PLEASE NOTE:


*

CCNet DIGEST, 15 June 1999
--------------------------

     QUOTE OF THE DAY

     "Lord Sainsbury of Turville, a science minister, is expected to
     announce today in the House of Lords, in an answer to Lord Tanlaw,
     that Britain will try to set up a European effort to track
     potentially dangerous asteroids."
     (Charles Arthur, The Independent, 15 June 1999)

    
     QUESTION OF THE DAY (TO BE RAISED IN THE HOUSE OF LORDS)

     The Lord Tanlaw, To ask Her Majesty’s Government what steps are being
     taken to form a National Spaceguard Agency, as part of a European
     Spaceguard programme, to improve the assessment and probability factor
     of impact hazard of a Near Earth Object on the continent of Europe
     or in the seas surrounding it.


(1) SCIENTIST LOSE HUGH ASTEROID
    THE INDEPENDENT (London), 15 June 1999

(2) ASTEROID 1999 AN10 EPHEMERIS
    Ron Baalke <baalke@ssd.jpl.nasa.gov>

(3) CORRECTION ON WHICH SIZE NEOS POSE THE MOST RISK
    David Morrison <dmorrison@mail.arc.nasa.gov>

(4) OBSERVATION OF 10-100 m BODIES
    Luigi Foschini <L.Foschini@isao.bo.cnr.it>

(5) ESTIMATED RISK FROM SMALLER NEOs
    Michael Paine <mpaine@tpgi.com.au>

(6) ASSESSING THE REAL THREAT OF 1998 OX4
    Scott Manley <spm@star.arm.ac.uk>

(7) A QUESTION ABOUT PROBABILITIES
    Gerrit Verschuur <GVERSCHR@LATTE.MEMPHIS.EDU>

(8) IDENTIFIED NEOs CAN ALWAYS GET LOST
    Robert Clements <Robert.Clements@dva.gov.au>

(9) IVORY COAST IMPACTS(S)?
    Bernd Pauli HD <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>

(10) WATCHING METEORITES FALL ON THE MOON
     Bernd Pauli HD <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>

================
(1) SCIENTIST LOSE HUGH ASTEROID

From THE INDEPENDENT (London), 15 June 1999
http://www.independent.co.uk/stories/A1506929.html

By Charles Arthur, Technology Editor

Astronomers have lost track of an asteroid hundreds of metres wide that
could devastate the Earth in 50 years' time. Still, they are not unduly
worried: instead they are concentrating on the other 178 lumps of rock
that might destroy us first.

The "misplaced" asteroid, known as 1998 OX4, was discovered by a team
at the University of Arizona. They latched on to it for two weeks, but
have since lost sight of it. Early estimates put the chances of it
hitting the Earth at one in 10 million, and astronomers say there
are many more objects to be concerned about. The US space agency, Nasa,
lists another 178 "potentially hazardous asteroids", and is finding
them (sic!) at a rate of about one a week. A total of 20 have been
discovered this year; 55 were identified in 1998.

Lord Sainsbury of Turville, a science minister, is expected to announce
today in the House of Lords, in an answer to Lord Tanlaw, that Britain
will try to set up a European effort to track potentially dangerous
asteroids.

Astronomers say such a move is overdue. Dr Mark Bailey, director of
Armagh Observatory, said: "The hazards of an asteroid impact haven't
received due attention. When you multiply the likelihood of a collision
with the potential number of deaths, you get a figure which is very
like that which governments try to influence. It's comparable with the
risk of a nuclear power plant meltdown: not likely but very bad if it
happens."

Some people favour smashing incoming asteroids with nuclear missiles so
that they are small enough to burn up in the Earth's atmosphere. Others
believe this would multiply the risk.

A seven-mile-wide asteroid is thought to have triggered the extinction
of the dinosaurs 65 million years ago.

Dr Duncan Steel, an expert on asteroid threats, said: "Sooner or
later we will spot one which will have a one in a thousand or one in
one hundred chance of hitting within 10 years. We won't be able to
cover it up. The options are either to give up looking and keep your
fingers crossed, or do it properly and look for them."

Copyright 1999, The Independent

=======================
(2) ASTEROID 1999 AN10 EPHEMERIS

From Ron Baalke <baalke@ssd.jpl.nasa.gov>

The latest ephemeris of Asteroid 1999 AN10 is available here:

http://neo.jpl.nasa.gov/neo/an10_ephem.txt

The ephemeris is in 5-day increments covering the period from February
1, 1999 to December 31, 2004.

Ron Baalke

======================
(3) CORRECTION ON WHICH SIZE NEOS POSE THE MOST RISK

From David Morrison <dmorrison@mail.arc.nasa.gov>

Benny:

Please permit me to point out that both of the following comments from your
most recent posting on CCNet are flat wrong:

"asteroids of this size [roughly 300 m] are much more dangerous to us
[compared to objects 1 km or larger] because i) there are many more of them
and ii) because they will consequently impact more frequently."

"asteroids in the OX4 class are the most dangerous of all given both their
devastating impact effects *and* their impact frequency".

