CCNet DEBATE, 12 October 1998

    Richard A Kowalski <>

    James D. Perry <>

    Sir Arthur C Clarke

(4) THE COMET OF 1680/81
    Wolfgang Kokott <>

    Mike Baillie <>

    Roy Tucker <>


From Richard A Kowalski <>

Personally, I think that the use of an asteroid as a weapon actually
requires too much forethought, planning and "threat time" for even a
"madman" to use.

The idea of a threat is to create terror and chaos. It must also be
such that the "enemy" cannot counteract the weapon.

In other words, "Mad man X" builds or obtains an interplanetary launch
vehicle and the needed warheads or other technologies needed to change
the objects orbit to one of earth intercept. Then (s)he needs a large
lead time to allow for this "weapon"  to "find it's target", which can
be years or decades.

How likely is it that all of this could remain a secret until it is too
late to respond? I think very unlikely.

It is much cheaper, easier and much less costly to produce biological
or chemical or even obtain nukes, to do the job.

I think the threat from this type of weapon should be dismissed out of
hand when there are so many more realistic threats already being used.

Anyone for fuel oil and fertilizer, Sarin or Anthrax, et al?

-- Richard A Kowalski
Quail Hollow Observatory   761 Zephyrhills


From James D. Perry <>

Dear Benny,

Oliver Morton said,

  "While I'm not greatly invested in the Sagan/Ostro threat, I thought
  James Perry was a little too dismissive. His confidence that a
  strangelove-style madman would be easily controlled through PALs,
  etc, ignores the fact that most nuclear powers do not have universal
  PALs or similar controls."

The US, Britain, France, and Russia use PALs (or some analogue). 
Therefore the majority of all nuclear weapons are under PAL control.  I
don't know what the Chinese, Israelis, Indians, and Pakistanis use, but
this is a moot point, since these would probably not be the powers who
installed and operated an asteroid deflection system.

"What's more, he assumes at some  points that the risk is of a global
catastrophe, while engineered regional devestations are also possible.
They'd be harder to pull off, I agree, but politicians and generals 
have been known to attempt things they couldn't pull off while all the
time convinced that they could..."

I did address the issue of regional devastation, and concluded that
asteroids were not the best way to inflict such devastation.  It is
highly unlikely that the powers who would probably control the asteroid
deflection system (perhaps the Permanent Members of the UN Security
Council) would want to cause a regional catastrophe, but if they did,
they have more effective, reliable, and controllable means at their
disposal (nuclear-armed ICBMs) than asteroids.

"He also assumes that a collision would be engineered using an existing
deflection system, which is not necessarily the case. "

I'm not quite sure what you're getting at here.  How do you engineer a
collision with a deflection system that does not exist?

"And he ignores the fact that an asteroid, while unwieldy, might when
used as a weapon provide benefits in terms of leverage and

One could address this risk by ensuring that the operations of the
asteroid deflection system were completely transparent.  When asteroids
were detected -- or deflected -- this information would be made
available to scientists and the public worldwide in a timely manner. 
It would be hard to redirect an asteroid (or permit an asteroid to
continue on a dangerous course) if the world was looking over your
shoulder, so to speak.  Moreover, one must assume that professional and
amateur astronomers would continue to hunt for asteroids independently
of the asteroid detection system -- indeed, civilian scientists may
even be part of the detection system. This redundant capability would
make a "plausibly deniable" deflection that much harder to execute
successfully.  Finally, if the detection/deflection effort were
international, then a large number of countries would have to collude
to effect an "accidental" collision, which seems unlikely to me.

"Jens Kieffer-Olsen assumes that use of nuclear explosives means the
involvement of the military. While in the rest of the world this might
be the case, in the US nuclear explosives come under the remit of the
Department of Energy. As I understand it, this is the result of a
decision -- in the Eisenhower administration, or earlier -- that nukes
were too important to leave to the generals. It is the DoE that designs
and makes the things; nuclear tests were, when they used to occur, DoE
responsibilities, I believe. So a civilian use of nuclear explosives is
conceivable -- indeed, precedent suggests that American public opinion
and political prractice would both point to civilian control of
non-military nukes in such a context."

