From Duncan Steel <D.I.Steel@salford.ac.uk>

Dear Benny,

You have today (April 23rd) carried various comments from Ed Grondine in
which he has misrepresented my viewpoints as expressed in my message in
CCNet of April 19th.

>If I interpret Duncan's comments on the Siding Spring Observatory correctly

Grondine did not (interpret my comments correctly). I simply pointed out
that the UK already has an operational telescope that might be equipped in
precisely the same way as its twin at Palomar, the latter having now been
adapted for NEO searching by the NEAT team and colleagues (and good for
them). The telescope in question (the UKST) happens to be an instrument
which many UK astronomers would like to see relinquished so as to free up
some of the funds required for other astronomical research activities. It
would represent an invaluable complement to the Oschin Schmidt at Palomar if
equipped and operated in the same way for NEO searching.

Note that I made no comment at all about "Siding Spring Observatory", which
is an observatory operated as part of the Australian National University. It
simply happens to be the location of the UKST, which is operated as part of
the Anglo-Australian Observatory. By confusing my comments here, as
elsewhere, Grondine muddies the waters.

>it appears that he has accepted that the UK 3.5 meter telescope will not be
>built by a government facing very large bills ...

That is not the case at all and it takes some weird jump in imagination to
derive such a false belief. It is akin to suggesting that because a bicycle
becomes available for me to pedal to work then it follows that I will give
up saving to buy a new car.

Similarly Grondine's analysis of my comments on the Associated Press report
is entirely incorrect. The AP report was misleading because it made it
appear that the "NASA Spaceguard goal" is 90 percent of all 1 km plus NEOs
(i.e., including Earth-crossing comets), whereas the goal is recognised by
all those with close familiarity with the subject to involve only the NEAs.
And at that, only the NEAs with short-period orbits (because it is beyond us
to discover those 1 km asteroids with perihelion distances less that 1 AU
but aphelia beyond Neptune until such time as they enter the inner solar
system; ipso facto such long-period asteroids are not part of the population
of which 90 percent is the aim).

I made no expression of any personal belief as to whether that specific NASA
goal is adequate in the long term: I simply pointed out why comets and
long-period asteroids are not included in the goal. Indeed, as I am neither
a US citizen nor a US taxpayer, it is not my business to express any opinion
about what NASA should be doing. Perhaps Grondine thinks he has the right to
tell his next-door neighbour whether he (the neighbour) should buy a new car
or not. I do not presume any such right for myself. What I would say is
that, as a person who is not directly involved, I think the US search teams
are doing a wonderful job, and I am happy to lend them my verbal and moral
support. I can write books and magazine articles, I can appear on US radio
and TV, but I have no Congressman to lobby or threaten with losing my vote.
Elsewhere I am pleased to see some NEO activity, such as in Japan with the
new search and tracking activity, and similarly in Italy where apart from
NEO observations there is brilliant dynamical work under way. But it is not
my position to tell the Japanese or Italian astronomers or governments what
they should be doing. Nor is it my place to criticize the NASA Spaceguard
goal, especially since it is NASA-funded projects that are delivering most
of the NEA discoveries. On that basis, congratulations to the US public for
their support of this endeavour. You are leading the way. But in the same
way as one might admire the football or baseball team that is currently
leading the rankings, some of us have ambitions to overtake your efforts.

As regards what I do think myself, as a citizen of the UK, and a UK
taypayer, I permit myself to lobby the UK government in various ways. That
is one of the contributing reasons why the UK NEO Task Force report made
recommendations for the size limit of NEA discoveries to be set somewhat
lower than the NASA Spaceguard goal (and that necessitates larger search
telescopes), and also for scientific studies of the nature of the NEO hazard
(because a group of us in the UK regard giant comets undergoing
disintegrations as being a larger danger to the terrestrial environment than
is perhaps realised by researchers elsewhere).

Thus:

>Besides giving in to NASA's rather arbitrary goal for asteroids, Steel

I do no such thing, and I would thank Grondine not to make such baseless
statements. What NASA chooses to do is not my business, as I have written.
Similarly, what I choose to do is not NASA's business, and in the UK we have
a different target. In the future I hope that the UK and the USA and many
other nations will be able to work together, but I would expect that at all
times there will be differing opinions about what the priorities should be.
Such working together often takes the form of friendly competition, and if
higher goals are set elsewhere then this might have an influence upon the
goals set in the US. But, again, it is not my place to criticise what any
other nation might be doing.

