CCNet, 60/2000 -  22 May 2000

     "The job of spotting long-period comets is left to amateur
     astronomers, who scan the morning or evening skies with wide-field
     telescopes or jumbo binoculars. It's hardly a systematic search
     plan. So if one of these objects is Earth-bound, we'll have very
     little time to react once we see it: anywhere from a couple of
     years down to a few months. This reaction time is crucial. [...]
     So a tool that can help astronomers find small comets out to 3 AU
     could be a life-saver. Depending on its orbit, a comet at that
     distance would be from a few months to about a year from impact.
     If it were small enough - no more than a few hundred metres across
     - we might be able to defend ourselves with a system like Gold's.
     [...] The question is, will anyone put up the money needed to
     realise Gold's scheme? At the moment, we don't even know how much
     it would cost, because NASA isn't prepared to fund a second
     phase to the study, to look at engineering feasibility and prices.
     If tens of thousands of dollars seems like too much, who will
     spend hundreds of billions? 
        -- Dan Falk, in New Scientist, 20 May 2000

    SpaceViews, 19 May 2000

    NEW SCIENTIST, 20 May 2000, pp. 36-38

    Michael Paine <>

    Jens Kieffer-Olsen <>

    SpaceDaily, 22 May 2000


From SpaceViews, 19 May 2000

The recent discovery of a comet that passed through the inner solar
system nearly three years ago has raised questions in the astronomical
community about the efficiency of current asteroid and comet search

In an article in the May 18 issue of the journal Nature, a team of
Finnish and French scientists reported the discovery of a comet seen by
the Solar and Heliospheric Observatory (SOHO), a joint ESA/NASA mission
designed to study not comets but the Sun.

The comet was observed by the Solar Wind Anisotropy (SWAN) instrument
on SOHO, a device designed to detect "Lyman-alpha" emissions of light
from clouds of interstellar hydrogen gas around the Sun. Since
Lyman-alpha light is also emitted by clouds of gas around comets, they
also show up in SWAN images.

Scientists led by Teemu Mäkinen of the Finnish Meteorological Institute
scanned SWAN images from mid-1997 and found five separate bright spots
that could be comets. Four of the five were linked to
previously-discovered comets, including the famous bright comet
Hale-Bopp. The fifth, though, corresponded to no other observed comet,
and hence scientists believe it is a "new" comet not previously

Because of the orbit of the comet -- which took it to within 1.2
astronomical units (180 million km, 112 million mi.) of the Earth in
mid-1997 -- astronomers believe it could have been observed by
professional or amateur astronomers using small telescopes or even

"Because the comet was almost constant in brightness over several
months, it should have been easily observable from the ground," Mäkinen
and colleagues said in their Nature paper.

Other astronomers have pointed out that the comet was not visible in
the northern hemisphere, where the great majority of search efforts
take place, and that the comet itself was likely never brighter than
magnitude 11, making it a challenging object for amateurs to detect
using small instruments.

The fact that the comet, named 1997 K2, was not seen until scientists
went through the archival data from SWAN may be a cause for concern
about the efficiency of current efforts to detect potentially
hazardous near-Earth objects (NEOs), including both asteroids and

In a commentary accompanying the article, astronomer Michael A'Hearn of
the University of Maryland said that the failed detection of the comet
three years ago may be a sign that current search efforts are skewed
towards asteroids 1 km (0.62 mi.) or larger in diameter, despite the
fact there are likely many more smaller bodies that could wreak
major damage if they struck the Earth.

"For our peace of mind, it is important to know whether comets
represent 10 percent of the potential large impacts on Earth (as is
commonly thought) or a much larger fraction," A'Hearn wrote.

Some astronomers have said in recent months that the number of large
near-Earth asteroids is smaller than once thought, and that existing
search programs that have dramatically increased the discovery rate
of such objects in recent years may be sufficient to catalog 90 percent
of these objects within the next ten years.

However, Benny Peiser, moderator of CCNet, a mailing list used by the
near-Earth object search community, argues that those astronomers are
missing the point made by comet 1997 K2. "It could soon be that NASA's
flawed Spaceguard goal will be blamed for the failure of NEO surveys
to detect comets such as C/1997 K2 and others," he wrote.

This discovery, warns Peiser, is "a timely reminder that -- in spite of
all the hype, PR, [and] over-optimism -- we are still far from getting
a grip on the impact hazard."

