PLEASE NOTE:
*
Date sent: Tue, 17 Mar 1998 10:12:43 -0500 (EST)
From: Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject: CC DEBATE, 17/03/98
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
CC DEBATE, 17 March 1998
------------------------
(1) ON THE FUTURE DISTRIBUTION OF IMPACT WARNING TIMES
Duncan Steel dis@a011.aone.net.au
(2) WE DID NOT GO TO THE MEDIA WITH THIS STORY, THE MEDIA CAME TO
US
Garreth Williams, Associate Director, IAU Minor Planet Centre
(3) THE GIGGLE FACTOR IS STILL WITH US
Steve Koppes SKoppes@aol.com
(4) WHENEVER A NEW OBJECT IS DISCOVERED, THERE WILL BE A LARGE
LEEWAY
IN ITS ORBIT DETERMINATION
Ron Baalke BAALKE@kelvin.jpl.nasa.gov
(5) WHEN WORLDS COLLIDE
Oliver Morton in the FINANCIAL TIMES
==========================
(1) ON THE FUTURE DISTRIBUTION OF IMPACT WARNING TIMES
From: Duncan Steel dis@a011.aone.net.au
I liked most of the comments made different people on this list
concerning the 'XF11' affair: what a shame that it wasn't
discovered/reported a little earlier so that the 'F' would not
have
appeared, then we could have had a real-life 'X-file'.
Rob McNaught made some excellent observations (in writing;
previously
he's made many excellent observations at the telescope). He types
too
fast, though, making a few crucial typographical errors. In
particular
when he wrote, concerning his precovery of Comet Hale-Bopp,
"It has not
been shown (with astrometry from discovery to present day) that
my
precovery measure is accurate to around 1 arcsecond" he
meant to
intimate NOW rather than NOT.
I thought that David Morrison's short essay, previously
distributed on
his 'NEO News' list, was very useful and timely. Let me pick up
on one
point to amplify it. David wrote:
>(4) if an unknown asteroid should hit us, we would likely
have no
>warning at all. The first we would know of the danger is when
we saw
>the flash of light and felt the ground shake.
Let me pull David's tail a little. That's an exaggeration, since
we
would have some warning: possibly as much as 20-30 seconds. If
one
realizes that meteoric ionization begins at an altitude of about
140
kilometres, and bright fireballs are seen to begin at about 80
km, then
with a mostly likely entry angle of 45 degrees and an incoming
speed of
(say) 20 km/sec, the fireball phenomenon would begin about 5 to 6
seconds prior to impact on the Earth's surface. My point here is
that
being able to tell a questioner (media person), in reply to the
question "How much warning might we expect", that the
answer is "Five
or six seconds" has some dramatic effect.
This is important: A report from Radio Canada I heard yesterday
ended
by saying that although 1997 XF11 had been found 30 years ahead
of a
potential impact, for other asteroids "we might get only a
few weeks or
months warning." That's just wrong, as David has correctly
emphasized.
It might be useful to think of the probability distribution of
warning
times. If we assume for present purposes that an impact IS due
within
the next century:
P (impact by >1 km asteroid within next century) = 1
... and we further assume that with the current search and
tracking
effort there is only about a 10% chance that it will be
discovered on
the apparition (or earlier) b e f o r e the apparition of the
collision, then we can see that
P(warning < 30 seconds) ~ 0.9 (90%)
P(30 sec < warning < few years) ~ 0.005 (0.5%)
P(warning > few years) ~ 0.095 (9.5%)
One might suggest that such an asteroid c o u l d be seen simply
by
someone using a decent pair of binoculars, say, when it is at
about the
lunar distance, and thus hours to a half-day prior to impact (IF
coming
from the nightside). That's true; but I believe that the
probability of
such a spotting being translated into a prediction of imminent
impact
and thus a warning being communicated (to whoever) is effectively
zero.
I have a separate comment to the theme above. In communicating to
people the essence of this hazard, they often refuse to take it
seriously on the grounds that the average time between large
impacts
(whether one takes that to be 50,000 or 500,000 years) is too
long to
be of significance to them, or to people/civilization in general.
This
reaction is generally based upon a lack of understanding of
probabilities, and no matter how one argues it, the person/media
you
are dealing with will return to the timescale which they have in
their
mind: "Once in 100,000 years! You have to be joking if you
think we're
going to take that seriously!"
So let's play on that line of thought. What's the timescale for
dying
in an automobile accident (the highest-ranking cause of
accidental
death)? Averaged over industrialized nations I believe that the
car
accident rates indicate a probability of dying that way of about
one in
120. For the same nations the average life expectancy is about 80
years. Thus the timescale for dying in a car crash is of order
120 x 80
~ 10,000 years. Of course, that's also too long to take
seriously.
