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Cambridge Conference Debate - March 17, 1998

CC DEBATE, 17 March 1998
------------------------

(1) ON THE FUTURE DISTRIBUTION OF IMPACT WARNING TIMES
    Duncan Steel  

(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  

(4) WHENEVER A NEW OBJECT IS DISCOVERED, THERE WILL BE A LARGE LEEWAY 
    IN ITS ORBIT DETERMINATION
    Ron Baalke  

(5) WHEN WORLDS COLLIDE
    Oliver Morton in the FINANCIAL TIMES


==========================
(1) ON THE FUTURE DISTRIBUTION OF IMPACT WARNING TIMES

From: Duncan Steel  
 
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  

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  

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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