Copyright 2000, SpaceViews


From NEW SCIENTIST, 20 May 2000, pp. 36-38

Lurking beyond the outer planets are huge slabs of ice that could spell
our destruction. Can the world protect itself? Dan Frank inspects the

They are the stealth bombers of the Solar System. Almost invisible in
their pitch-black coats, they can come at us from any direction, giving
almost no warning.  Mostly they pass us by, but one day, one of these
marauders will be right on target.  And when it does it will devastate
the Earth.

These bringers of doom are known as long-period comets. Because they
have the advantage of surprise, it might seem almost impossible to
defend our planet against them., But there is hope. A NASA study, to be
made public this summer, outlines an array of defensive measures that
could prevent many catastrophic collisions. Meanwhile, Finnish
astronomers have hit upon a new kind of early warning system for comets.

It is common knowledge that cosmic collisions have taken a toll on our
planet. An Impact at the end of the Cretaceous, about 65 million years
ago, is widely believed to have finished off the dinosaurs. More
recently, in 1908, a comet fragment or asteroid is thought to have
exploded above the remote Siberian town (sic!) of Tunguska. The blast
killed reindeer and levelled trees within a 20-kilometre radius.

And then there was the great crash of 1994, when Shoemaker-Levy 9
smashed into Jupiter.  The event, recorded by dozens of telescopes and
spacecraft, seemed to bring home a feeling of global vulnerability.

How great are the risks? Estimates vary, but roughly speaking we can
expect a 100-metre body to hit the Earth once in a thousand years. That
would be big enough to cause massive regional damage, perhaps killing
millions of people if it hit a densely populated area. A 1-kilometre
comet or asteroid, which could be large enough to wipe us out, might hit
us once in a hundred thousand years. Robert Gold, of Johns Hopkins
Applied Physic Laboratory in Laurel, Maryland, puts it starkly. "The
greatest natural threat to the long-term survivability of mankind is an
asteroid or comet impact with the Earth."

But asteroids and comets present different threats. Asteroids are dens
chunks of rock or metal that inhabit the inner Solar System, with orbits
that mostly lie near the ecliptic - the plane of the planets. That makes
them relatively easy to spot.  Astronomers can gradually catalogue all
these objects, and then project their orbits far into the future. If we
find that an asteroid is due to hit Earth in, say, twenty years, we'll
have plenty of time to do something about it.

Comets are another matter. Astronomers believe that these "dirty
snowballs" start out wandering in a vast swarm of icy bodies surrounding
the Solar System, called the Oort Cloud.  Every now and again something
disturbs part of the cloud, sending a few lumps of ice plummeting
inwards. After many trips around the Sun, comets eventually get captured
within the inner Solar System, they become "short-period comets", in
orbits that are almost as easy to predict as those of asteroids.

The wild-cards are the long~period comets, with orbits that take
thousands of complete. They travel at 50 kilometres per second, compared
with 10 to 20 kilometres per second for asteroids, and on average
they're larger. So even though they probably account for only about ten
per cent of Earth impacts, according to Gold, they're more like 40 per
cent of the total threat to humanity.

Worst of all, long-period comets are frighteningly difficult to detect.
In, the outer Solar System, they are effectively invisible - there is
nothing to see but a tiny nucleus covered in a tarry substance about as
bright as charcoal. Only when a comet draws closer to the Sun does it
become brilliant. Sunlight evaporates its ices, which are ionised by the
solar wind. The ions glow, forming the comet's coma and tail.

What's more, the job of spotting long-period comets is left to amateur
astronomers, who scan the morning or evening skies with wide-field
telescopes or jumbo binoculars.  It's hardly a systematic search plan.
So if one of these objects is Earth-bound, we'll have very little time
to react once we see it: anywhere from a couple of years down to a few
months. This reaction time is crucial.

But governments and space agencies are beginning to take the threat
seriously. Last year, NASA's Institute for Advanced Concepts asked Gold
to study cosmic collisions and find ways to fight the threat. At a
meeting in Poland this summer he will present phase 1 of his

Gold's report proposes a three-part defence system: a set of orbital
telescopes, dubbed Sentry, designed to identify and track threatening
objects; a set of spacecraft, called Soldier craft, deployed to
intercept an incoming body; and an Earth-based control centre to oversee
the network.  The system could be built within the next 10 to 40 years.