Duncan Steel
(dis@a011.aone.net.au)
============================
(2) WE DID NOT GO TO THE MEDIA WITH THIS STORY, THE MEDIA CAME TO
US
From: Garreth Williams, Associate Director, IAU Minor Planet
Centre
[circulated on meteorobs mailing list]
: There was a *press release* issued by CBAT. Not just a
circular. Had
: it been just a circular, this situation would have been a lot
: different. They should have collected the additional data
before
: issuing the press release.
The "press information sheet" was not *issued* by CBAT.
The PIS was
put on the website so that any journalist who read the IAUC could
find
answers to the standard questions that journalists ask in a form
that
nonscientifically-trained journalists can understand. We did not
send the PIS to any media outlets. You may think this is a
question of
semantics, but it is not. We specifically note at the foot of
each PIS
that the document should not be redistributed. If third-parties
chose
to ignore this and redistributed the PIS, that cannot be our
responsibility.
: Certianly the public press is not the way to contact the
astronomical
: community.
And it never is. The IAUCs (and MPECs and MPCs) are the way to
contact
the astronomical community. But there are a number of newspaper
and TV
journalists who receive the IAUCs. Everything that was written on
IAUC
6837 was correct, given the information available at the time.
Since we
had just finished preparing the 1998 March batch of Minor Planet
Circulars, the 88-day arc orbit on which the original predictions
had
been made would have been available to the community. Anyone who
integrated the orbit forward looking for forthcoming close
approaches
to the earth would have found the 2028 encounter. Wouldn't they
have
thought it strange, having found the extremely close encounter
(and
there are quite a number of groups, including some amateurs, who
could
have found this event), that we had not put out a call for
further
observations? And that the call be made in a restrained manner as
on
IAUC 6837?
I hasten to add that in *every* interview we gave (particularly
those
given prior to the identification of the 1990 prediscovery
observations
by Ken Lawrence of Eleanor Helin's group) we were very careful to
stress both the uncertainty and the need for further observations
before we could say anything definitive about the 2028 encounter.
Guess which bits of the interviews ended up on the cutting-room
floor?
TV news, in particular, is looking for sensationalism.
We did not go to the media with this story. The media came to us
If you feel it necessary to assign blame for the coverage of this
event, I suggest looking towards (certain parts of) the media and
the
culture to which they cater.
------------------------------------------------------------------------
Gareth V. Williams, MS 18, 60 Garden Street, Cambridge, MA 02138,
USA.
Associate Director, IAU Minor Planet Center
http://cfa-www.harvard.edu/iau/mpc.html
========================
(3) THE GIGGLE FACTOR IS STILL WITH US
From: Steve Koppes SKoppes@aol.com
Benny said that, "The real issue at stake was never whether
the 'newly'
detected asteroid 1997 XF11 will miss us by 30.000 or 600.000
miles --
but rather becoming aware of the uncomfortable fact that a
similarly
large object can -- and at some unknown point in the future will
--
impact the earth, thereby causing widespread devastation." I
agree, but
I fear that isn't what members of the lay public will remember
about
this episode. What far too many of them will remember is that one
day a
distinguished scientist told them that an asteroid might hit the
earth
in 2028, and next day some other scientists basically said
"never
mind." I'm sure you all recall that something similar
happened with
Comet Swift-Tuttle in 1992.
The subscribers to this list all know that science is a process,
and
that's what we saw played out in the news media last week. But
members
of the public by and large still don't know that science is a
process.
They still think science is a static collection of facts. Benny
sees
March 12, 1998, as a day that "will go down in history as
the day the
entire human race became aware of our precarious place in
space." I
hope he is correct, but the editorial cartoonist of the Atlanta
Journal-Constitution looks at March 12 another way. He drew a
cartoon
depicting a little boy playing basketball outside an observatory.
Some
scientist inside the observatory sees the boy's basketball
through the
telescope and exclaims, "Oh-my-Gawg! Asteroid headed this
way!!"
As a science writer, I found last week's news exciting,
regardless of
the details. As a person who has spent the last 13 years writing
news
releases and doing public relations for major research
universities, I
wish we could have had better orbit calculations before the first
wave
of publicity rolled around the globe. As the Atlanta newspaper
cartoon
demonstrates, the giggle factor is still with us, and it may get
worse
before it gets better.
