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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