PLEASE NOTE:


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CCNet DIGEST, 13 October 1998
-----------------------------

(1) WHAT IS THE UK DOING TO MONITOR ASTEROIDS CLOSE TO EARTH?
    Jonathan TATE <fr77@dial.pipex.com>

(2) GIACOBINIDS SURPRISE SKY-WATCHERS
    Daniel Fischer <dfischer@astro.uni-bonn.de>

(3) NASA TO STUDY POSSIBLE HYPERVELOCITY IMPACT CRATER IN BOLIVIA
    Mike DiMuzio <mdimuzio@cisnet.com>

(4) NEW STUDY ON COLLISION PROBABILITY OF 1997 XF11
    Karri Muinonen <muinonen@cc.helsinki.fi>

(5) UPPER BOUNDS FOR THE EARTH-XF11 COLLISION PROBAILITY
    http://www.aas.org/publications/baas/v30n3/dps98/S110.htm

(6) COULD ASTEROID 1997 XF11 COLLIDE WITH EARTH?
    P. W. Chodas, D. K. Yeomans (JPL/Caltech)
    http://www.aas.org/publications/baas/v30n3/dps98/S110.htm

(7) THE IMPACT HAZARD IN THE CONTEXT OF OTHER NATURAL HAZARDS &
    PREDICTIVE SCIENCE
    C. R. Chapman (SwRI)
    http://www.aas.org/publications/baas/v30n3/dps98/S110.htm

=================
(1) WHAT IS THE UK DOING TO MONITOR ASTEROIDS CLOSE TO EARTH?

From Jonathan TATE <fr77@dial.pipex.com>

Benny,

I thought that the CC network might be interested in the following
statement that Spaceguard UK has just received from the British
National Space Centre. I have also been invited to visit the BNSC to be
“put straight” on the extent of the British contribution.  Apparently I
am quite wrong in saying that it's minimal! I expect that you will
judge for yourselves from the passage below (we still seem to be
muddling “space debris” with NEO studies!).

I would welcome any comments, so that I can consolidate them, and pass
them on to the BNSC as a coherent document.

All the best

Jay
______________________________________________________________

WHAT IS THE UK DOING TO MONITOR ASTEROIDS CLOSE TO EARTH?

Asteroids are not the only examples of what we call Near Earth Objects
(NEOs).  Comets have also been known to pass close to Earth, not to
mention the many objects launched into space from Earth in the last 40
years. But none of these poses an immediate danger to Earth.  Most will
burn up in the atmosphere and will be seen from Earth as meteors, more
familiarly known as shooting stars.

However, many scientists agree that the Earth will be hit by a really
big asteroid about once every 100,000 years.  So it is important to
define the level of risk - to calculate when the next big collision is
likely to happen.

The UK is a member of the European Space Agency (ESA), which is
mounting a study to produce an inventory of the worldwide capability in
NEO search and then plans to run a pilot project to demonstrate the
operation of a Spaceguard system to coordinate observations and
communicate the results.

BNSC is seeking to keep near Earth space as clear as possible to ensure
any observation platforms that are operated in Earth orbit, such as the
Hubble space telescope, are not damaged by debris.  As debris can
appear as quite bright objects or tracks in the sky, minimising debris
will help in the discrimination of NEOs, this will assist space and
ground based observations. The Particle Physics and Astronomy Research
Council (PPARC), a BNSC partner, continues to support the UK Schmidt
Telescope (UKST) archive at the Royal Observatory Edinburgh for NEO
studies, as for other similar activities.

The UK contributes to these ESA studies and to related work at DERA
(Defence Evaluation Research Agency).  DERA is a pioneer in developing
computer models which predict the movement of space debris (old bits of
satellites as well as natural debris such as meteoroids).

Knowing more about the structure of comets and asteroids will help us
to predict their path in space and give us the scientific knowledge to
counter possible collisions. As the exact composition of asteroids is
difficult to define, the debris resulting from any attempt to blow up
an asteroid may be as dangerous as any collision threat.  Therefore we
are also funding instruments for the comet mission Rosetta, an ESA
science mission being built by the UK company Matra Marconi Space (UK)
Ltd.  Rosetta will be launched in 2003 and will rendezvous with the
comet Wirtanen in 2008, following it for many months, collecting and
analysing samples. Rosetta is the follow-up mission to the UK-built
Giotto probe, which in 1986 sent back the first pictures of the core of
a comet.

But ultimately this is an international issue which needs an
international plan of action. The UK plays a key part in discussions on
space activities at the United Nations Committee on the Peaceful Uses
of Outer Space (UNCOPUOS). This committee has already presented
documents related to NEOs to the UN General Assembly.

