PLEASE NOTE:
*
Subject: "Three Minutes to Impact"
To: Cambridge-Conference@livjm.ac.uk
Date sent: Mon, 10 Feb 1997 23:04:24 -0600 (CST)
From: pib@nwu.edu
On February 9, 1997, the Discovery Channel here in the States
aired a
two-hour program entitled "Three Minutes to Impact" on
the threat
posed by cosmic impacts. I have only watched the program once so
I may have missed some crucial tidbits.
The program began with Duncan Steel tagged as "Doomsday
Astronomer,"
followed closely by Gene Shoemaker labelled as hailing from
"Lowell Obeservatory" (does it have to go on a diet?),
followed by
David Morrison posed against a background tableau of gaming
tables
(in Los Vegas, I assume). Based upon these scenes I had the
sinking
feeling that watching the following two hours might prove to be
an
ordeal. Fortunately, I was wrong. The rest of the program
was much better than the first few minutes seemed to indicate.
Gene Shoemaker and his wife Carolyn were shown scouring the
Australian
outback for potential impact structures. They spend up to three
months
a year doing this. Gene Shoemaker has a close working
relationship
with the Space Shuttle program. He suggests possible impact sites
for
radar imaging based upon his ground work.
Hildebrand and Sharpton squared off on the size of the Chicxulub
crater. Recent work by investigators from Imperial College,
London
to settle the question of the crater size was featured. (These
researchers were shown but I do not believe they were named.
I assume they were Morgan and Warner.) Their preliminary results
indicate a crater diameter of 150 miles, the average of the sizes
previously proposed by Sharpton and Hildebrand.
Mike Baillie and Michael Rampino discussed the possible impact
origin of the atmospheric veil of 536 A.D. This segment briefly
discussed the importance of tree rings and ice cores in
reconstructing
climatic interventions. Also offered was the suggestion that
the "dragons" of mythology -- for example, in the King
Arthur legends --
might be allegorical references to comets and meteors.
David Levy's obvious enthusiasm was infectious as he talked about
the impact of Shoemaker-Levy 9 on Jupiter. The roles played by
Brian Marsden, Paul Chodas, and Jim Scotti received mention.
Images of the impacts on Jupiter, taken with several different
instruments, were presented. Unfortunately, no one commented
on what the Jovian impacts told us about Jupiter's structure.
Michael Rampino elaborated on the relationship between impact
events and
mass extinctions. He suggested that the Permian killer impactor's
crater might be found near the Falkland Islands.
Ramiro de la Reza discussed his investigation of the
"Brazilian Tunguska"
of 1930. This included an interview with an eyewitness to the
event.
I will be very interested to learn what his upcoming ground
expedition
to the possible impact site reveals.
Shin Yabushita and Duncan Steel offered a sobering analysis of
the
dangers posed by impact-generated tsunamis.
Duncan Steel narrated a chilling segment on the deleterious
global effects
which would result from the impact of a several kilometer
diameter object
with New York City as the bullseye.
David Morrison commented on the probabilities of death by impact.
He noted that there are few professionals working in locating
near-Earth objects which might threaten us. The budgetary woes of
some of the few who are -- Tom Gehrels, Duncan Steel, Eleanor
Hellin --
were emphasized.
I liked the graphic illustrating how pock-marked the Earth would
appear if it had not developed an atmosphere. There would be
twenty
times more craters on the Earth than on the moon.
A few results from probes sent to Halley's comet in the
mid-1980s,
during its last passage through the inner solar system, were
presented.
Curiously, I don't believe NASA's upcoming NEAR mission was
discussed
at all, although Clementine II received a nod.
Several proposed methods for deflecting objects on a collision
course
with the Earth were highlighted with attractive animations and
interviews with folks like Edward Teller. David Morrison
underscored
some of the holes in current defense strategies.
Statistics such as "forty-five tons of cosmic debris strikes
the Earth
every day," and "two hundred or so asteroids cross
Earth's orbit at any
given time," were stressed.
Both Nemesis and galactic oscillation were offered as possible
causes
of comet showers.
There was little discussion of the relationship between comets
and asteroids.
