From Bob Kobres <>

Unless my ciphering was way off or physics has become kinder and
gentler over the last dozen years, I'm still inclined to believe that a
stony object 350 meters in diameter (~1998 OX4?) with a geocentric
velocity of 25 kilometers per second will dump the equivalent explosive
power of around 5,000 megatons of TNT into Earth's biosphere. That's a
substantial punch and, as noted in my 1987 Whole Earth Review article
<>, this level of energy
release is within range of a "Nuclear Winter" scenario.  Though there
would obviously be differences, between nuclear and impact source, in
how this energy dissipated, I doubt that our numerical models of what
could follow actually reflect reality much better than fun-house
mirrors. We do not know empirically how events of this energy range
might influence climate and thus food supply. Critical would be when,
where, and how this amount of energy was pulsed into the environment.

The original reason that I became interested in the threat posed by
extraterrestrial objects is, I thought, that the danger might help to
focus our technical prowess on goals a bit more constructive than
building increasingly sophisticated instruments for
mass-life-destruction. It intrigues me as to why such a fixation on
odds and hierarchy of risk has developed with regard to this particular
threat. Is this mindset simply an extension of an 'acceptable
destruction level' as per nuclear war games? I know from experience
that in the 1980s many well informed people had come to the conclusion
that we were eventually going to blow the shit out of ourselves with
nuclear weapons--it was just a matter of when.
<>  That's why not a few
'in-the-know' viewed my suggestion of an Earth defense initiative as
just a tad short of hilariously insane (although I was certainly not
totally alone in this delusion).
<>  An interesting confirmation
of this idea being perceived this way came last year in the wake of the
1997 XF11 flap when Rich Rusk, a son of former US Secretary of State
Dean Rusk, confided to me that "We all thought you were crazy but you
were right!" I had discussed this issue with the elder Rusk early in
the eighties and learned that he was somewhat familiar with the topic
due to being in office when concerns about the asteroid Icarus were
being expressed. <>  Dean Rusk
also mentioned that one of his colleges (I forget who) at that time
speculated as to whether asteroids like Icarus could be used as
weapons; so it goes within the paranoid nationalist mindset.

Personally, I believe that the seminal issue to focus public attention
on is that in the entire history of Life's mounting and probing on
Earth there has never been such an opportunity to expand horizons both
in time and space. Dwelling on odds and energy levels is confusing to
people not accustomed to thinking in that fashion and so
counterproductive.  It also needs to be stressed that this chance will
not have an open ended duration!  With nukes at our fingertips and NATO
taking the RAW DOG out for walks now and again it's becoming more
likely that the old beast will get itself unleashed again and BOOM back
to cracking rocks we go. Another time constraining factor is human
population growth, which will continue to have a not fully predictable
social and environmental impact.
<>  The point is that
we need to do something that encourages international cooperation and
captivates the constructive creative potential within our species
repertoire of behavior. Rapidly developing our capacity to exploit and
manipulate objects in Outer-space can provide a positive project which,
if recognized as a necessary effort to protect and better understand
Earth's biosphere, will help to form an enduring global social cement.

So back to this fixation on quantifying our chances of being zapped by
this or that type or size object--What difference does it make?  Unless
we are prepared or are fortunate enough to identify the next due event
distant enough in time for us to get ready to deflect it, we're
eventually going to get popped regardless of our calculations and
observations. I also question the belief that comets pose less risk
than our local swarm of dark objects.  For one thing we do not yet know
what fraction of these short period objects might be stealth comets and
so still have sufficient volatile material to covertly fart around with
their orbit near perihelion. As for active comets--by Jove we could get
in trouble quickly.

Our closest recognized brush with an out-gassing object occurred in
1770 when a comet discovered on June 14 of that year, by Charles
Messier, came within 0.015 AU of Earth around two and a half weeks
later--the evening of July 1.  On that night the comet's coma appeared
to be about five times the apparent diameter of the Moon!  The most
interesting thing about this happening, from an Earth defense
viewpoint, is the cosmic gymnastics that comet 1770 I Lexell underwent
between 1767, when Jove lobbed it into our neck-of-the-solar system and
1779, when after only one other plunge near the Sun in 1776 the mighty
Jupiter tossed it to who knows where.  In other words, prior to 1767
this comet reached perihelion at around 3 AU and could not affect Life
on Earth, however, after getting a bit too cozy with Jove around the
middle of that year it became a potential hazard to Earthlings with a
lead time of just three years! How often do these rather flamboyant
members of our solar system get tossed around like this?  Do such
orbital contortions generally leave the object discrete or are the
victims of Jupiter's pull more often scattered into a cosmic hail-storm
of sorts, as we witnessed with Shoemaker-Levy 9? Did Earth collect a
bit more dust than typical due to this close encounter (177 Earth
diameters) with 1770 I Lexell so soon after that comet was wrenched
from its former orbit and what size object was this--kilometers across,
tens of kilometers, hundreds?  Don Yeomans, in his COMETS (1991, page
162) reports that eight comets (inclusive of Lexell) came within 2500
Earth radii during the eighteenth century--Did dust from these visits
contribute to the factors that produced such variable and often
unseasonably cold weather in the 1700s?
<> Perhaps I'm wrong, but I
don't think we have a reliable observational-base long enough to
accurately answer such questions.

I suggest that our most prudent course of action with regard to PHOs is
to adopt the policy that has brought Life to its present situation on
Earth: Mount and probe; mount and probe--this is how Life learns and
spreads. A wait and see approach to this threat is a gamble that could
prove fatal--Why take such risk when we do have the tools to more
aggressively address the situation?  It's not going to break us or take
food from the mouths of starving children; it should rather reduce the
number of Cruise Missiles, B-1s, and similar ilk being produced.

To more quickly reach a point were adequate precautions are being
implemented, we need to devote more attention and resources to
revealing the record that remains beneath our feet. I obviously assume
here that there have been recent significant events that we can recover
evidence for, but considering the relatively low cost of focused
digging and discerning, it is an aspect of information gathering that
could well become more convincing to the wait-and-see crowd than the
bevy of PHOs already identified. Financial support for such activity
should certainly be added to allotments that have been awarded to sky
focused fact gathering! Such research would seemingly coordinate nicely
with climate change investigations and could substantially broaden
awareness of this issue among more down to earth researchers.

In my opinion, we are not adequately addressing even the front end of
this situation until we have placed detectors where it doesn't matter
whether the weather is fine or foul.  We can, in the clear light of
Space, find, catalog, and keep track of all those little bits and
pieces that, while not globally threatening, would not be welcomed into
anyone's neighborhood!

May a small planetesimal not fall on your land!/?  ;^)


Bob Kobres
Main Library
University of Georgia
Athens, GA  30602

CCCMENU CCC for 1999