============================
(2) GIACOBINIDS SURPRISE SKY-WATCHERS

From Daniel Fischer <dfischer@astro.uni-bonn.de>

Dear Benny,

I haven't seen an article on what this year's Giacobinid meteors were
like on CCNet yet - perhaps you can use the following two from my
Internet newsletter that are based on reports from around the world.

http://www.geocities.com/CapeCanaveral/5599/mirror/107.html

----------------------------------------------------------------------------
Update # 107 of October 9th, 1998, at 12:05 UTC

Giacobinid meteors came early, up to 700 per hour

Once more a meteor stream has surprised astronomers: The moderately
hyped Giacobinids or Draconids (see previous update) were strong but
missed a storm level last night - and the maximum of activity, with up
to 700 meteors per hour in dark skies, came several hours early.
Observers in Asia were thus favored, while Europeans missed the fun:
According to both visual counts from Japan and radar observations
from Europe, the shower reached its maximum around 13:30 UTC on Oct.
8th, 4 hours earlier than even the 'earliest' predictions.

An early analysis received minutes ago from Japan - that divided time
into 10 minute intervals - has the Zenithal Hourly Rate peaking at 760
between 13:10 and 13:20 UTC, tapering off towards 200 only one hour
later. Averaging by the hour, we have ZHRs of 147 between 12:00 and
13:00, 371 between 13:00 and 14:00, and 174 between 14:00 and 15;00
UTC. All this is nice, beating the 1993 Perseids by some 40% in maximum
strength. But to qualify as a storm, the ZHR should have exceeded 1000,
if not 3000 by other definitions, for intervals of several minutes. 

The visual observations from Japan are corroborated by radio echo and
radar observations from Europe, that can be performed regardless of
daylight and adverse weather (see the nice diagram linked to on the
right). The conversion of radar data to visual counts is tricky, but
the time development matches the Japanese data. When darkness had
finally fallen in Europe around 18:00 UTC, only 10 Giacobinids 
were seen per hour, and at 19:00 UTC all activity had ceased.
(Vereinigung der Sternfreunde Press Release #5 of Oct. 9, 1998 +
a message from Koseki Masahiro)                 

http://www.geocities.com/CapeCanaveral/5599/mirror/108.html
----------------------------------------------------------------------------
Update # 108 of Oct. 12, 1998, at 18:45 UTC

The Giacobinids: Almost a Storm

More reports from Asia have been received, and the maximum rate of
meteors seen there needs probably a revision upwards (see also Update
#107). A combined analysis from Japan, e.g., including the data of 23
visual observers, gives a maximum Zenithal Hourly Rate of 950 +/-
600 at 13:15 UTC. Of course, this was only the sharp peak of an
approximately triangular function. The hourly mean of the 13:00-14:00  
UTC interval was 600 +/- 300. Nonetheless a rate around 1000, however
briefly, does qualify as a minor meteor storm according to some      
definitions (although some want to have at least 3600, i.e. one meteor
per second for that).                                         

Regards, Daniel

========================
(3) NASA TO STUDY POSSIBLE HYPERVELOCITY IMPACT CRATER IN BOLIVIA

From Mike DiMuzio <mdimuzio@cisnet.com>

I came across this upcoming mission to South America.

Mike
***************************************

NASA To Study Impact Crater:  Scientists from NASA Goddard leave Oct.
14 for a scientific expedition to explore evidence of a possible impact
crater in northern Bolivia. The circular feature was originally
discovered in a satellite image and could be one of the youngest,
large-scale hyper-velocity impact craters ever found on Earth. Students
from around the world will be able to follow the expedition via the
Internet. Joining the scientists on this 10-day journey will be Tom
Albert, a Howard County, Md. science teacher who is on assignment at
Goddard. Albert will conduct 30-minute interactive educational sessions
on the Internet and answer questions posed by Maryland junior high and
high school students. Goddard PAO Contact: Cynthia O'Carroll at (301)
614-5563.

====================
(4) NEW STUDY ON COLLISION PROBABILITY OF 1997 XF11

From Karri Muinonen <muinonen@cc.helsinki.fi>

Dear Benny,

I have run out of time to write more about XF11. Next week, I will be
giving a talk about the collision probability at the Division For
Planetary Sciences -meeting in Madison, Wisconsin. In fact, the
abstract very briefly summarizes the upper bounds for the XF11 collision
probability as a function of time (adding more observations to the data
set):

http://www.aas.org/publications/baas/v30n3/dps98/S110.htm

All the best,

Karri Muinonen

-------------
(5) UPPER BOUNDS FOR THE EARTH-XF11 COLLISION PROBAILITY

From http://www.aas.org/publications/baas/v30n3/dps98/S110.htm


DPS Meeting, Madison, October 1998
Session 10. Asteroid Dynamics I
Contributed Oral Parallel Session, Monday, October 12, 1998,
 