This failure to recognize the hierarchy of risks from objects of different
sizes unfortunately undercuts much of your argument on OX4.  Perhaps you
could point out to your readers that objects in this size range represent
between one and two orders of magnitude *less* risk than those in the
Spaceguard range.  This is a fundamental fact about the impact hazard, and
it is precisely the reason Spaceguard concentrates on objects larger than 1
km.  For background, see the NASA Spaceguard Report (1992), the 1994 Nature
paper by Chapman and Morrison, or any of several chapters on risk in the
1994 book Hazards Due to Comets and Asteroids.  Or look at the NASA impact
hazard webpage (http://impact.arc.nasa.gov).

David Morrison
NASA Ames Research Center
Tel 650 604 5094; Fax 650 604 1165
david.morrison@arc.nasa.gov or dmorrison@mail.arc.nasa.gov
website: http://space.arc.nasa.gov
website: http://astrobiology.arc.nasa.gov
website: http://impact.arc.nasa.gov

=====================
(4) OBSERVATION OF 10-100 m BODIES

From Luigi Foschini <L.Foschini@isao.bo.cnr.it>

Dear Benny,

I have greatly appreciated your note of 14 June 1999 about "THE
SPACEGUARD PARADOX: OR WHY WE NEED TO SEARCH FOR THOSE ASTEROIDS MOST
LIKELY TO HIT US HARD". I agree with you when you said that although
small asteroids can produce local damage, they are much more dangerous
because of their high impact frequency and their smallness (therefore,
they are very difficult to observe and to follow).

Already Paolo Farinella, during his talk in the plenary session at the
Torino workshop, underlined this fact.. Specifically, he said that
bodies in the range 10-100 m are poorly observed, in spite of their
dangerousness. For example, the Tunguska cosmic body was about 60 m, but
it destroyed an area of 2200 square kilometers.

In my short presentation during the Subgroup 2 session, I have added
also other things and I asked for more studies and observations of
these bodies. Indeed, we have also theoretical problems: from studies on
meter-sized bodies we know that they break up at dynamical pressures
lower than their mechanical strength. Ceplecha et al. (Astron.
Astrophys. 279, 1993, 615) found five classes of mean fragmentation
pressure, from 0.08 to 1.1 MPa. Comparing these data with known
mechanical strength of cosmic bodies (from 1 to 200 MPa), we can see
that small asteroids break up at dynamical pressures up to 200 times
lower than their mechanical strength.

It is worth noting that actual models for the asteroid fragmentation in
the Earth's atmosphere consider that the body break up when the
dynamical pressure is *equal* to the body mechanical strength (e.g.
Hills and Goda, Astron. J. 105, 1993, 1114). But observations suggest
that this is not true. Even though almost all known cases are in the
range 1-10 m, there are some episodes, such as Marshall Islands (Febr.
1, 1994; r~13 m) that suggest that this feature may be valid also for
larger bodies. Therefore, we cannot set a quantitative threshold and we
need also for theoretical studies, in order to assess the hazard.

Recently, I have proposed a new approach to the problem based on the
stagnation temperature, rather than the pressure (Foschini, Astron.
Astrophys. 342, 1999, L1). But we have only some preliminary
(encouraging) data and there is still a lot of work to do. In any way,
we need for observations of airburst (explosion with energy greater than
10 kton, at least) in order to better understand what occur when a small
asteroid enters the Earth's atmosphere.

Moreover, in collaboration with Paolo Farinella, Christiane Froeschle',
Robert Gonczi, Tadeusz J. Jopek and Patrick Michel, we are studying the
interplanetary dynamics of these bright bolides. Paolo spoke about first
results in his talk and you can download a preprint at my personal home
page (http://www.fisbat.bo.cnr.it/homepp/dinamica/foschini.html) or at
Paolo's home page
(http://tycho.dm.unipi.it/~paolof/homefarinella.html).

Cheers,

Luigi

======================
(5) ESTIMATED RISK FROM SMALLER NEOs

From Michael Paine <mpaine@tpgi.com.au>

Dear Benny,

Re: Your comments on 14 June - here, here (or should that be "hear,
    hear" for the House of Lords)

My notes in the CCNet Special on 20 April covered the issue of
detecting asteroids under 1km diameter. I concluded that "there is a
high risk of another Tunguska event occurring without warning over the
next 50 years...". My subsequent guesstimates of the risk to inhabited
regions (http://www1.tpgi.com.au/users/tps-seti/spacegd7.html#inhabit )
suggest that there is a 1 in 900 chance of a Tunguska style event
occurring over an inhabited region in any one year and that the typical
death toll would be about 1 million (but is highly variable of course).
I agree with the current Spaceguard Survey priorities - they should
effectively deal with most civilisation-threatening 1km+ NEOs. The
Survey will also enable better estimates to be provided for the risk
from smaller NEOs but will not make much difference to the chances of an
undiscovered small NEO (<200m) striking without warning. Spaceguard
will be a great start - let's get going!

Michael Paine

=====================
(6) ASSESSING THE REAL THREAT OF 1998 OX4

From Scott Manley <spm@star.arm.ac.uk>

OK... so we've lost it... but it's not all doom and gloom.