This is not precisely accurate. In 1946, the Truman administration
established the Atomic Energy Commission, and gave the AEC physical
possession of all nuclear weapons, to be handed over to the military
only at the President's discretion. This practice did not last very
long, however. In the early 1950s, the military began to assume custody
of weapons, and by the late 1950s the entire stockpile had been handed
over to the military. The principal impetus for this was the
development of ICBMs, whose short time of flight rendered impractical
any scheme in which the military could not respond immediately to an
enemy attack. After its establishment in the 1970s, the Department of
Energy became responsible for the research, development, testing,
production, and retirement of nuclear weapons. However, the operational
deployment (and potential employment) of the weapons is in the hands of
the Department of Defense.

It is true that "civilian use of nuclear weapons is conceivable" -- and
a reasonable case could be made that asteroid deflection is a "civilian
use" of nuclear weapons.  Note that there is a strong correlation
between timely detection and nuclear control/safety.  The sooner a
dangerous object is detected, the more time we will have to plan the
deflection, and the safer the operation will be. 

James D. Perry


From Sir Arthur C Clarke

Dear Benny,

Amused by Brian's reference to 'the rather bizzarre (sic - it's a word
I've never been able to spell either) character who succeeded Newton'.
I'd have given Sir Isaac 9 out of 10 in that category...

                   All best,
                             Arthur  Clarke     8 Oct 98

(4) THE COMET OF 1680/81

From Wolfgang Kokott <>

Great scientists are quoted constantly, but read rarely. Edmond Halley
shares this fate. He had noticed that his parabolic orbits for the
comets of 1531, 1607 and 1682 were quite similar and on these grounds
tried successfully to represent the older observations by means of the
1682 elements -- ending up with the famed 76-years periodicity.
Subsequently, he noticed that prior to 1680, comets had appeared in 531
and 1106, and <lacking observational evidence> conjectured that IF these
three apparitions were again of the same object, a period of 575 years
would result. On this basis, he again adapted his parabola. The big
'if' is by Halley himself <the 'Synopsis', both the 1705 and the 1749
versions>, and it did not work out. Up to now, the spurious evidence of
531 and 1106 did not lead to reliable orbits for these objects. The
definite orbit of C/1680 was finally computed by J.F.Encke in 1818;
he did make use of the modern theory of planetary perturbations. His
orbit is also an ellipse, albeit with a period of about 9600 years and a
marked 'uncertain' tagged to this value.



From Mike Baillie <>

Thanks to Brian Marsden for clarifying the debunking of Halley's 575
year return time on the 1680 comet. By way of explanation let me inform
the readership of a rather curious coincidence. In studying tree-ring
records and writing odd articles it happens that among other dates I
have covered (without prior knowledge of Halley's 575 year period) are
2911 BC, the 2354-2345 BC inundation event, the 1628 BC possibly
Santorini event, the 1159 BC so called Hekla 3 event, the 207 BC and
536-545 AD events. For good measure and prompted by Kevin Pang's
Chinese history and Val LaMarche's 43 BC frost ring event, I have
discussed the 44 BC event (for which we have no Irish oaks).

Now the curious thing about this list of dates, independently derived
from tree-ring series, is the proximity of several of them to the 531
AD, 44 BC, 1194 BC, 2344 BC and 2919 BC "Halley 1680 returns". 
Obviously this is just a bizarre coincidence. Or is it? How would we
know?  Is it possible that there are 'episodes', which might involve
comets or their debris, at around the interval that Halley proposed? I
wouldn't pretend to know.

Incidentally, the reason I refer to the 2354-2345 BC event as 'the
inundation event' is that we have pretty good tree-ring evidence that
just at that time the level of Lough Neagh in Northern Ireland, the
largest water body in the British Isles, rose suddenly.  Even more
curious is that the prehistoric section of the Irish Annals records
"lakes breaking out" in 2341 "BC", while Archbishop Usher (aka Ussher)
of County Armagh (just south of Lough Neagh) was the individual who
provided the biblical date 2349/48 "BC" for the Flood of Noah; the very
date that Halley and Whiston used.