Space sentry

The three Sentry telescopes would each be similar to the Hubble Space
Telescope, scanning visible and infrared wavelengths. Ideally they would
orbit at the same distance from the Sun as Venus, a vantage that would
let them see asteroids whose orbits take them close to the Sun. Sentry
would monitor the whole sky, allowing it to hunt comets as well as
asteroids. The telescopes would also see long-period comets on the far
side of the Sun, giving up to nine months' more warning than we have
now. This could turn "an uncorrectable disaster into a potentially
correctable one," says Gold.

The Soldiers, meanwhile', would be kept ready to launch ' perhaps in
orbit around Venus, from where they would be able to use planetary
"gravity-boosts" to reach their targets more quickly. Their job would be
to nudge any threatening object away from a collision course with Earth.

The movie 'Armageddon' took some liberties with the technique -
splitting the asteroid would be more dangerous than pushing it off
course - but they were right about the need for nukes. The simplest
method would be to explode a nuclear bomb above the object's surface,
blasting material off the body to deliver a kick.

The earlier an Earth-bound object is discovered and reached, the smaller
the nudge required. Take a body 100 metres in diameter.  If intercepted
a year ahead of impact, it could be deflected with a tiny nuclear
explosion, equivalent to just 100 tonnes of TNT.

As the size of the object increases, so does the required warning time
and payload. For a "global killer" much more than a kilometre across, a
Soldier craft would need to intercept the object more than a year ahead
of time, even if armed with a multi-megaton bomb. Given the time taken
for a Soldier to reach the object, that means a need for even earlier
detection.  Cold suggests a grander Sentry scheme' using many telescopes
based as far out as the orbit of Jupiter.

Chase the comet

In the hunt for wayward comets, any new detection tool is welcome.  The
latest comes from a seemingly unlikely source.  The SOHO satellite,
launched in 1995, was designed to study the Sun, its atmosphere and the
solar wind, but a team of Finnish and French scientists has noticed that
the spacecraft is also a surprisingly adept comet spotter.  This week,
they report finding 18 comets on images captured by SOHO between late
1995 and mid-1998 (Nature, vol. 405, p 321).  These images were produced
by the spacecraft's SWAN (Solar Wind Anisotropies) detector, which
monitors a type of ultraviolet radiation known as Lyman alpha emission.
This radiation is characteristic of hydrogen ions, which make up much of
the solar wind and, as it happens, the coma and tail of a comet.

Most of the comets seen by SOHO, had already been detected by other
means.  But one of them, along-period comet dubbed C/1997 K2, was A,SOHO
original.  "Our work shows that one of the bright comets of 1997 passed
by unnoticed," says Teemu Maekinen of the Finnish Meteorological
Institute in Helsinki.  It would have been a little too faint to see
with the naked eye.

Because it wasn't designed explicitly for the purpose, SWAN is not a
good instrument for detecting comets, Maekinen says.  But the principle
is sound.  "If we had some kind of super-SWAN - a similar instrument but
with much higher resolution - it would be the ultimate comet chaser," he

The ideal Lyman-alpha detector would be space-based, like Gold's
proposed Sentry telescopes.  He suggests placing it at one of the
Lagrangian points - stable points where the gravitational tug from the
Sun and the Earth cancel each other out. SOHO sits at the L1 Lagrangian
point on the sunward side of Earth, orbiting about 1.5 million
kilometres closer to the Sun than Earth's own orbit.

Michael M'Hearn of the University of Maryland in College Park agrees
that the Lyman alpha method could be an important technique for finding
comets.  Optical detectors need ultra-high resolution to pick out a
distant comet's tiny visible-light image, but the Lyman alpha emissions
from a comet cover a much larger swathe of sky.  With a detector
sensitive to this radiation, you can use a much lower spatial
resolution, says A'Hearn.  This makes it easier to search large areas of
the sky.

There is a catch, though. Lyman alpha detectors lock in on the glowing
ions that surround a comet's nucleus, and this glow only exists when the
comet is within about 3 astronomical units of the Sun, (1 AU is the
radius of the Earth's orbit, or about 150 million kilometres).  SWAN
registered Comet Hale-Bopp when it was 2.9 AU out, roughly twice the
distance of the orbit of Mars.  That was a year after Alan Hale and
Thomas Bopp had seen it through small optical telescopes, when it was
still beyond the orbit of Jupiter, at a distance of more than 5 AU.