Hypothetically were the object to really be a threat to the Earth on
its 2046 close approach then there must be a range of orbital solutions
for which it will hit. In which case during the next opportunities it
might be wise to search for the object on orbits matching these killer
solutions. While this still represents an area of the sky the area is
far smaller than the entire error based on the observations. (The
searchable area will surely tend to grow linearly with time, rather
than with the square of the time).

If we don't find it then we can be safe in the knowledge that we're
likely to be safe from this object for at least the forseeable future.

Scott Manley (who hope's he's not missing the point)
Armagh Observatory
http://star.arm.ac.uk/~spm/welcome.html

==================
(7) A QUESTION ABOUT PROBABILITIES

From Gerrit Verschuur <GVERSCHR@LATTE.MEMPHIS.EDU>

Would someone on the List please relate to a relative lay person as
regards orbit calculations just what your probability estimates mean.

The context of my question concerns standard deviations that pertain to
a calculation. For example, if you calculate the most probable distance
of a close passage for a NEA expected to fly by in 2027, what does the
claim that there is a 1 in 500,000 chance of a collision actually mean?
Is that the limit of a 3 sigma error bar or something equivalent?  If
so, please explain what that means.

If you state that the error ellipse may bring the NEA as close as
39,000 km from the earth's center, what does that mean?  Is that the 3
sigma or 5 sigma or 1 sigma deviation from the most probable point of
closest approach?

No doubt this discussion has been held between the experts but it sure
would be good to have a nice, simple explanation of what these
probabilities actually mean.

Thanks
Gerrit Verschuur

===============
(8) IDENTIFIED NEOs CAN ALWAYS GET LOST

From Robert Clements <Robert.Clements@dva.gov.au>

I'm surprised that you were surprised about the interest.

From my observations: if the mainstream audience really understood that
the majority of identified NEOs were effectively unobservable a fair
percentage of the time; & that lack of observations put significant
margins of error in many published NEO orbits; funding Spaceguard
programs around the world wouldn't be such a difficult operation.
There's no doubt in my mind that people who read about objects such as
1999 AN10 & 1998 OX4 instinctively assume that - once discovered -
astronomers can automatically monitor their flightpaths NORAD-style from
the moment of first observation... an incorrect assumption, sure; but an
assumption that that communicators in (& around) the field need to take
full responsibility for.

Under these circumstances: a story that began with a potentially serious
threat being described as lost was always going to make a good 10 second
grab....

All the best,

Robert Clements <Robert.Clements@dva.gov.au>
<http://www.ausnet.net.au/~clemensr/welcome.htm>

==============
(9) IVORY COAST IMPACTS(S)?

From Bernd Pauli HD <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>

Culled from the French astronomy magazine CIEL & ESPACE:

Ciel & Espace, No. 349 - Juin 1999, p. 11: Impacts en Côte-d'Ivoire ?

[B. Pauli's translation] I am a medical entomologist ... and while
prospecting in the vicinity of Bouaké in the central part of the Ivory
Coast, I discovered one or two meteorite impact craters. I wasn’t able
to accurately localize the craters as such, but close to these two
sites, about 10 km distant from each other, the nature of the rocks is
distinctly different from the adjoining soil. First of all, there are
bulbaceous, folded rocks (tektites) which look astonishingly like small
magmatic flows. Numerous lateritic (= a reddish ferruginous soil formed
in tropical regions by the decomposition of the underlying rocks) rocks
enclose metalliferous glomerules which are very probably the vestiges
of the meteoritic material itself. Other siliceous rocks exhibit
several successive, black layers which I’d classify as soot or as black
clay. At one site, I even found black pieces of tree trunks and
silicified branches, vegetal matter that must have been calcinated
during the impact. In my opinion, these two sites contain a veritable
mineralogical treasure [...] I am not a proficient expert in such
phenomena and I’d like to share my observations with those who are
interested in such a discovery. I have in my possession several
specimens and, well, the impact sites are not very far away from where
I live. (Frédéric Darriet, Bouaké)

==========
(10) WATCHING METEORITES FALL ON THE MOON

From Bernd Pauli HD <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>

From Ciel & Espace, No. 349 - Juin 1999, p. 17: Si, c'est possible !

[B. Pauli's translation] Watching meteorites fall on the Moon -
just a joke to impress first graders? No, says the study group of J.L.
Ortiz -  it is within reach of (modest) amateur telescopes. Because the
Moon doesn’t have a substantial atmosphere, meteorite impacts there are
much more violent than here on Earth liberating much more energy: 20
million joules for a 1-kg block. As seen from the Earth, this would
produce a flash of magnitude 9 to 15 (the faintest stars visible to the
unaided eye in a non-polluted environment are about mag. 6). Tests that
are being undertaken with a telescope of 250 mm aperture (a 10-inch
scope) have yielded the first results. The Spanish team says they have
already observed several impacts - this will still have to be
confirmed. According to J.L. Ortiz, the Leonids in November will offer
a suitable opportunity for research for both amateurs and
professionals. As the Moon will be in its first-quarter, observing the
regions that are still in the lunar dark will do the job.

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