Part of my interest is how scientists are supposed to deal with such
loose clusters of information. Bluntly, how can one assess significance
with intrinsically weak data, but quite a lot of it?  This is very much
in keeping with Bob Kobres' recent listing on how do we infer
significance from mythological information which is intrinsically weak,
though there is a lot of it.

Mike Baillie
Palaeoecology Centre
School of Geosciences, Queen's University, Belfast
(01232) 335147


From Roy Tucker <>

Dear Dr. Peiser,

If the following text is deemed appropriate, I would appreciate its
posting to the Cambridge Conference forum. Thank you very much.

Sincerely yours,
   Roy Tucker


A proposed mechanism for the generation of comet showers

     The geological record contains tantalizing evidence of the
occurence of 'comet showers', geologically brief periods during which
impact events were much more frequent than at the present time.
Speculations regarding the causes of such showers have involved
gravitational perturbations of the Oort cloud by passing stars or a
faint red dwarf companion of the sun or passage of the sun through
molecular clouds in the galaxy. I wish to offer, for comment by the
members of this forum, another possible mechanism.

     I would first like to call attention to a few facts or conjectures:

Fact 1 - Chiron and other known outer solar system minor planets can be
quite large, approximately 200 kilometers in diameter.

Fact 2 - Chiron, originally thought to be a minor planet, has in recent
years displayed a cometary coma and is apparently a huge comet. This may be
generally true of these outer solar system bodies.

Fact 3 - Many of these bodies are in unstable orbits that will evolve
greatly in periods of time much shorter than the age of the solar
system. This may offer them the occasional opportunity to interact with the
major outer planets.

Conjecture 1 - Many Oort cloud comets may indeed have highly eccentric
orbits that permit them to approach the outer giant planets.

Fact 4 - The Kreutz family of sun-grazing comets, consisting of
apparently many hundreds of fragments, is likely to have resulted from the
disruption of a single parent body at around 371 BC (Marsden, AJ 1989,

Fact 5 - Close approaches to a giant planet can either eject a comet
from the solar system or greatly reduce its semimajor axis so that it
becomes a short-period comet.

Fact 6 - At least one comet (Shoemaker-Levy 9) has been observed to be
disrupted by a close approach to a giant planet (Jupiter) into
kilometer-sized fragments.


    It is possible for a large Chiron-class object or Oort cloud comet
to pass within the Roche limit (approximately 2.456 planetary radii or
about 108,000 km for Jupiter) of a major planet and not only be
disrupted into a large number of fragments but these fragments may also
be injected into short-period orbits with perihelia deep within the
inner solar system. Bear in mind that a 200 km object such as Chiron
would produce 8,000,000 one km fragments if equally divided. This is an
extreme but plausible example. The high orbital inclination of the Kreutz
family clearly demonstrates that it was not disrupted by an encounter with
a major planet but it does show that, at least in a single case, a large
parent comet has been disrupted into hundreds of smaller ones.

     The population of outer solar system minor planets is only now
being investigated and their abundance, sizes, and average orbital
characteristics are not well known. The frequency with which large,
outer solar system minor planets may approach the giant planets is not
well known since we have had the ability to detect such objects for only
a very few decades.

     For such a disruption and comet shower to occur, the object must
pass within the Roche limit but not impact the planet. The ratio of the
circular area within the Roche limit in a plane perpendicular to a
tangent of the object's path at periapse to the cross-sectional area of
the planet is approximately six. It is more than five times more likely to
be disrupted and pass the planet than to impact the planet.

     This is, I believe, a plausible mechanism whereby the passage of a
single outer solar system minor planet/comet near a giant planet, such
as Jupiter, may result in a cosmic shotgun blast at the inner solar

     Thank you very much for your attention and consideration. I will
appreciate receiving your comments.

                                        - Roy Tucker

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