But Hale-Bopp was a colossus, far brighter than most comets.  So a tool
that can help astronomers find small comets out to 3 AU could be a
life-saver.  Depending on its orbit, a comet at that distance would be
from a few months to about a year from impact.  If it were small enough
- no more than a few hundred metres across - we might be able to defend
ourselves with a system like Gold's.

The question is, will anyone put up the money needed to realise Gold's
scheme?  At the moment, we don't even know how much it would, cost,
because NASA isn't prepared to fund a second phase to the study, to look
at engineering feasibility and prices.  If tens of thousands of dollars
seems like too much, who will spend hundreds of billions?

* Dan Falk is a science writer and broadcaster based in Toronto

* Further reading: Impact! The threat of comets and asteroids
  by Gerrit L. Verschuur (Oxford University Press, 1996)

Copyright 2000, New Scientist



From Michael Paine <>

Dear Benny,

I believe your comments on NASA's NEO search plans were unduly harsh.
As I stated in my CCNet posting on 4 May, Don Yeomans from NASA
explained to me "The current plan is to find the big ones first, then
as the detection technology improves, extend the search to smaller and
smaller objects". Unfortunately these words were edited from my story. The other point is that the search 'planned' by NASA,
although focusing on large Near Earth ASTEROIDS, will pick up a good
sample of other objects and therefore help to better quantify the
hazard. At present it is all too easy for politicians to ignore the
issue because of perceived uncertainty (even disagreement) about the
magnitude of the hazard.

I think one of the problems is that NASA's OFFICIAL line does not seem
to acknowledge the hazard from comets and small asteroids. The website
of NASA's Near-Earth Object Program Office still has the following,
somewhat outdated FAQ:

What Is The Purpose Of The Near-Earth Object Program?

The purpose of the Near-Earth Object Program is to coordinate
NASA-sponsored efforts to detect, track and characterize potentially
hazardous asteroids and comets that could approach the Earth. The NEO
Program will focus on the goal of locating at least 90 percent of the
estimated 2,000 asteroids and comets [?] that approach the Earth and
are larger than 1 kilometer (about 2/3-mile) in diameter, by the end of
the next decade. In addition to managing the detection and cataloging
of Near-Earth objects, the NEO Program office will be responsible for
facilitating communications between the astronomical community and the
public should any potentially hazardous objects be discovered.

The fact that a comet slipped undetected through southern skies one
year after the Australian government closed down the 'Spaceguard
Australia' program was a good opportunity to stir up the local
politicians. Copies of my recent emails are at

Michael Paine
The Planetary Society Australian Voluunteers


From Jens Kieffer-Olsen <>

    Loren C Ball <> wrote:

> Unless I am sadly mistaken, no two plants in this country are alike.
> That is, any given plant must learn to live with its own peculiar set
> of problems and cannot use the history of its neighbors to any
> advantage because each is unique. This seems like a silly way to spend
> a few billion dollars. The obvious answer to me is in economy of scale.
> Let's simply decide on a design and freeze it so we can build a dozen
> or so that are identical. A huge part of each plant's budget is in
> design. Am I missing something here?

I suspect that rather Sailor and van der Zwaan may be missing something!

Forty years ago it was argued that known uranium reserves were too few
to supply the world with energy for much more than 50 years. Since then
new yellowcake deposits may have been discovered, but also breeder
reactors have fallen from grace such that the yield per kilogram is
reduced. Did the article provide an estimate of the period over which
they envisage feeding 4000 reactors with fissionable uranium?

Fusion energy on the other hand remains the elusive panacea to provide 
the world with energy free of pollution. Success from Tokamak research
is just round the corner, and surely there is laser light at the end of
the tunnel :-)  

Jens Kieffer-Olsen, M.Sc.(Elec.Eng.)
Slagelse, Denmark


From SpaceDaily, 22 May 2000

Scientists Take Issue With Solar Innocence

Los Angeles - May 19, 2000 - Following an article published in the UK
science magazine New Scientist, a group of solar physicists have taken
issue with the article's slant that the Sun is not to blame for global

The scientists further argue that the original article was
misinterupted (sic) as suggesting the sun does not play a key role in
our recent detection of global warming.

