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Cambridge Conference Digest - March 30, 1998

CAMBRIDGE-CONFERENCE DIGEST, 30 March 1998
------------------------------------------

(1) A LETTER TO TIME MAGAZINE FROM THE SPIRITUS RECTOR OF SPACEGUARD
    Sir Arthur C Clarke

(2) HOW THE ASTEROID 1997 XF11 STORY HIT
    Brian Marsden 

(3) IMPACT HAZARD AND THE XF11 AFFAIR
    Clark Chapman 

(4) GERVASE'S 1178 'LUNAR IMPACT' HAS PROBLEMS
    Brad Schaefer 

==========================

(1) A LETTER TO TIME MAGAZINE FROM THE SPIRITUS RECTOR OF SPACEGUARD

From: Sir Arthur C Clarke

To Leon Jaroff
   TIME
   (Via Russ Galen)
        
Dear Leon,
         
TIME must have a short memory!  I am astonished, and rather annoyed, 
that your write-up of 1997 XF11 didn't mention the fact that in 1992 
you commissioned The Hammer of God which described exactly such an 
event and what we should do about it. The short story was published in 
your special issue of 28th September and the novel came out from Bantam 
the next year.
         
Also it was optioned by Dreamworks, and presumably parts of it have 
been incorporated in Deep Impact - in fact the scene TIME shows might 
very well have been taken from Hammer. When Worlds Collide is a totally 
different story, because it concerns another solar system, and an event 
which would take place over hundreds of thousands of years!
         
You might also mention that I introduced the term "Spaceguard" in 
Rendezvous with Rama. This name is now being used by NASA and others. 
Rama has just been optioned by Morgan Freeman (who appears in Deep 
Impact.)
         
Incidentally, have you heard the suggestion that the Chicago fire was 
actually due to a shower of meteorites?  Apparently, there were 
conflagrations all around Chicago that could not have spread from the 
City in such a short time - and there were also reports of phenomena in 
the sky. This might be well worth investigating.
         
               All best,
         
               Sir Arthur Clarke
         
P.S.  Department of Modest Coughs 
On another topical subject - I discussed lunar ice mining - with an 
illustration, in The Explorations of the Moon (1954) and there is a 
romantic description of tractor trains carrying ice from the south 
polar mines in 2061:Odyssey Three.

======================
(2) HOW THE ASTEROID 1997 XF11 STORY HIT

From: Brian Marsden 
 
** This is an extended version of an article that appears on pages E1 and E2
   in the FOCUS section of the "Boston Sunday Globe" on 1998 March 29 
 
HOW THE ASTEROID STORY HIT: AN ASTRONOMER REVEALS HOW A DISCOVERY SPUN 
OUT OF CONTROL
 
Brian G. Marsden
 
There was a dramatic worldwide response to my announcement earlier this 
month that an asteroid known as 1997 XF11 would pass perhaps 
uncomfortably close to the earth on a date 30 years hence, with an 
exceedingly remote chance that it could strike, subject to further 
study of its path.
 
Less than 30 hours later, it was still true that the asteroid would 
pass close to us, though not excessively so, on that date. But the 
worry was off, and initial concerns had been replaced by jokes about 
astronomers making mistakes, as in, "No wonder math education in this 
country has its problems".
 
Along with such comments came accusations of "Chicken Little" behavior 
by "irresponsible" Harvard astronomers neglecting to check their 
"cockamamie calculations" with colleagues first (columnist William 
Safire), and complaints that some NASA scientists were muscling in on a 
matter that really didn't concern them, a case of "professional 
discourtesy" (Malcolm Browne, in The New York Times).
 
Of course, as many other scientists and journalists pointed out, the 
now greater distance from the earth of this asteroid's projected path 
did not alter the fact that there will come a next time, when a sizable 
comet or asteroid strikes with disastrous consequences, but it provided 
some reassurance that, for the moment at least, we can sleep easily.
 
So what went wrong with asteroid XF11?  In my view from the eye of the 
storm, the problem was an overeager use of e-mail and public relations 
by a supervisory scientist at NASA's Jet Propulsion Laboratory (JPL). I 
also believe that for us not to make the announcement as we did would 
have led to  condemnation that science was being stripped of its 
essential openness.
 
Asteroid passes are more frequent and closer than most people think.  
Just 30 years ago, on June 14, 1968, the asteroid Icarus, roughly the 
same size as 1997 XF11, passed 4 million miles from the earth. That 
seems like a tremendously safe distance (and it is), but much of the 
public and the press did not think so at the time. A younger and 
slimmer yours truly was interviewed about the Icarus encounter a day or 
two beforehand by a younger and slimmer Chet Curtis of Boston's Channel 
5, a cult gathered on a peak in Colorado to escape from the anticipated 
slide of California into the Pacific Ocean, and I spent several minutes 
on the phone calming a woman whose mother was terrified about the 
impending end of the world.  
 