Steve Koppes
===========================
(4) WHENEVER A NEW OBJECT IS DISCOVERED, THERE WILL BE A LARGE
LEEWAY
IN ITS ORBIT DETERMINATION
From: Ron Baalke BAALKE@kelvin.jpl.nasa.gov
I think Brian Marsden did the right thing, but the news media
seems to
blow things out of proportion.
This situation with Asteroid 1997 XF11 is very similar to Comet
Swift-Tuttle from about 5 years ago. Comet Swift-Tuttle was
recovered
in late 1992, and prelimary analysis by Brian Marsden indicated a
chance (albeit a very small chance) that the comet could collide
with
the Earth in the year 2126. The news media got wind of this and
trumpeted an Earth impact in their headlines, often leaving out
the
details that there was a large error margin and that that there
was a
very low probablity of impact. Additional observations of the
comet
were obtained, including matching the comet up with a previous
appearance in 1737. Based on the additional data, Marsden
recomputed
the comet's orbit and found the comet would miss the Earth by a
comfortable 15 million miles in 2126, and retracted the collision
possiblity.
Note the similarity with 1997 XF11?
More details on the story is available here:
http://www.as.wvu.edu/~jel/skywatch/swfttle.html
Then there was Comet Shoemaker-Levy 9. The comet was discovered
near
Jupiter in 1993. There was a large error margin with the initial
orbit,
which was refined over time as more observations were made.
Marsden
first determined that the comet was in a temporary orbit around
Jupiter. Later on, he determined that half of the fragments could
possibly collide with Jupiter. Don Yeomans and Paul Chodas then
chipped
in, and they concluded that the entire comet train would impact
Jupiter
with a 64 percent probablity. With additional observations, the
impact
probablity became 100%, and the rest was history.
The fact is, when a new object is discovered, there will be a
large
leeway in its orbit determination, which will get refined over
time.
There will be more instances of Comet Swift-Tuttle and asteroid
1997
XF11 in the future - it is only inevitable. The thing to make
clear is
up front is the initial orbit is "work in progress" and
there are
inherent large errors initially which will decrease with time as
new
data is obtained.
Ron Baalke
=========================
(5) WHEN WORLDS COLLIDE
From: FINANCIAL TIMES, 14 March 1998
THAT ASTEROID: WHEN WORLDS COLLIDE
Oliver Morton considers if the end of the world prospect may make
us less
parochial
Well, that's all right then. For a moment there, things were a
little scary.
The comforting planetary parochialism which says that everything
of consequence is decided on the surface of the earth came under
attack. Just as Londoners find the concept of culture in Leeds
hard to accept, just as the idea of a Belgian software firm looks
a little silly in Silicon Valley, so earth-dwellers tend to find
the idea that things beyond our planet really matter - well, a
bit
funny.
For a day or so this week, that complacency wavered. The world
was forced
to think, for a moment, about the fact that the human environment
does not
end at the top of the atmosphere. On Wednesday the International
Astronomical Union's Central Bureau for Astronomical Telegrams
(yes, it uses e-mail) announced that the mile-wide asteroid 1997
XF11 stood a small - but not completely negligible - chance of
hitting the earth on October 26 2028.
Such an impact would be a very bad thing indeed. If an asteroid
that size
hit dry land, the shockwave and fire would scour the life from a
fair-sized country; if it hit one of the great ocean basins the
resulting waves would drown thousands of miles of seaboard,
cities
and all; either way, the impact might well throw enough muck
and/or steam into the atmosphere to cause a short, sharp climatic
change, a non-nuclear winter that would write off one or more
agricultural growing seasons all around the world. If so,
billions
could starve.
The calculations that put 1997 XF11's trajectory about as far
above our heads as a TV satellite, with a margin of error that
included Armageddon, fired imaginations all over the globe. It
also set the small world of searchers-after-asteroids frantically
checking their records.
The calculations, based on observations made since the asteroid's
discovery
late last year, showed not only where 1997 XF11 would be in the
future, but also where it had been in the past. A picture taken
in
1990 was found showing the then-undiscovered asteroid, and with
the help of this piece of far-flung data the orbit was
recalculated with greater accuracy. The result is that this time
the world dodges the bullet - 1997 XF11 will pass at a decorous
distance of some 1m kilometres.
Planetary parochialism may now reassert itself, perhaps with a
vengeance.
Astronomers who devote themselves to finding and tracking the
asteroids
and comets that occasionally cross the earth's orbit will
probably
sink back into obscurity, unfairly derided for having cried wolf.