Paal Brekke a solar physicist with the SOHO project told SpaceDaily
that there is growing evidence that the sun and its relationship with
the ebb and flow of cosmic rays is responsible for a substantial
portion of the increase in global tempurates.

In an article published on the University of Oslo website Paal Brekke
and Nigel Marsh provide details on the growing evidence that Cosmic
Rays have a significant influence on the Earth's cloud cover [...].

In a scientific report from the Danish Meteorological Institute (Report
99-9) Thejll and Lassen revisit the correlation between the sunspot
cycle and Northern Hemisphere temperature trends.

They conclude that the solar forcing that is described by the solar
cycle length model no longer dominates the long-term variation of the
land air temperature.

Their result was presented in New Scientist on 6 May 2000 with the 
title "Don't blame the Sun" and the opening words: "Greenhouse effect
sceptics may have lost their final excuse". This short article will try
to clarify a few facts about these statements.

First of all, it is striking that the journalist uses the forceful 
language mentioned, when one compares it with the more cautious last 
quote from Thejll: "We're now seeing that the Sun plays a role, and
something in addition to the Sun". We interpret this to mean that the
Sun is still an important contributor to the temperature trends.

The results referred to in the New Scientist article have not yet been
published in the peer-reviewed literature. Nevertheless they were
presented in a press release and they made news in the media.

The central proposition, that the temperature no longer follows the
cycle length, is not new. Henrik Svensmark published a similar figure
as in New Scientist more than a year ago (see Figure 3 in his paper,
Physical Review Letters, 81, p. 5027, 1998.).

Svensmark stated that the long-term trend of cosmic-ray variation 
follows the warming trend better that either the sunspot number or the
solar cycle length (the latter deviates in the last few years).

The results from Thejll and Lassen cannot be used to conclude anything 
about the relationship between the Sun and the climate. Obviously the
Sun's behaviour is much more complex than sunspots alone can show.

We now know that the Sun's interplanetary magnetic field and the solar
wind have increased by a factor 2 the last 100 years, and this variation
does not follow the variation in sunspots.

Recently it was found that the Earth's cloud cover, observed by
satellites, is strongly correlated with galactic cosmic-ray flux. One
interpretation is that the cosmic rays are the dominant source of ions
in the free troposphere and stratosphere. These ions may grow via
clustering to form aerosol particles, which may ultimately become cloud
condensation nuclei and thereby seed clouds.

Clouds influence vertically integrated radiative properties of the
atmosphere, both by cooling through reflection of incoming short-wave
radiation (sunlight), and heating through trapping of outgoing
long-wave radiation (thermal radiation).

The net radiative impact of a particular cloud mainly depends upon its
height above the surface and its optical thickness. High optically thin
clouds tend to warm, while low optically thick clouds tend to cool it.
With a current estimate for the net climatic forcing of the global
cloud cover as a cooling of 17- 35 W/m2, clouds play an important role
in the Earth's radiation budget. Any significant solar influence on
global cloud properties can potentially be very important for Earth's

To summarize, the pattern of systematic change in the global climate
over recorded history seems to follow the observed changes in
cosmic-ray flux, and it is consistent with the explanation that a low
cosmic-ray flux corresponds to fewer clouds and a warmer climate, and
vice versa. There was a systematic decrease in the cosmic-ray flux by
about 15% over the course of the last century, caused by a doubling of
the solar coronal-source magnetic flux.

By reconstructing cloud cover from the cosmic ray flux and using the
estimates for cloud radiative forcing, one can infer form Svensmark
1998 a warming of approximately 1.5 W/m2, over the past century

This is potentially important, considering that over the same period
the estimated heating from increased CO2 emission is 1.5 W/m2, while
changes in the solar irradiance at Earth are said to be 0.4 W/m2
(Lockwood and Stamper, Nature, 399, p. 437, 1999).

Whether the global warming trend recently measured is dominated by
anthropogenic effects or has a significant or even dominant solar
component is not yet understood.

The climate of the future will be the sum of man-made and natural
variations, but the man-made part cannot be estimated reliably until the
contributions of natural agents (Sun, volcanoes, El Nino) have been
defined, and subtracted from the observed changes of the past 100

Copyright 2000, SpaceDaily

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