It was all unnecessary. Icarus had been expertly tracked by astronomers 
from its discovery in 1949 frequently through 1967, and the distance of 
4 million miles was precise.  But because it was only the first time an 
asteroid had been predicted to come that close, many people went wild.
 
Icarus is the fifth entry on the list of "potentially hazardous 
asteroids", or PHAs, that have the possibility, over the next several 
centuries, of coming within 5 million miles of the earth and that are 
more than perhaps a tenth of a mile across.  Icarus next comes to a 
distance of 5 million miles in 2015.  And it will continue to induce 
scares, as it did in fact just a few weeks ago, when there appeared in 
many countries a claim in the press that it will definitely hit the 
earth just eight years from now! This was complete nonsense, for the 
miss distance in 2006 will be 30 million miles: even the planet Venus, 
almost as large as the earth, comes closer than that, and it does so 
every 19 months.
 
More of a worry in 1968 was the fact that there were perhaps half a 
dozenother known PHAs (though we didn't call them that then) that had 
been lost since within weeks of their discoveries.  The first PHA, 
known as Apollo, had been discovered way back in 1932.  It was a bit of 
long shot, but in 1973 I worked with two colleagues using the 61-inch 
telescope in Harvard,Mass., in a successful hunt for Apollo.  As a 
result of this rescue, we now know where Apollo will be for centuries 
to come--and we know that the earth is safe from it.  
 
On the other hand, Hermes, observed for only four days in 1937 (with 
the first known photograph also having been obtained at the Harvard 
station), is still very much lost.  It could be anywhere around its 
orbit. Some October day (or, perhaps, an April day) in the years to 
come, Hermes could indeed be a threat to us. With luck, the programs 
that search for PHAs and other asteroids that come moderately near the 
earth will accidentally record Hermes well before that day.  With 
appropriate measurements, we shall be able recognize that it really is 
Hermes.  The rediscovery of Hermes is one of those prizes that quite a 
few astronomers wish for at the back of their minds. Furthermore, for 
each Hermes, there are 20 or more unknown possible threats of 
comparable size that we don't already know.
 
The first program set up specifically to search for "NEOs" (i.e., "Near 
Earth Objects", a more general term than PHAs) was initiated in 1973 by
Caltech's Eleanor Helin in collaboration with the late Gene Shoemaker and
using wide-field telescopes at the Palomar Observatory in California.  
The Helin and the Shoemaker programs went their separate ways in the 
early 1980s, when Gene began to collaborate with his wife, Carolyn.  
The other early entrant into the NEO search business was Tom Gehrels, 
who was photographing asteroids already in the 1950s and who in the 
1980s set up the University of Arizona's "Spacewatch" project, the 
first program to make the asteroid detections efficiently by electronic 
means, rather than from scanning conventional photographs by eye.  In 
1995, Helin's program also "went electronic", and her team in 
California is now engaged in the analysis of images relayed to them six 
nights a month from a telescope operated by the Air Force in Hawaii.  
 
The programs of the veteran researchers Gehrels and Helin have recently 
been joined by an excellent third search program, which also uses an 
Air Force telescope (in New Mexico) and is operated by a group at MIT's 
Lincoln Laboratory here in Lexington. My offices at the 
Harvard-Smithsonian Center for Astrophysics in Cambridge have worked, 
and continue to work, closely with all these search programs, as well 
as with other astronomers (professional and amateur) around the world 
who make follow-up observations of interesting objects that are found.  
We correlate and otherwise organize the data from the various groups 
and observers, compute orbits as appropriate and attend to the 
communication of the results under the auspices of the International 
Astronomical Union (IAU), the international association of professional 
astronomers.
 
It was an assistant in the Shoemaker program who, in 1989, discovered 
the asteroid Asclepius, which at a distance of only 430 thousand miles 
came closer than any known asteroid since the lost Hermes.  There was 
the particular worry that Asclepius had actually made its pass a week 
before it was discovered, and that was because it came at us from the 
direction of the sun.  
 
Beginning in 1991, there were several occasions when Spacewatch 
discovered tiny asteroids, only tens of feet across, at distances of 
100 thousand miles and even less.  Objects this small really are of 
little concern, because even if they hit, they are likely to burn up 
completely and harmlessly in the earth's atmosphere.  
 