I further wrote (rather clearly, I believe):

>So far as I am aware the majority of very large objects on
>Earth-crossing orbits observed over the history of astronomical research
>have been comets, mostly in near-parabolic orbits. Finding 90 percent of
>those is not feasible, because they spend most of their time near aphelion,
>making it possible to find them only as they enter the planetary region."

To which Grondine stated:

>Carolyn Shoemaker disagrees with him, and is seeking $170,000,000 for a
>telescope for exactly this purpose.

Again, Grondine has made a false statement based upon his own lack of
understanding of what is involved, even though it is quite simple. Spotting
long-period/near parabolic comets as they cross the 3 AU threshold at which
water starts to sublimate, or rather further out where weaker comae are
produced by the more-volatile constituents (methane, ammonia, CO etc.), is
trivial (compared to finding 1 km asteroids at similar distances). Thus it
is straightforward to find the majority of such comets that enter the inner solar system, but only as they do so. (There are, however, some long-period comets that are not
easily discoverable well ahead of an impact if only Earth-based search
systems are employed, for example if they cross the 3 AU threshold while
near superior conjunction.)

As I wrote, it is not feasible to find any substantial fraction of the total
numerical population because one cannot spot comets at 10,000 AU no matter
how much you spend on telescopes, and no-one with half an ounce of
intelligence has suggested that you can. As I wrote, there are 100 million
comets per square degree that are not discernable as individual objects.
Spotting the few that enter the inner planetary region each year is easy, in
most cases.

The problem, as I pointed out previously, is that even if such a comet were
spotted when still some distance away from impact (say when it is at the
distance of Saturn), still a timely intercept is not feasible using
presently-available propulsion systems. You give me a system capable of
achieving a delta-vee of 100 km/sec in short order (that is, not an ion
engine that might reach that speed after a three-year gradual acceleration),
and you have it sitting on a launch pad waiting to go, and I could intercept
most such comets. The reality, however, is not that. Grondine and others
interested in looking into this need to start at the beginning, by examining
the sorts of warning times that are feasible for long-period comets (see the
chapter by Marsden and Steel in 'Hazards Due to Comets and Asteroids',
edited by Tom Gehrels, 1994; if we were lucky we might get 250 to 500 days).
Having understood what is involved in terms of the celestial mechanics, next
they could try to invent an interceptor for some characteristic cometary
orbits, using presently-available propulsion systems. Good luck.

In the meantime, those wanting to move the subject forward and decrease the
chance of a major impact taking us unawares will continue to support the
efforts aimed at tackling the simplest part of the hazard, that associated
with asteroid impacts predictable on a long-term basis (decades). All hail
those NEO search programmes that are delivering the goods now, whilst other
talk and wring their hands. Congratulations to the dynamicists who have
developed the techniques making impact predictions and probabilities
calculable. Once the 1 km goal is achieved, then it can be dropped to half a
kilometre, and then smaller still. The UK NEO Task Force report indicates
what some of us think our own nation should be aiming for in the short term
(the next decade or so). Maybe others will follow suit. In the same way as
we (humankind) have eradicated smallpox, so we can eradicate the danger
posed by large short-period asteroids. Next we'll move on to polio, rubella
and measles, or your disease of choice. The fact that we cannot at present
cure cancer or even the common cold is irrelevant, because by wiping out
some diseases we do enhance the individual's chance of long-term survival.
Similarly it is irrelevant that we cannot hope to tackle the long-period
comets in the near-term, although we'll keep it in mind. When there are
limited resources available they should be directed to where they can do
most good. In our own countries, and the larger organisations of which they
are a part (like the European Community, or the United Nations), we strive
to enhance the resources allocated to the NEO impact hazard. As I indicated
previously, there will come a time when the asteroid problem is solved, and
then long-period comets take over, just as at present there is very little
spent on tackling smallpox. By then maybe we will have the propulsion system
necessary, and everything else required.

Getting the NEO impact hazard accepted by the general public and by
politicians, and then getting the appropriate actions taken to ameliorate
the danger, require clear and distinct signals to be given. The Associated
Press story added to the signal, but also enhanced the noise/confusion level
slightly because in certain aspects it was incorrect. Grondine's message
contained a number of false statements and incorrect deductions which
amplify the noise without adding any significant signal.

Duncan Steel

-p (Never piss off an Aussie)