In fact this small band - enough people to run a small
McDonald's, as one
of them once put it - do a rather remarkable scientific job with
sparse resources at a time when they could be forgiven for
becoming somewhat dispirited. Their doyens are old or - in the
case of Gene Shoemaker, whose team discovered the comet that gave
Jupiter a good seeing-to a few years back - dead. Their
programmes
are marginal and underfunded. The UK puts no money into looking
for nearby asteroids in spite of the fact that one of its
telescopes in Australia is perfect for the job. As a result of
such neglect, most of the 2,000 or so asteroids as big as 1997
XF11 in orbit that might lead to a collision with the earth are
still undiscovered.
Finding them would not be that difficult, but it would require
moderate
and consistent expenditure. That would ensure that the giants of
the field such as Tom Gehrels, who runs the Spacewatch programme
that found 1997 XF11, or Eleanor Helin, whose Palomar survey
turned up the pictures which narrowed down its orbit, could rest
easy in the knowledge that their work would carry on without
them.
Ironically, on Thursday researchers announced the discovery of
the most
distant galaxy ever seen. Astronomers and cosmologists dote on
such
far-off objects for fine intellectual reasons; these distant
beacons teach us about the history of the universe and may even
reveal some of the forces shaping that history. However, they
have
no relevance other than the intellectual. The light we see from
them has been travelling since before the sun was born.
If a small fraction of the money that is spent on looking at the
most
distant objects in the universe went into looking for the
nearest,
a thorough survey of the potential threats would be possible in a
couple of decades. If it were discovered that an asteroid were
headed our way - and the odds are against that - the actual
impact
would still, in all likelihood, be decades or at least years
away.
That would provide enough time to try to do something about it
with nuclear explosives or, if the impact were really a long time
in the future, some more gentle form of celestial suasion.
It may be that this week's brush with the possibility of
catastrophe
will clarify some policymakers' minds and that a serious survey
will be funded. All it takes is an understanding that not
everything in space is irrelevant to the earth.
Last week we saw some of that understanding when NASA announced
that ice had been discovered on the moon, a piece of hoopla which
introduced to a lot of people the idea that there are natural
resources in space that could be used to make its exploration
cheaper or even, in some cases, profitable.
In this respect the moon may prove to be something of a red
herring.
The real action lies among the asteroids. They are not only
objects that may obliterate the world but may hugely enrich it.
Some asteroids are made of almost pure metal, metal that, if
mined, may be worth hundreds of billions - even trillions - of
dollars. There are asteroid- like bodies in similar orbits which
seem to be old comets, hot and dry on the outside but icy within,
like mountain-sized baked alaskas. One such object might contain
more water than the whole moon. And water is very valuable in
space, basic to life support systems and to rocket propulsion.
Asteroid exploration has not been a high priority for space
explorers, any more than asteroid surveys are important to
ground-based astronomers. But three asteroids have been
photographed by probes on their way elsewhere, and soon a small
Nasa spacecraft will catch up with the asteroid Eros and
accompany it around the sun for a year.
The fact that spacecraft are becoming much cheaper may mean there
will
be more such missions. A company called SpaceDev, based in San
Diego, is planning to build a spacecraft and send it to an
asteroid for only $50m, the cost of which will be borne by
experimenters and space agencies paying for their instruments to
be taken along or for data that others send back. In the
long run, SpaceDev would like to be in the asteroid mining
business.
Less profitable, but perhaps more stirring, is the possibility of
using
extraterrestrial natural resources to assist the exploration of
Mars.
In 1990 Bob Zubrin, an aerospace engineer then with Martin
Marietta and now running his own company, suggested a means of
getting to Mars far cheaper than those then being considered by
Nasa.
His idea turned on the fact that the Martian atmosphere could,
with
ingenuity and a little added hydrogen, be turned into rocket
fuel.
So spacecraft could be landed on Mars with their fuel tanks
empty,
and stripped of the enormous expense of sending enough fuel along
for the return journey. That would make missions to Mars
considerably more affordable. Explorers on earth have always done
best when they have learned to live off the land, argues Mr
Zubrin. Why should space exploration be any different?
There are things for human explorers and exploiters to use on the
moon, among the asteroids and on the surface of Mars. Natural
resources are not limited to the surface of the earth - and nor
are natural disasters - just because humanity is.
In fairness, the parochial prejudice that limits our serious
thinking
to one planet does not do humanity much harm. The moon is not the
most exciting desert under the sun, Martian exploration is not
the
most important priority for humanity, and we will not need the
all-but-limitless mineral wealth of the asteroid belt for some
while.
That said, the prejudice doesn't do much good, either. It robs us
of a richer, grander view of our world. And it might - just might
- get us all killed. (C) Financial Times 1998
--------------------------------
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