Coverage of the origin of asteroids was inadequate. There was no
mention of
coherent catastrophism, the giant comet hypothesis, or the Taurid
complex.
There was no mention of comet families derived from
fragmentation.
There was no discussion of asteroidal moons, contact binaries,
rubble piles,
or recent suggestions about terrestrial crater chains (other than
the
Henbury craters).
The Tunguska blast was ascribed to a cometary fragment, but not
to the
Taurid complex. The standard view of workers here in the States
--
that the Tunguska impactor was a non-cometary stony body -- was
not
mentioned. I would have liked to see an interview with someone
who
had actually worked at the Tunguska site. Likewise for Sikhote
Alin.
There was no mention of the effects of impact events on recent
human
history except for the possible 536 A.D. event. There was no
discussion
of damage to people or property caused by historical small-scale
impacts.
The definition of punctuationalism offered -- as evolution driven
by impacts -- is certainly not that proposed by its originators,
Gould and
Eldredge. This is likely to confuse someone not already familiar
with the standard definition of punctuationalism.
Gene Shoemaker noted that without Jupiter as
"protector" the
Earth would have been be struck at least 100 times more
frequently.
I wish his comment would have been followed up with a discussion
of
the consequences of such an enhanced impact flux on the Earth's
biosphere. I doubt that life here would have developed past the
stage of simple organisms.
There was no mention of the role of comets in delivering
volatiles,
and possibly pre-biotic compounds, to the inner planets.
I found "Three Minutes to Impact" to be entertaining. I
liked its
limiting interviews only to workers actively involved in research
on impacts and impact defense. I learned a couple of things I did
not know about before, such as Shoemaker's connection to the
Space Shuttle program, and the planned expedition to the site of
the 1930 Brazilian impact.
I would be interested in hearing comments and reactions from
others
who watched the program.
-- Phil "Pib" Burns
Northwestern University, Evanston, IL. USA
pib@nwu.edu
http://pibweb.it.nwu.edu/~pib/
*
Date sent: Mon, 10 Feb 1997 09:33:41 -0500 (EST)
From: HUMBPEIS B.J.PEISER@livjm.ac.uk
Subject: Re: DEAR OLD COMETS II
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
BBC2, NEWSNIGHT: Friday 7th February 1997
Kirsty Wark (News Presenter): Imagine a gigantic massive
rock the size of Newcastle hurtling its way towards
Earth. This is not an off-cut from a new movie "Mars
Attack"; it's for real. It's a comet wittily named
Hale-Bopp which is due to hove into view on March 22nd.
And the star-gazing community is split about whether it
will be the most spectacular astronomical event this
century. Some expert say its light will be more
concentrated than any of the previous comet encounters.
Others say it will be a damp squib. And a lucky few have
already enjoyed a distant sighting over Clapham Junction.
However there is new research which suggest we should be
seriously concerned about aerial bombardment.
Huge chunks of rock the size of cities cruise around in
space. They are potential missiles whose collision with
Earth could be catastrophic. There are tow machines
firing these missiles. The established wisdom is that
about 2000 asteroids are been flung into the stellar
system from the asteroid belt between Mars and Jupiter.
But the number of comets from the Oort Cloud, a place at
the edge of the solar system, has always been thought
much smaller. But Prof Mark Bailey at the Armagh
Observatory has done a calculation which suggest that
instead of the previously known 20 comets there could be
as many as 5000.
Mark Bailey: The comets move much faster; mass for mass
they are more dangerous than asteroids. And also, if it
is true that there are so many of them undiscovered, they
pose a much greater unknown threat than the observed
asteroids.
News Presenter: A simplified version of his calculation
is as follows: recognizable comets enter the stellar
system at a rate of 1 a year. It seems that one in a
hundred evolves into a Halley-type comet. Each comet
orbits for about half a million years before been kicked
out. So simple multiplication of one in a hundred or 0.01
times the number of years they survive, that's half a
million, gives a figure of 5000 comets [0.01 x 500,000 =
5,000]. So in theory at least there could be 5,000 in
orbit at any time.
Mark Bailey: There is no way that this figure [~ 5,000]
could possibly be turned in that figure [20]. Therefore
we are left with a paradox. There are far more predicted
Halley-type objects than there are observed and we have
to look into the reasons why that might be.
