lower atmosphere like
glass traps heat in a greenhouse. At the end of the last ice age, roughly
18,000 years ago, atmospheric CO2 levels were only 180 parts per million,
less than half the current (and rising) level of 366 ppm. Martin argued that
huge blooms of phytoplankton were responsible for the lower CO2 levels in
that period; they reduced the earth's insulation and lowered the global
temperature. With more and more of the earth's water tied up in expanding
glaciers, he reasoned, winds pushed iron-rich dust from the continents'
parched surfaces, creating new phytoplankton blooms and freezing even more
water - a positive feedback loop for global cooling. Martin believed that if
this effect were triggered again on a smaller scale, it might even
counteract the contemporary problem of global warming. "Give me half a
tanker of iron," he joked, "and I'll give you the next ice age."

Martin, a charismatic, polio-stricken oceanographer whom the media called
Iron Man and Johnny Ironseed, found himself at the center of a blistering
controversy because of these views. Oceanography is conventionally dedicated
to studying the ocean, not changing it. Martin's peers warned that his
"Geritol solution" could screw up the very system he was trying to study,
that too little was known about oceanic dynamics to simply start casting
iron on the waves.

In two weeks, 1,000 pounds of iron produced the biomass equivalent of 100
full-grown redwoods, sucking 2,500 tons of CO2 from the sky.

Martin died of prostate cancer in 1993 at the age of 56, a few months before
a research mission he'd planned, called IronEx I, set off to test iron's
impact on the Desolate Zone. Two oceanography colleagues ran the experiment
in his place: Richard Barber of Duke University and Ken Johnson of Moss
Landing Marine Labs, a public research center affiliated with San Jose State
University. For two days, while the Columbus Iselin traversed a
25-square-mile grid of HNLC ocean, Barber's team dumped 1,000 pounds of
granular iron sulfate, dissolved in a weak acid solution, into the ship's
wake. Lasers from a NASA P-3 Orion airborne optical lab zapped the waters
from above, scanning for new chlorophyll.

The results were promising but mixed: IronEx I produced phytoplankton, but
it yielded four times less biomass than Martin's team had predicted. In
1995, a project led by Kenneth Coale (now the acting director of Moss
Landing Marine Labs) tried to increase the yield in a follow-up expedition
called IronEx II. This time scientists ladled out the thousand-pound iron
payload in three separate servings. And this time the dead seas sprang
dramatically to life. Overnight, the HNLC waters clouded green. Fish were
attracted by the harvest, and within days sharks and turtles were chasing
the new food supply. By the end of two weeks, IronEx II had produced the
biomass equivalent of 100 full-grown redwoods - touch-of-life results that
inspired Johnson to rave about "a phytoplankton explosion of almost biblical
proportions." The experimenters calculated that they had pulled 2,500 tons
of CO2 out of the atmosphere, and claimed they could do it again in desolate
zones all over the world.



From Herald Sun, 14 December 2000,4057,1516634^421,00.html


THE nation's plunging birth rate has sparked a two-year study into why
couples are shunning children.

Researchers from the Australian National University hope to uncover the
reasons for the low reproductive rate of 1.72 children per woman.

Dr Gordon Carmichael, from the ANU's centre for epidemiology and population
health, said the trend was threatening Australia's growth.

FULL STORY at,4057,1516634^421,00.html

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