Then, in 1996, came the PHA with the closest known pass, 280 thousand  
miles, for an object perhaps one to two tenths of a mile across. It was 
discovered photographically by two enterprising students in Arizona, 
Tim Spahr and Carl Hergenrother, only a few days before its closest 
approach.
   
The subject of the latest concern, 1997 XF11, was discovered in 
December by Jim Scotti of Spacewatch and is the largest of the 11 PHAs 
added last year.
 
(A complete list of the 112 known PHAs appears in our Web site at 
http://cfa-www.harvard.edu/iau/lists/Dangerous.html. The site also has 
a list of all the predicted approaches of asteroids and comets within 
about 19 million miles of the earth during the next third of a century: 
see http://cfa-www.harvard.edu/iau/lists/CloseApp.html.)
 
On March 11, when my colleague Gareth Williams and I were making our 
regular monthly update of our Web files on March 11, we were startled 
to find 1997 XF11 singled out for a passage less than 30,000 miles from 
the center of the earth on Oct. 26, 2028.  In more than 40 years of 
computing orbits, I had never seen anything like that before.  Of 
course, we realized that the actual distance was uncertain and that the 
object could easily pass at or somewhat beyond the distance of the 
moon.
 
Nevertheless, to have the earth right at the center of the uncertainty 
range was startling.  What really surprised us, however, was that 
nobody else --the folks at JPL, for example, or even a knowledgeable 
amateur astronomer with a PC--seemed to have done this same calculation 
yet, since all the information necessary had been available on the Web 
for five days.
 
In fact, nobody seemed to have taken much interest in the object at 
all, even though it was obvious already in December that XF11 was an 
asteroid that could come particularly close to the earth and that it 
was in the largest 20 percent of all PHAs.  This reinforces the 
impression that we must hunt for PHAs because if we don't do so, we 
shall someday go the way of the dinosaurs. Yet some colleagues appear 
to assume that the PHAs we have already detected cannot possibly hurt 
us, and we don't need to study them any more.
 
With our attention drawn to XF11, the obvious next course to us was to 
encourage further observations, either in the future--with the object 
now getting rather faint and due to move into daylight in a couple of 
months--or in the past, with images perhaps to be found in photographic 
archives.  
 
I therefore put out an "IAU Circular" stating the facts and telling 
observers where to look for XF11 between now and early July.
 
As we sometimes do with a particularly interesting development, we also 
put a popular version of it into our Web page.  The popular rendition 
mentioned the possibility of finding images of XF11 on photographs 
taken in 1990 and earlier. By "clicking" on a particular year, one 
could see where in the sky the object was.  If earlier images were 
found, they could provide more precise determination of the asteroid's 
course than we had available.
 
Eleanor Helin (who, as it happens, is also now located at JPL) and 
assistant Ken Lawrence checked the Web site, realized they had suitable 
Palomar telescope films in 1990, inspected them, quickly found the 
images of XF11 from March 22 and 23 of that year, measured them and 
reported the measurements to us. Great.  
 
Williams worked the 1990 data into the orbit solution, revised the 2028 
miss distance to 600,000 miles, and I prepared another IAU Circular 
with the new results. (This will still be the record predicted approach 
for an asteroid or comet during upcoming decades.  Although we know of 
an asteroid that will come just a little closer in 2086, it seems to be 
smaller than 1997 XF11.)
 
So where did things go awry? The media, of course, make an easy 
scapegoat. But responsible science writers, such as Browne and David 
Chandler of the Globe, wrote quite commendable articles. These writers 
receive the IAU Circulars on a regular basis anyway. What's the 
alternative way of getting news out? Should we prohibit anyone with 
press credentials from even looking at our Circulars? Some of my 
colleagues are looking into ways of preventing information on wayward 
PHAs from getting to the press and the public. To me, that smacks of 
censorship.
 
No, I think the problem lay with some of those very colleagues, eager 
to make pronouncements. And the reason this is a problem now is the 
easy availability of e-mail. E-mail is a wonderful tool--often better 
than the telephone--for getting quick answers to urgent questions.  But 
many e-mail devotees use it not just to send a message to someone but 
to copy that message simultaneously to a couple of dozen other people.
 
This prompts responses and remarks between other pairs of participants, 
with the messages again copied to all the members of the gang, plus, 
perhaps, a few more friends. Those friends also have their regular 
e-mail correspondents, of course, so both information and 
misinformation can proliferate rapidly, like a pyramid scheme.
 
Paul Chodas is a fine scientist at JPL, and on receiving the message 
about XF11, he performed some experiments on the uncertainty of the 
miss distance to see whether there was possibility the object might hit 
the earth in 2028. Chodas's computations were not, in fact, 
significantly different from mine. The difference was that an official 
there e-mailed his results to all and sundry, thereby also bringing 
them to the attention of the press.
 