News Presenter: It may be that some of the potential
missiles disintegrate of their own accord. But the
suggestion is that many have not been recognized because
they are inert and so don't have fiery gases to identify
them.
Mark Bailey: The risk is of kilometre-sized asteroids or
cometary asteroids or even a comet itself running into the
Earth in an unexpected way - in the sense that we are
unaware of the comet's previous existence or of the
asteroid's previous existence. We have this prediction of
a large number of asteroids that are of cometary origin
orbiting in periods of less than 200 years in orbits of
all inclinations and coming essentially from all
directions. Currently, there are no surveys of the sky
run by astronomers with which we have a chance of
discovering these objects.
News Presenter: It was a missile from space that hit
Earth 65 million years ago marking the last days of the
dinosaurs. A study of craters suggest that a major impact
occurs every 100,000 years, lesser ones of a type that
might just wipe out an area the size of Northern Ireland
occur every 300 years.
Mark Bailey: If we design aircraft, we try to make sure
that they don't fall out of the sky that often. And when
we are designing nuclear reactors, we make sure that the
risk of a significant event is way down in the parts per
million rather in parts per hundred thousand.
News Presenter: The US Airforce is taking this very
seriously. They're worried about an asteroid attack. It
is now sponsoring a project to develop probes to examine
comets and asteroids in the hope of eventually being able
to intercept them.
John Pike (Space Policy Director, Fed. American
Scientists): The big problem with dealing with incoming
comets or asteroids is that we don't know how they're
built. We don't know if they are a single, very solid
object or a loose clump of a number of much smaller
objects loosly held together. CLEMENTINE 2 is the first
experiment to try to decide this question: if it is a
single large object, maybe you'de use a hydrogen bomb; if
it's much more of a small object just clumped together,
you'de have to use a very different approach because
otherwise you'de just be turning a bullet into a shotgun
blast.
News Presenter: Some defense scientists have even thought
it might be possible to round up all the ballistic
missiles of the Cold War and set them to more
constructive use.
Douglas Miilard (Curator, Space Technology Science
Museum): The whole Star-Wars thing that was going on
during the Reagan administration was something which
created or gathered a lot of attention and a lot of
headlines and a lot of controversy. And many people felt
that it wasn't a realistic system; so although
substantial amount of work was done we still do not have
anything approaching some sort of anti-ballistic missile
defensive system of that magnitude.
News Presenter: So when you next look up at the sky at
night - have a care. There are comets up there. And one
could be headed for you.
I'm joined now from Sheffield by Dr David Hughes, Reader
in Astronomy, and here in the studio by Dr Victor Clube,
astrophysicist at the Department of Physics at Oxford
University.
Dr Clube, is this a problem? Are we really in danger of a
doomsday comet?
Victor Clube: Not immediately are we in danger. But these
things undoubtedly exist. The real point of note is that
we have been accumulating information throughout the
Space Age, and the nature of our immediate environment
has completely and fundamentally transformed. We are
now all aware of the general idea of an asteroid coming
in - knocking off the dinosaurs 65 million years ago.
News Presenter: What else do you think these asteroids or
comets were responsible for in the past?
Victor Clube: Well, the fact is they are coming in nearly
all the time. When I say 'all the time' - there are long
intervals between each arrival.
News Presenter: Thousands of years? Hundreds of years?
Victor Clube: Millions of years for the really big ones.
But the interesting ones from the point of view of
civilization are the smaller ones which come with less of
a bang but more frequently. And less of a bang may be
dramatic or may not be dramatic.
News Presenter: Dr Hughes. Should we be doing something
about this now?
David Hughes: I don't think we should. I don't think we
should be going around trying to frighten the living day
lights out of people about these Armageddon asteroids and
killer comets. We know there is a risk but it's such an
infinitesimal risk. There are much more things out there
to be worried about than these things in space.
News Presenter: But the American Airforce and NASA seem
to think that they should actually do something about the
threat.
David Hughes: The American Airforce are desperate for
something the fire missiles at. They have lost their
enemy and they are asking astronomers to provide targets.
