PLEASE NOTE:


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LETTERS TO THE MODERATOR, 23 June 1999
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(1) A RESPONSE TO BOB KOBRES
    Paolo Farinella <paolof@tycho.dm.unipi.it>

(2) SPACE DEBRIS DETECTION AT THE OCA SCHMIDT TELESCOPE
    Alain Maury <Alain.Maury@obs-azur.fr>

(3) IMPACT PROBABILITIES & PUBLIC INTEREST
    Jens Kieffer-Olsen <JKO@dst.dk>

(4) TUNGUSKA '99
    Luigi Foschini <L.Foschini@isao.bo.cnr.it>


==================
(1) A RESPONSE TO BOB KOBRES

From Paolo Farinella <paolof@tycho.dm.unipi.it>

Dear Benny,

Let me comment on some aspects of the recent eloquent essay of Bob
Kobres (although I am afraid my English style is much less colourful!).
I happen to have been active in a scientists' pro-nuclear disarmament
organization (http://twilight.dsi.unimi.it/~uspid/)  for almost 20 years
now, so I have given some thought to the issues he mentions.

First, I think that the analogy between the effects of an impact and
the 'nuclear winter' effects of even a small nuclear conflict is not
sound from a physical point of view. It is true that current modeling
work on both scenarios is fairly primitive, but nuclear winter effects
arise mostly from the soot generated by extended fires, not from blast
energy; therefore a critical factor is the number and geographical
distribution of the explosions. A single big bang is very different
from many smaller ones from this point of view.

As for the argument that we need the impact threat to

> focus our technical prowess on goals a bit more constructive than
> building increasingly sophisticated instruments for
> mass-life-destruction.

as Bob says, why not climate change? poverty? vaccinations?
biodiversity? and above all, war? If we dislike wars, why don't we
focus on this issue? Abolishing war is a long-term objective, I agree,
but also the impact threat is significant on a long time horizon only.
Abolishing nuclear weapons at least isn't any longer an utopia after
the end of the Cold War, as many influential politicians and military
men are now admitting. I am a proud member of the Pugwash movement (the
1995 Nobel Peace Prize winner), which has recently published some
authoritative studies on this issue
(http://www.pugwash.org/publications.htm).

As for the rest, is Bob aware that the impact threat has been widely
used by Edward Teller and his fellow Los Alamos scientists to support
continuing work on super-bombs, new-generation nuclear weapons and so
on - in particular to divert relatively small NEOs? and that for some
time China used the impact threat argument to justify her resistance to
sign the Comprehensive Test Ban Treaty? And what about the Sagan-Ostro
scenario of impact-diverting technologies used to transform NEOs into
super-weapons? The recent understanding (Milani et al. 1999) of the
resonant and non-resonant Earth encounter cascades for objects such as
AN10 adds a new dimension to this, I think:  we now have some concrete
cases of bodies for which a small Delta V imparted at the right moment
in the relatively near future could cause an impact some years or
decades later. I wouldn't be too surprised if somewhere in the world
some scientists were already at work on this possibility.

About comets: the (admittedly uncertain) estimates about the fact that
comets pose <10% of the hazard take into account the dynamics,
dominated by Jovian encounters, of the Jupiter-family comets. The
dynamical effects of Jovian encounters are at least as difficult to
model and predict as the effect of Earth encounters for AN10 and its
siblings, but I think that here the main risk is related to
undiscovered objects (especially long-period comets) rather than to
chaotic dynamics. As for the dust collected by Earth during encounters
with comets, I am not an expert but back-of-the-envelope estimates
suggest that, given the low density of dust in typical comae and trails
(apart from the nucleus' immediate vicinity), the dust flux on Earth
should seldom exceed the 'background' average. Of course things would
be different for a giant Chiron-sized comet, but most (not all) experts
believe that such events are extremely rare.

Finally, there has already been a long and detailed debate on the
possible merits of NEO searches from space. My understanding is that,
given the current cost of space activities, this is NOT a viable
strategy - with the possible exception of NEAs with relatively peculiar
orbits, such as Atens or putative Q<1 AU bodies. In general, searches
from the ground are much more effective and will remain so in the near
future.

If on some of these issues I am wrong, I'd appreciate being corrected
by colleagues who may have studied the corresponding problems in depth.
But I think we need to improve our quantitative understanding more than
our rhetorics on these issues. And we should refuse giving up
science-based rationality in favour of emotions and politics.