Chodas and I agreed, as did two other scientists making similar 
calculations, that it would be very difficult to bring XF11 within 
15,000 to 20,000 miles of the earth's center in 2028. But that is 
closer than the geosynchronous artificial satellites. Furthermore, the 
other scientists working on the problem agreed with me that it was 
rather rash to say that there was absolutely no chance of a strike, for 
it was impossible to claim there could not be other unconsidered 
effects (such as an abnormal distribution of errors, the ignored 
gravitational effect of a close approach to another asteroid, the 
possible reaction of the object to the explosive vaporization of ice on 
the surface).
 
A rip-roaring e-mail barrage on such small points quickly developed. As 
far as I was concerned, the argument was irrelevant. Matters would be 
solved once and for all if someone would do what I suggested and look 
for images of XF11 on past photographs. In any case, as Chandler later 
described in the Globe, there was an error in Chodas's 
computations--and Chodas was man enough to admit it.
 
And, of course, as soon as the 1990 observations became available, it 
was obvious that my group and the JPL group would obtain the same 
result with the 600,000-mile miss: revealing absolutely no danger.  
Again, what I thought inappropriate was the release of the new data by 
an official to colleagues and the press, with no mention that we and 
JPL were in agreement, given that the Circular with Williams's 
calculation (and a revision to our Web page) had been issued 90 minutes 
earlier.  Contrary to reports, there was no "mistake" in either set of 
computations made by our group in Cambridge. What there was were new 
data, properly reported.
  
A few of my colleagues have questioned whether it was appropriate to 
issue an IAU Circular with a call for observations of XF11, when I 
could instead perhaps have contacted Helin and others directly with 
regard to checking past photographs. My response to this is that I did 
not know in advance whether she or others (which others?) would have 
appropriate old films. If there were no old films at all, it was 
obviously important to make future observations, and time for these was 
running short.  
 
If there were no sense of urgency, there would be no incentive to 
search archives immediately, and they might not have been searched 
until future observations became impossible.  In any case, it is 
precisely for the timely acquisition of follow-up observations like 
this that the IAU Circulars exist. If one asks observers individually, 
that is much more inefficient, and there are bound to be some who do 
not get asked--and who may as result feel a bit miffed.  As it 
happened, we had a response from an astronomer in Germany concerning a 
possible image--not confirmed, it seems--of XF11 from way back in 1957. 
Would I have thought to solicit that astronomer directly?  
 
The only other known positive past detections of XF11 to date are from 
the Shoemaker team, also made in 1990.  The fact that there were such 
detections (but not the measurements themselves) was relayed to our 
offices some six hours after Helin informed us that her team had 
detections, and in the mean time she had provided the necessary 
measurements. Science may strive to be objective, but scientists are as 
competitive as anybody else. We made the information about where to 
look in 1990 available in the Web. That put all the film searchers on 
an equal footing. Nobody had an unfair advantage over anybody else.
   
At a meeting organized by NASA in Houston on March 17 some 
consideration was given to changing the procedures for announcing 
possible "end of the world" scenarios in the future. There was talk of 
establishing a special committee to "verify the orbit computations", as 
well as to alert those who might be able to make further observations 
and search for images in past archives. This is one of those proposals 
that may sound good, but as I have just indicated, there would clearly 
be problems as regards crediting priority for observations and archival 
searches--indeed, also, as regards crediting priority for ideas.  
"Science by consensus" is really not a palatable way to go, and 
decisions by committees are the food for cover-ups. In any case, the 
XF11 orbit computations announced were the correct conclusion from the 
data available at the time, and there was independent verification of 
this by both Williams and myself.  Furthermore, it is surely naive to 
believe one can stop everyone everywhere from talking to his or her 
favorite reporter.
 
Certainly, I appreciate that there was a problem that the leaderships 
of both the IAU and NASA were embarrassed by this episode, in the sense 
that they had not in fact seen the initial Circular before they were 
overwhelmed by the press. I have indeed apologized to them for catching 
them unawares and hope that a way can be found to warn them and perhaps 
others of this kind of thing in the future.
 
I don't expect to be around in 2028 myself, but I can say that, weather 
and intervening disasters permitting, astronomically inclined residents 
of Massachusetts ought to be able to follow the asteroid on the morning 
and evening of the appointed day. A tiny starlike object will move from 
east to west (and in near full moonlight, if the night stays clear).
 