And I don't like this. I think that this idea firing lots
of missiles into space with nuclear warheads is going to
be much more dangerous than the odd comet or asteroid
that is going to get close. Don't forget that if you want
to destroy civilization on this Earth, you are going to
gave to wait nearly a million human generations for that
to happen and we just don't know what humanity is going
to be like in a million generations.
News Presenter: We are tempting fate, Dr Clube?
Victor Clube: No, there are some parts of what David
Hughes is saying that I would actually agree with. The
point is we must not be talking about the really big ones
in the first instance. The day will come when no doubt we
are clever enough to handle big objects. What we do not
understand at the moment is how to handle dangerous
events that arise on timescales of a hundred years.
News Presenter: But do you see it as being possible to
nuke one of these comets in its way in?
Victor Clube: No, and I am not even talking about that
problem. The problem here is the debris of comets that is
shed onto the Earth from time to time. Only two years ago
we saw a comet break up and bombard Jupiter. And it was a
very dramatic event. Such streams of debris are flying
around in the inner solar system unseen by astronomers at
the present time. And what happens from time to time is,
we run into these streams of debris. We have no notice of
it and when that happens we will see fireballs in the sky
and all astronomers will predict: 'maybe there is a big
one'.
News Presenter: But what you might be talking about is
hundreds of thousands of years when we have to spend a
lot of money looking fro this to happen. Around the world
people will spend money for different defense systems.
How can that be justified?
Victor Clube: The danger when it happens will in fact be
within a short time span and it is very unlikely that we
would be able to develop the technology to handle the
danger when the fright is in the sky.
News Presenter: When you say 'short time span' ...
Victor Clube: I'm talking about a decade or so.
News Presenter: A decade! Dr Hughes what do you make of
that?
David Hughes: I think this is just scare-mongering. I
just don't agree with Victor at all about this. I mean, I
agree that this dear old comet broke up by going to close
to Jupiter; but this was a very rare event and of course
all that happened there was that these bits burned up in
the atmosphere. If this comet had hit Earth, the bits
would have burned up in our atmosphere. In fact, I've
spent many years studying cometary decay and looking at
lovely meteor streams produced by this - and the bits
don't get down to Earth. And they do not damage us.
And also, if Victor is interested in the small things
that might hit the Earth, the small things unfortunately
are undetectable with our present astronomical ability.
We've got telescopes about 5 metres accross. We've only
got this small space telescope. We need much bigger
telescopes if we ever want to get anywhere near detecting
these.
News Presenter: Gentlemen, thank you very much.
*
Date sent: Mon, 10 Feb 1997 08:27:12 -0500 (EST)
From: HUMBPEIS B.J.PEISER@livjm.ac.uk
Subject: Re: DEAR OLD COMETS
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
DEAR OLD COMETS & LOVELY METEOR STREAMS. Part I
Last Friday night (7 February), BBC2's NEWSNIGHT TV
programme featured a report about Prof Mark Bailey's
research on so-called 'dead comets' (see THE TIMES
4/2/97). This feature on Britain's top news programme was
complemented by information about three additional
subjects:
i) the anticipation of comet Hale-Bopp; ii) the efforts
to develop an effective spaceguard and asteroid
detection/deflection programme, and iii) a concluding
debate on the potential hazards from cosmic debris.
Regrettably, the final debate included some ungentlemanly
remarks from a senior member of the astronomical
community. The debate between Sheffield based astronomer
David Hughes and Oxford based astrophysicist Victor Clube
was a stark reminder of the unbroken tension between
'coherent catastrophism' and its critics.
While some of the derogatory remarks speak for themself,
it remains doubtful whether Hughes' main argument against
Clube's risk-assessment is valid: his claim that
Shoemaker-Levy-9 - had it impacted the Earth instead of
Jupiter - "would have burned up in our atmosphere",
seems
to lack support by the astronomical evidence. In fact,
some "bits" of SL9 constituted half-kilometre-sized
objects - big enough to cause enormous demage had it
impacted the Earth. Such objects are certainly not
"lovely" since they 'get down to Earth and damage us'.
The following text is a complete transcription of the
BBC2 NEWSNIGHT report. For technical reasons I have
mailed it with a separate message.
Benny Peiser