Paolo Farinella

Paolo Farinella               Tel. +39-040-3199223
Dipartimento di Astronomia    Fax  +39-040-300479
Universita` di Trieste
Via G.B. Tiepolo 11           e-mail paolof@dm.unipi.it
I-34131 Trieste, Italy        WWW: http://tycho.dm.unipi.it/~paolof

=====================
(2) SPACE DEBRIS DETECTION AT THE OCA SCHMIDT TELESCOPE

From Alain Maury <Alain.Maury@obs-azur.fr>

Dear Benny,

You got me worried when I saw mention of "the french NEO search
programmes" in your latest CCNet digest. A proper title could have
been something like "space debris detection at the OCA Schmidt
telescope". The observing campaign for space debris was indeed
achieved this year (with about 4500 individual frames taken and 8 new
near geostationnary space debris detected), and we are now working on
the real time detection and identifications of objects as well as a
new faster observing procedure (fast reverse scanning). A newer
camera is being planned, but we don't have firm dates as far as when
we will be reobserving both asteroids and space debris.

Yours,
Alain

===================
(3) IMPACT PROBABILITIES & PUBLIC INTEREST

From Jens Kieffer-Olsen <JKO@dst.dk>

RE: ANOTHER ANSWER REGARDING IMPACT PROBABILITY CALCULATIONS

From Karri Muinonen <muinonen@cc.helsinki.fi>

> In order to compute the collision probability, one must specify a time
> window: the collision probability at a single moment in time is zero!
> For example, for the AN10-Earth encounter in August 2039, I made use of
> the time window August 4.0-11.0, just to be on the safe side. In this
> case, the time window could be decreased to less than one hour in
> August 7, 2039.

Dear Benny,

I recall no attempt so far to pinpoint the time window in 2044 over
which the 1:500,000 impact risk from 1999 AN10 accumulates. Judging
from Karri Muinonen's contribution I gather the risk is concentrated
over a few days with a much narrower window of maximum probability
density.

Using an impact probability density from currently unknown objects
>1km estimated at 1x10**(-9) per hour I find it misleading as some do
to dismiss the AN10 risk in 2044 as minor, when in fact the impact
probability density based on current data works out as something like
1x10**(-7) per hour over 10 - 20 specific hours. ( Or 1x10**(-6) per
hour if concentrated over 1 - 2 hours).

I agree that observations of objects with an impact probability
density, which at no point in time exceeds the current 'background
risk' of 1*10**(-9) per hour, should be considered irrelevant news
and kept out of the public domain.

But whenever observations lead to the conclusion that over a specific
time window the hourly impact risk is abruptly increased by several
orders of magnitude owing to a certain asteroid, it makes no sense at
all in my view to brand it alarmist to alert the public in a big way.

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

===================
(4) TUNGUSKA99 EXPEDITION

From Luigi Foschini <L.Foschini@isao.bo.cnr.it>

The starting day for the Tunguska99 Expedition is coming. The departure
is confirmed for July 14, 1999 from Forli' airport, by means of a
charter flight. The necessary equipment will be loaded on July 13.

Time is running and preparations are deeper and deeper, both for
defining details of the scientific program and for taking care of last
logistic problems.

Today, June 22, participants were at the Rosario lake, near Bologna, in
order to test the inflating catamaran "Kulik", so named in honour of
Leonid Kulik, the Russian scientist who organized the first expeditions
to the Tunguska site (photo 1). This catamaran is powered by a 20 HP
motor and has a platform of 6 x 3 m, able to hold a 6 and half tons
load. It has also an a-frame 3 m high with a winch able to deploy 500
kg. The catamaran will be used as support for exploring the bottom of
the Ceko lake.

The camping equipement and all the material necessary for survival in a
hostile environment, such as the Tunguska marsh, was also succsessfully
tested (photo 2).

Sir Arthur C. Clarke has passed to his TV producer our information about
the Tunguska99 expedition. He has informed us that the House of Lords
debated his SPACEGUARD proposal last week.

More informations are available at the web site:
http://www-th.bo.infn.it/tunguska/

Bologna, 22 June 1999

For the Tunguska99 Press Office
Luigi Foschini (mailto:L.Foschini@isao.bo.cnr.it)

Photos by Gio' Palazzo fax +39 011 720031

-----------------
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