Few will remember it as 1997 XF11 then, because it will have received a 
real name, perhaps at the time of its 6-million-mile pass in 2002. But 
some will remember the brief fiasco in 1998 and perhaps reflect that 
this represented a genuine turning point. For one thing, perhaps 1998 
would signal the beginning of a genuine breakthrough in significantly 
improving the quality of U.S. education in math and science all the way 
through grade 12. If so, the passage of XF11 in 2028 would be treated 
with the knowledge and the respect it deserves, with Heavensgate-type 
behavior and its associated ignorance a thing of the past. Furthermore, 
recalling the conclusions of the Spaceguard Survey Report of 1992 that 
a concerted survey both to discover and to track more than 90 percent 
of the most dangerous PHAs would take two to three decades, our 
successors watching the skies of 2028 might appreciate that XF11 
provided the inspiration that led to funds to patrol the skies for 
PHAs much more thoroughly than before.
 
___
Brian G. Marsden is associate director for planetary sciences at the 
Harvard-Smithsonian Center for Astrophysics in Cambridge and director 
of both the Central Bureau for Astronomical Telegrams and the Minor 
Planet Center of the International Astronomical Union

================================
(3) IMPACT HAZARD AND THE XF11 AFFAIR

From: Clark Chapman 
 
You may be interested in a revised case study I have prepared 
concerning the impact hazard, including its history up through, and 
including, an evaluation of the recent 1997 XF11 affair. It is an 
intermediate revision of a document written as part of a project by the 
Geological Society of America and the National Center for Atmospheric 
Research (sponsored by the NSF) to evaluate the role of "predictive 
science" in the public policy arena.  A link at the top of my URL, 
which follows, will tell you more about that larger effort, which 
includes earthquake prediction, the Weather Service, global warming,
etc.
 
www.boulder.swri.edu/clark/ncar.html
 
Clark Chapman

====================
(4) GERVASE'S 1178 'LUNAR IMPACT' HAS PROBLEMS

From: Brad Schaefer 

Here is a contribution for the Cambridge Conference, with the topic of 
Gervase's 1178 event inspired by the recent note:
 
GERVASE'S 1178 'LUNAR IMPACT' HAS PROBLEMS

Carl Sagan's Cosmos dramatically portrayed the report of Gervase of 
Canterbury, that on the evening of 18 June 1178 a group of monks near 
Canterbury saw what J. B. Hartung (1976 Meteoritics, 11, 187) 
interpretted as a giant meteor hitting the Moon. Gervase says "... five 
or more men who were sitting there facing the Moon. Now there was a 
bright new Moon, and as usual in that phase its horns were tilted 
towards the east; and suddenly the upper horn split in two. From the 
midpoint of this division a flaming torch sprang up, spewing out, over a 
considerable distance, fire, hot coals, and sparks..." Hartung's 
identification of the 'impact' site with the young crater Giordano 
Bruno is highly evocative.

In 1984, Ken Brecher (BAAS, 16, 476) made the nice connection of this 
Canterbury Event with the swarm of meteors, comets and asteroids 
associated with the orbit of Encke's Comet. This association is made 
solely on the basis of the date. Christened the "Canterbury Swarm", the 
dangers of impacts from swarms of debris is well highlighted.

But Gervase's report has a two serious problems which strike at the 
heart of Hartung's hypothesis. The biggest problem is that the crescent 
Moon would not have been visible on the stated date (Meeus 1990, JBAA, 
100, 59). [With all my theoretical and observational experience on 
crescent visibility questions, I chide myself for not having done Meeus 
calculation first, but after the fact I do confirm Meeus' conclusion.]  
So the direct  statement of Gervase cannot be correct, nor is it 
possible that a backside impact could have lit up the Moon enough to 
allow visibility.

If Gervase merely reported the wrong date, then perhaps it might 
be possible to save the claim. Indeed, Gervase misreports 15 dates that 
I have identified, including for three solar eclipses. However, there 
is no independent reason to suggest a date error. Once anyone 
starts getting into the game of 'let-us-arbitrarily-change-the- 
text-so-as-to-fit-my-preconceived-hopes', then the proof of anything is 
possible. In particular, the arbitrary assumption of a date invalidates 
the connection with the Canterbury Swarm since the date is the only 
connection.

Another serious problem is familiar to readers of ancient and medieval 
chronicles, where many fabulous prodigies are reported second-hand.  
Gervase has his share of them, so the authority and believability leave 
too much to modern assumptions.

So our community should not make too big a deal about the Canterbury 
Event, or skeptics can use this to discredit by connection all the 
other very strong evidence of large impacts.

Cheers,
Brad Schaefer
Yale, Physics, JWG 463
New Haven CT 06520-8121 USA

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