[10.08] Upper Bounds for the Earth-XF11 Collision Probability
 
K. Muinonen (Univ. Helsinki)
 
For a given time interval, upper bounds for the collision probability
of two planetary bodies can be established using maximum likelihood
collision orbits, i.e., orbital elements that minimize the
observational residuals with the condition of collision some time
within the given interval. The maximum likelihood collision orbit lies
on a certain confidence boundary---assigning all the probability
outside the boundary to collision provides a robust upper bound for the
collision probability. Using the collision orbits and other
newly-developed statistical methods, the asteroid 1997 XF11 close
approach to the Earth (time interval 2028 October 24.0-31.0 TDT) is
analyzed in detail starting from 1997 December 6. Three days after
discovery, in December 9, the orbit is still highly indeterminate, the
collision probability being smaller than 0.007. The December 19 and 21
observations bring the upper bound below ~10-42. In 1998 February 4,
formally at ~10-966, the upper bound is negligibly small and, in March
4, the number further diminishes to ~10-1117. Archive observations from
1990 put the final upper bound at ~10-9772. In conclusion, the upper
bound for the collision probability decreases steadily when more and
more observations are incorporated into orbit determination. By 1998
December 21, the collision probability has decreased to a negligible
level---assuming that all relevant factors affecting the orbit
determination have been correctly accounted for.
 
============================
(6) COULD ASTEROID 1997 XF11 COLLIDE WITH EARTH?

DPS Meeting, Madison, October 1998
Session 7P. Asteroid Observations II

[10.07] Could Asteroid 1997 XF11 Collide with Earth?
 
P. W. Chodas, D. K. Yeomans (JPL/Caltech)
 
Asteroid 1997 XF11 received much notoriety in March 1998 when for a
time, orbit solutions indicated that it would make a remarkably close
approach to the Earth on October 26, 2028. The miss distance calculated
from these orbit solutions was less than one quarter of a lunar
distance, and possibly even smaller, making it easily the closest-ever
predicted approach of a minor planet to the Earth. The fairly large
size of the asteroid, probably over a kilometer across, also made the
object notable. Interest in this object spread rapidly when initial
reports to the press suggested that a collision in 2028 could not be
ruled out.. But, in fact, a complete analysis of the observations
available on March 11 (an 88-day data arc) shows that the probability
of impact in 2028 was very tiny, essentially zero. When XF11's position
uncertainty ellipse is plotted in the plane perpendicular to the
geocentric velocity vector, the ellipse is seen to be extremely
elongated, over 1000 times longer than its width. This elongation is
due to the fact that the position uncertainty along the orbit grows
linearly with time over the 30-year prediction period, while
uncertainties perpendicular to the orbit vary only periodically. The
great length of the uncertainty ellipse makes it difficult to predict a
precise miss distance, but the narrow width of the ellipse allows the
computation of a likely minimum possible miss distance, about 28,000 km
in the case of XF11's passage in 2028. As it turns out, on March 12,
additional pre-discovery images of the asteroid were found, which
greatly strengthened the orbital solution and moved the predicted close
approach out to an unremarkable 980,000 km. But these observations were
not needed to rule out the possibility of a collision in 2028. We also
investigate the close Earth approaches of 1997 XF11 and associated
uncertainties for a few decades beyond the year 2028.

=============================
(7) THE IMPACT HAZARD IN THE CONTEXT OF OTHER NATURAL HAZARDS &
    PREDICTIVE SCIENCE

DPS Meeting, Madison, October 1998
Session 7P. Asteroid Observations II
Contributed Poster Session, Tuesday, October 13, 1998, 4:15-5:20pm,
Hall of Ideas

[7P.16] The Impact Hazard in the Context of Other Natural Hazards and
Predictive Science

C. R. Chapman (SwRI)

The hazard due to impact of asteroids and comets has been recognized as
analogous, in some ways, to other infrequent but consequential natural
hazards (e.g. floods and earthquakes). Yet, until recently, astronomers
and space agencies have felt no need to do what their colleagues and
analogous agencies must do in order the assess, quantify, and
communicate predictions to those with a practical interest in the
predictions (e.g. public officials who must assess the threats, prepare
for mitigation, etc.). Recent heightened public interest in the impact
hazard, combined with increasing numbers of "near misses" (certain to
increase as Spaceguard is implemented) requires that astronomers accept
the responsibility to place their predictions and assessments in terms
that may be appropriately considered. I will report on preliminary
results of a multi-year GSA/NCAR study of "Prediction in the Earth
Sciences: Use and Misuse in Policy Making" in which I have represented
the impact hazard, while others have treated earthquakes, floods,
weather, global climate change, nuclear waste disposal, acid rain, etc.
The impact hazard presents an end-member example of a natural hazard,
helping those dealing with more prosaic issues to learn from an
extreme. On the other hand, I bring to the astronomical community some
lessons long adopted in other cases: the need to understand the policy
purposes of impact predictions, the need to assess potential societal
impacts, the requirements to very carefully assess prediction
uncertainties, considerations of potential public uses of the
predictions, awareness of ethical considerations (e.g. conflicts of
interest) that affect predictions and acceptance of predictions,
awareness of appropriate means for publicly communicating predictions,
and considerations of the international context (especially for a
hazard that knows no national boundaries).


If you would like more information about this abstract, please follow
the link to http://www.boulder.swri.edu/clark/ncar.html. This link was
provided by the author. When you follow it, you will leave the Web site
for this meeting; to return, you should use the Back comand on your
browser.

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